What is heart rate variability and does it matter?

Marco Altini highlights the importance of an overlooked marker of fatigue

As a cyclist experiences stress - physical or psychological their body responds via changes in autonomic nervous system activity. This innervates the heart, affecting heart rhythm. This is why measuring heart rate and heart rate variability (HRV) gives us insights into the stress response.

HRV refers to the variability between heartbeats-because even at a steady heart rate, heartbeats are not uniform or entirely regular. Measured in milliseconds, HRV is the variation in timing between consecutive beats. As such, HRV captures information not present in heart rate alone, and is a more s a cyclist experiences stress - physical or psychological their body sensitive marker of stress. As a non-invasive proxy of our body's response to stress, HRV allows us to better understand how we are responding to training and other stressors, enabling us to make meaningful adjustments. Aside from training, stressors that may have an effect on resting physiology include psychological stress, sickness, alcohol intake, travel, and general life demands.

Very strong stressors usually have a clear visible effect on our resting heart rate. However, more subtle stressors such as small changes to training are better captured by HRV. Everyone experiences stress, so HRV is a useful tool regardless of the level at which you're training and competing. In fact, in many cases HRV is more useful to recreational athletes who need to balance training with work and other commitments, potentially dedicating less time to proper recovery.