HRV monitoring for strength and power athletes 

Guest post by Andrew Flatt, PhD student in Exercise Physiology at the University of Alabama.

​Andrew's research pertains to HRV monitoring in athletes as it relates to training load and physiological adaptation.

• A listing of his research publications can be viewed here
• His Blog can be found here
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​Intro

​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.

The closest we’ll get to such a definitive training approach, (in my opinion) may be autoregulatory training. This concept accepts the 2 facts listed above and attempts to vary training accordingly in attempt to optimize the acute training stimulus to match the individual’s current performance and coping ability.
 
Improvements in physical performance are the result of adhering to sound training principles rather than strict, standardized training templates. A thorough understanding of sound training principles enables good coaches and smart lifters to make necessary adjustments to a program when necessary to maintain continued progress. In other words, good coaches can adapt the training program to the athlete rather than making the athlete to try and adapt to the program. This is the not so subtle difference between facilitating adaptation and trying to force it.
 
The theme of this article is not about traditional training principles, but rather about recovery and adaptation concepts that when applied to the process of training, can help avoid set-backs and facilitate better decision-making with regards to managing your program. Given that this site is about HRV, naturally we’re going to focus on how daily, waking measures of HRV with your Smartphone may be useful in this context. For simplicity, we will focus on one HRV parameter called lnRMSSD which reflects cardiac-parasympathetic activity and is commonly used by most Smartphone applications. Drawing from research and real-life examples of how HRV responds to training and life-style factors, I hope to demonstrate how HRV can be used by individuals involved in resistance training-based sports/activities to help guide training. 

Training factors affecting cardiac-autonomic activity

​Cardiac-parasympathetic activity is suppressed during a training session and sympathetic activity predominates. This is necessary to support blood distribution requirements and to enhance muscle contraction. Factors affecting the recovery of HRV to baseline following the training sessions are numerous and include clearance of circulating catecholamine’s, removal of lactate and other metabolic by-products, restoring fluid balance, normalizing body temperature, etc. (See review by Stanley et al.[1] for more info). How factors such as inflammation and certain hormone fluctuation affect the return of HRV to baseline has not been well studied, but likely also has a role. The content of your workout ​(set/rep configuration, rest periods, etc.) therefore likely have an impact on this process. For example, a recent study showed that acute HRV recovery after a workout was delayed by training to muscular failure compared to stopping the set well short of failure [2]. In addition, a recent study found that bodybuilder-type workouts cause a greater increase in plasma osmolality and aldosterone concentrations compared to strength workouts[3] which consequently may affect fluid balance and HRV.   

Daily HRV change in response to training

So how does this affect my HRV the next morning? Will my HRV reflect previous day training load? Not really. At least not in a conventional sense where greater loads always cause greater reductions in HRV and lesser loads always cause smaller reductions in HRV. Rather, HRV may respond to training in different ways for different reasons. A heavy and hard training session can be well tolerated with quick recovery, provoking little change in HRV the next morning. In contrast, moderate training sessions can take more out of you than expected and result in a greater change in HRV the next morning.  
 
Training status for example, likely affects how HRV responds to your training session. An intense session will be a tremendous stressor to novice or detrained individuals. They will experience greater muscle damage, more soreness and greater metabolic and hormonal responses to a training session [4]. The result of which is a considerable homeostatic disturbance requiring a longer recovery period. Well trained athletes on the other hand will have been well adapted to this stimulus. They will experience less muscle damage, less soreness and a smaller metabolic and hormonal response and ultimately recover faster [4]. Hence, the higher level athlete you are, the less likely training will cause major changes in HRV the next morning. However, your training status changes over time as will your HRV response to training.

Highly trained individuals are more likely to see a pronounced decrease in HRV the following morning in response to a training session under certain conditions:

1. The training stimulus is considerably greater than the individual typically experiences (e.g., an abrupt increase in load).

In a study involving elite Olympic weightlifters, HRV was suppressed for 48 hours following a gruelling 2-hour workout that was preceded by 10 days of rest [5]. 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 [6], daily HRV measures showed a progressive decreasing trend (> smallest worthwhile change [0.5XCV]) during a 6-day overload microcycle (2 sessions/day involving loads >85%) 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. Drawing on some data I’ve collected, the trends below feature a one week baseline of normal training, an overload week and then about 10 days of normal training in two high-level sprint swimmers. Observe how their trends differ after being subjected to the same training structure. The vertical gray bars represent perceived wellness and the horizontal dashed line represents the smallest worthwhile change. A is the HRV trend of a veteran and higher level athlete while B is younger and less experienced. A experiences large fluctuation in response to an abrupt increase in load, but the recovery to or above baseline facilitates an overall stable trend. In contrast, B experiences maintained suppression of HRV and decreasing wellness, good indications of inadequate recovery. The overload was apparently much harder for B than for A. This is an example of how both training status and an abrupt increase in load affect HRV. 

