In the past, it was always very difficult to measure fatigue accumulation during training. Most methods were subjective and lacking in precision, especially in the long term. More recently, athletes have begun to measure excess post-exercise oxygen consumption, better known as the EPOC prediction method, to determine how well they have recovered after a single session, as well as over longer periods of time.
Measuring Physiological Fatigue
EPOC can be defined as the amount of oxygen the body needs to recover after a training session. It is measured in milliliters of oxygen per kilo of body weight (ml/kg) and must be calculated from heart rate variability (HRV) data rather than a simple heart rate score. This is because heart rate may remain the same during two training sessions, even when one is harder and more fatiguing on the body. Heart rate variability is the only way to measure this fatigue.
During exercise, the body consumes more oxygen than while at rest. This means that higher intensity exercise involves a higher consumption of oxygen, both during and immediately after a workout, leading to greater fatigue. A higher EPOC value, therefore, means that the athlete is more physiologically tired.
While EPOC value will always increase with exercise intensity, it does not always with duration, explains JDS Sport Coaching. This means low-intensity workouts often lead to a low EPOC value even if they are long in duration, while high-intensity sessions allow for a higher value to be reached in shorter time.
The Real Value of EPOC
The EPOC value is a measure of training load and cardiovascular fatigue. Its main purpose is to describe stress caused to the body after endurance activities, such as running, cycling, and swimming, with a focus on the respiratory and cardiovascular systems. It works best for continuous type training rather than interval workouts.
Unlike other methods, EPOC allows athletes to see when fatigue is contributing to their performance. This eliminates the chance of wrongly supposing that performance has deteriorated when, in fact, the athlete is simply physiologically tired.
EPOC also has important long term significance: oftentimes the body may seem to have recovered quickly from training, even though long-term fatigue has actually remained and continues to build up over time. Athletes can more easily see when they need to spend more time recovering and when it would be the most beneficial to incorporate recovery weeks into a program.
The real value in EPOC lies in the ability of coaches, athletes, and trainers to use its feedback to create personalized workouts that improve training efficiency and endurance performance.