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Devices that measure heart rate variability (HRV), such as Whoop and Oura Ring, are becoming increasingly popular. Like any tool, these devices are only useful if we understand what they are measuring and are able to intelligently use the information the instrument provides. Here is a brief overview of the autonomic nervous system and the various measures associated with the autonomic nervous system.

The autonomic nervous system

The autonomic nervous system (ANS) regulates several physiological processes such as respiration and blood pressure.

The autonomic nervous system is divided into:

  • Friendly: This system is responsible for increasing the heart rate, speeding up breathing, dilating pupils and stimulating the body. This system is sometimes called the “fight or flight” system since it is this system that comes into play in the event of a dangerous or stressful situation.
  • Parasympathetic: this system opposes the sympathetic system by slowing down the functions of the organism. This system is sometimes referred to as the “rest and digestion” system because it primarily deals with rest and digestion.

Physical activity has an effect on the autonomic nervous system by increasing parasympathetic activity and decreasing sympathetic activity, which has a protective effect against cardiovascular problems. Additionally, overtraining, which affects about 65% of high performance athletes at least once in their careers, has an effect on the autonomic nervous system. The effect of overtraining on the autonomic nervous system is not yet clear, but it is theorized that at first the sympathetic system is dominant, then subsequently the sympathetic system is inhibited and the parasympathetic system becomes dominant.

The three primary measures of autonomic nervous system status are heart rate recovery, resting heart rate, and heart rate variability (or variation).

Is heart rate training still relevant?

Heart rate recovery

Heart rate recovery (HRR) is a measure of the time it takes for the heart rate to reach resting values ​​after physical exertion. The increase in heart rate after the onset of exercise, as well as the decrease in heart rate after the end of exercise, are both regulated by the autonomic nervous system. The increase in heart rate is caused by an increase in the activity of the sympathetic system and a decrease in the activity of the parasympathetic system. The decrease in heart rate at the end of exercise is caused by a reactivation of parasympathetic activity and a decrease in sympathetic activity.

HRR can be a good indicator of an athlete’s physical condition. Indeed, a rapid return to the rest frequency following an effort is an indicator of a high state of form. For example, HRR has been shown to decrease (therefore recovery time is faster) after eight weeks of training in untrained people. Additionally, when we compare untrained people to athletes, we notice that HRR is better in athletes.

In addition to being a good indicator of physical condition, the HRR is also a good indicator of the state of recovery. Indeed, in periods of overload (exceeding or even overtraining) Heart rate recovery time from exercise increases, which means that an athlete should consider reducing the training load or taking a day of rest.

How to measure HR

There are several ways to measure HRR. It is important to use the same test each time to see if there is really an improvement or a deterioration in the RFC. The important thing is not to use a fixed intensity, for example power on a bicycle or speed while running, but rather to use a relative intensity as a percentage of the maximum heart rate. For example, you can measure the decrease in heart rate for a period of one or two minutes after exercising for five minutes at an intensity between 90 and 95% of maximum heart rate. Thus, depending on your state of form, the intensity (watt or speed) corresponding to 90 to 95% of the maximum heart rate will vary, which makes it possible to really determine the improvement or the deterioration of your HRR without it being affected. by the intensity of the effort.

Heart rate at rest

Resting heart rate (RHR) is also a good indicator of fitness status, as well as the level of recovery or overwork. Additionally, an elevated heart rate while resting is a sign of high risk for cardiovascular disease and is a better clue than a small change in heart rate.

With training, the resting heart rate tends to decrease. This has the effect of increasing the heart rate reserve (HR reserve), or the difference between maximum heart rate and resting heart rate.

The advantage of measuring resting heart rate is its simplicity, both for measuring and analyzing. This is because unlike HRV, which is a more complex measurement, resting heart rate is a very simple measurement. You just need to measure your heart rate while lying down, or measure it while sleeping using a device like the Whoop or Oura Ring.

Heart rate training explained

Heart rate variability (HRV)

Heart rate variation (HRV) is a measure of the change over time between each heartbeat. The most accurate way to measure HRV is to use an EKG and measure the time variation between “R” peaks, but it is also possible to measure HRV using a heart rate monitor, at the same time. wrist with a device like Whoop, or finger with a device like Oura Ring.

Although HRV is a relatively simple measurement, there are several ways to measure the change in heart rate, which makes this measurement more complex and makes it difficult to compare HRV values ​​between different devices. In addition, many devices that measure HRV do not indicate the method used for measurement, or whether the data is measured in the morning upon awakening or at night when sleeping. If, for example, HRV is measured during sleep at a specific time rather than taking an average for the whole night, the measurement may be affected by the sleep cycle (deep or light). All of these factors therefore complicate the measurement of HRV. However, this remains an interesting and relevant measure.

HRV is affected by hard training – either hard workouts or a big block of training. (Psychological stress also affects HRV). An elevated HRV indicates an increase in parasympathetic activation and a decrease in sympathetic activity, which means that an athlete is in good shape and ready to perform. A decrease in HRV is indicative of fatigue. A low HRV is not necessarily bad, as it means the athlete has a good training load and is accumulating fatigue, but if the HRV remains low for a very long time, it may indicate a period of overload – too much training and / or not enough rest.

In short, heart rate recovery, resting heart rate and heart rate variability are all interesting measurements that can give a good idea of ​​an athlete’s state of fitness and recovery. Personally, I use the Whoop bracelet and am as interested in HRV as I am resting heart rate. However, it reminds us that these measures are tools to guide our training, and that we should not rely 100% on these measures. For example, it is also important to take into account perceived exertion, perceived fatigue at rest and during training, and level of motivation. All of this information needs to be taken into account, rather than relying on just one measurement.