EPOC, or excess post-exercise oxygen consumption, is a phenomenon in which your body consumes more oxygen than it normally would at rest for a certain period after a workout. This makes sense. During exercise, your body's normal state is disturbed, so it has to work harder to restore that normal state. In fact, the whole point of training is that afterwards your body restores its normal state and improves it slightly. It is exactly this “better than before” – also known as “supercompensation” – that improves your fitness and makes you a little faster.
Since the amount of oxygen your body uses is directly related to the amount of energy it uses, EPOC is an ideal measure of how much a workout disturbs your body's normal state (homeostasis). In other words, EPOC is an excellent measure of training volume or load, because it shows how much work your body has to do to restore its normal state and reach a slightly better level of fitness.
Measuring EPOC directly requires sophisticated laboratory equipment and a lot of time. However, Firstbeat has developed a patented method for estimating EPOC based on heart rate data recorded during exercise. These EPOC estimates form the basis for determining your training effect, weekly training load and training status.
