White Paper: An Introduction to MAF – Maximum Aerobic Function

By June 22, 2016 November 27th, 2016 Fat-Burning Journal, Original Research
MAF White Paper

A systematic approach to building health and fitness while improving overall human performance and preventing injury, illness and disease.

Dr. Philip Maffetone


In a society strongly emphasizing health, well-being and physical performance, it is an unfortunate contradiction that illness, injury and disease are now the norm.

Despite the fact that most common health and fitness problems are preventable, healthcare costs have created a serious worldwide economic burden. There is widespread confusion about how to exercise and how to eat well. Quality of life has stagnated, risk of illness remains high, and the incidence of chronic disease is on the rise.

Defining Health and Fitness

Health is a state in which the aerobic system, along with all others (nervous, hormonal, digestive, etc.), work in harmony. Fitness is the ability to be athletic — to apply the body’s physical abilities towards achieving exercise goals.

For nearly 40 years, the MAF Method has helped individuals in all walks of life pursue well-being. This approach recognizes a key foundation for both health and fitness that is often neglected — the aerobic system, which uses stored body fat to power the body with nearly unlimited energy. To underscore the significance and importance of the aerobic system, we call our program MAF, which stands for Maximum Aerobic Function.

Our philosophy integrates nutrition with exercise to optimize the body’s true aerobic, or fat-burning, system.

Any impairment in the aerobic system can create global problems in the body’s upkeep and function. The result can be ill health, including common chronic diseases such as diabetes, cancer and heart disease. For this same reason, athletic or fitness dysfunctions such as recurring injuries, a lack of improvement and the overtraining syndrome, can usually be traced back to aerobic dysfunction. In effect, the MAF Method assesses and intervenes in the aerobic system to reduce risk of poor health and chronic disease, while simultaneously expanding a person’s athletic potential. To that end, this method relies on a variety of unique and simple assessment tools that individuals can use to measure the aerobic system, helping to ensure optimal fat-burning. By improving both health and fitness, the MAF Method is highly conducive to sustaining fitness gains that would otherwise be lost to illness, injury or overtraining, and has been shown to produce a significant rate of personal-best athletic performances.1,2

I. An Unhealthy Society

Over the past 40 years, the consumption of junk food, mostly in the form of refined carbohydrates, has increased dramatically, while fat and protein intake has remained almost the same.3 This dietary change alone has significantly reduced aerobic function in millions of people, and increased their risk for chronic illness.

Most people, including athletes, have moderate and high risks for chronic disease, which accounts for 90 percent of healthcare spending.7 In the U.S. alone, the Kaiser Family Foundation estimates that 2015 expenditures will be $4 trillion.

Changes in Markers of Increased Illness

Global obesity has more than doubled since 1980.4 This is associated with increased rates of cardiovascular diseases, cancer and other chronic illness. Diabetes now affects more than half of all Americans.5 There is a dramatic rise in prescription medications.6

Most people, including athletes, have moderate and high risks for chronic disease, which accounts for 90 percent of healthcare spending.7
In the U.S. alone, the Kaiser Family Foundation estimates that 2015 expenditures will be $4 trillion.

II. Fit but Unhealthy

While inactivity is severely detrimental to health, increasing physical activity has not been the panacea it is often assumed to be. Improper exercise actually can create enough physical, chemical and mental stress to cause great harm to the body. In essence, many people try to build more fitness while sacrificing health.

Health Consequences of Inactivity

  • Almost 80 percent of Americans perform inadequate levels of physical activity.8
  • Physical inactivity is linked to more than 5 million deaths worldwide per year — more than those caused by smoking.9

For example, the popular “no-pain, no-gain” trend — high intensity exercise — has been shown to reduce markers of health and fitness: It can create damaging oxidative stress,10 decrease immune function,11 promote inflammation,12 decrease skeletal muscle diameter through increased breakdown,13-16 impair aerobic function and fat-burning,17 and cause gait dysfunctions.18

Furthermore, those who are physically active, including millions of recreational athletes worldwide, are at high risk for developing overuse injuries and illnesses, including the overtraining syndrome. This is arguably the most serious exercise-induced chronic health problem (and a common result of high-intensity training). Markers of overtraining are commonplace in athletic populations. For example, Division I National Collegiate Athletic Association (NCAA) athletes had significantly more pain, depression, and decreased physical function compared with controls.22

