Tennis anyone? How about team sports and car-racing? We all need aerobic fitness to prevent injuries, get healthy, and burn off more fat.

Endurance athletes know the importance of building the best-possible aerobic systems. A high percentage of the total energy used to participate in activities such as distance running, triathlon, cycling and cross-country skiing is generated through the aerobic system.

Training slow to get fast is an often heard comment in the MAF camp. It appears counter-intuitive, but building endurance involves optimal development of our slow-twitch muscles, also called aerobic. For example, 99 percent of the energy needs in a marathon comes from the aerobic system. For an Ironman triathlon it’s more than that, and in relatively shorter races such as a 10k run, it’s still 95 percent. Even for events such as the mile, 65 percent of the required energy depends on the aerobic system.

Aerobic fitness also has important benefits for those who participate in power sports, including team competition, as well as sports like track and field. Developing the aerobic system helps support explosive activities like lifting and sprinting. In addition, aerobic function is a key to optimal well-being, especially for all athletes who want to avoid injuries, ill health and overtraining while lengthening their careers.

Other improvements for all types of athletes include added movement and cross-training benefits.

While the no-pain, no-gain trend has dominated the fitness boom for several decades, its success is highly questionable if not a complete failure. Injury rates are soaring, athletes are equally susceptible to disease as sedentary people, rates of obesity have tripled, and even a high percentage of athletes are now part of the worldwide overfat epidemic.

One clear problem is that most exercise and athletic training programs completely ignore the value of the aerobic system, and most also do not establish an adequate aerobic base before adding anaerobic workouts.

Minimalist workouts for maximum performance

I developed the the 180 Formula to help professional and amateur endurance athletes, as well as everyday health enthusiasts, achieve their fitness goals. I’ve also used these same principles to help others in a wide variety of athletic endeavors, including, football, baseball, tennis, swimming, car-racing, sailing and even hot-air ballooning. The same principle always applies — a well-developed aerobic system is the basis for optimal performance.

This system involves a high volume of low-intensity exercise. Not only does this have an effect on muscles at the cellular level, it also increases the body’s ability to burn fat as fuel — yes, even for sprinters — while improving the immune system and reducing the risk of injuries.

A frequently asked question is whether different heart rates should be used for different sports. For example, should the maximum aerobic heart rate, as determined by the 180 Formula, while swimming be different when the same athlete is cycling or running? How about walking, or tennis? The short answer is no. The 180-Formula holds true for all aerobic training activities.

At the same heart rate, all sports require essentially the same levels of metabolic activities. However, other aspects are quite different when comparing swimming to running, for example. One significant difference is perceived exertion. One objective factor that makes perceived exertion so different is gravity stress. The difference in this stress between swimming and running is dramatic; there is very little gravity influence in the water, but that same force is maximally affecting the body during running. A great deal of energy may not have to go into countering gravity stress in the pool, but just the opposite is true during a run. And, partly related to gravity stress is the increased volume of muscle activity during running compared to swimming.

Of course, the time to start aerobic training for all athletes is long before competition begins — soon after the conclusion of the previous season is ideal. Measuring progress during this period with a heart monitor is important not only for the athlete, but for the coach, trainer, healthcare professional, and others involved in the overall conditioning process. Once more sport-specific training begins, the heart-rate monitor can still be used to ensure proper warm-up and cool-down, interval-type workouts and overall recovery.

Because I’ve worked with athletes in virtually all sports, my approach to overall conditioning — improving fitness and health and building aerobic function — is very similar. Below are examples of the use of heart monitors in different sports. But all sports are not listed: Once the general idea is clear, applying these methods in any sport or exercise will be relatively easy.

Tennis

Endurance is a significant component in tennis. Consider the length of time — from the start of a warm-up to the conclusion of the final round, especially if it’s a long and difficult match. In these events a significant amount of energy (perhaps 50–60 percent or more) comes from the aerobic system. So a tennis player relies heavily on aerobic function to get through an event. And, the more aerobically trained (the more readily a player can access fat-burning for energy), the more glycogen will be conserved. As the player gets to the later games and sets, there will be more anaerobic function for speed and power instead of significant fatigue. We all know that a long tennis match can be won or lost in later sets, and we can recall some of the great matches of tennis legends such as Bjøn Borg, Jimmy Connors, John McEnroe, Venus and Serena Williams, and Billie Jean King that taxed the bodies of these competitors to the very end. It often comes down to who has the most energy left rather than mere talent.

By training the aerobic system, tennis players can ensure more than adequate reserves at the end of their matches, and nearly unlimited energy overall, reductions in injuries, and the many other benefits the aerobic system provides.

Using a heart monitor will not only help develop the aerobic system but will provide important feedback regarding aerobic progress. For example, a player starting out may play a one-hour match with an average heart rate of 150, with heart rate peaks hitting 185. After developing a good aerobic system, this same player may now be able to compete in the same match with an average heart rate of 130 and the heart rate never going over 155. This is a dramatic difference, and shows the power of good aerobic function. Conserved glycogen, maintained muscle balance (to prevent fatigue and optimize the swing), improved neurological function (eye-hand coordination), improved hydration, and many other benefits follow.

During the aerobic training period (before the competitive season), a heart-rate monitor should be worn during play and the maximum aerobic heart rate not exceeded. As time goes on, the player will be able to perform much harder without the heart rate going up as much. This reflects increased energy, which allows the rest of the body — especially the brain and muscles — to function at much higher levels. If a tennis player regularly uses a stationary bike or runs to help train the aerobic system, that player will improve in these activities as well (i.e., biking or running faster at the same heart rate).

Basketball

During the off-season, common in virtually all team sports, an athlete can develop a great aerobic base through running, biking, swimming, or any endurance workout. During this period, getting on the court also can include wearing a heart-rate monitor, as long as the athlete does not exceed the maximum aerobic heart rate. As the weeks go by, more and more intensity can be gained on the basketball court at the same heart rate, so that as the preseason approaches, a high-level practice game may not bring the heart rate nearly as high as during the start of aerobic training. Players who develop an aerobic base have much more energy, better eye-hand coordination, and overall better function, especially in the latter part of a game.

Motor Sports

Among the more interesting sports in which I’ve introduced athletes to the use of heart-rate monitors is race-car driving. I’ve worked with Mario and Michael Andretti, Derek Bell, Al Holbert, and others. Like with many traditional sports, including baseball and football, bringing new ideas into motor sports was not easy. My entry was helped originally after  working with a young, unknown driver named Chip Robinson. I trained him like an endurance athlete so his brain and body functioned better behind the wheel going at triple digit speeds in heavy traffic. He wore a heart monitor during all his preseason endurance training, which included mostly running and walking. He even entered some running races for fun.

However, behind the wheel during practice sessions the stress of driving was evident. So I had him wear a heart monitor during these driving sessions (and even during races). I discovered that his heart rate, which I later confirmed in other drivers, nearly paralleled his driving speed in miles per hour. Chip’s, however, was more over-reactive than the other drivers’, demonstrating his need to build a bigger aerobic base.

A race-car driver may be running the car at relatively slow warm-up speeds of 90–100 miles per hour, for example, and the heart rate will often be at that level too. Driving poses a certain amount of inherent risk, and a high level of alertness is necessary to perform well and avoid crashes. This all translates into stress, which raises the heart rate — the faster the speed the higher the heart rate. I’ve seen 180 mph equate to heart-rate peaks of 180.

For a race-car driver, this information is very important, especially for those who overreact while driving fast, which was one of Chip’s problems. If a better aerobic system is developed, the heart rate will not overreact, although it will still rise to “normal” race levels. An appropriate heart rate, considering the stress of driving at very high speeds, improves a driver’s ability and makes him or her a better competitor. It also improves eye-hand coordination and adrenal function.

A feature common to all sports and physical activities is that a highly developed aerobic system translates into greater efficiency — allowing an athlete to run, walk, play, ride and drive faster at the same lower heart rate. This also is reflected in increased burning of stored fat for energy, reducing the body’s storage of fat, an added benefit to this type of training.

Join the discussion 55 Comments

  • James Ammon says:

    For weight lifting – would you do one less rep or less weight so you don’t go over your heart rate?

  • Dan says:

    Very nice! I would like to see an article that addresses injuries and recovering methods; something that orthopedic Drs don’t get into. In my case severe tress fractures after fast paced running with minimalist sandals, even though I took things slowly up to that point, in terms of speed and and mid foot striking adaptation. Thanks

  • Richardrkibbey says:

    Have you used. MAF with boxers?

  • John Campise says:

    Thank you. Makes so much sense.

    Does it matter for a race car driver if the MAF is developed using running, swimming, biking, or other?

  • JPW says:

    Would be very interested to see a similar article dealing with benefits of MAF for martial arts, MMA, sports jujitsu, karate, judo etc. and how much is the right amount of MAF style training- minimal effective dose, or at least a method for calculating your individual MAF volume.

    • JPW:

      I’ve noticed that Conor McGregor uses a very low-intensity training system as his method. Even though it’s not exactly “MAF,” most of us in the MAF team look at his training and see MAF training by another name. You should check it out.

    • Dimitri says:

      Agreed. Perhaps an article in the near-future regarding MAF training, as it pertains specifically to combat sports/arts (boxing, wrestling, judo, mma, etc.) based on Dr. Phil’s prior experience with such athletes. I’m positive a lot of readers of this site would find it helpful and useful.

  • Ingrid says:

    My daughter is interested in using this method for high school cross country training. Is this applicable in training for a 1600 meter competition? Hopefully she can convince her coach to read your material.

