A simple introduction to Heart Rate Variability
One of the biggest challenges most non-professional athletes face is balancing the physiological stresses from training and racing with those of everyday life. Many of us have families, jobs and other commitments which contribute to our overall level of stress. When physiological stress is high, our ability to train and recover well is compromised. Several studies in recent years have shown a strong link between increased mental and physical stress from non-training sources (such as busy periods at work) and overtraining, even when training volumes were held constant. So how do we account for these sources of non-training stress when planning and monitoring training programs for an athlete?
Unless you’re lucky enough to have a full time lab team testing and monitoring your cortisol (the stress hormone) levels, you’ll need a simple, cheap and repeatable alternative. This is where Heart Rate Variability (HRV) steps in.
There is some reasonably complex biological science behind HRV which I’m not going to try to explain (as I’m certainly not qualified to do so), however I will offer as simple an explanation as I can:
Your heart does not beat at a perfectly constant rate. For example, if you were sitting comfortably and measured your heart rate at 60bpm it is unlikely that your heart is beating precisely every second. There might be a 1 second gap between most beats, but some will be 0.9 seconds apart, some will be 1.1 seconds apart etc. This variation has an inverse relationship to the level of stress your body is under (i.e. high HRV is associated with low levels of physiological stress). By measuring and tracking these small differences over time, we can extract an indication as to the level of overall stress you are experiencing (relative to your personal baseline).
For those of you interested in the detail, there is a significant amount of reading available on the internet and a few good starting points are listed at the end of this article.
So how do we use this as athletes (and coaches)?
Intrinsically, we all know that we don’t perform well when we are suffering from increased stress. We may not have been sleeping well, have been flat out at work, be worried about our kids, have an underlying illness, consumed alcohol the night before, or simply have done several hard days riding in a row. The difficulty is determining when that level of increased stress is tolerable, or whether we should allow our bodies more time to rest and recover. Fortunately, with HRV monitoring becoming easily available to everyday athletes, this determination is made easier.
In recent years, several smartphone apps have been developed which offer a non-invasive and simple way to record HRV. Typically these require athletes to undertake a short test every morning, right after waking up, involving either a chest strap heart rate monitor or simply holding the athlete’s finger over their smartphone camera for a short period of time (typically 30 or 60 seconds). There is usually a short questionnaire about perceived physical and mental stress as well. Over days, weeks and months, we are able to build up a baseline view of ‘normal’ for each athlete, and can quickly identify when stress (of any form) is having a detrimental effect on the athlete. We can then make smart decisions about whether to proceed with training as planned, to take further rest, or to look at other areas in the athlete’s life that may be able to be adjusted, all to ensure the athlete is getting the most bang for their training buck.
By way of example, if an athlete regularly has HRV values in the 80-100ms range* and notices one morning a measurement of 45ms, this could potentially be an indication of overtraining or even an early indication of oncoming illness. When considered in the broader context of the athlete’s life (have they just completed a significant hard block of training, had a few late nights in a row, or are generally feeling slightly run-down), the athlete (and their coach) may alter short term training plans to reduce the risk of making things worse.
At Kilowatt Cycle Coaching we offer HRV tracking as part of our coaching services for athletes who wish to use it. Our approach is to work with each athlete to help them understand their own HRV baseline and to support them in making athlete led decisions about whether and when to defer training due to excess physiological stress. We link your HRV tracking into Training Peaks to allow us to review it as part of ongoing athlete management. As always, Will and I love talking about this stuff, so feel free to reach out if you have any questions!
Until next time, ride safe.
*rMSSD - Root Mean Square of Successive Differences, the primary time domain metric used in HRV measurement.