Since researchers first found significant changes in the nervous systems of athletes involved in hard training for the rowing world championships (Iellamo, 2002), a number of studies have tried to use HRV as a tool to monitor overtraining. In general such studies show that HRV is much lower in overtrained athletes than healthy ones (Mourot, 2004).

The problem is, when you are overtrained it is too late. It might take weeks or months to get back to full fitness, so what you need is a daily measure to tell you how well your nervous system is doing. Daily monitoring using standard HRV methods have shown that listening to you heart via HRV can not only stop you overtraining but actually make your training more effective. (Manzi, 2009).

The idea is quite simple. Monitor your HRV every morning and train as normal. If your HRV drops significantly, take this as an early warning that you are overloading the system. A small drop is OK as long as you recover. Training is, after all, about stress and recovery and a hard session, especially on top of accumulated fatigue, will lower your HRV.

But if your HRV stays low even with rest you could be on the edge of trouble. In my opinion, using daily HRV to monitor training stress is the best thing you can do to make your training safe and effective. So listen to your heart.