    • Ingrid:

      The principles surely are. It will probably end up being the case that the coach modifies this from the specific numbers we suggest. But for just about every sport, a majority of the training should be aerobic. How much is enough depends on the specific sport.

  • Joshua says:

    Hi there, I am a professional squash player. My sport regularly includes big spikes in heart rate. Rallies average 30 seconds and can last as long as 2 minutes at high intensity with only a short rest, maybe 20 seconds, in between. I often do a lot of interval training but still find I am fatiguing in matches. I’ve read much of your research and articles. Can you recommend the optimal way to avoid fatigue in this kind of sport?

    Please let me know your articles have been very enlightening and completely changed my perspective on training.

    Best, Josh

    • Joshua says:

      Also. Matches last anywhere from 30 minutes to 2 hours.

      Best, Josh

    • Joshua: Avoidance of fatigue in all sports is primarily the domain of Type I “slow twitch” muscle fibers, which are trained through prolonged low-intensity training that does not culminate in fatigue. Fast-twitch muscle fibers (which are developed preferentially by interval training) are not fatigue resistant by nature, so interval training does little to further increase fatigue resistance of an already relatively fit body. Training to fatigue, while increasing psychological habituation to fatigue, actually decreases physiological tolerance of fatigue over the long-term.

      Put another way, the best way to develop the systems that protect against fatigue is to (perhaps counterintuitively) train the body to remain in a prolonged state of easy activity that does not increase fatigue. This is what we refer to as “aerobic training.”

      My specific suggestion to you is to take your off-season and break it down into 2 parts: an aerobic base training block (2-3 months, ideally) and a sports-specific training block that you have ascertained is enough to regain your competitive edge.

      As far as your regular, in-season training, I would recommend that you replace the interval training sessions that were intended to build fatigue resistance with low-intensity aerobic training.

      • Joshua says:

        Awesome! Thanks for the response. My off season has just started and I will definitely do this!

        I have another question. Will the low intensity aerobic training during the regular competitive season suffice as to keep my heart and lungs in optimal condition? I.e. My muscles will be fatigue resistant, but will my heart and lungs suffer? (When those 20 odd seconds of rest come inbetween rallies I have to make the most of them to recover).

        Also. Is it okay to continue to build muscle through weight training while building an aerobic base?

        Please let me know you guys have helped me very much!

        • Joshua:

          Thanks for your answer, sorry I couldn’t answer earlier. I’m very busy, and it’s only me answering comments and e-mails in order to keep up the quality!

          The answer is that your heart and lungs won’t “suffer” or get atrophied by low-intensity aerobic training during the competitive season. To the contrary—aerobic training actually occurs in the optimum range of operation for the heart and lungs: the intensity where you’re getting the most oxygen and pumping the most blood for the organs’ efforts. So in a very literal way, aerobic training optimizes the heart and lung functioning. However, there are other reasons to maintain some interval training, such as maintaining your neuromuscular edge.

          So keep doing intervals. What I meant is that if you were doing additional interval sessions, not for the purpose of neuromuscular or cardiovascular training, but to improve fatigue resistance, remove the fatigue resistance ones and only do the ones you were doing for neuromuscular training. Typically, very few kinds of athletes whose sports have a significant aerobic component need more than 20-25% anaerobic/high intensity activity (of their total athletic activity including events) during the competitive season.

          While you are building an aerobic base, you cannot build more muscle through weight training. It is 2 very different things. This is why the most elite athletes will religiously devote themselves to their off-season and their base-training season, and do little else than appropriate aerobic training. Whenever you see an athlete deviating from this, expect to see an article about how overtraining ended their career a few years down the line.

          • Joshua says:

            Thank you again for the response! I really appreciate you taking the time.

            Last question. I think..

            When you say do interval sessions for the sake of neuromuscular training are you referring to interval training such as ladder drills and sports specific court movements?(Exercises like with quick movements and long rest) Or intervals such as bike sprints and anaerobic exercises for neuromuscular training?(Intervals on the bike or track usually consist of 60 seconds – 100 seconds on with 60 seconds rest).

            And, last one for sure now.. when is the best time to integrate weight training?

            Thank you again for your insight

          • Joshua:

            While both of those training types classify as high-intensity from a metabolic perspective, ladder-drills and sports-specific court movements are all about explosive power development within the specific skill paradigm of your sport—these are much more characterizable as “neuromuscular training”. In contrast, interval training is high-end metabolic training that hones the body’s energy utilization and metabolic recovery. In other words, both kinds of training are neuromuscular and high-end metabolic, but sports-specific stuff explicitly hones the neuromuscular aspect and intervals explicitly hones the high-end aspect of the metabolism.

            Both are important, and should form part of your routine.

            If by weight training you mean hypertrophy training, then that is best included immediately after a period of base-building. During the core training season I like doing a mixture of aerobic to weight to intervals to sports-specific (something like 70-10-10-10) but if we were to blow this up over the course of the year, I would do: 2-3 month aerobic base building with a bit of low-intensity skill training, 1 month skill (with a bit of hypertrophy), 1 month hypertrophy (with a bit of skill), and then 1 month focusing more on high-end metabolic training (30 anaerobic 70 aerobic).

            This what I would do in a very general sense. The demands of a stacked competitive season, or the characteristics of specific athletes might warrant considerable modification to this model.

            The reason I like doing it this way is because I like building skill as early as possible (without it getting in the way of aerobic base building), then adding in strength once I know that my skill is good enough, and then adding in high-end metabolic (which is the likeliest to injure) once the body is strong and skillful enough to resist that kind of demand.

      • Joshua says:

        Also, training usually consists of intervals in the morning followed by an on court session and a weight session/yoga in the afternoons. Do you recommend building the aerobic base before the on court/ weights or at the end of the day for optimal recovery and results?

        • James says:

          Hi Ivan
          When you say ‘muscle building’ do you specifically mean hypertrophy specific training and not strength training? As Mark Allen strongly recommends strength training whilst also training aerobically -in this article https://www.markallencoaching.com/time-crunched-training/

          • James:

            Yes, I mean hypertrophy-specific training.

            Notice that the article title is “time-crunched training”—meaning that it’s not for aerobic base-building. Hypertrophy-specific training is important and awesome to do while also doing aerobic training, but this type of training is known as polarized training, and constitutes the nucleus of a typical athlete’s training season. While crucial, it does not satisfy the requirements for “building an aerobic base.” (It does, however, satisfy the requirements for other stuff, which is why it’s important and Mark Allen recommends it).

            Effectively, “doing aerobic training” and “building an aerobic base” are 2 different things: the first is one is including a type of training in your workout routine (which may also include any of a number of other exercise types in significant proportions). The second is creating the environment conducive to the development of an aerobic base (especially one which has been stressed or degraded by a racing season, lifestyle stresses, hasn’t been built in the first place, or must be taken to greater heights of competence).

            And (supposing you don’t live in a pastoral or hunter-gatherer context where you are obligated to walk for tens of miles every day) this can only be done with a chunk of time set aside for it every year. In other words, to create or maintain an aerobic base, you need a sizable chunk of time every year where you purposefully “un-crunch” your training and dedicate yourself to building one.

            Hope this helps.

      • James says:

        Hi Ivan,
        Great comment as usual conveyed in an easy to understand way. Most of the (amateur) team sports competitors I know (soccer, rugby etc) do virtually no ‘true’ (as MAF would define it) aerobic training. Yet they wonder why they fatigue so much towards the end of a match and don’t recover quickly from hard plays. Most of those in team sports culture (as well as general fitness enthusiasts who go to the gym etc) still believe that ‘slow’ aerobic training ‘slows you down’.

        • Thanks!

          I fully agree, but let me temper that with a caveat: if you want to fold more steel into a knife and make it stronger, it has to lose its edge in the process (but not its quality). Aerobic training is like re-forging a knife, and anaerobic training is like sharpening its edge. Hope this metaphor makes sense.

          Sometimes, when a knife is constantly losing its edge, you have to upgrade it, and then, after it’s upgraded, you can put the edge back on (and expect the knife to hold it better).

  • Jasen borshoff says:

    I’m a Division 1 wrestling coach and I have recently had two different people in two different countries tell me to read about this type of training. Without asking many questions at first, can you link me Connor McGregor training regime (the most precise you have found)? I’d like to delve into that and more of your content before I ask any questions!

    Thank you

    • Jasen:

      Thanks for your comment.

      At the moment I don’t have a good in-depth source. My best suggestion at the moment is to use “Conor Mcgregor Slow Sparring” as search terms. McGregor doesn’t use slow training expressly for its metabolic advantages (he uses it for their neuromuscular training advantages). However, we at MAF believe that McGregor has been reaping both metabolic and neuromuscular advantages from this kind of training—which we believe his dominance in the sport is partly attributable to.

      Some neuromuscular advantages:
      – Low accumulated fatigue (means maintenance of voluntary contractile power)
      – Lower speed allows a higher ability to troubleshoot and perfect skills, and to train higher-level skills

      Some metabolic advantages:
      – Training slow implies low intensity, which means low homeostatic disturbance
      – Low intensity means increased fat oxidation and therefore greater development of endurance

      A caveat, of course, is that a significant portion of McGregor’s training is the classical high-intensity stuff that helps development of power. But we believe that his sophisticated approach of including a large volume of low-intensity exercise is key to his success.