Injuries Associated with High-Intensity Training

  • On average 56 percent of Ironman athletes suffered either an overuse injury or illness while training for races.19
  • The high-intensity “no-pain, no-gain” sport of CrossFit has an estimated injury rate of 73.5 percent with 7 percent of these injuries requiring surgery.20
  • Even those who engage in aerobic dance, group workouts, strength training, and use gym equipment see injury rates of over 50 percent.21

For these reasons, the MAF Method recommends a period of low-intensity training and natural movement to improve aerobic function and health before embarking on higher-intensity training. A common criticism of this approach is that it typically cannot match the rate of fitness gains provided by high-intensity exercise. But given the above-mentioned dangers of protracted high-intensity exercise, the MAF Method provides a better return on the investment of time and energy spent exercising than high-intensity programs that provide quicker, often short-term, fitness gains at the cost of health.

Consequences of the Overtraining Syndrome

Muscular injuries, decreased immunity, hormone imbalance, sleep disturbances, depression, neurological dysfunction,23 and impaired cardiac function.24

III. Assessing MAF

In order to monitor progress and help take the guesswork out of making lifestyle improvements, the MAF Method employs a set of tools, metrics and principles to help a coach, health specialist, athlete or any individual find ways to promote aerobic function in order to increase benchmarks of health and fitness. This holistic approach incorporates various ways that individuals can self-assess. The chart below gives some samples of these assessment tools.

Tools of the MAF Approach

  • Using the 180-Formula to individualize exercise intensity.
  • Perform the MAF Test to measure progress.
  • Nutrition using the Two-Week Test to help reduce consumption of refined carbohydrates and overcome sugar addiction.
  • Overall lifestyle assessment and determination of risk factors using surveys.
  • These and other tools can be found on www.philmaffetone.com and in the
    MAF app.

IV. The New Aerobics

The aerobic system generates significant amounts of energy from fat, allowing long periods of optimum performance without fatigue or physical impairment.25 While the body uses varying amounts of fat and sugar (glucose) at any given time, fat is by far the more health-promoting and reliable fuel source for long-term energy without fatigue.

The aerobic system is implicated in all the processes that result in burning more body fat. Essentially, this makes it a “supersystem”: It integrates components of the cardiovascular, respiratory, musculoskeletal, endocrine (hormonal), nervous and other systems.

For this reason, aerobic function promotes health and fitness by improving the heart, lungs and circulation, controlling blood sugar, reducing excess weight and body fat, increasing muscular endurance and flexibility, and optimizing overall function in the body and brain. The MAF Method, therefore, develops and monitors the aerobic system, utilizing the level of aerobic activity in the body as a baseline — a common denominator — of its overall health and function.

Aerobic muscles also play an important role in power and team sports. They assist anaerobic fibers by providing much-needed circulation that brings in added oxygen and other nutrients, removing and processing metabolic by-products, and speeding recovery following a hard workout or competition.26

There are trade-offs to be made between using fat and glucose in exercise. Fat is far more plentiful, even in lean individuals, but provides more energy at a constant rate. Sugar is not as plentiful and provides less energy but very quickly. Low-intensity exercise, given its lesser energy needs, has been shown to increase the use of fat as fuel, and therefore readily engage the aerobic system.27

Two Fuels, Two Types of Muscle Cells

Aerobic “slow-twitch” muscle fibers, which burn fat for energy and are fatigue-resistant, are highly concentrated in the muscles that also provide the main support for joints, bones, and indirectly to all soft tissues such as tendons and ligaments.24

Anaerobic “fast-twitch” muscle fibers, which consume sugar at high rates but have limited energy, are primarily utilized for (a) short, high-intensity exertions and (b) quick movements.

Fat- and sugar-burning can be measured in a laboratory setting through a process called respiratory exchange ratio using a gas analyzer during an exercise treadmill or similar test. However, most people are unable or unwilling to perform this test due to availability, cost and other factors. Fortunately, it is also possible to perform accurate assessments through the use of simple questionnaires by surveying the body’s abnormal signs and symptoms (for much less cost and without examinations).<sup>28</sup> The aerobic system can be evaluated using this format, and the MAF Method employs such surveys.

