How to monitor fatigue levels with GPS data

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The prescription of the optimal training dose for team sports players is a constant balance between ‘fitness levels’ and ‘fatigue levels’. On the one hand, higher workloads are beneficial for maintaining or improving the fitness levels of the players. On the other hand, a lower training load (or a day-off) will restore the physical performance for the next training session or match. Hence, monitoring the fatigue status of your players is of great importance when determining the optimal load for the individual players. 

Exertion and recovery app

One of the ways to monitor the fatigue levels is via questionnaires: players fill in scores on 5 recovery scales on their mobile phone (i.e. subjective data). This is an easy to use and powerful method to get insights into the recovery status of the players. In this blog, we will explain how positional data (i.e. objective data) can further inform on the fatigue levels of the players.

What causes fatigue?

It is known that soccer matches induce acute fatigue (less than 3 hours after the match) and residual fatigue (72 hours after the match) in players. This can be seen by a decreased maximal force production and increased concentration of muscle damage markers up to 24-48 hours after the match. These effects are caused by repeated performance of eccentric muscle contractions in the match. For which the high-intensity movements (sprinting and accelerations) will have the most impact on fatigue levels. 

Training sessions or matches

The low- to moderate intensity movements (walking or jogging) will only cause a low magnitude of muscle damage. Even though the total distance covered is the most commonly used variable by coaches, it will not give insights into the fatigue induced by a training session or match. In contrast, sprinting distance (i.e. distance >20km/h) and the number of high accelerations (>3m/s2) are able to give information about the fatigue induced by a training session or match.

What to do in practice

Do these results mean that players who usually sprint or accelerate the most during a training session or match also need longer recovery times than the other players? No, that is not always the case. When a player is already familiarized with a high eccentric load, this will fasten the recovery rate. Hence, we may not be interested in the absolute numbers to determine the fatigue levels of a player.  The relative numbers are more interesting: did the player perform more or less high-intensity movements than usual? A rough guideline for this is: if a player performs 20-30% more high-intensity load than usual in a match (or conditional session), this should give an indication of higher fatigue levels in the following 24 to 48 hours. In that case, extra recovery methods or lowering of the workload (especially in the high-intensity domain) in this time period are advised.

The impact of fitness levels

In addition, fitness levels will also impact fatigue levels after a session. When a player returns from an injury or has not been able to perform the whole training program in the last week(s), this will have a negative effect on the fitness level. Performing the same high-intensity load, as usual, might cause higher fatigue levels, and thus longer recovery times. So even though the relative numbers might provide important information about the fatigue induced by a session, it is essential to interpret it in the context of the individual player! 

Insight in fatigue levels

Even though the total distance covered is the most commonly used variable by coaches to monitor their team, it will not give insights into the fatigue levels of the players. Rather, the high-intensity movements (sprint distance and high accelerations) should be used to get an indication of this status. However, absolute numbers will not provide enough information. Instead, the relative numbers (percentage of what a player usually does) will give a better indication. And even for the relative numbers, it is of great importance to interpret these in the context of the individual player.

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