Heart rate variability (HRV) during taper

Research and practical insights

For feedback or comments, you can reach me on Twitter (@altini_marco)

You’ve been preparing your race for several months and it’s finally time to taper. Training went really well and you are doing everything right: reducing volume, maintaining some intensity, paying attention to your diet and sleep.

And yet, your heart rate variability (HRV) reduces.

Well, don’t sweat it. In this blog, I’ll cover some of the research behind HRV changes during taper, and show a case study highlighting how reduced HRV during taper can lead to optimal performance.

Special thanks to Dave for many stimulating conversations during our runs and for providing his data for this blog.

2 hours and 49 minutes. Rotterdam 2021.

First of all, we should recognize that tapering is basically an outlier, something that happens rarely, and can be done in many different ways (variable in duration, volume reduction, or intensity management, for example). All of these factors, together with the type of sport practiced, the profile of the athlete, level of the athlete, and other circumstances, will impact the physiological response to tapering. Additionally, the psychological component of real-life tapering (approaching a race that matters to you) might be quite different from study protocols where training load is modulated before a lab test.

All of this makes it quite challenging to generalize, but let’s start by looking at published literature.

What does the research say?

Common sense says that during taper, HRV should increase. After all, this is when we finally start reducing load so that we can be ready to perform.

In a few studies, the expected relationship between load and HRV has been observed: training load increases up to a point, leading to reduced HRV, then during taper, HRV rebounds. This makes sense as the load was already having a strong impact on the athlete’s physiology, possibly to a point in which a negative response was already reached (reduced HRV). This is the case for athletes of different levels [1, 2, 3].

Below you can see an example of this physiological response before two different races.

HRV trends before two different races. A poor physiological profile is shown prior to the taper, for both events. Maladaptation is detected and HRV is highly suppressed (below normal values). The last 10 days in each screenshot show the taper, with a rebound of HRV within normal values, and a positive physiological profile. Learn more about trends detection in HRV4Training, here

It is important to highlight, however, that reduced HRV during increased load is not the response we normally target or hope to see. Increased load, when coping well with training and responding positively, should result in a stable or increased HRV. As a matter of fact, functional overreaching is associated with increased HRV, despite high load [2].

Recent studies [4, 5] have however shown the opposite relationship: reduced HRV with reduced load during tapering. Notably, this reduction was associated with world-class performance, highlighting how the reduction was not detrimental to performance. Why does this happen? The reduction in training volume might elicit lowered blood plasma volume, and therefore decreased stroke volume, and in turn, increase heart rate and reduced HRV [4]. This reduction in HRV reflecting reduced parasympathetic activity and increased sympathetic activity during tapering could be potentially linked to a better physiological state in the context of competition (i.e. readiness to perform). This is typically the case for well-trained or elite athletes, where most likely HRV has been trending well during periods of higher load.

Another reason for HRV to reduce could be associated with a suppressed heart rate during periods of high load. As we taper and reduce load, resting heart rate increases, re-normalizing, from the acute fatigue state in which it is often suppressed. As such, HRV will also decrease a bit. This is similar to the behavior of exercise heart rate, which might stay suppressed during periods of high load, as a sign of fatigue, but increase faster when reducing load or tapering.

These cases are quite different from rebounding from a period of suppressed HRV due to a poor response to a high load. Another reason for suppressed HRV either during high volume blocks or taper, without a negative association (non-functional overreaching, overtraining, or poor performance) is parasympathetic saturation. Plews has shown how athletes in which HRV was suppressed during high load were most likely saturated, and therefore they were not responding poorly as one would derive if looking only at HRV data [6] (this is another reason to make sure you take a multiparameter approach, as covered here).

Finally, a reduction in HRV following functional overreaching has been documented in other studies [5], where HRV remained relatively elevated, but lower than during a previous phase of higher training load, somewhat consistent with the studies previously mentioned.

