One of the greatest challenges for coaches, competitive athletes and even novice trainers is how to best tailor training load so as to optimise training adaptations and ultimately performance. The problem with one-size-fits-all exercise programs is that every individual responds differently to a given training stimulus. Therefore there is a need for new tools that offer more independent assessment of one’s response to a given training stimulus. Heart rate variability (HRV) is one such tool that is quickly gaining in popularity. This exciting training tool can now be used by anyone with a compatible heart rate monitor and smartphone.
What is Heart Rate Variability?
Heart rate variability (HRV) is defined as the heart’s ability to produce fluctuations in the beat-to-beat interval in response to different situations1. In scientific gobbledygook, it defined as the natural logarithm of square root of the mean sum of the squared differences between R-R intervals (i.e. Ln rMSSD). To the average Jo Bloe that won’t mean anything, so suffice to say quantification of HRV can be used as a non-invasive method for assessing autonomic nervous system cardiovascular response to training. The autonomic nervous is made up of two arms, namely sympathetic (fight or flight response) and parasympathetic (rest and repair). To understand why HRV can be a useful tool in gauging the stress response to exercise, it’s helpful to have a basic understanding of the sympathetic and parasympathetic nervous system.
Sympathetic Nervous System
The sympathetic nervous system predominates during emergency “fight-or-flight” reactions and during exercise. Under these conditions, the overall effect of the sympathetic nervous system is to prepare the body for strenuous physical activity. On a physiological level, sympathetic nervous system activity will increase the flow of blood that is well-oxygenated and rich in nutrients to tissues in need, in particular, the working skeletal muscles. The activation of the sympathetic nervous system is typically measured by what is termed the low frequency domain1-3, a sample of which can be seen in the picture below from a sample app that measures HRV.
Parasympathetic Nervous System
The parasympathetic system (relaxation, repair, rest) on the other hand predominates during quiet, resting and repair conditions, where the overall aim is to conserve and store energy and to regulate basic body functions such as digestion and urination. The level of parasympathetic activation is typically gauged by a measure termed high frequency or HF1-3 as shown on the above picture. Another useful measure is the trend in LF and HF over time as shown below. If there is a general trend for HF to decrease, this means the individual is not getting enough rest and repair and should modify their training accordingly.
Heart Rate Variability for Exercise/Program Prescription
When devising a weight training program, volume and intensity are key elements but the amount of recovery betweens sets and the frequency with which different body parts are trained is also key. Heart rate variability is a tool that can allow coaches and athletes to monitor the stress response to training loads that differ in the above variables. For example, when athletes are training with heavy loads during a period of time, training can produce cumulative stress-related effects. The magnitude of this stress response can be observed by the activation of the sympathetic arm of the autonomic nervous system and the resulting variations in autonomic balance, which can be indirectly assessed using HRV analysis4. The ultimate goal for any athlete measuring HRV regularly is to optimally vary training load and recovery so as to arrive at an ideal tapering period that produces better performance and prevents any potential overtraining5.
How To Measure Heart Rate Variability
To measure your heart rate variability, you will need a compatible heart rate monitor (most require bluetooth functionality to sync with smartphone), a smartphone and one of the many apps that are available for measuring HRV. The picture below shows an example of some of the technical data that is provided while measuring HRV.
HRV is best measured at the same time of day everyday and takes 2-5 minutes depending on the app you are using. During this time one needs to remain stationary and calm. While there is debate as to the best time of day for measuring HRV, the general consensus and trend for most athletes is to measure immediately after waking up and while still lying in bed6. This tends to minimise the impact of environmental conditions (i.e. noise, light, temperature) that have been known to affect autonomic nervous system activity7. The picture below shows an example of a summary screen following a HRV measuring session.
A recent study has shown that daily HRV values averaged over 1 week provide a better representation of training-induced changes than HRV values taken on a single day8. So it would appear that weekly trends in HRV provide the best indication of adaptation to training load. The picture below shows an example of the trend in HRV over time from a sample HRV app.
