Heart rate variability (HRV) and strength training

some thoughts

A typical question we get a lot is the following: “does it make sense to use HRV if I do resistance or strength training”?

Let’s look at the big picture. Physiological stress comes from different sources, all having an impact on our ability to deal with additional stress (there is only so much we can take!) and therefore to maintain or improve our health and performance.

At the end of the day, it does not really matter what sport you or your athletes do, stress is part of everyone’s life (there’s travel, work, family, you name it). Training is just one of the stressors, and obviously keeping stress in check is relevant way beyond endurance sports, if we care about our own and our athlete’s health and performance.

But let’s try to get more specific now.

If you are interested in strength training, I would highly recommend following experts in the field that have a comprehensive understanding of the topics of strength, power, periodization, and stress, such as Carlo Buzzichelli (author of Periodization: Theory and Methodology of Training, together with Bompa) or Andrew Flatt.

In particular, Andrew wrote this piece for the HRV4Training blog years ago, and below I will mainly quote his words:

“A definitive training program or manual on how to improve a given physical performance quality in highly trained individuals of any sport does not exist. Nor will it ever. This is because of (at least) two important facts:

1. High inter-individual variability exists in how individuals respond to a given program.

2. The performance outcome of a training program is not solely dependent on the X’s and O’s of training (i.e., sets, reps, volume, intensity, work:rest, frequency, etc.) but also largely on non-training related factors that directly affect recovery and adaptation.”

While point 1 is clear to most coaches, point 2 seems to be absent from the conversation. Most research on strength training takes an extremely simplistic approach, for example, having ten young men with strength training experience doing hypertrophic and maximum strength loadings once and then measuring HRV following exercise, on a single occasion (example paper here).

However, it is also quite obvious to me that a 1 rep max done once is very different from training and competing over weeks and months while dealing with the cumulative effect of training, traveling, getting sick, menstruating, and all the other stressors that are part of real life, and here is where HRV becomes useful (note that even in the study mentioned, rMSSD was reduced after the single session, clearly showing that stress is captured by HRV — and will pile up when you take this out of the lab, on repeated days, etc. - similar to what we would see for aerobic exercise).

Maybe the misconception is again that in these studies researchers look for that kind of perfect relationship between load and “recovery”, but that makes little sense (the human body is more complex than that, and of course, it adapts, so over time you get better at handling the stressor). I’ve discussed in the past how, as a matter of fact, a parameter that correlates perfectly with training load, is of no use as it does not add any information to the training and recovery equation.

HRV tells you how you are handling stress. If we take well-trained individuals, we don’t expect HRV to be highly suppressed the day after aerobic exercise either, if that’s an exercise that they can handle well. An ideal response is all about stability.

Back to Andrew’s article, he also explains in more detail how strength and power athletes can respond to very high acute stressors as well as how things differ with the cumulative effect of more sessions, in terms of HRV:

“In a study involving elite Olympic weightlifters, HRV was suppressed for 48 hours following a grueling 2-hour workout that was preceded by 10 days of rest. Once HRV returned to baseline, so did 1RM strength. This is a nice example of an acute bout resulting in an HRV response that takes several days to return to baseline. What happens when insufficient recovery between sessions is provided? In a recent study, daily HRV measures showed a progressive decreasing trend during a 6-day overload microcycle in 15 trained powerlifters. HRV trended back towards baseline in the 4 days following the overload. 1RM Bench and Squat followed a similar pattern with a decrease compared to baseline by the end of the overload followed by a return to baseline 4 days after.”

Obviously, you cannot capture any of this if your protocol consists of doing 1 exercise and measuring right after (no longitudinal measurements over weeks, no repeated loading, etc.). Unfortunately, there are many studies that have little to do with how things work in real life, and should not be used to provide recommendations to practitioners, in my opinion.

Andrew mentions three main reasons why HRV is useful for strength athletes (not surprisingly, these are as good for any other sport):

• The training stimulus is significantly greater than the individual typically experiences

• The training stimulus is novel or different from what the individual is accustomed

• Training is otherwise normal, but non-training-related stressors are affecting recovery

I am sure you can see the link between these and what we have previously covered, or showcased in our case studies.

Back to Andrew, I’ll report point 3, which is easily applicable to anyone and really the main point that coaches and athletes should understand, no matter what sport they practice:

“Non-training related stressors are tremendously important to consider for trained athletes. These factors affect HRV and they affect your ability to handle and adapt to training. These factors likely contribute to large acute changes in HRV in response to otherwise “normal” or familiar training that typically wouldn’t cause such a change.”

“Gains in strength and hypertrophy largely depend on the balance between protein accretion and protein breakdown favoring the former. Chronically elevated stress results in catabolic activity and may shut off protein synthesis, thus shifting the balance in favor of protein breakdown. Also impacted from high stress is immune function. Combine your regular training regimen with high non-training-related stress and your chances of getting sick go up. When you’re sick, you can’t maintain your normal training and naturally, progress is derailed.”

And finally:

“if you believe that an important part of the training process is managing stress, then stress should be monitored. Training load gives us an indication of physical stress, wellness surveys give us a good indication of perceived stress and HRV provides a good indication of its effect. Thus, when taken together, each variable provides unique and meaningful insight regarding the amount and type of stress that is being experienced and importantly, how we’re handling it. Therefore, HRV is most useful when used in conjunction with these other recordable metrics.”

Isn’t that so obvious?

Objective data is not here to replace how you subjectively feel but to be combined with it and with training load information so that you can make better decisions, no matter what sport you do.

I hope this was a decent overview of common misconceptions about strength training and HRV. We have the technology to go beyond unrealistic laboratory settings or one-time measurements following isolated protocols, and we should really try to do studies that reflect how various stressors interact in real life.

I hope this was informative, and thank you for reading!

Marco holds a PhD cum laude in applied machine learning, a M.Sc. cum laude in computer science engineering, and a M.Sc. cum laude in human movement sciences and high-performance coaching.

He has published more than 50 papers and patents at the intersection between physiology, health, technology, and human performance.

He is co-founder of HRV4Training, advisor at Oura, guest lecturer at VU Amsterdam, and editor for IEEE Pervasive Computing Magazine. He loves running.

Twitter: @altini_marco

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