This article was reviewed by David W, DPT.

In recent years, with the advent of the smart watch, smart phone, and fit bit, the general public has become increasingly fixated on taking their health into their own hands. Everyone has heard of monitoring one’s heart beat, blood pressure, how many steps you’ve taken in a day, and is somewhat familiar of how maintaining these measures in a normal range helps optimize your health. A somewhat new unit of measurement has in recent years begun to break its way into the lay population as well, and it is called heart rate variability.

All of us have a heart beat, and when we are healthy and at rest, it should be between 60-100 beats per minute as per current guidelines.  However, heart rate variability is the measurement between two successive heart beats, and is typically measured in mili-seconds, and gives us a way to measure our autonomic nervous system (ANS).  Most people know the ANS as the sympathetic (fight or flight) and parasympathetic (rest and digest) nervous system’s involvement. When we are sleep deprived, stressed, hung over, or maybe we have worked out too hard- our sympathetic nervous system goes into overdrive, and our heart rate variability becomes less variable – less able to adapt. When we have recovered and our parasympathetic nervous system increases, our heart rate variability increases, as does our body’s ability to recover.

This is a potentially useful tool for several reasons.  If we were to just look at the heart rate of an athlete who may be chronically over training, their heart rate alone may or may not reflect the increased stress in their system.  By keeping track of heart rate variability, we can reliably track the effects of stress/lack of sleep on our nervous system. It’s one thing to know that pulling an all nighter, or drinking too much isn’t good for you, but when you can directly see and measure the consequences on your own body, it gives you extra incentive and perhaps agency over your habits.   What’s more, is that we might even be able to use HRV to prevent injury.

The pathogenesis of overuse injuries is not totally understood, but we do know that there is often an abnormal inflammatory response present in our muscles and tendons that occurs prior to the presence of pain.  Research findings indicate that HRV may give us a window into our ANS, and alert us when our sympathetic drive might be too high, and when we might be at risk of injury. In a recent study examining a small group of competitive cross fit athletes, there was a positive correlation between low HRV, increased workload, and subsequent report of an overuse injury.  Although there is a lack of evidence to fully connect the dots, and no studies to date that show how HRV can be used to reduce rate of injury, many athletes and fitness enthusiasts are attempting to utilize HRV to their benefit.

On days when your heart rate variability is decreased (indicating higher sympathetic drive, potentially due to inflammation) perhaps that isn’t the day to set a personal record at the gym. Maybe doing a lighter work out, doing some restorative and mobility work, meditation, and getting to bed earlier is in order.  Conversely, when you have a higher HRV, you are less susceptible to injury, and may be able to push yourself a bit more in your work out. To track your HRV is pretty simple- you can use one of the many apps for your smartphone. The key is to use it daily,and track your quality of sleep, life stressors, workout intensity and overall health, to paint a larger trend.

Source:

Gisselman et. al, “ Musculoskeletal overuse injuries and heart rate variability: Is there a Link?” Medical Hypotheses 87 (2016) 1-7
Williams et. al,” Heart Rate Variability is a Moderating Factor in the Workload-injury Relationship of competitive crossfit athletes. “ Journal of SPorts Science and Medicine (2017), 16, 443-449.