Let’s look at some data: meet Dave

Dave just ran the Rotterdam marathon in 2 hours and 49 minutes, achieving his goal time (sub 2 hours and 50 minutes). In the weeks preceding the race, he had experienced a reduction in HRV, which led to a few interesting conversations and also this blog post.

Normally, Dave’s HRV is rather stable. Additionally, training has been going very well, hitting goal workouts and showing a stable physiological profile in the months prior to the taper. Yet, we can see a reduction in baseline HRV, with quite a few daily values below his normal range, in the two weeks taper, which I have highlighted in the figure below:

Resting physiology and training load in the period preceding the marathon, and the following week. Courtesy of HRV4Training Pro

During the 2 weeks taper, there are 7 daily measurements below his normal range, while there are very few in the previous months. The second plot shows training load, highlighting again how we have very good responses to the late August / beginning of September increased load, and a rather stable profile afterward.

Interestingly, just after the race and the 24-hours acute drop, Dave’s HRV rebounds quickly to pre-taper levels or even a bit higher.

This data seems consistent with previous research in trained or elite athletes, where functional overreaching is associated with increased HRV, and then a reduction in HRV is reported prior to competition, despite reduced load [4,5,6].

Takeaways

As covered in this blog, positive responses to increased training load should result in stable or increasing HRV. This increase in HRV is associated with a functional overreaching state which is also reflected in reduced resting heart rate and exercise heart rate. However, during this phase, performance can be impaired (due to the high load).

Following this phase and response, during tapering, we might have a drop in HRV. There could be multiple reasons behind this reduction in HRV, as covered in Daniel Plews’ research, for example, reduced plasma volume due to less aerobic stimulus, parasympathetic saturation, or simply the race getting to you. Needless to say, this reduction has no implications for performance. This is somewhat similar to having a suppressed score on race day.

On the other hand, If your training has been less than optimal or your HRV has been often below normal, you might see a rebound with tapering, as most likely a reduction in load was long overdue.

I hope you have found this blog useful, take it easy

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.

Marco is the founder of HRV4Training, a data science advisor at Oura, an Editor at IEEE Pervasive Computing (Wearables), and a guest lecturer at VU Amsterdam.

He loves running.

Twitter: @altini_marco

References

[1] Flatt, A. A., Hornikel, B., & Esco, M. R. (2017). Heart rate variability and psychometric responses to overload and tapering in collegiate sprint-swimmers. Journal of science and medicine in sport, 20(6), 606–610

[2] Le Meur, Y., Pichon, A., Schaal, K., Schmitt, L., Louis, J., Gueneron, J., … & Hausswirth, C. (2013). Evidence of parasympathetic hyperactivity in functionally overreached athletes. Med Sci Sports Exerc, 45(11), 2061–2071

[3] Iellamo, F., Legramante, J. M., Pigozzi, F., Spataro, A., Norbiato, G., Lucini, D., & Pagani, M. (2002). Conversion from vagal to sympathetic predominance with strenuous training in high-performance world-class athletes. Circulation, 105(23), 2719–2724

[4] Plews, D. J., Laursen, P. B., Stanley, J., Kilding, A. E., & Buchheit, M. (2013). Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports medicine, 43(9), 773–781.

[5] Bellenger, C. R., Karavirta, L., Thomson, R. L., Robertson, E. Y., Davison, K., & Buckley, J. D. (2016). Contextualizing parasympathetic hyperactivity in functionally overreached athletes with perceptions of training tolerance. International journal of sports physiology and performance, 11(5), 685–692

[6] Plews, D. J., Laursen, P. B., & Buchheit, M. (2017). Day-to-day heart-rate variability recordings in world-champion rowers: appreciating unique athlete characteristics. International journal of sports physiology and performance, 12(5), 697–703

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Marco Altini

Founder HRV4Training.com, Data Science @ouraring Lecturer @VUamsterdam. PhD in Machine Learning, 2x MSc: Sport Science, Computer Science Engineering. Runner