IV. Heart-Rate Monitoring, Stress and Energy Utilization

The use of a heart-rate monitor can greatly aid in exercising at a relatively low level of intensity (resulting in a lower heart rate), during which the body secretes hormones necessary for aerobic function and fat-burning. Conversely, high-intensity efforts prompt the release of stress hormones that:

  • Raise the heart rate to higher levels.
  • Increase the rate of sugar-utilization.
  • Decrease the rate of fat-utilization.

The 180-Formula was engineered as an easy-to-use accurate estimator of an individual’s Maximum Aerobic Function Heart Rate (MAF HR), at which stress levels are low enough that sugar is being utilized at a minimum, but fat-burning activity is at its highest.

The 180-Formula

This formula takes an individual’s age, personal health (such as frequency of illness, injury and medication), and fitness factors (such as constancy of training and race performance) into account, all of which importantly affect exercise outcomes.

The MAF Test tracks the change in an individual’s aerobic speed (at the MAF HR) across time. Increases in speed at the same heart rate indicate aerobic development, while a decrease in speed signifies that aerobic function is impaired. Continuous decreases in MAF speed indicate that the aerobic system is beginning to atrophy. The MAF Test allows its user to easily and accurately measure aerobic function in real time, and adapt their training or lifestyle accordingly. (Other measurements can also be used for the MAF Test, including power/watts, time, laps, etc.)

In the chart below, we show MAF Test results of a runner during a 19-month period using the same 5-km course. The first 12 months were kept exclusively at the MAF heart rate, while the following seven incorporated substantial anaerobic training. The runner’s progress plateaued at the onset of anaerobic training, and began to deteriorate after three consecutive months of anaerobic training.

MAF Aerobic Training Graph

VI. Conclusion

The central observation of the MAF Method remains that any problem with the aerobic system hinders the body’s ability to provide for its long-term performance and health. In effect, aerobic impairment sows the seeds for poor health and fitness, and even chronic disease, by forcing the body to rely on sugar, which is the less reliable — and in large quantities, unhealthy — energy source.

A poor diet, along with the extremes of fitness — overtraining and inactivity — can also impair aerobic function leading to reduced fat-burning. This creates a cascade of signs and symptoms common in many individuals: fatigue, high body fat, physical injuries, intestinal dysfunction, reduced immunity (frequent colds, flu, other infections) and increased risk of chronic disease.

In contrast, improving the aerobic system increases fat-burning, reduces or eliminates abnormal signs and symptoms that reflect poor health, and can significantly improve fitness, especially for athletes.


