Training - Physiological Analysis by Firstbeat - EPOC
EPOC (excess post exercise oxygen consumption, ml/kg) is the first physiology based measure to monitor the accumulation of training load and fatigue during a training session.
Graph above: Example of EPOC accumulation during cross-country skiing training session.
Read more about EPOC, the interpretation and use of it from white papers EPOC as a measure and EPOC white paper
Correlation between the measured and heart beat derived EPOC in a validation study by Rusko HK et al. 2003.