  • Ray says:

    The difficult question is always, how much aerobic training do you need? I totally get the need for all athletes to have some aerobic base, but do you have any guidelines with regards to different sports.

    For example a defensive lineman in the NFL, probably needs some aerobic training but you don’t want to spend too much time developing that system at the detriment of their power development.

    • James says:

      Ray – Ivan will no doubted give a more in depth response than myself but I think its fairly straightforward to analyse different sports and look at how much aerobic training is required. At a basic level the longer the event the more aerobic training will dominate – for example long distance running, triathlons, mountaineering. Then at the opposite end of the scale sports like NFL and powerlifting. Sports such as tennis, soccer, rugby, squash are somewhere in the middle of the two extremes. I’d say you have to look at the individual to determine how much aerobic training they need. If they perform poorly at the end of matches compared to the start (relative to their competition) then I’d say they need more aerobic training. With better endurance you can actually express a higher percentage of max power at the end of a match.

  • Mircea Andrei Ghinea says:

    Hello!

    I’m trying to understand the 180-formula for various sports.

    “The 180-Formula holds true for all aerobic training activities.”

    I understand that MAF means the max of aerobic engine – just when is about to start the anaerobic engine. More intensity than MAF and the anaerobic engine works more and more, from now on the body will start to use also type 2 fast twitch muscle fibers, use sugar for good, and start accumulating lactic acid. I understand that the MAF has a specific heart rate (very very close to 180-formula).

    At the moment it’s very hard for me to understand the relation between the heart (metabolic engine) and muscles (machine engine). It looks clear that there is a strong relation, since over the MAF the body starts the anaerobic engine.

    (It’s hard for me to formulate the question i have in my mind, i’ll try)

    Lets say we have a good bike rider, that pedals efficient, with strong aerobic engine. Most of the work is done by the lower body (strong legs) and very very little by the upper body (which is very little developed, very little muscle mass/strength). This rider has an 140 bpm MAF while cycling, and lets imagine doing 300 watts for an hour.

    Now this rider wanna get some swimming, he has good technique (from when he was a kid), he’s relaxed, no stressed at all. Gets in the water and starts to swim. His upper body is very little developed for swimming, but he’s trying. His upper body muscles are not developed at all almost in all aspects: volume, strength, aerobic, etc – since never really trained in the water. This guy is a real pro on the bike, while in the water he is a total amateur.

    What will his heart and upper body muscles do while swimming? His heart is well trained to pump big blood for big leg muscles (300 watts for an hour, aerobically), but now has to supply blood for the little not developed upper body muscles. If swimming at his cycling MAF heart rate, isn’t his upper body muscles screaming in pain, working very hard, asking for sugar and actually performing anaerobically?

    Thank you for having the time to read my comment!
    Best regards,
    Mircea

    • Mircea:

      Good question. No, his muscles can’t perform anaerobically for any significant period of time while his heart stays under the MAF HR.

      One of the things that increase the heart rate are the same stress hormone (cortisol & adrenaline) that engage the anaerobic system. So even if you have powerful aerobic muscles on one part of your body, having to go anaerobic on a different part raises your heart rate through stress hormones. And because stress hormones work systemically, it ends up creating a hormonal situation where fat breakdown and oxidation across your body drops and sugar burning increases.

      So having one part of your body work hard for more than a few seconds creates the conditions that (a) raise your heart rate and (b) increases sugar-burning across your body even though some of the muscles now working off of sugar could have been producing that same power output off of fats.

  • Mircea Andrei Ghinea says:

    Thank you, Ivan!

    “his muscles can’t perform anaerobically for any significant period of time while his heart stays under the MAF HR.”
    This shows (i think) that the transition from aerobic to anaerobic is done by what the heart “feels”, like an inner clock built within, a certain BPM number (MAF HR); and is not done by what the muscles “feel”, the power they produce. Interesting.

    “one of the things that increase the heart rate are the same stress hormone (cortisol & adrenaline) that engage the anaerobic system.”
    The stress that come from? I suppose from the muscle that can no longer perform in aerobic mode and, being at the limit (stressed), asks for more (asking for sugar, asking to turn on the anaerobic engine). Here it looks like the muscle dictates the switch – from aerobic to anaerobic. Interesting.

    Soon i will come back with another example (working on it), i think a much better one, where it’s more clear what i’m curious about, about the mixture between the machine power (muscles) and the metabolic power (heart rate – fats/sugars) and what comes out of it.

    At the moment i am happy because i just finished to read all the articles and comments from here (just some podcast left). I learned a lot! I had no idea what aerobic and anaerobic truly means, no idea about fat burning and sugar burning, no idea about the stress on the body if too much time spent while anaerobic. Very recently I got a heart rate monitor and i am trying to keep it at/under MAF HR. It looks good so far.
    Thank you very much for your time and work!

    Best regards,
    Mircea

    • Mircea:

      The reason the muscles can’t perform anaerobically while the heart stays under the MAF HR is because the stress hormones that allow the muscles to go into the anaerobic zone kick up the heart rate past MAF. Whenever you have been moving for more than 2-3 seconds, the heart rate is responding to the levels of stress hormones in the body. Whenever those stress hormones rise enough for the the muscles start to working anaerobically, the heart rate has also risen to a certain point due to those hormones. That point is the MAF HR.

  • Mircea Andrei Ghinea says:

    Thank you, Ivan!

    In the meantime i finished my best example of trying to understand the two systems working together: the machine engine (muscles) and the fuel system (aerobic and anaerobic). I am sorry it got so long, i didn’t intend.

    Let’s say we have a very good bike rider, who trained for long long time only aerobically, so that his legs muscles (machine engine) are at the same level of development (and that’s important) with his aerobic system (fuel system) – which means this rider is very efficient aerobically. Let’s say he can produce an average of 300 watts per hour at 140 MAF HR.

    He gets on a high tech stationary bike (the reason for this is to eliminate the handling of the bike, so really stress free). He is very relaxed with a heart rate of 70 bpm – let’s say. He is ready to warm up.

    He starts pedaling, his muscles are starting to produce some power. The heart follows and raises the bpm so that it supplies blood into the legs. The watts are growing and growing, 50 watts, 100 watts, 150 watts, everything being smooth and stress free. The heart is pumping more and more, supplying blood to the engine (legs muscles), aerobic system is on. By this time the power is at 150 watts and the heart is pumping at 110 bpm – let’s say.

    The power slowly and smoothly goes up, 200 watts, 250 watts, 300 watts. By this time the power is at 300 watts and the heart is pumping at 140 bpm – let’s say. Now, in this moment, the rider is at his MAF HR, aerobic engine is full on, pumping aerobic blood into the legs.

    From here on the legs can not produce more power aerobically, they are not able to. But they can ask for help, they can ask for the second fuel system, the anaerobic system (asking for sugar). The power goes up, 350 watts, 400 watts, etc, all by the help of the anaerobic system, and the heart is pumping more then 140 bpm.

    How did we get here? Looks like as the muscle is producing more and more power simply the heart is pumping more and more blood. So the muscle is asking, the heart replies.

    What happens when we cut in half the engine, meaning cut off one cylinder (one leg), so the system is running only with one cylinder (one leg)?

    Lets imagine this: the left crank suddenly disconnects with the spindle (actually there is such crank-device for training). The left crank is still there in place at the bottom bracket, resting downwards with its pedal at bottom dead center, having no extra friction with the spindle, the left leg resting too in an extended position more or less. The left crank and the left leg are out of the equation, they can not produce any power.

    We are left only with the right side, the right crank and the right leg having no modifications, they can perform normally. Basically our engine is cut in half, from two cylinder engine (two legs) to a single cylinder engine (one leg).

    In the meantime the metabolic engine did not change at all, the system (the heart) can deliver same amount of fuel (blood) as before.

    Now, since the engine performs only with one cylinder (one leg), from 300 watts we are at 150 watts – and, of course, we adjust gears so that the gear ratio matches the engine power.

    What is the heart doing in this context? We know from the warming up phase that at 150 watts coming from two cylinders (two legs) the heart was pumping at 110 bpm. Now, at 150 watts, coming from one cylinder, isn’t the same thing, isn’t the heart gonna pump aerobically at 110 bpm?

    The metabolic engine is not changed at all, it can deliver plenty of fuel (aerobically). But the machine engine (one cylinder – one leg) is smaller now and can not use the fuel amount that the metabolic engine is capable of.

    From here, my one cylinder engine (one leg) is at its max aerobic power (150 watts) but it can get more power by asking for the second fuel source (sugar). And now the power can raise from 150 watts to 160 watts, to 170 watts, etc.
    But how did that fuel (sugar) come to my one cylinder engine (one leg)? I suppose from an increase in the heart’s bpm, the heart went from 110 bpm to 125 bpm, to 140 bpm maybe.

    And here is my point (question), to me it looks like:
    – two cylinder engine (two legs) can perform 150 watts aerobically at 110 bpm;
    – two cylinder engine (two legs) can perform 300 watts aerobically at 140 bpm;
    – one cylinder engine (one leg) can perform 150 watts aerobically at 110 bpm;
    – one cylinder engine (one leg) can perform 170 watts anaerobically at 140 bpm – because the heart got stressed (cortisol & adrenaline) starting from 110 bpm, because the one cylinder engine (one leg) was at its aerobic limit once reaching 150 watts, so it asked for more, asked for anaerobic support to raise the power up.

    This is what my math thinking says about, what i think it would happen in this context of: two cylinder engine versus half of the same engine, along with the Same Fuel System that did not change at all (Same Fuel System that’s composed by two metabolic engines – aerobic and anaerobic).