Weight Training & Heart Rate Variability
While much of the research concerning the effect of exercise on HRV has centred on aerobic exercise, there are a series of recent studies which have looked at the specific effect of different modes of resistance exercise on HRV in different populations. While long term aerobic training in older men has been shown to improve HRV9-11, the effects of resistance exercise on HRV in the elderly are not so clear. For example, one study which focused on the effect of eccentric training in older men found that while it increased strength, there was a tendency for an autonomic imbalance towards sympathetic predominance12. Yet another study which looked at the effect of isometric strength training in older men found that it was neutral in terms of its effect on HRV13.
Yet another study concerning the interaction of HRV with resistance exercise compared the effect of concentric-focused versus eccentric-focused resistance exercise in young males. The study found that the eccentric-focused resistance training produced the most favourable responses both in terms of strength gains and HRV14.
Lastly another cleverly designed study sought to determine the relative effect of resistance exercise using upper limbs versus lower limbs on HRV. Contrary to what some may have expected, the study found that HRV decreased the most following resistance exercise using upper limbs15.
Considered together these findings concerning the effect of different modes of resistance exercise on HRV demonstrate the multi-factorial nature governing responses. HRV response depend on age, training status, type of resistance exercise and body part being training. Regular measurement of HRV can help individuals determine their unique response to their training load and how to structure their training to produce the best results.
In closing it can be said that regular measurement of HRV is one of the more promising methods for monitoring individual adaptation to training. Non-functional overreaching and/or negative adaptation to training is thought to be generally associated with reductions in HRV, whereas increases in fitness and exercise performance are thought to be more associated with increases in HRV16.
- Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology. Heart rate variability: Standards of measurement, physiological interpretation and clinical use. Circulation 93: 1043–1065, 1996.
- Berntson GG, et al. Heart rate variability: origins, methods, and interpretive caveats. Psychophysiology. 1997;34(6):623-48.
- Billman GE. Heart rate variability - a historical perspective. Front Physiol. 2011;2:86.
- Seiler S, et al. Autonomic recovery after exercise in trained athletes: Intensity and duration effects. Med Sci Sports Exerc. 2007;39:1366–1373.
- Morales J, et al. Use of heart rate variability in monitoring stress and recovery in judo athletes. Journal of Strength and Conditioning Research. 2014;28(7):1896–1905.)
- Buchheit M. Monitoring training status with HR measurements. Do all roads lead to Rome? Frontiers in Physiology. 2014;5(73):1-19.
- Achten J & Jeukendrup AE. Heart rate monitoring: applications and limitations. Sports Med. 2003;33:517–538.
- Plews DJ, et al. Monitoring training with heart-rate variability: How much compliance is needed for valid assessment? International Journal of Sports Physiology and Performance. 2014;9:783-790.
- De Meersman RE. Heart rate variability and aerobic fitness. Am Heart J. 1993;125:726–31.
- Stein PK, Ehsani AA, Domitrovich PP, et al. Effect of exercise training on heart rate variability in healthy older aduts. Am Heart J. 1999;138:567–76.
- Melo RC, Santos MDB, Silva E, et al. Effects of age and physical activity on the autonomic control of heart rate in healthy men. Braz J Med Biol Res. 2005;38:1331–8.
- Melo RC, et al. High eccentric strength training reduces heart rate variability in healthy older men. Br J Sports Med. 2008;42:59–63.
- Takahashi AC, et al. The effect of eccentric strength training on heart rate and on its variability during isometric exercise in healthy older men. Eur J Appl Physiol. 2009;105(2):315-23.
- Gois MO, et al. The influence of resistance exercise with emphasis on specific contractions (concentric vs. eccentric) on muscle strength and post-exercise autonomic modulation: a randomized clinical trial. Braz J Phys Ther. 2014;18(1):30-37.
- Machado-Vidotti HG, et al. Cardiac autonomic responses during upper versus lower limb resistance exercise in healthy elderly men. Brazilian Journal of Physical Therapy. 2014;18(1):9-18.
- Plews DJ, et al. Training adaptation and heart rate variability in elite endurance athletes: opening the door to effective monitoring. Sports Med. 2013;43:773–781.