  1. Høeg T, Maffetone P. The Development and Initial Assessment of a Novel Heart Rate Training Formula. Poster presented at the Medicine & Science in Ultra-Endurance Sports 2nd Annual Conference; May 2015; Olympic Valley, CA, USA.
  2. Maffetone P. Complementary Sports Medicine. Champaign, IL: Hum Kinet; 1999.
  3. Centers for Disease Control and Prevention (CDC). Trends in intake of energy and macronutrients—United States, 1971-2000. MMWR Morb Mortal Wkly Rep. 2004;53(4): 80.
  4. Alwan A et. al. Global status report on noncommunicable diseases, 2010. World Health Organ. 2011.
  5. Menke A, Casagrande S, Geiss L, Cowie C. Prevalence of and Trends in Diabetes Among Adults in the United States, 1988-2012. JAMA J Am Med Assoc. 2015;314(10):1021.
  6. Scott I, Hilmer S, Reeve E et al. Reducing Inappropriate Polypharmacy: The Process of deprescribing. JAMA J Am Med Assoc Intern Med. 2015;175(5):827.
  7. LeRoy L, Bayliss E, Domino M et al. The Agency for Healthcare Research and Quality Multiple Chronic Conditions Research Network: Overview of research contributions and future priorities. Medical Care. 2014;52:S15-S22.
  8. Centers for Disease Control and Prevention et. al. Adult participation in aerobic and muscle-strengthening physical activities—United States, 2011. MMWR Morb Mortal Wkly Rep. 2013;62(17):326.
  9. Lee I, Shiroma E, Lobelo F, Puska P, Blair S, Katzmarzyk P. Effect of physical inactivity on major non-communicable diseases worldwide: an analysis of burden of disease and life expectancy. Lancet. 2012;380(9838):219-229.
  10. Powers S, Jackson M. Exercise-Induced Oxidative Stress: Cellular Mechanisms and Impact on Muscle Force Production. Physiol Rev. 2008;88(4):1243-1276.
  11. Walsh N, Gleeson M, Shepard R et al. Position statement part one: immune function and exercise. Immunol Rev. 2011;17:6-63.
  12. van de Vyver M, Engelbrecht L, Smith C, Myburgh K. Neutrophil and monocyte responses to downhill running: Intracellular contents of MPO, IL-6, IL-10, pstat3, and SOCS3. Scand J Med Sci Sports. 2015.
  13. Szivak T, Hooper D, Dunn-Lewis C et al. Adrenal Cortical Responses to High-Intensity, Short Rest, Resistance Exercise in Men and Women. J Strength Cond Res. 2013;27(3):748-760.
  14. Fitts R, Costill D, Gardetto P. Effect of swim exercise training on human muscle fiber function. J Appl Physiol. 1989;66:465-475.
  15. Harber M, Gallagher P, Creer A, et al. Single muscle fiber contractile properties during a competitive season in male runners. Am J Physiol Regul Integr Comp Physiol 2004;287(5):R1124-R1131.
  16. Trappe S, Harber M, Creer A et al. Single muscle fiber adaptations with marathon training. J Appl Physiol. 2006;101(3):721-727.
  17. Boyd A, Giamber S, Mager M, Lebovitz H. Lactate inhibition of lipolysis in exercising man. Metabol. 1974;23(6):531-542.
  18. Munoz I, Seiler S, Alcocer A, et al. Specific Intensity for Peaking: Is Race Pace the Best Option? Asian J Sports Med. 2015;6(3).
  19. Andersen C, Clarsen B, Johansen T, Engebretsen L. High prevalence of overuse injury among iron-distance triathletes. Br J Sports Med. 2013;47(13):857-861.
  20. Hak P, Hodzovic E, Hickey B. The nature and prevalence of injury during CrossFit training. J Strength Cond Res. 2013:1.
  21. Gray S, Finch C. Epidemiology of Hospital-Treated Injuries Sustained by Fitness Participants. Res Q for Exerc Sport. 2014;86(1):81-87.
  22. Simon J, Docherty C. Current Health-Related Quality of Life Is Lower in Former Division I Collegiate Athletes Than in Non-Collegiate Athletes. Am J Sports Med. 2013;42(2):423-429.
  23. Kreher JB and Schwartz JB. Overtraining Syndrome. A Practical Guide. Sports Health. 2012;4(2):128–138.
  24. 24. Le Meur Y, Louis J, Aubry A et al. Maximal exercise limitation in functionally overreached triathletes: role of cardiac adrenergic stimulation. J Appl Physiol. 2014;117(3):214-222.
  25. 25. McArdle W, Katch F, Katch V. Exerc Physiol. 3rd ed. Philadelphia, PA: Lea & Febiger; 1991.
  26. Haseler L, Hogan M, Richardson R. Skeletal Muscle Phosphocreatine Recovery in Humans is Dependent on O2 Availability. Med Sci Sport & Exerc. 1999;31(Supplement):S278.
  27. Putman C, Jones N, Hultman E et al. Effects of short-term submaximal training in humans on muscle metabolism in exercise. Am J Physiol. 1998;275:E132-E139.
  28. Ganna A, Ingelsson E. 5-year mortality predictors in 498 103 UK Biobank participants: a prospective population-based study. Lancet. 2015;386(9993):533-540.

Special thanks to Ivan Rivera for assistance in writing and editing, Hal Walter for editorial and Simon Greenland for formatting.


  • Richard G says:

    I have been looking at developing my endurance base for trail running and cycling. I have a history of strength training (power lifting) over many and some canoe marathons. I also enjoyed long heavy pack hikes at altitude. In essence I would consider myself an all rounder but am looking to reduce body weight through improved body composition ( lose visceral fat). So, moving forward towards more endurance goals I found out about the MAF method.
    My question is this: can I do a MAFs style HR controlled session each day ( say, in the morning bike or run) and then a HIIT session possibly 3 times a week, say in the evenings? Or do all training sessions need to be under my MAFs HR cap ( 180 – 56 = 124) ? Would this interrupt the process of training my body to burn more fat? Also, how far below your HR cap can you drop before it isn’t effective as training?
    Thanks in advance.