    The only way the rider can perform with one leg, 170 watts, 140 bpm, AEROBICALLY, is if his legs muscles are more aerobically developed than his aerobic metabolic system.
    But how that can be possible since he was training for a long long time at 140 bpm MAF HR producing those 300 watts in normal two legs pedaling context?

    What is your opinion?

    I think it would be a really cool test to do it for real and to measure the RQ (i think this is the name – where you measure how much fat or sugar you burn) to really find the MAF HR for each situation alone:
    -one where slowly and smoothly increasing the power on the bike using both legs,
    -one where doing the same thing but only with one leg.
    Such test would show if MAF HR is a result of a built in clock inside the heart (a certain bpm number), or if MAF HR is a result of the stress inside the working muscles (a certain power number).

    THANK YOU VERY MUCH for reading my comment! (which got quite long, didn’t expect it – sorry for that)
    Best regards,
    Mircea

    • Mircea:

      Thanks for your comment,

      The metabolic engines are all found in the muscles: Type I fibers are wholly aerobic; Type IIa fibers are hybrid; Type IIb fibers are wholly anaerobic. So a body cannot have a more aerobically developed aerobic system than is found in the muscles. The body can theoretically bring more oxygen in than the muscles can use, but the “aerobic engine” is the entire system top to bottom, from the nose to the lungs to the blood vessels and red blood cells to the capillaries to the muscles.

      The heart needs to pump harder to get the same energy that was previously going into 2 cylinders into 1 cylinder because that same blood has to circulate the body much faster.

      If
      1L of blood is carrying 1g of sugar (say)
      and
      you need 2g of sugar to run at 50w (say)
      and
      you are using 2 legs
      that’s
      1L (25w) per leg

      You only need to pump 1 liter of blood through the leg in a given time interval.

      But if
      you are using 2 legs
      that’s
      2L (50w) for one leg

      You need to pump 2 liters of blood through the leg in a given time interval.

      This is even more important for clearing anaerobic waste from the leg: it is absolutely critical that enough blood to clear twice the anaerobic waste passes through the leg in a given time interval.

      But there’s more: pumping twice as hard with one leg means a lot more stress. In other words, it’s much less work for the body to distribute its labor between two legs, than to concentrate it in one leg: even if the output is equivalent, thework isn’t. And for example, the body needs to pump further stress hormones in order to dilate the blood vessels more (though of course they’ll never be able to be twice the size) in order to get more blood through them. The body is doing this on many, many levels.

      Although the body is doing a lot of things to compensate for only using one leg, you can still expect the heart to need to pump much, much faster if only using one leg, perhaps even more so than if using both legs for the same power output.

      • Mircea Andrei Ghinea says:

        Thank you, Ivan!

        “But if
        you are using 2 legs
        that’s
        2L (50w) for one leg”

        Did you mean 1 leg (instead of where you wrote 2 legs)?

        “the body needs to pump further stress hormones in order to dilate the blood vessels more”

        I thought that the sympathetic nervous system and stress hormones (adrenaline) constricts the blood vessels – not dilate them.

        I think i understand what you mean overall: if you cut the engine in half (one leg only) and wanna produce same power as before (same as with two legs) then the fuel system (heart) has to work harder to supply same fuel (blood) for a given time to only one part of the engine (one leg). Yup, makes total sense.

        Thank you & best regards,
        Mircea

        • Mircea:

          Yes I meant one leg. About stress hormones, I was speaking in shorthand. Various mechanisms in the body that derive from an increase in stress hormone activity cause vasoconstriction globally (across the body) but vasodilation locally (in the blood vessels that feed the muscle) in order to be able to shunt blood where it’s needed. This occurs by the action of adrenaline on the blood vessels’ Beta-2 receptors. (You can find that function detailed here: https://en.wikipedia.org/wiki/Beta-2_adrenergic_receptor#Function).

  • Mircea Andrei Ghinea says:

    Thank you, Ivan! Interesting how clever the body is, by placing blood where is needed via vasoconstriction/vasodilation.

    About our example of one leg vs two legs.

    So far we have (lets say):
    – two legs, aerobically, 150 watts, 110 bpm;
    – two legs, aerobically, 300 watts, 140 bpm (MAF HR).

    And we have (lets say):
    – one leg, aerobically, 150 watts, that for sure performs with HIGHER THAN 110 bpm (because the heart must pump more to supply blood for one leg only – as you said).

    The question is how much higher than 110 bpm? Because:
    – one leg, aerobically, 150 watts, for sure is performing with LOWER THAN 140 bpm (as when two legs involved, both powering 300 watts).

    Just for saying, lets place the bpm somewhere in between, something like 125 bpm. So now we have:
    – one leg, aerobically, 150 watts, 125 bpm.

    My question is:
    – what will happen with the heart when that one leg performs over 150 watts? for sure it will pump more than 125 bpm.

    We know that 150 watts were the max power that one leg muscles can perform aerobically. And, as you said, “The metabolic engines are all found in the muscles. So a body cannot have a more aerobically developed aerobic system than is found in the muscles”.

    From what i think, from what you wrote, and from what i understand by reading on this great website, to me it looks like from now on the one leg engine will ask help from the anaerobic muscles, so that the power can go up. Which means, in this context of one leg engine, that 125 bpm is “the new” MAF HR.

    What do you think?

    Thank you & best regards,
    Mircea

    • Mircea:

      If the leg is pumping twice as hard, the heart will ballpark have to pump twice as much blood through in the same amount of time.

      The reason the anyone’s heart rate exceeds MAF under every circumstance except for activity that lasts under 2 seconds is because the brain recruits anaerobic muscle fibers on top of the aerobic fibers that are already working. So when you say that the leg “asks for help from anaerobic muscles,” you are describing a straightforward example of anaerobic exercise.

      The MAF HR remains the same. (If we had said that the MAF HR was 110 BPM, then it remains as 110 BPM for the purposes of your example).

      • Mircea Andrei Ghinea says:

        Thank you, Ivan!

        The MAF HR i wrote about was 140 BPM when two legs performing at 300 watts – not 110 BPM (that was a value for two legs at 150 watts, or a reference value that for sure will be higher when one leg at 150 watts).

        More simply said, we have this context:
        – two legs, 300 watts.
        Here the heart pumps blood at 140 BPM, being at MAF HR.

        Then we have this context:
        – one leg, 150 watts (aerobically – since this is the max aerobic one leg power).
        What is the heart doing in this context? Will it stay the same at 140 BPM or will it get lower?

        To me it looks strange for the heart to stay at the same BPM since the power is really half.

        Thank you & best regards,
        Mircea

        • Mircea Andrei Ghinea says:

          Hi Ivan!

          My last sentence from above was just a feeling, just an impression.
          The question is real though. I am really curious what do you think about? What’s the heart gonna do in that context? Context where: the power is cut in half from 300 watts to 150 watts, because one leg is off with one leg remaining and keep performing. Will the BPM remain the same, get lower, get higher?

          Thank you!
          Best regards,
          Mircea

          • Mircea:

            Thanks, no worries.

            The body is a very complex system. For example, because the body is designed to move contralaterally (with one leg moving opposite to the other), one-legged movement is bound to create a turbulent movement requiring a much greater stabilizing response by the upper body. So even though the leg may be only putting out 150 watts, other muscles may have to be working harder to compensate for this one-legged movement. So we can’t really think of 150 watts from one leg being “half” of 300 watts from two legs.

            That said, my guess is that the heart rate will decrease significantly. The body’s overall fuel and oxygen utilization when using only one leg at the aerobic threshold of the leg muscles is dramatically lower than when using 2 legs. Furthermore, because one leg is turned off, there’s comparatively little blood going to that leg, which means that major blood flow is concentrated in the other leg. In other words, the heart isn’t really pumping blood “to the whole body” in this example: it’s pumping it to one leg only.

            This example is essentially the reverse of the example where 1 leg is doing the work of 2 legs: in that example, the engagement of the muscles’ anaerobic fibers, and the hormonal activity that implies, as well as the need to clear anaerobic waste, increases the heart rate far beyond the aerobic threshold. In this example, there is no such increase in hormonal activity (because there is no engagement of anaerobic muscle fibers), and there is no need to clear anaerobic waste (because there is no anaerobic activity). So the only thing contributing to raise the heart rate is the need to provide the equivalent of 150w of fuel and oxygen to one leg.

            This means that the body will most likely be able to get away with a much lower heart rate. In broad strokes, we can make the distinction as follows. If the aerobic threshold of this body occurs at 300w:

            1) 150 w (1 leg): fully aerobic
            2) 300 w (2 legs): fully aerobic
            3) 300 w (1 leg): extremely anaerobic

            The point that I’m trying to draw here is that the aerobic or anaerobic element is much more important to defining how the body is functioning than the wattage itself, because “aerobic” and “anaerobic” are types of body function, while “150 w” and “300w” are degrees of body function. So examples 1 and 2 are relatively similar (the difference is only that of degrees), while example 3 is different from 1 and 2 (because it is of a different type).

  • Mircea Andrei Ghinea says:

    Thank you very much, Ivan!

    I really think the same with everything you wrote.

    (with a little exception – not about what you wrote, but about what you misunderstood in one case. i never wrote about one leg performing 300 watts – which is our example for two legs max aerobic power, but i wrote about two legs performing 150 watts – which is our example of one leg max aerobic power.)

    Anyway, TOTALLY agree with everything you wrote.

