Both performance and injury treatment rely on the optimal balance of imposed stress and recovery. Training stresses the body and recovery allows it to adapt. But it can be hard to know how much is too much or not enough of either one. Our ability to adapt can fluctuate on a weekly basis. Athletes’ perceived efforts or states of readiness to train can be vague. Ideally, athletes can use their own perceptions and input in conjunction with an objective measure of preparedness for training. Heart Rate Variability (hrv) monitoring is one promising way of doing this. HRV measures the difference in timing between successive heart beats. If your heart beats 60 times per minute those beats are not perfectly spaced. The variability of that spacing provides insight into the autonomic nervous system’s cardiovascular control. The autonomic nervous system consists of the sympathetic and parasympathetic divisions. The sympathetic division is most famous for its “Flight or Fight or Freeze” function. Both divisions influence heart rate and its variability. The parasympathetic nerves decrease heart rate and increase its variability. The sympathetic nervous system has the opposite response. Very simply, as exceptions do occur, an increase in hrv is considered a sign of good recovery whereas decreases in HRV can, at times, suggest poor recovery and indicate an athlete is not ready to train.
HRV can be measured with a simple smart phone application (ithlete or Bioforce for example) and a chest-or finger-based heart rate monitor. The HRV is measured daily at the same time in a seated position. The process takes less than three minutes. A weekly average of the daily results is calculated and daily fluctuations or weekly changes can be compared to this initial baseline. In endurance athletes a positive adaptation to training is an increase in the weekly hrv average. During heavy bouts of training, hrv will tend to decrease and this decrease can continue if the athlete does not recover. There are, however, other factors not related to training that can influence hrv which complicates its use in guiding training including, emotional stress, alcohol consumption, poor sleep and nutrition. Dr. Andrew Flatt (hrvtraining.com), a top researcher of hrv has also shown that increased fluctuations (i.e. high variability) in daily hrv measurements correlate with poor performance in race times in elite runners. In other words, a high number of changes in hrv are correlated to slower performances. It’s essential that athletes make training judgments based on measures of hrv combined with other methods. Doing so could help boost fitness. Consult your coach or any number of online resources with explicit experience using and supporting HRV.
Greg Lehman is a physiotherapist, running injury therapist and chiropractor at the Urban Athlete in Toronto. Follow him at www.greglehman.ca