Interactions between training sessions – Part I: Load, Fatigue and Adaptation

A fundamental problem in training planning is the way you sequence the various training sessions inside one micro-cycle. Even though this problem is present for any sport, when it comes to triathlon training it assumes a particularly important role. Due to the different characteristics and muscle groups involved in swim-bike-run, it is often hard to see how the interactions between training sessions effect training adaptations.

The training process can be loosely modeled as a series of sequenced processes composed of:

Training Load (session) -> Fatigue -> Adaptation(recovery) -> Performance

Obviously the training load imposed is a central aspect of training planning. However, fatigue plays an important role in the whole training process. In this context, fatigue can be defined as a natural response to a training load characterized by a lessened capacity for work. The evaluation and monitoring of the level of fatigue of an athlete, either quantitatively or qualitatively, a priori or a posteriori, is the most accurate way of checking the level of an athlete’s adaptation to training. Fatigue has several characteristics, but when it comes to planning training, we are mostly interested in fatigue as a function of time.

It is intuitive to everyone that different training sessions cause different levels of fatigue and that, more important, have different time-frames to recover from and to adapt to. Sessions with a higher training load take more time to recover from than sessions with a lower training load. When designing a micro-cycle routine, the temporal characteristics of the fatigue caused by a specific session need to be taken into account. On top of that, the interactions between the several Load -> Fatigue -> Adaptation processes need to be estimated in order to access the fatigue status at a given time. This fatigue status is extremely important because it determines the maximum load an athlete can perform at a given time.

Like I mentioned above, evaluating and monitoring fatigue can be done both quantitatively or qualitatively. For years and years, coaches have been predicting, evaluating and monitoring athlete’s fatigue levels in a qualitative way, in order to prescribe training. And rightfully so, since only through monitoring fatigue we can evaluate adaptation to training. Many coaches and athletes see training as a mere accumulation of fatigue, expecting that rest periods (days, weeks and even months) will be enough to recover from fatigue and allows for adaptations to training to happen. This way of thinking fails to realize that recovery occurs at all times that stress is not applied, and that adaptation to stress occurs at all times, even while stress is applied. Correctly modeling fatigue, even if in a qualitative way, is paramount for a correct prescription of training.

In the next part of this series, I will talk a bit about how the level of fatigue is connected to the level of recovery, the timings of fatigue/recovery and how all that that determines micro-cycle planning.