    So, we have: one leg, at 150 watts, at max aerobic muscles function. And we have: a HR that for sure is smaller than 140 BPM (which is the MAF HR when two legs perform at 300 watts) and, just for placing a number, lets say that HR is 125 BPM.

    Well, it looks like we have a “new” MAF HR.

    We have a MAF HR of 125 BPM when performing one leg. Because any number above 125 BPM means that the one leg engine must ask help from the anaerobic muscle fibers. Right?

    That is what i am thinking and trying to explain: that we have different MAF HR depending of how many numbers of muscles in the body are working.
    – the less numbers of muscles working the lower the MAF HR and the easier for the heart/body.
    – the more numbers of muscles working the higher the MAF HR and the harder for the heart/body.

    And, yes, once the muscles ask help from the anaerobic engine, the more numbers of muscles working the harder the body has to work to clear anaerobic waste.

    What do you think?

    Thank you for reading & all the best,
    Mircea

    • Hello Mircea:

      We wouldn’t say that we have a “New” MAF HR because the aerobic threshold is a measure of the global function of the body, a.k.a. the whole engine. The MAF HR is the level at which the body reaches its present physiological maximum rate of fat-burning.

      Under the conditions you propose in your example (1 leg at 150 watts), the body has been temporarily and contingently disabled from reaching its physiological maximum rate of fat-burning, because the whole engine isn’t in use. But the heart rate at which the whole engine’s physiological maximum capability is achieved hasn’t changed, a.k.a. the MAF HR hasn’t changed. To put it in the terms of your examples, the Maximum Aerobic Power of the body may be something like 300 watts (supposing that we think of the body as nothing more than two legs). That’s still its maximum. If you put the body in a situation where it is only able to use one leg, you’re going to see the heart rate skyrocket all over the place as it uses the anaerobic muscle fibers to move, etc. But that just means that it’s only using part of the aerobic engine. The engine’s maximum power hasn’t changed.

      Let’s say that the maximum aerobic function of a single leg is 150 watts, and that corresponds to a heart rate of 120 (and the “whole body” MAF HR is 150). If you try using that leg say, at 165 watts, you’ll see the heart rate climb well past the “whole body” MAF HR (up to say 165, or MAF+15). If using one leg reset the MAF HR so that there was a “new” MAF HR of 120, then the heart rate would only climb up to 135 (MAF+15)—the same difference as before. But that’s never what we see, because as far as the whole body is concerned, 135 is still an aerobic heart rate, and the body is doing significant prolonged anaerobic work (which is incompatible with an aerobic heart rate).

      Let’s take this further: if you force the body to use only one leg until the other atrophies, effectively bringing the body’s physiological maximum aerobic function to 150 watts (say), you’ll see that the body will reach 150 watts at the same heart rate than it reached 300 watts previously (correcting for age and health risk factors, which may have changed).

      • Mircea Andrei Ghinea says:

        Hello Ivan,

        Pfff, i don’t understand…
        Please, if possible, follow and make corrections within my example (so i can understand). Thank you!

        – two legs, 300 watts, 140 MAF HR – aerobic muscle fibers working at full power.
        – one leg, 150 watts, 125 BPM – aerobic muscle fibers working at full power.

        Now this (the most important thing):
        – one leg, 151 watts… so only one watt more than the leg’s full aerobic power.

        Here the BPM will be just a touch more than 125… here the anaerobic muscle fibers will start working… here the body will start clearing some anaerobic waste… So why did we not pass the Max-Aerobic-Function point?

        125 BPM is the place where the aerobic muscle fibers are working at full power, where the muscle is not asking help from the anaerobic muscle fibers, where there’s no need to clear anaerobic waste, thus here is the place where the MAF HR happens. ANYTHING more than that (one more watt) gets the muscles working anaerobically, meaning passing the MAF point.

        It’s just the same thing you said it very well here:
        “The reason the anyone’s heart rate exceeds MAF under every circumstance except for activity that lasts under 2 seconds is because the brain recruits anaerobic muscle fibers on top of the aerobic fibers that are already working. So when you say that the leg “asks for help from anaerobic muscles,” you are describing a straightforward example of anaerobic exercise.”

        It doesn’t matter that the body is capable of having a good fuel system, meaning a good fat burning at 140 BPM, as long as at 130 BPM the body is using the anaerobic muscle fibers and producing anaerobic waste it means we passed the MAF HR (of that context – performing one leg only).

        The body will clear anaerobic waste faster here, in this context of one leg only, simply because the anaerobic engine is smaller in relation with the whole body. So it will be not so hard for the body and heart (as when two legs performing), but it will be hard for the muscle – a muscle that is working hard with its aerobic fibers at full power plus its anaerobic fibers at some power.

        If it’s not like that what am i missing?

        Thank you & best regards,
        M

  • Every time you exceed the local aerobic threshold of a given set of muscles, and stay at that intensity, the heart rate will quickly leap upwards beyond the real MAF HR.

    The heart is an organ that addresses the whole body, and pertains to the whole body’s function. It simply cannot represent the local aerobic threshold of one muscle or body part. If it could, we would be able to observe someone doing anaerobic arm curls while having their heart rate much lower than their MAF HR. That never happens (because it can’t): if one body part goes and stays anaerobic, the whole body always follows, and the heart rate responds accordingly.

    There is simply no direct connection between the heart rate and one muscle or one body part. One body part influences what happens to the whole body, and then that affects the heart rate. These are separate things. This is why the heart rate never corresponds to what is predicted if you just sum up the blood flow / energy requirements of whatever parts of the body you are presently using. The heart rate responds to the degree of aerobic vs. anaerobic function of the whole body, and that whole-body function is determined by the hormone mixture needed to run a given body part at a given level of intensity for a given amount of time.

    While we can say that the heart rate that corresponds to the aerobic threshold of a given set of muscles is X, this is not a useful distinction as it has no real bearing to the body’s function: as soon as we exceed the intensity X, the response of the heart rate will be not to exceed X, but to go far beyond until it exceeds the MAF HR. Furthermore, the body’s hormonal and neurological fatigue, and its residual stress will be what you expected by looking at HR alone, despite the fact that energy expenditure was much lower than if the whole body had been engaged. If the HR was connected in any meaningful way to a given subset of muscles, you would be able to predict the heart rate by calculating the blood flow that needs to go to those muscles based on their energy expenditure (but you can’t). What you can do, however, is predict the heart rate by looking at global variables that affect the whole body, such as brain activation and hormones. This is what I mean when I say that the heart rate is not connected to any given subset of the body’s musculature, or indeed, to any individual “part” of the body, whatever that may be.

    • Mircea Andrei Ghinea says:

      “Every time you exceed the local aerobic threshold of a given set of muscles, and stay at that intensity, the heart rate will quickly leap upwards beyond the real MAF HR.”

      which in our one leg pedaling case it’s like this: the power SMOOTHLY goes up to 150 watts while the heart SMOOTHLY pumps blood till 125 BPM. then only 1 watt more (muscles start performing anaerobically) and the heart INSTANTLY jumps over 140 BPM – the “official” MAF HR. so there will be no 127 BPM, no 131 BPM, no 138 BPM, but INSTANTLY to over 140 BPM. it looks weird.

      “If it could, we would be able to observe someone doing anaerobic arm curls while having their heart rate much lower than their MAF HR. That never happens (because it can’t)”

      it happens – according to my experience – the body does arm curls, anaerobic, with a BPM lower than the “official” MAF HR. i did that to check. i checked also an interesting exercise, like stepping on a chair (which means one leg lifting your whole body weight, then get back down). did 20 reps with the right leg, then pause so that the heart got lower, back to 80 BPM, then another 20 reps with the left leg, then heart back to 80 BPM. that is one set. i did 10 sets like this. then, right after, to make it harder, did the same thing but with 40 reps per leg for 5 sets. how was my max BPM? well, it was low… was much lower than my “official” 142 MAF HR, it was only 125 BPM… (while running/cycling my BPM easily gets much higher). next days i was really sore in the legs, so the muscles worked hard. like what? like anaerobically. why was that as long as i was well under the “official” MAF HR? well, because i WAS NOT under the MAF HR of that particular exercise, i was over it. at those 125 BPM i was over the MAF.

      yup, doing these exercises and keep pushing, there will come a time when the heart rate will increase over the “official” MAF HR and that’s because those arm curls (or whatever) spent too much time into anaerobic mode. so, yup, in the end the heart will go higher and higher passing the “official” MAF HR.

      “The heart rate responds to the degree of aerobic vs. anaerobic function of the whole body”

      i think the same. and if just a small body part implicated then a smaller increase in the heart rate – and opposite. it’s about the AVERAGE work of the whole body. the heart rate responds to the degree of aerobic vs anaerobic function of the whole body’s average work.

      in our one leg pedaling example, if that rider performs at 130 BPM that rider will be in the anaerobic zone (it doesn’t matter that his two legs results into 140 MAF HR) and it will not last long like that. why? because his MAF HR for one leg was 125 BPM and he passed that. at 130 BPM he is over MAF, not under. the body will get stressed fast because there are more than 150 watts performed (max one leg power), meaning the anaerobic fibers are ON. the heart at 130 BPM is pumping over the MAF HR of that one leg pedaling, so the body is anaerobically stressed here – not relaxed cause 10 BPM under the two legs MAF HR.

      i totally agree with everything you say about what happens When The Body Get Stressed. all i am saying is that the body get stressed SOONER in some cases (smaller/less muscles involved), which requires lower BPM, meaning there is also a lower MAF HR in that case. case in which if you keep working at that “official” MAF HR then you are already in anaerobic work – not aerobic as the “official” MAF HR suggests. this is all i am saying.

      thank you & best regards,
      M

      • Hello, Mircea.

