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Heart Rate Variability: what it is and how It helps with training and racing

By April 29, 2015July 1st, 2020Exercise

An Interview with Simon Wegerif, creator of “ithlete” app that measures stress and recovery on a daily basis.

For many endurance athletes, the racing season is here. And with the warmer weather naturally comes the desire to increase training levels and intensity. But too often, this temptation for additional mileage and workout hours leads to overtraining—and then to fatigue, injury, or illness. These problems can all be easily avoided by proper nutrition and by taking the maximum aerobic function (MAF) test—and then adjusting one’s training accordingly. There is another way to see if your body is stressed from over-training—and that is using heart-rate variability.

Never heard of the term? You aren’t alone. Measuring heart-rate variability, or HRV, though long used in hospitals for treating heart patients, is a relatively new biofeedback concept for endurance athletes. Soviet Union sports scientists started keeping track of their elite athletes’ heart rate variability in the 70s. And in the past decade, college sports teams and world-class athletes have been increasingly using HRV to monitor fatigue and recovery from workouts.

Simply put, HRV is a measure of the time gap between individual heart beats while your body is at rest. The heart, in fact, speeds up when you inhale, and slows down when you exhale. This difference is known as HRV. A healthy, well-rested body will produce a larger gap, and higher HRV than a stressed-out, overtrained body.

To understand why this difference occurs, we need to take a quick look at the autonomic part of our nervous system.

The autonomic system is comprised of two parts – sympathetic and parasympathetic. The sympathetic part raises your heart rate and blood pressure, increases muscle power and speed, and other actions used in a race. We feel this as pre-race tension, an important way to prepare for competition. The parasympathetic part is important for recovery, relaxation of muscles, slowing the heart rate and lowering blood pressure. And, it turns on the intestines for improved digestion.

The sympathetic has been compared to the accelerator in your car, making the vehicle go faster, while the parasympathetic component is likened to the brakes, slowing it down.

While the autonomic system functions automatically, we can influence it through our lifestyle. The sympathetic part tends to be ready to go into action much of the time, so we control autonomic function mostly through the addition of more parasympathetic activities to balance both. We can do this by choosing to relax, by meditating, and avoiding too much caffeine (a sympathetic stimulator).

When autonomic imbalance occurs, it’s usually associated with too much sympathetic and too little parasympathetic activity. Initially, overtraining results in higher resting and training heart rates. The negative consequences of overtraining are often gradual. The body is quite good at masking the earliest symptoms. But overtraining is a canny adversary. The problems it engenders will triumph in the end, unless changes are made regarding one’s training, diet, and stress level.

As you would expect, autonomic balance, as measured by HRV, can be maintained following an aerobic workout; however, after an anaerobic workout autonomic balance is slightly disturbed until the body recovers. Endurance athletes who maintain a good balance of autonomic function, as indicated by HRV, perform better in competition.

Until recently, measuring one’s HRV was expensive and time-consuming. But there’s a new and affordable device called the “ithlete” which is a specially designed receiver and app that is compatible with the iPhone or touch-screen iPod, The ithlete allows you to record your resting heart beats for one minute using a standard chest strap heart monitor, and accurately calculates your HRV. The device provides great animation of heart and lungs in action, graphs of your results, stores your personal information and allows for daily testing for comparing your weekly and monthly results. As such, it warns you if HRV reduces or worsens, indicating an autonomic imbalance and the need for additional rest that day, with an easy rather than hard workout.

Simon Wegerif, an endurance athlete, is the creator of ithlete and Founder/President of HRV Fit. Before launching ithlete in late 2009, Wegerif, 46, worked as an engineer for ten years at Philips Electronics in Silicon Valley, where he was involved with the early development of digital signal processing and high-definition television.

In the following interview conducted by Bill Katovsky, Wegerif, who now lives outside London with his family, explains in greater detail the significance of heart-rate variability for all multisport athletes, how to avoid overtraining, the importance of rest and recovery, and why he created ithlete. For more information and a brief video demo, go to


Question: Why is overtraining such a misunderstood or neglected concept among endurance athletes – runners, cyclists, and triathletes?

Simon Wegerif: That’s because the vast majority of endurance athletes don’t appreciate the simple truth that you don’t get fitter during exercise; instead you get fitter recovering from exercise. The emphasis is therefore always on maximizing training time (and usually intensity as well) in order to give the body the biggest stimulus for adaptation. That only works if the body has been able to repair and adapt before the next exercise session. As well as needing ample time for recovery, the body requires to be looked after in other ways in order to recover fully – quality of sleep, nutrition, and an absence of stress all play major roles here.

Q: What are symptoms or red flags associated with overtraining?