  • Mark copp says:

    Hi Ivan
    I’m am just about to start maf training and would just like a bit of advice!
    I have not really trained for about a year due to small injuries I have previously completed ironman and have started to gain weight. I have signed up for ironman race for next year which gives me 13 months! You have suggested 3-months of just pure aerobic base work but my question is would i be able to do weight training in this period?

  • Madalin Popa says:

    I have just found your website. I am trying also to lower my heart rate. For two months I made 2 sesions of shill sprints and one long (30-40km) hard trail run per week. To lower the heart rate would it be ok to make very slow runs, like 130 bpm on a 10k run and this between the sprints days and long run? To have it as a recovery run but to stay in aerobic range. Or I should revise entirely my training plan and focus only on slow runs? I will have the first ultra for this year in may so it is difficult to change entirely my training plan. Thanks a lot!

    • Madalin –

      That is a good middle-of-the-road approach. While adapting you training plan, consider that your ultramarathon will be overwhelmingly powered by the aerobic system. In other words, as long as you don’t neglect strength and speed, any training done under the MAF HR (aerobic threshold) will be especially useful towards your ultramarathon performance.

  • Ken says:

    I think you only partially answered Dieter’s question. Setting the 180 formula HR, MAF allows up to +5 for those who’ve already been exercising consistently for preceding two years, is what I recall when I started. Of course, MAF cautions on kidding oneself so better to be on conservative side. Nevertheless, someone like Dieter who’s been faithfully training w MAF, shouldn’t he qualify for potential +5 HR adjustment, after the age subtraction?
    Q2: after 10 months of MAF, my base HR declined by 10-12, to 47-48, but I seem to have plateaued , i.e., unable to improve speed at threshold. Do I just persevere at same threshold and patiently wait for 2nd improvement?
    Q3: what training adjustments to prepare for long races with speed?
    I’m a fan ready to learn next stage!

    • Celso says:


      If you’ve been faithfully following the method for 10 months and have plateaued, then perhaps a new training stimulus is required to further see improvements. If you look at the example of the skier provided in be article, anaerobic training actually decreased the speed in the MAF test. It was only after excess anaerobic training that progress reversed. So perhaps some anaerobic training for a month or so could be beneficial, as long as you revert back to aerobic training.

      You could also try working on improving running economy by strengthening other factors such as core strength, arms, and legs. There’s plenty of research in literature that shows a positive correlation between resistance training and running performance. It’s important to incorporate a balanced workout schedule and not overdo it on the power/anaerobic side of things, but by adding more variety to the body I think you’ll see improved performance and well-being in the end.

  • Marcin says:

    Hello, great site and I love method MAF especially because it focuses on healthy eating. But I have a question. My friend is 21 years old and she is on the level of running 10 km in about 42 minutes. If she want to use MAF method she should run with heart rate 154-164. Is this method ready for young people? It looks good for someone who is 30 or 40 years old, but for 21 or 25 years old people suggestions of running with rate 150 seems to be too high?

  • I am competing in my first official marathon this weekend. I have been training MAF for over a year, so we will see how I get on. I have raised £1000 sterling for a children’s charity in the UK.

  • dieter pohl says:

    I have been doing aerobic exercise for 9 years, 5 years with MAF. All comments usually refer to the 180 formula for a person starting out. How do you calculate the formula year over year, as a person gets older? Does one reduce the max heart rate year for year as one gets older or does one also take into consideration the improving aerobic endurance achieved over 5 years?

    • Dieter:

      One reduces MAX HR as they get older, once per year. As your aerobic endurance improves, your resting heart rate should fall, widening your total aerobic range. The distance from your resting HR to your MAF HR becomes wider (or stays the same), plus your body produces more power per heart rate increase.

  • Daree says:

    I have am total convert! Thank you! One thing that I have noticed when training at my MAF heart rate of 126 is that on warmer days I have to run MUCH slower if not just walk to keep my heart rate down. Is that normal?

  • Hi Ivan,
    I’ve been doing MAF for a few weeks now and it’s going swell but an odd event keeps happening. My MAF number is 145bpm and I primarily run trails. When I have a big hill coming up, I stop before ascending, let my HR settle down to about 130bpm and then commence walking up the hill. If my HR gets to 140bpm, I’ll stop again and let it drop a few beats before continuing the climb. But sometimes when I stop, it just keeps climbing. I’m standing perfectly still, doing deep diaphragmatic breathing and it’s climbing from 140-152 before dropping back down sub-MAF. What gives?