        There is no exercise-specific or limb-specific MAF HR.

        Let me explain what I mean by “leap upwards” if you “stay at that intensity.”

        If you would keep doing anaerobic arm curls without stopping, the heart rate would go up beyond the MAF HR. We’re talking about sets of 100+ reps. This is even if the overall power output is much less than what you’d expect for the heart rate to increase beyond the MAF HR. What you’re doing is letting the body recover.

        If you would sustain the step exercise for the legs (and it was anaerobic for the legs), you would see the heart rate climb steadily (slowly if it’s only marginally anaerobic, or quickly if it’s quite anaerobic) until it rises above the MAF HR, even when the overall power output is less than what you’d expect for the heart rate to increase beyond MAF. Even for slightly anaerobic exercises, this will probably occur within a minute or two of sustained anaerobic exercise with no recovery. It’s not that the heart rate rises IMMEDIATELY. It’s that it never ever STABILIZES under the MAF HR when the exercise is anaerobic, continuous, and sustained. If it was aerobic for the legs (or, in the case of curls, for the arms), that limb would be able to easily sustain 1,000+ continuous reps without the heart ever going above the MAF HR.

        More specifically, if an exercise is anaerobic for any one body part, large or small, the heart rate will rise (slowly if it’s slightly anaerobic and quickly if it’s very anaerobic) and then stabilize at some point above the MAF HR. It will stabilize higher above the MAF HR depending on how anaerobic it is.

        If there is such a thing as an “exercise-specific MAF HR,” you should see the heart rate be able to STABILIZE at some heart rate between resting and the MAF HR while one small part of the body is doing continuous, sustained anaerobic work well beyond 100 or even 1,000 reps. Why? Because the heart would only have to go above that limb’s “MAF HR” and stabilize there, below the real MAF HR. This never happens. The only time the heart rate stabilizes under the MAF HR is when the body is working aerobically wholesale, (and the degree of anaerobic work is minimal and very intermittent, such as for maintaining your balance).

        This applies across the board: when you are barely learning how to type, the reason you get quickly tired and have to stop is because the body has never had to develop many mitochondria in the local muscles (and endurance motoneurons, etc. etc.). In other words, it’s because the exercise is anaerobic. If you decided to continue typing, in a sustained and unbroken fashion (i.e. 80-100 words per minute) even after fatigue, it would feel almost impossible to do so. The only way to continue would be to “rev yourself up” and change the global hormonal activity in your body in order to allow your liver to continue feeding sugar to your hand muscles (among other things). And with that global change in hormonal activity comes a commensurate increase in heart rate. (One of the reasons this almost never happens is because it is obnoxiously difficult to rev yourself up to use a very small body part in a sustained anaerobic fashion—but that’s a different story).

        Why?

        The heart rate simply doesn’t respond to the body’s average work. For that matter, it also doesn’t respond to total work at any given moment, either. We know a lot about the physiological wiring that affects the heart rate. The heart rate responds to the level of stress, which has a bidirectional causal relationship with both the degree—and not the “total amount”—of anaerobic activity and the global ratio of fat to sugar utilization (which are also bidirectionally causally related to each other). The reason heart rate seems to respond to overall work is that the most common reason for an increase in stress is an increase in overall work. But when the average work increases slightly but the stress levels increase phenomenally (such as when one part of the body is forced to continue in protracted anaerobic work), the heart rate doesn’t respond to the increase in the limb work rate. It responds to the stress of the entire body produced by needing to keep that limb working anaerobically. (This is why the heart rate can rise when you’re having a heated argument with your spouse, while sitting down on the couch.)

        It’s because of this that we can say that the heart rate always and only responds to the organism’s state of physiological arousal. The only way for one small chunk of a limb to produce sustained, continuous anaerobic work is to raise the state of physiological arousal of the entire organism. The reason the entire body rallies like this even when one small chunk of an arm is working anaerobically in a continuous and sustained fashion is because evolutionarily, 99.999% of the time that there is a need to increase the physiological arousal of the organism (for every step in our evolutionary ladder, mind you) is because the entire body needs to go anaerobic for fleeing, attack, or defense. (We can easily map out the neurological and hormonal “wiring” implicated in these effects.) The situations where the vast majority of the body can be resting but one small part of the body has to be working anaerobically continuously and in a sustained fashion are, to put it mildly, not common. In other words, these situations are rare enough that there is no physiological wiring that allows the body’s level of arousal to tune itself to the anaerobic work needs of only that limb or muscle while considering that the rest of the body is at a different, aerobic work rate—hence, there is no limb-specific or muscle-specific MAF HR.

        If you want to discuss why it can feel very difficult to cycle at the MAF HR while it is very easy to run at the MAF HR, that is a very interesting conversation, but it is altogether different (although related) to the one we are having here.

        • Mircea Andrei Ghinea says:

          Hello Ivan! Thank you for such consistent reply and for our communication! I was reading many times your reply. The thing is that i agree with most most you are saying – which has to do with how the body reacts while on stress, either physical of psychological. Yet, i think i am talking about something else. I’ll try to be short, sometimes better communication/understanding like this.

          We both agree on this:
          – two legs, 300 watts, 140 MAF HR – aerobic muscle fibers working at full power.
          – one leg, 150 watts, 125 BPM – aerobic muscle fibers working at full power.

          In the two legs context we know that performing at MAF HR is very efficient, meaning keeping the same power for very very long time while the heart easily stabilizes itself at that BPM (yup, we know, actually the power will decrease slowly slowly over time, but for our discussion lets just say that you can keep the same power or, better said, that it’s highly efficient). And we also know that performing at some few BPM lower than MAF HR will result in some fewer watts, but in terms of efficiency it’s the same thing, meaning same high efficiency – being able to keep that power for very very long time while the heart easily stabilizes itself at that BPM.

          How will it be to pedal in one leg context at 130 BPM?
          By numbers that’s 10 BPM lower than the MAF HR, by numbers it looks very safe and very efficient. It looks like the heart easily will stabilize itself at that 130 BPM and the power found here will be stable too, keeping same watts for very long time (yup, as we said, the power slowly slowly will decrease over time).
          Is it like that?

          Thank you & best regards,
          Mircea

          • Mircea:

            Always a pleasure.

            It’s not the same high efficiency. Anaerobic (Type II) muscle fibers are different from aerobic muscle fibers (type I) in 4 important respects:

            1) They have much fewer mitochondria than Type I fibers, so they fatigue much more quickly.
            2) They are hooked up to motoneurons that also fatigue much more quickly than the motoneurons of Type I fibers.
            3) They are called “fast-twitch” in part because their minimum contraction speed is much faster than Type I fibers, so they incur more damage through use.
            4) Type I (aerobic) fibers by default have access to fat stores all across the body, whereas Type II fibers by default have access almost only to local sugar stores.

            (Type IIa fibers are hybrid aerobic/anaerobic, and Type IIb fibers are fully anaerobic, but this doesn’t alter the substance of the example here.)

            This means that if you are using a leg at an anaerobic intensity, the muscle fibers will quickly start fatiguing, and they will put out less and less power as they do. In order to have the same work output, the body will have to raise its arousal to stimulate them more. And local sugar stores are getting depleted, so that fatiguing muscle fibers have lower sugar concentrations to play with, which means that sugar can’t go into the fibers at the same rate. Conveniently, higher physiological arousal increases muscle fiber stimulation while pouring sugar into the bloodstream at the same time, helping these anaerobic fibers avail themselves of more of their fuel source. And as they tire, and the new sugar in the bloodstream begins to deplete, the body must raise its level of arousal yet again. All of this increases the heart rate because if everything’s working harder and fatiguing, you need to make sure that more and more blood runs through the muscles to bring in sugar and oxygen (to let the aerobic fibers help as much as possible) and to clear CO2 and anaerobic wastes.

            If we were talking about aerobic muscle fibers being used, we’d see these fibers comfortably chugging along, pulling from a vast pool of mitochondria, and bringing in oxygen and fats (and some sugar) moving around in the bloodstream. So as long as the you’re using the leg’s anaerobic muscle fibers, you’re playing a whole different game than if you’re using aerobic muscle fibers at the same heart rate.

            In order to pedal at 130 BPM based on your example, you’d have to use the leg’s anaerobic muscle fibers. What you’ll see is that in order to stay at 130 BPM your leg would quickly tire, as the anaerobic muscle fibers will use up all the fuel stored locally in the muscle but the body isn’t increasing its blood sugar because it’s not releasing the hormones it needs to in order to maintain it (which would raise the heart rate commensurately). So the muscle can operate anaerobically until its local fuel supply is exhausted.

            I actually need to add a dimension here. Now that I see your question more clearly, I can see that there are important limitations to the examples we have been using. I should have brought this up sooner but I guess I was blinded by the examples:

            The bottleneck in the aerobic system is rarely in the muscles. In other words, the total contractile power of aerobic (Type I) muscle fibers of any given muscle is almost always greater than the oxygen and fat that the heart can distribute to them if it were distributing to all uniformly. This is because the body is often doing fully-aerobic exercises where it is using one set of muscles (say the upper body) and fueling mostly those with the rest of the aerobic system while the others are at rest. In these cases, the muscle’s aerobic maximum is being pushed, while the maximum of the entire aerobic infrastructure is not. So there’s plenty of opportunities for specific muscle groups to be trained aerobically at their local aerobic maximum while the overall aerobic demand is much lower. So aerobic maximum of all the muscles together is often higher than the ability of the rest of the aerobic system to take in oxygen and break down fats for muscle use.