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

Similar to the point above, but with subtle distinctions. This was one of the first observations I made from my own training when I started experimenting with HRV several years ago. Introduce a novel stimulus (e.g., major change in exercise selection; taking all sets to failure when not done typically, etc.) and the body will often respond to a greater degree than had the stimulus been familiar. This is typically reflected in your HRV by showing a marked decrease for a day or two following the workout. However, positive adaptation to this stimulus will generally be reflected with smaller HRV responses to the not so novel (anymore) stimulus over the next few sessions. Look at the figure below showing individual HRV responses to week 1 and week 3 of an off-season training program involving 11 collegiate soccer players coming off over one month of rest. Mondays involved a 1-hour lifting session (full body, strength emphasis) and some interval training. In week 1, nearly every athlete showed a decrease in HRV following Monday. However, by week 3 this isn’t the case. Several athletes are showing signs of faster recovery while others are not. This provides unique insight regarding how individuals are adapting to training and conceivably can be used to make modifications to the program if necessary for certain individuals.

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

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. Training stress + Non-training stress = a greater stress response and is typically reflected in your HRV. Before and after a 12-week resistance training program, 135 college students completed a survey about their perceived stress levels. The sample was divided into a “low stress” and “high stress” group based on survey results. The low stress group experienced a significantly greater increase in 1RM Bench and Squat compared to the high stress group following the training program [7]. Though HRV was not measured in this study, the association between high stress and low HRV is well established [8]. Further, perceived stressors have been shown contribute to changes in HRV and non-functional overreaching in elite wrestlers [9]. Other non-training related factors known to impact HRV include alcohol consumption [10], travelling [11], academic stress [12], work stress [13], hydration status [14], sleep quality [15], pharmaceuticals (e.g., anabolic steroids [16], anti-depressants [17]) and although less studied, dietary factors such as Omega-3 fatty acid intake [18]. Gains in strength and hypertrophy largely depend on the balance between protein accretion and protein breakdown favoring the former [19]. 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. Observe the series of events that occur in the trend below for an example​.

​The vertical gray bars represent perceived training load and the horizontal dashed lines represent the smallest worthwhile change. Combined academic stress with training stress results in greater HRV fluctuation during exam week compared to before exams. Following exams is a full day of travel consisting of 3 flights (with delays, cancellations and re-bookings no less). Then, cold symptoms appear on the morning corresponding to the major decrease in the trend. Training stops while symptoms and poor sleep persist for over a week. When symptoms start to clear up, training resumes and workouts of less volume and intensity are perceived to be as tough as much heavier and longer workouts from the weeks before as some detraining has occurred. HRV is useful here to guide training load back to previous levels and avoid the all too common issue of doing too much too soon while the body is still fighting off the infection despite being asymptomatic. 

HRV and strength/power performance

Unfortunately, HRV is not a reliable tool for predicting performance potential in strength/power/speed athletes. In other words, just because HRV is at or above baseline doesn’t mean you’re going to perform better than if HRV was below baseline. For example, sprint times in high level swimmers correlated with cardiac-parasympathetic activity on race day, meaning that lower HRV was associated with lower (i.e.,faster) race times [20]. This may be due to higher sympathetic activation contributing to greater neuromuscular performance, but pre-competitive anxiety is an important confounding variable in these contexts (i.e., the most nervous/anxious person doesn’t always win). In overtrained lifters (reduced 1RM performance for several weeks), sympathetic activity demonstrated a compensatory increase as a result ​of decreased B2-adrenergic receptor density [21]. Then there’s the research mentioned earlier that showed 1RM strength to return to baseline after a single session [5], or multiple sessions [6] when HRV returned to baseline. However, correlations were not reported in these studies, so it’s difficult to know how this works on an individual basis. In my experience, you’re better off using a simple performance test (i.e., sub-maximal bar velocity) to predict and monitor strength/power performance than HRV. 

To manage stress, we need to measure stress

​A limitation of HRV is that it is sensitive to various stressors, both physiological and perceived psychological. This can make attributing a change in HRV to a specific variable challenging. However, 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.

Practical guidelines 

​Having applied HRV monitoring with athletes of various sports disciplines (strength/power, sprinters, endurance and team-sport), I believe that interpreting the data is easiest in strength/power athletes. This is because endurance training and conditioning are training variables that greatly affect HRV in various ways that can get a bit tricky to interpret. Additionally, overtraining in endurance and team-sport athletes can be characterized by parasympathetic hyperactivity (i.e., increased HRV at rest and reduced sub-maximal heart rate during exercise) [22] or withdrawn parasympathetic and increased sympathetic activity (i.e., decreased HRV at rest and increased submaximal heart rate during exercise) [23]. HRV trend interpretation is a little more cut and dry when high volumes of endurance training and conditioning are not involved, as with strength/power athletes.
 
