Heart rate is a performance indicator which many coaches ask athletes to record every morning. A high resting heart rate is linked with lower physical fitness and higher blood pressure, body weight, and levels of circulating blood fats¹; therefore, a lower resting heart rate is associated with positive physiological benefits. Factors other than training can affect your resting heart rate too. These include your age, past experience of training, temperature, dehydration, stress, genetics, and your mental health – and all these factors don’t just affect heart rate directly, they also interact with each other to affect it indirectly.

It is a helpful measure of performance readiness as a sudden increase in resting heart rate can tip us off that we are overreaching. Athletes who are “overreaching” by running too many miles experience poor race performance, irritableness and fatigue and this principal doesn’t just apply to athletes with increased training loads. Stress works on the body in the same way no matter what inflicted it (For a really good explanation of how training and daily stress cohabitate read this). An increase in your resting heart rate of 2-3 beats per minute can be a sign of overreaching – but it is not definitive. You should use other markers such as mood, food cravings, and fatigue levels to gauge whether the change in heart rate is something to be concerned about.

One more factor to consider is the fact that your heart is not actually a metronome. The heart, in fact, speeds up when you inhale, and slows down when you exhale. The difference is known as heart-rate variability (HRV) and is a great indication of your overall health, stress levels and readiness to train.

By knowing your HRV, you can objectively measure your body’s response to stressors. Often this coincides with your feelings or subjective measures, but there will be times when your HRV indicates that you really need to take it easy, or take a rest day. Once you respond to this signal you will find you can train harder or just do more the next day.

Heart rate variability was previously a diagnostic measure used mainly in hospitals, but with the increasing availability of wearable sensors, it is no longer out of our reach.

A decrease in heart rate variability is associated with physiological changes which are linked to ill health². Simply re-prioritizing rest and recovery may provide a quick solution, but sometimes longer term lifestyle changes are also required.

So rather than just use your wearable device to demonstrate to colleagues that you got NO SLEEP last night, or how many steps you complete after midnight on a Friday – try recording the different heart rate measures alongside your mood and feelings of well or ill-being. You can then use this data to predict when you are likely to experience injury or illness and take a step back before it happens.

If you are repeatedly experiencing a decreased ability to perform – analyse your stressors and make a change!

References

1. Jensen MT, Suadicani P, Hein HO, et al. Elevated resting heart rate, physical fitness and all-cause mortality: a 16-year follow-up in the Copenhagen Male Study
   Heart 2013;99:882-887.

   http://heart.bmj.com/content/99/12/882.full?sid=90e3623c-1250-4b94-928c-0a8f95c5b36b

2. THAYER, J. F. and STERNBERG, E. (2006), Beyond Heart Rate Variability. Annals of the New York Academy of Sciences, 1088: 361–372. doi:10.1196/annals.1366.014 http://onlinelibrary.wiley.com/doi/10.1196/annals.1366.014/abstract

Other Reading

• http://www.livestrong.com/article/105256-normal-heart-rate-sleeping/
• https://www.t-nation.com/training/heart-rate-variability-training
• http://www.myithlete.com/wp-content/uploads/2014/10/ithlete-guide-to-training-with-HRV.pdf