            This gets us to the reason that the body raises the heart rate in the first place: to switch over to sugar because it can’t pull fat out of the fat cells quickly enough. At this point, it has to increase the hormone that increase sugar release and production in the liver and across the body (cortisol) in order to keep the muscles fueled with something. This means that there’s a whole bunch of muscle fibers that can be potentially fueled with fat (but they’re not) because it’s just not available. The problem is that the body can’t just go and use the sugar to fuel only these aerobic muscle fibers without engaging the anaerobic ones: the hormonal situation in the body has changed, and those hormones also specifically activate muscle fibers with an anaerobic component (IIa hybrid fibers and IIb fully anaerobic fibers). In other words, the body isn’t really switching over to the anaerobic system due to exercise intensity; it’s switching over to the anaerobic system due to metabolic fuel and/or oxygen availability.

            If you had a body with identical muscle power except it could break down and burn a whole bunch more fats, you’d see a much higher work output from aerobic muscle fibers at the same heart rate despite the fact that the demand on the heart theoretically seems higher. This is because fat concentrations in the bloodstream would be higher (so you are getting more fat and oxygen to the muscles per heartbeat) and the heart does things like increase its stroke volume, and lung and muscle blood perfusion would be much greater as capillary networks would be more developed). Not coincidentally, these are exercise adaptations you see in aerobic athletes, but not anaerobic athletes.

            But what it can’t do (because of the way it’s wired) is to switch over to more sugar/less fats without engaging the anaerobic system across the board. (This is what I meant in my previous comment when I said that “The heart rate responds to the level of stress, which has a bidirectional causal relationship with both the degree—and not the “total amount”—of anaerobic activity and the global ratio of fat to sugar utilization (which are also bidirectionally causally related to each other).” So if you have a local supply of sugar in the muscle, you can use the anaerobic muscle fibers while you still have it, without having to increase the heart rate (as sugar concentrations go down, you’d see power go down). But as soon as that fuel supply is gone, you have to get the sugar from somewhere, and the only way to do that is to increase physiological arousal across the board.

            So at 130 BPM you may be able to put out some more power until those anaerobic muscle fibers tire/run out of their local sugar supply. As this happens, work rates will drop relatively quickly until you see minimal anaerobic function due to things:

            1) Some anaerobic fibers will still be activated due to the level of local muscle arousal.
            2) some sugar is still getting to the muscles to power them.
            3) Type I fibers adjacent to the Type II fibers will still be comfortably chugging out ATP, allowing those Type II fibers to avail themselves of some and keep contracting.

            Truth be told, we need to complexify this discussion even further, as it’s likely that the aerobic output of 1 leg when only that leg is in play may be higher than the aerobic output of each leg when both are working, when the body is at or below the MAF HR. (But the same would not be the case for anaerobic output at most HRs.) This is for metabolic/fuel utilization reasons related to the above, not for the cardiovascular reasons we had been previously discussing.

            Ivan

  • Mircea Andrei Ghinea says:

    Hello Ivan! Again, thank you! for such consistent reply, full of details. This way i learn more and more.

    The thing is that overall you are saying what i believe is happening there (how i see the big picture, while you know/say about this and about much more details of this big picture), so you agree with me actually. I don’t know if you are aware of that.

    A true aerobic work out means to be able to sustain same power (well, actually it will decrease slowly slowly over time), for a very long time, for same BPM, so it means to have have safe-efficient-stable BPM/power for a very long time.

    Once you go into anaerobic it will happen this, there are two options:
    -either you try to keep same BPM. if you do that the power will not be stable, it will decrease quite fast.
    -either you try to keep same power. if you do that the BPM will not be stable, it will increase quite fast.
    So either way you are out of the efficiency area, out of a true aerobic work out.

    As you say, in our example of one leg pedaling, at 130 BPM you are already working the anaerobic muscle fibers, so at 130 BPM you are biting into anaerobic work… which means no more safe-efficient-stable BPM/power. How is that possible as long as here, at 130 BPM, we are at 10 BPM lower than MAF-HR? We know that performing under/at MAF-HR is safe-efficient-stable, but we do not find that here at 130 BPM one leg pedaling. Why? Because we passed the real-MAF-HR of this context.

    Only if you stay at 125 BPM you will have a safe-efficient-stable BPM/power for a very long time, because there you can find the max aerobic power of the muscles, muscles which are performing without anaerobic help, so there at 125 BPM we have the real-one-leg-MAF-HR.

    Yes, you came up with a new idea/info: the muscles aerobic function is stronger than the fuel system aerobic function. But, you will see, it changes nothing for our subject (which is the real-MAF-HR?).
    It’s like the leg can perform alone, aerobically, 160 watts (instead of 150 watts – half of two legs working). Ok. And now lets say the heart rate is 130 BPM for this to happen.
    We have the same question: what is the heart doing at 135 BPM?
    -is it 5 BPM lower than the MAF-HR? so everything very aerobic, very safe-efficient-stable?
    -is it 5 BPM higher than the MAF-HR? because the muscle is biting into anaerobic work, the muscle is asking help from anaerobic muscle fibers since passing the 130 BPM mark?
    So how is it?
    Me, i think the same as the other example: one leg pedaling at 135 BPM is already anaerobic, meaning no safe-efficient-stable BPM/power for a very long time, meaning here we passed already the real-MAF-HR of this context.
    Only if you stay at 130 BPM you will have a safe-efficient-stable BPM/power for a very long time, because there you can find the max aerobic power of the muscles, muscles which are performing without anaerobic help, so there at 130 BPM we have the real-one-leg-MAF-HR.

    Which means that we have not one-single-official-MAF-HR, but we have many MAF-HR depending on muscles’ power (a combination of muscles number/size/strength). The less muscles’ power the lower the MAF-HR, the more muscles’ power the higher the MAF-HR.
    (also it depends on how fit those muscles are, on how fit the fuel system is, and on how these two interact each other)

    To have one-single-official-MAF-HR is an exception and/or it will happen every time when the engine (the muscles’ power) is stronger than the fuel system.
    To work it would be like this: one leg pedaling to be able to produce 170 watts (lets say) aerobically (so no anaerobic muscle fibers involved) at 140 BPM… Here, in this context, simply the fuel system matches the engine (either an engine of 300 watts performed by two legs, either an engine of 170 watts performed by one leg). Yup, here, in this context we have one-single-official-MAF-HR.

    What i’m trying to point is: what if a smaller engine is involved while having a strong fuel system? what if the engine is weaker than the fuel system? Well, here, the MAF-HR would be lower than the official-MAF-HR.
    Here’s a good example: a strong cyclist has a big legs engine and a big fuel system. What if this cyclist has to pedal with his hands (like in America’s Cup sailing yachts racing)?
    Well, he can do it, yup, but his engine is very small for this activity (while his fuel system is top) so, in this case, his muscles will decide the MAF-HR (not his fuel system). For those little muscles (that the cyclist has in the upper body) to not pass over the MAF, to not ask help from the anaerobic engine, the cyclist has to use very little power, which automatically requires little blood, which automatically requires lower BPM, which automatically means that this cyclist’s MAF-HR is lower when hand pedaling.
    So, this cyclist has a higher-MAF-HR while on the bike (cause powerful muscles), and a lower-MAF-HR while hand pedaling on the sailing yacht (cause much less powerful muscles) – this because the fuel system adapts to the engine’s power.

    (by the way, this years America’s Cup was won by New Zealand, score of 7 to 1, by having a very very special yacht where they used legs power, meaning they were really pedaling on a stationary bike. i find it very funny-interesting-story, that this was happening only now, 2017.)

    That is how i see, understand the MAF-HR story.

    Thank you & best regards,
    Mircea

    • Hello, Mircea.

      The MAF HR story as you understand it is not the MAF HR story as we have told it.

      The muscles do not decide the MAF HR, as the MAF HR defines the maximum potential of the function of the full aerobic system, not parts of it on a case by case basis. If we say that the body is a six-cylinder engine (each arm is one cylinder and each leg is two cylinders) then you are using a third of the engine if you are hand-pedaling. A third is not a maximum. Just because you can’t use the total potential of the fuel injection system (lungs, blood vessels, heart, capillaries, lipolysis, etc.) of a 6-cylinder engine to feed only 2 cylinders does not mean that the engine’s maximum horsepower (or its maximum RPM, or its maximum torque, or its injection maximums etc. etc.) has gone down. (And just because you may not be able to reach the maximum in that situation also does not mean that the maximum has gone down.)

      It means you are using a chunk of the maximum, but this doesn’t change the maximum.

      The MAF HR has the name “maximum” for a reason: because it tells the story of what the complete engine is capable of. It applies far beyond exercise to longevity, stress, and lifestyle. Your discussion on this “contingent MAF HR” does not. The MAF HR must continue to mean what it means in order to enable us to tell these other stories, and tie the story of exercise to longevity, stress and so forth. If we unmoor the MAF HR from its true meaning—to outline what the full powertrain is capable of—we become disabled from tying together the many aspects of the body’s function across domains of human activity. (So I won’t let that happen.) And even if we did unmoor it, we’d still need a new concept that does and describes exactly what the concept “MAF HR” does now.

