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Why use HRV in training?

This is an excerpt from Heart Rate Variability by Sylvain Laborde,Marco Altini,Emma Mosley,Dan Plews.

The idea behind HRV-guided training is to use the data in the best way possible so you can understand how your body is responding to your training plan and make adjustments. In particular, HRV-guided training aims to provide the most appropriate training stimuli in a timely manner. This means applying it when your body is ready to receive it so positive adaptation can occur and you will be able to improve performance. We all intuitively understand that the timing of stressors matters and that not all days are the same. HRV can help us quantify these factors and adjust the timing of a stressor (e.g., when to do a hard workout).

We have seen in previous chapters how HRV allows us to capture the body’s responses to the input we provide (e.g., training, environmental stressors such as heat or altitude), but the challenge remains deciding how to act on this information. In this respect there is a fundamental principle to understand, and we reiterate it here to ensure it is clear: HRV is nothing more than a proxy for cardiac vagal activity and, by extension, an indicator of how well the body is coping with stress. Hence HRV is about our response, and as such, it is of great value when measured hours after a stressor. What we seek with HRV is the chance to observe the body’s ability to bounce back to homeostasis in a reasonable time, not record the stressor itself. The goal is not to eliminate stress—that would amount to a perfect recipe for lack of growth. If we forget this, we end up simply capturing acute transitory stressors or all sorts of other factors that affect HRV but have nothing to do with the way our body responds to stress.

The first step in measuring HRV in our opinion is always to be aware (a concept we emphasize in chapter 14 when discussing the habits you can build around regular HRV measurement). Being able to objectively see how things are going can be eye-opening, no matter how in tune you are with your body. Being aware of how your body responds to stress can be beneficial for a myriad of applications in health and sports because it allows us to combine our subjective feelings with an objective assessment of our condition, which leads to better-informed decisions. Note also that HRV measurement, as the name implies, involves a measurement, not an estimate. This means we are actually measuring our heart rate variability, not generating a fabricated metric like wearables do with readiness, recovery, or stress scores. Hence, once we measure our HRV in ideal settings, we capture data representative of how our body responds to the combined lifestyle, psychological, and training stressors present in our lives.

Once we measure HRV, we can simply observe our data and balance things based on our own experience. However, we might use HRV in different ways. For example, we might prioritize recovery if our HRV value is low, whether acutely or chronically. Alternatively, we could look at the scientific literature and see how scientists in the field have carried out interventions using HRV in the context of performance. Hence, the follow-up question that matters most to coaches and athletes alike is the following: How can we use HRV to adjust training so that in the medium to long term performance is improved?

Although maintaining performance while reducing load and stress is quite an ­achievement—reducing the risk of injury, saving time, and mitigating other issues—there is, of course, a strong interest in determining whether we can go beyond this. Specifically, can we improve performance by applying better-timed stressors? Note that no published study to date has shown a reduced or less strong improvement in any performance-related variable for HRV-guided training with respect to standard periodization. This means that despite the reduced load and intensity used in most HRV-guided training programs—based on the principle of not going hard when your body is not ready—this reduction in training load and intensity is at least not harmful and likely better for your performance.

When looking at a study, it is important to fully understand the protocol used and interpret the results within the context of that protocol and the aim of the study. HRV is simply a means of capturing the way in which your body responds to stress. What ultimately works or does not work is how you act on this information with the aim of improving performance. Most importantly, we have seen how in all studies mentioned here either performance-related parameters (such as V̇O₂max) or performance itself (time trial) improved as a result of HRV-guided training. This makes this approach really interesting for athletes, sport scientists, coaches, and other practitioners looking to maximize performance and adaptation to training.

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