SW: Most coaches regard a drop or plateau in the athlete’s performance, despite continued training being a reliable indicator of overtraining. In addition, fatigue, mood disturbances and abnormal food cravings are all signs that overtraining syndrome may be developing. Overtraining is caused by too much physical stress combined with too little recovery over a period of time (usually a few weeks). It progresses from functional overreaching (the overload principle of training), through non-functional overreaching (when the body is unable to repair itself fast enough) to what’s called sympathetic overtraining. This is the state that can sometimes be detected by looking for an elevated pulse during the traditional morning pulse check. The sympathetic branch of the nervous system is often referred to as the ‘fight or flight’ branch since its purpose is to prepare us to fight or run away. It also involves production of stimulant hormones such as adrenaline and cortisol. We were never designed to have these hormones flowing around us for long, extended periods, and they are known to lead to problems including heart disease if they remain present for too long. Unfortunately, athletes will still keep on pushing and progress their overtraining to a state known as parasympathetic overtraining, when the fight or flight hormones become exhausted and extreme fatigue follows.

Q: But properly using a heart rate monitor keeps training in check.

SW: Provided the athlete knows his or her personal heart rate aerobic and anaerobic zones. The use of an heart rate monitor (HRM) during exercise can help to prevent base training workouts from becoming anaerobic – a very frequent mistake that athletes make (especially those not under coach supervision).

Q: What about using your resting heart rate when you first wake up in the morning as a gauge of overall health and fitness?

SW: Measuring your resting pulse first thing can tell you two things. One is that if the number is below 60 beats per minute, you are regarded as an athletic individual (many top cyclists have been below 30 bpm!). Secondly, by measuring the pulse every day, you can potentially spot an abnormally elevated heart rate that may signal sympathetic overtraining. However, the amount of change may be only 2 to 3 beats per minute in the overreaching stages, making it difficult to detect reliably. Another problem is that endurance athletes can get to a state of parasympathetic overtraining quickly, where the resulting lowered morning pulse rate is sometimes mistaken for improved fitness!

Q: But the resting heart rate fluctuates during the day.

SW: Resting heart rate fluctuates according to your body position (sitting, standing or lying down), whether you have recently eaten or taken stimulants such as caffeine, how warm or cold you are, whether you are excited or stressed, sleepy or alert, and of course, how physically active you had just been. With so many factors able to influence resting heart rate, it is not generally regarded as a sufficiently robust indicator of the onset of overtraining.

Q: So heart rate variability offers a more accurate assessment than resting heart rate.

SW: Contrary to popular belief, the heart does not beat with metronome regularity, but varies according to the instructions it receives from the nervous system. Heart rate variability, or HRV as it’s often known, allows us to observe the separate branches of the nervous system directly, rather than having all the signals mixed up together, as they are in the resting-pulse measure. Unlike resting pulse, a higher HRV is a good thing, and by making regular measurements, you can identify changes in the all-important balance between the sympathetic (fight or flight) and parasympathetic (rest and recovery) branches that can signal the earliest stages of overtraining

Q: How does the ithlete work?

SW: The ithlete is an app for the iPhone and iPod touch that, together with the ithlete ECG receiver and a regular chest strap, allows the athlete to make a simple 60-second measurement of his or her HRV every morning right after waking up. Each day’s reading is compared to one’s personal baseline measure to give a recommendation on training for that day. This recommendation can range from “train normally” to “take it easy” to a “rest day”. Longer term trend indicators help identify improving or declining aerobic fitness, giving you the precise opportunity to continue going with your program or make changes and find out what works for you.

Q: Knowing one’s HRV with the ithlete, when does one first notice results in training?

SW: You notice results in your training after about a week, once your baseline has been established. Then you know how you’re likely to feel both during and after the session. During base building, you should notice an upward trend in your HRV that signals improving aerobic fitness. That will almost certainly translate into better form in the racing season.

Q: Are there any additional benefits?

SW: By knowing your HRV, you can objectively measure your body’s response to each workout. Often this coincides with your feelings or other measures, but there will be times when ithlete indicates that you really need to take it easy, or take a rest day, then you will find you can train harder the next day. Conversely, you may be feeling sluggish after a long day at work, but with a normal ithlete reading, you can head out confidently for a bike ride or run and feel much better as a result. One of the biggest benefits is that you can consistently improve performance without the normal risks of injury or illness. Most injuries happen when the body is stressed or tired, so by avoiding hard sessions when your body is already fatigued, you minimize that risk. You can also keep your training more flexible, allowing yourself to be guided by ithlete’s recommendation, helping to reduce another common problem of training monotony in endurance athletes. Because HRV is much more sensitive that resting heart rate, you get feedback at an earlier stage that helps avoid the development of true overtraining. Also, for the first time, you can perfect your taper before a major race or competition by resting and watching your daily HRV rise to your optimum readiness level.

