You’re probably wondering which parameters are used to determine your Fitness, Fatigue, and Form.
Your Fitness, also referred to as chronic training load, is a measure of how much you’ve trained in the past. In general, the term fitness describes your overall physical capacity and your ability to perform physical activities. It includes strength, endurance, flexibility, and body composition. While maximal oxygen uptake (VO₂max) is an important indicator of cardiovascular fitness, there are other relevant aspects as well. Therefore, fitness is a comprehensive concept that encompasses various dimensions of physical health and performance.
In the Fitness-Fatigue Model, your past training sessions are analyzed in terms of volume and intensity and evaluated using training load. The training load from recent days is aggregated and processed using an Exponentially Weighted Moving Average (EWMA).
The EWMA ensures that your most recent training sessions have a greater influence on your fitness than those from, say, four weeks ago. Typically, the last 42 days are considered in calculating fitness.
Your Fatigue, also called acute training load, is generally based on the training load of the past 7 days. It reflects your current training-induced fatigue. Again, the EWMA is used to apply exponential weighting. After a series of high-intensity training sessions, fatigue increases, and with a few lighter or rest days, it decreases again. A high level of fatigue negatively impacts your performance—even if your fitness is high.
Now let’s talk about Form. Your form is calculated as the difference between Fitness and Fatigue and describes how good you currently feel and how well you’re able to perform. You’re in top form when your fitness is high and your fatigue is low — meaning you’re well-trained and well-rested.
In summary:
Fitness increases your capacity to perform.
Fatigue reduces it.
Form reflects how ready and fresh you are by balancing both.
Through tapering, for example, you can reduce fatigue faster than you lose fitness, allowing you to be in peak form on race day.
Sources:
Banister, E. W., Calvert, T. W., Savage, M. V., & Bach, T. (1975). A systems model of training for athletic performance. Aust J Sports Med, 7(3), 57–61.
Skorski, S., Mujika, I., Bosquet, L., Meeusen, R., Coutts, A. J., & Meyer, T. (2019). The temporal relationship between exercise, recovery processes, and changes in performance. Int J Sports Physiol Perform, 14(8), 1015–1021.
Busso, T., & Thomas, L. (2006). Using mathematical modeling in training planning. Int J Sports Physiol Perform, 1(4), 400–405.
Hellard, P., Avalos, M., Lacoste, L., Barale, F., Chatard, J. C., & Millet, G. P. (2006). Assessing the limitations of the Banister model in monitoring training. J Sports Sci, 24(5), 509–520.
Vermeire, K., Ghijs, M., Bourgois, J. G., & Boone, J. (2022). The fitness–fatigue model: what’s in the numbers? Int J Sports Physiol Perform, 17(5), 810–813.