    • Chris:

      When that happens, it’s your body clearing lactate.

      It’s a miniature version of what happens when your heart starts pumping when you sprint: in a sprint, the heart rate isn’t actually pumping blood primarily to bring oxygen and nutrients to the muscles (that’s a critical but secondary function). There’s already enough oxygen in the muscles to process a lot of the lactate you’ll produce in a 10 second sprint. The primary function is to increase the rate of blood flow yes, to bring more oxygen to the muscles, but more importantly to be able to swiftly transport the resulting CO2 to the lungs, and excess lactate to the kidneys.

      Several studies have shown that the body’s stress response doesn’t increase in a big way due to O2 deficiency. (It does, but not quickly). But when there’s CO2 excess, it skyrockets. This is because the lungs’ most critical short-term function is to regulate the body’s pH. Too much CO2 (a.k.a. carbonic acid) or positive hydrogen ions from anaerobic function, and tissue quickly acidifies to the point of breaking down. So, when the heart rate rockets up, or stays high after ceasing activity, it’s because it’s moving blood in the effort of restoring the body’s pH balance.

      Hope this explanation helps.

      As far as how to deal with it, I wouldn’t sweat it. Trailrunning by nature is a hybrid activity. It’s excellent to make a habit out of keeping a sub-MAF effort, but when your heart rate rises for a few seconds (and you deal with it promptly), it won’t substantively affect your aerobic training stimulus. 100% sub-MAF is of course better, but nobody’s perfect.

  • Connie says:

    To the MAF Team,

    I strapped on the my HR monitor this evening and could not run slow enough to stay in my MAF 123 bpm zone. At 5’2″ my stride felt super un-natural and I felt like I was marching instead of running! I have recently returned to my beloved sport after a long hiatus, and this past month has seen me running at what I thought was a beyond comfortable pace until the monitor indicated otherwise. Could I simply be so completely out of shape?


    • Connie:

      Yes to your question, but “yes” doesn’t really cover what is happening. The body has two different engines: a fat-burning engine and a sugar-burning engine. When people talk about being “in shape” and go to the gym to get in shape (such as by doing bootcamp and typical spinning classes) they are primarily training the sugar-burning engine. So it’s not so much that you aren’t “in shape” but rather that the fat-burning engine, which is fundamental for endurance, health, and longevity, isn’t nearly as powerful as your sugar-burning engine. So, by training MAF, and almost exclusively using that fat-burning engine, you feel very “out of shape.”

      Hope this answers your question.

      • AJ says:

        Hey Ivan,

        I am in the same boat as Connie. It is crazy I just started MAF and I am running around 12 minute miles to stay under my zone when I normally run 8 min miles. It is so slow it is almost awkward to do my run. What would you say the typical rate of improvement is? I subtracted an extra 5 hb because I am coming back from a break, should I go to the normal 180-age?

        @Connie, have you noticed any improvement in your time?

        • AJ:

          I would go conservative. To give you an example, I have a slight hip problem (from a long time ago) which means that I subtract 5 BPM, even though I don’t have any pain, obvious muscle imbalance, or even to some degree perceptible lack of functionality.

  • David Macdonald says:

    Phil, i’m a complete convert to your methods and diet advise, thank you for the influence! I’m 51 years old and keen to ensure i’m working in the right zone for the base building. I have been following your formula for 4 weeks now using a Max MAF Hr of 130. Last week I carried out a metabolic lab test (biking) and my max Hr was 193, zone 1 is under 148 bpm (7.9 fat/ 4.7Carbs burn/min) and 126 bp was (8.4fat/1.9Carbs). I’m concerned i’m working on 130 bpm which may be too low.. should i be using the 148 as my MAF hr ? just curious under lab conditions what the criteria is that would override the 180 less rule set with age? happy to share the full results of my test too if required. Kind regards

    • David:

      The MAF HR corresponds to Fat Max, which is the highest rate of fat-burning. So you would probably be very close to 126 BPM (for example, your fat max might be 8.5 at 130 BPM). But it’s unlikely that it’s closer to 148, since your rate of fat-burning is already decreasing at that heart rate.

Leave a Reply