Training by heart-rate variability

Runners are famously poor at discerning the subtle differences between “really tired” and “too tired” – except in hindsight. Knowing when you need to pull back on your training for a day or two can be a huge advantage, because it allows you to accumulate more training in the long term without breaking down. That’s why researchers and coaches have been searching for objective measures of fatigue and recovery, to take the guesswork (and the ego) out of these decisions. One of the leading candidates is heart-rate variability, or hrv, a measure of the subtle f luctuations in the time between successive heart beats. Measuring this quantity when you wake up in the morning gives a useful snapshot of the state of your autonomic nervous systems, and – according to advocates – can guide training decisions.

Does it really work? Evidence so far remains sketchy at best, but a new study with members of the French national cross-country ski team offers some interesting insights. A total of 18 skiers took part in a two-week altitude training camp, and measured their hrv each morning. Half of them adjusted their training based on the measurement; if the high-frequency portion of their hrv decreased by 30 per cent or more from one day to the next, they reduced their training load that day. If it decreased again on a consecutive day, they took a day completely off.

The results, published i n the European Journal of Applied Physiology, suggested that the hrv group had experienced less disruption of their autonomic nervous system, thanks to an average of three days of adjusted training. In theory, that should lower their risk of developing overtraining and excessive fatigue in the long term. In terms of actual performance in 10k ski trials immediately after the training camp and three weeks later, the two groups had similar improvements. The ultimate conclusion remains unclear – but studies like this are a good start toward testing the claims made by wearable tech companies.