To end, I’ll leave you with some basic guidelines that I’ve put together based on personal experience and the available research but Keep in mind that mind that there are always exceptions. Personal experimentation with HRV monitoring is the best way to improve your ability to interpret the data.  

References

1. Stanley, J., J.M. Peake, and M. Buchheit, Cardiac parasympathetic reactivation following exercise: implications for training prescription. Sports medicine, 2013. 43(12): p. 1259-1277.
2. González-Badillo, J., et al., Short-term Recovery Following Resistance Exercise Leading or not to Failure. International journal of sports medicine, 2015.
3. Boone, C.H., et al., Changes in plasma aldosterone and electrolytes following high-volume and high-intensity resistance exercise protocols in trained men. The Journal of Strength & Conditioning Research, 9000. Publish Ahead of Print.
4. McMillan, J.L., et al., 20-Hour Physiological Responses to a Single Weight-Training Session. The Journal of Strength & Conditioning Research, 1993. 7(1): p. 9-21.
5. Chen, J.L., et al., Parasympathetic nervous activity mirrors recovery status in weightlifting performance after training. J Strength Cond Res, 2011. 25(6): p. 1546-52.
6. Christoph Schneider, O.S., Christian Raeder, Thimo Wiewelhove, Alexander Ferrauti, Effect of an intensive strength training microcycle on resting heart rate variability. 20th Annual Congress of the European Congress of Sport Sciences, At Malmö, Sweden, 2015.
7. Bartholomew, J.B., et al., Strength gains after resistance training: the effect of stressful, negative life events. The Journal of Strength & Conditioning Research, 2008. 22(4): p. 1215-1221.
8. Dishman, R.K., et al., Heart rate variability, trait anxiety, and perceived stress among physically fit men and women. International Journal of Psychophysiology, 2000. 37(2): p. 121-133.
9. Tian, Y., et al., Heart rate variability threshold values for early-warning nonfunctional overreaching in elite female wrestlers. The Journal of Strength & Conditioning Research, 2013. 27(6): p. 1511-1519.
10.  <Alcohol Has a Dose-Related Effect on Parasympathetic Nerve Activity During Sleep.pdf>.
11. Botek, M., P. Stejskal, and Z. Svozil, Autonomic nervous system activity during acclimatization after rapid air travel across time zones: A case study. Acta Universitatis Palackianae Olomucensis. Gymnica, 2009. 39(2): p. 13-21.
12. Zaripov, V. and M. Barinova, Changes in parameters of tachography and heart rate variability in students differing in the level of psychoemotional stress and type of temperament during an academic test week. Human Physiology, 2008. 34(4): p. 454-460.
13. Clays, E., et al., The perception of work stressors is related to reduced parasympathetic activity. International archives of occupational and environmental health, 2011. 84(2): p. 185-191.
14. Carter, R., et al., The influence of hydration status on heart rate variability after exercise heat stress. Journal of Thermal Biology, 2005. 30(7): p. 495-502.
15. Takase, B., et al., Effects of chronic sleep deprivation on autonomic activity by examining heart rate variability, plasma catecholamine, and intracellular magnesium levels. Biomedicine & pharmacotherapy, 2004. 58: p. S35-S39.
16. <Cardiac autonomic dysfunction in anabolic steroid users.pdf>.
17. van Zyl, L.T., T. Hasegawa, and K. Nagata, Effects of antidepressant treatment on heart rate variability in major depression: a quantitative review. Biopsychosoc Med, 2008. 2(1): p. 1-10.
18. Villa, B., et al., Omega-3 fatty acid ethyl esters increase heart rate variability in patients with coronary disease. Pharmacological research, 2002. 45(6): p. 475-478.
19. Sandri, M., Signaling in muscle atrophy and hypertrophy. Physiology, 2008. 23(3): p. 160-170.
20. Merati, G., et al., Autonomic modulations of heart rate variability and performances in short-distance elite swimmers. European journal of applied physiology, 2015. 115(4): p. 825-835.
21. Fry, A.C., et al., β2-Adrenergic receptor downregulation and performance decrements during high-intensity resistance exercise overtraining. Journal of Applied Physiology, 2006. 101(6): p. 1664-1672.
22. Le Meur, Y., et al., Evidence of parasympathetic hyperactivity in functionally overreached athletes. Med Sci Sports Exerc, 2013. 45(11): p. 2061-71.
23. Baumert, M., et al., Heart rate variability, blood pressure variability, and baroreflex sensitivity in overtrained athletes. Clin J Sport Med, 2006. 16(5): p. 412-7.