      Just because we can coerce one term into applying to both a full maximum as well as an infinite number of permutations of “sub-maximums” (that are similar to each other in their fundamental difference to the full maximum, which is that they do not apply across domains) is not a good reason to do so: It’ll be very hard to hold on to the fact that the full maximum has a fundamental and crucial difference to the “sub-maximums.” Furthermore, the best way to isolate and illustrate that difference (and to help people hold on to it) is to create a new term that captures it and only it. So we’ll be back where we started: a MAF HR with an identical definition to the present one, only by another name.

    • The discussion you want to have on the aerobic threshold of muscles and body parts is also useful within the domain of sports physiology, but it is not a discussion of the MAF HR. Furthermore, it is not really a discussion of sports performance, as the sport that requires people to stay below a “contingent MAF HR” hasn’t been invented yet. You’ll never see people hold below this HR in yacht racing, for example. It’s never really used (because it doesn’t apply to the full organism, when it’s the full organism, and not the upper body, that is involved in the sporting event.) For example, 2-handed pedaling in yacht racing (or say, rowing sports) will almost always have a very strong anaerobic component to the athletic use of the upper body itself.

      The discussion of the aerobic threshold of individual muscles or body parts is really an academic one: it is very difficult to apply (and to my knowledge never applied) to training and racing strategy even in the granular physiological pedagogy of elite sports. The most fundamental reason is that the physiological arousal requirements of the sport context take over the organism. The alertness requirements alone of yacht racing (without discussing the rest of the phenomenal physical requirements that apply to paddling with the upper body) would—and always do!—require the organism to be aroused far beyond the MAF HR.

      We can by all means have this discussion, but we must do so by another name than “MAF HR.”

  • Mircea Andrei Ghinea says:

    Hello Ivan!

    “Just because you can’t use the total potential of the fuel injection system of a 6-cylinder engine to feed only 2 cylinders does not mean that the engine’s maximum horsepower has gone down.”

    This i really don’t understand… As long as the engine is working at 1/3 of its power (since 2 cylinders working instead of 6) the horsepower is definitely going down… Yup, we know that virtually the engine is capable of much more (if using all cylinders), the engine has big potential, yes, but unfortunately what matters is the reality (in this case only 2 cylinders are working).

    You are talking about the maximum aerobic function regardless of context, like maximum ever of all possible aerobic muscles power and all possible aerobic fuel system power combined. Yes, i understand and agree such thing exists. And now it’s called MAF HR.

    The problem is: what do you do when you have to use smaller amount of aerobic engine power along with top aerobic fuel system power? And this happens in real life, it’s not a myth. A top cyclist who wanna become an endurance swimmer is in such position. If he starts his swimming training at the MAF HR he will be in trouble, that will not be an aerobic training, but an anaerobic one. Because at that official MAF HR his swimming muscles will perform anaerobically. If you want that then that’s fine, but if you wanna train at the threshold between aerobic and anaerobic (meaning at muscles MAF) you have to lower the BPM, getting it lower than the official MAF HR.

    I don’t know what is the name of this “type” of MAF (small-engine-plus-big-fuel-system), but it looks real. If you wanna train your aerobic muscle fibers then you have to not jump into the anaerobic ones, not asking help to the anaerobic muscle fibers. Once you go into anaerobic, even though you are under/at the official MAF HR, it is impossible to call it an aerobic training. Thus, in this context, the muscles decide if you are under/at MAF or over MAF. What’s the name of this context? I don’t know. There should be a name, i think.

    When the aerobic fuel system power is weaker than the aerobic engine power then, yes, here it’s another story. Here the fuel system reaches first its limit, so here we must be patient with the fuel system, let it develop, so that the muscle do not ask help to the anaerobic fibers. Here is basically the MAF HR you are talking about (which i totally agree with).

    Now to try my best example:
    We are in 2018, Chris Froome just won Tour de France for the 5th time. He plans to switch sports, he plans to become an endurance swimmer. On the bike he was king, with those big strong legs being able to maintain 300 watts aerobically for many hours at a heart rate of 140 BPM. Now, for the new sport, he is really unfit, his upper body (where the main power comes from in swimming) is very very underdeveloped, meaning low volume muscles, low strength, low endurance, low everything. He needs to start training. We know that now, in his beginning phase, he needs totally aerobic work out (anaerobic work out will come much later), so he needs to work at MAF HR, meaning his muscles to perform totally aerobic and not asking help from the anaerobic fibers. But the big question is: what is his SWIMMING MAF HR – because we know his CYCLING MAF HR, which is 140. Those 140 BPM supplied big blood for big engine. Now the swimming engine is much much smaller. I could bet that his swimming engine at this moment is maximum 1/4 of the cycling engine. But lets say his swimming engine is stronger than that, like 1/3 of the cycling engine, meaning his aerobic swimming engine is 100 watts. Well, here, in this context of swimming, his heart must supply blood to only 100 watts. Yes, his heart and his fuel system is top top in the world, one of the best fat burning systems out there. But this is no help, because his swimming engine is totally amateur. Which means his heart will supply blood to that 100 watts swimming engine at much lower rate than that 140 BPM (his cycling MAF HR), lets say 120 BPM for those 100 watts. Well THIS is the new MAF HR for this new context (swimming), meaning 120 MAF HR. ANYTHING more than that, any watts more than that means the engine is asking help from the anaerobic fibers. Does he wants that?! I think not, because he is in the building up phase, he needs to develop his aerobic muscle fibers. He is just very very lucky that his heart and his fuel system is top top, no need to develop that at the moment. If he will train in the water at 140 BPM (cycling MAF HR) then he will be a lot anaerobic… yup! That’s 20 BPM more than his real swimming MAF, meaning his anaerobic muscle fibers working like crazy. Does he want that, does he need that?! No, No, No. He needs good training, he needs developing the aerobic muscle fibers, their power, his aerobic engine. Slowly slowly this aerobic engine will grow, being able to produce 125 watts, then 150 watts, and so on. In the meantime his fuel system will slowly decrease. Why? Because there’s no need to be a very very good fat burner cause there’s no engine to consume that big amount of fuel – this for the moment. And then there will come a point when the aerobic muscle engine will match the aerobic fuel system – lets say that will happen when power at 200 watts – and from now on they will develop both at the same time, helping one another to grow. As the swimming aerobic power increase, as the aerobic muscle fibers get more powerful, as the fuel system becomes a better fat burner, same does the MAF HR. After three and a half years of swim training we have: a new Chris Froome, looking totally different, now with skinny legs and bigger upper body, being able to perform 300 watts at 140 MAF HR (similar with his long ago cycling MAF HR).

    Thank you very much for everything, for reading my comments, for your patience, for your reply!
    Best regards,
    Mircea

    • Hello, Mircea:

      There are engines such as Dodge V8 Hemi models that can use only 4 cylinders instead of the full 8. The engine is still considered to have 350 HP. These engines are never discussed to have “less” horsepower when only using 4 cylinders. The engines’ power, a.k.a. their capacity, hasn’t changed. Horsepower is not a measure of the output. It is a measure of the maximum output possible by the engine—even when you hook it up to a poor transmission, meaning that it can’t express its power through the wheels, the engine’s horsepower hasn’t changed. It literally doesn’t matter how much power the engine can presently express. A 350 HP engine that has been completely taken out of the car, with no fuel source and no possible way of even turning on is still a 350 HP engine. This is why it is even possible to mention that a power plant is working at “half capacity” due to a storm. Taking your discussion at face value, we should have to speak of the power plant as working at “full capacity” even when it’s working at half capacity—and that’s not the case. These are not controversial statements.

      We should no more talk about sports-specific MAF HR than sports-specific VO2 Max.

      I believe I finally understand your question. I realize that I have to retract some statements made in previous comments. I got too locked into our discussion of wattage and heart rate on a per-muscle basis and I missed the forest for the trees. I apologize for seeming like I’m moving the goalposts. I shouldn’t have gotten locked in like this.

      Chris Froome’s trained cycling MAF HR would be the same as his untrained swimming MAF HR. This is because the physiological arousal considerations (neurological + hormonal) that apply to anaerobic muscle fibers also apply to aerobic muscle fibers: in order to run the aerobic muscle fibers of a given muscle at 100%, the fuel mixture needs to be calibrated to the needs of running those aerobic muscle fibers at 100%, regardless of the fact that the amount of fuel that the body can avail at that arousal level is much higher than what’s needed to run muscles that are weaker than are usually run. Similarly, the particular set of motoneurons that run the aerobic muscle fibers of the swimming muscles need to be aroused to their maximum in order to run those aerobic muscle fibers at their maximum. And because the heart rate is a result of neurological and hormonal phenomena, it will be at the MAF HR.

      When aerobic muscles are very weak compared to the rest of the aerobic system, it is often seen that the muscles will start to produce lactate at a lower heart rate (as there is minimal blood perfusion from the outside, meaning that the muscles are working with the minimal oxygen they have locally). But as the body warms up, the heart rate will rise and lactate levels will drop as blood perfusion into the muscles increase (and the muscles start working systemically with the body). At this point, regardless of how trained the aerobic muscles are, if they are working at their maximum aerobic capacity, the body will be at its MAF HR.

      Let me finish by saying that you can try this at home: do an activity that you don’t regularly do while keeping at the heart rate that lets you maintain the maximum power output you can maintain (with only a minimal drop) for 500 sustained, continuous repetitions. That’s going to be at the same MAF HR that works across activities.

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