Q: What is the correlation between ithlete/heart-rate variability and workouts using a heart-rate monitor?

SW: The most interesting observation is the relation between exercise intensity as measured by an HRM during exercise and the resulting fatigue, as measured by ithlete. For instance, an hour long run at a pace just below aerobic threshold produces very little fatigue, whereas a set of anaerobic intervals up to 30 minutes present the body with a heavy recovery load, often resulting in a significant drop in HRV the following morning, and an ithlete recommendation to have a light training day.

Q: What has been your own personal experience using the ithlete and/or relying on heart-rate variability?

SW: I’m no elite athlete, but I’ve been engaged in triathlons and endurance cycling events for many years. I now try to ride 150 miles per week, usually with strong club and amateur cyclists, and frequently place in the top 20 percent in events that I enter. I once practiced the ‘no pain no gain’ principle, but was often frustrated about my inability to train or compete as often as I would like due to both fatigue and minor illness such as viral colds. Since using ithlete, I have got to know my body much better. Best of all, my bike times started falling, in part, because I was now taking more rest or easy training days–specifically determined by my daily HRV readings. I had also come across the “Maffetone Method” approach to performance after being impressed with the results of several local elite cyclists who were very disciplined in keeping their long training rides fully aerobic. I decided to look into the science behind aerobic development and found that Phil wrote clearly and persuasively about the methods and benefits. This last winter, I kept my own training 80 percent aerobic using the 180 formula and watched my HRV rise from an average of about 62 to 68 on the ithlete scale. That may not sound a lot, but the ithlete scale is logarithmic, so it actually represented a 30 percent increase in heart-rate variability.

Q: What made you decide to create ithlete?

SW: Like many endurance athletes – runners, cyclists and triathletes – I use a heart rate monitor. It helps me measure how hard my body is working during training as well as keeping me just to the right side of the red line during competition. Since I wasn’t getting any younger and I liked to keep pace with the top local and yes, younger riders, I began investigating smarter training methods that would improve my performance but without the risk of injury due to overtraining. And this is how I found out about heart rate variability. In time, I became convinced that I needed to incorporate HRV as part of my own athletic training. My bike times had leveled off and I often wondered if I had been training too intensely without allowing for sufficient recovery. So I looked around to see what commercial products were available and came across software from companies such as Omegawave and FirstBeat Technologies. Both products are highly regarded, and used by top athletes under coach supervision. Yet these products cost from $1,000 to more than $20,000. And even though HRV is now included in high-end heart rate monitors from Polar and Suunto, they lacked several important measurement criteria, such as color-coded warning indicators, the ability to visualize your trends graphically, and the simplicity of a quick morning test that anyone can fit into his or her daily routine.

I came to the conclusion that there was not an easy-to-use, affordable product that could give one a direct and daily measure of HRV. But all was not lost. I am an engineer by profession. With my background and work experience at Philips Electronics, building an HRV system did not seem particularly daunting, though the process would turn out to be a longer journey than I first anticipated. I read almost 500 research papers on HRV and consulted with many experts, cardiologists, coaches and trainers. My device had to be scientifically valid, practical, and uncomplicated to use.

By early 2009, I had completed ithlete’s first working system (which I immediately submitted to various patent offices in several countries). Several months later, I had created a small receiver, as well as a working app for the iPod touch and iPhone, which I specifically chose because of the great user interface and processing power. During this time, as I used the ithlete prototype, my confidence and belief in HRV continued to grow. Here was a simple measurement that took only 60 seconds each morning, and seemed to know my body better than I did.

Q: What has been the response so far to ithlete?

SW: The first customer to download an app from the iTunes and obtain a receiver from the ithlete website was a cyclist from Wiltshire, U.K. Since then, close to 500 athletes have purchased ithlete – and the number continues to grow, and not just in England but worldwide. Orders have come from Australia, South Africa, United States, Sweden and even Greenland, to name a few. Users have ranged from recreational 10K and half marathon runners, who have had injuries and want to avoid repeating them, to cyclists who train heavily to competitive time-trial cyclists, and to regular middle-aged people wanting to lose weight using a frequent exercise program and who want to avoid doing too much too soon.

Q: Have there been any scientific studies on heart-rate variability and triathletes, runners, or cyclists?

SW: Yes, HRV has been frequently used in sports science research with professional cyclists and elite Ironman competitors, leading to the conclusion that HRV is a sensitive indicator of current and accumulated fatigue. In the past two years, there has been a round of published sports studies appearing in professional journals indicating strong correlations between increases in HRV and race time improvements. This is definitely an area to watch!