Non-Ergodicity in Load and Recovery: Group Results Do Not Generalize to Individuals

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Purpose: The study of load and recovery gained significant interest in the last decades, given its important value in decreasing the likelihood of injuries and improving performance. So far, findings are typically reported on the group-level, whereas practitioners are most often interested in applications at the individual-level. Hence, the aim of the present research is to examine to what extent group-level statistics can be generalized to individual athletes, which is referred to as the “ergodicity issue”. Non-ergodicity may have serious consequences for the way we should analyze, and work with, load and recovery measures in the sports field. Methods: We collected load, i.e., rating of perceived exertion (RPE) * training duration, and total quality of recovery (TQR) data among youth male players of a professional football club. This data was collected on a daily basis across two seasons and analyzed on both the group- and the individual-level. Results: Group- and individual-level analysis resulted in different statistical outcomes, particularly with regard to load. Specifically, standard deviations within individuals were up to 7.63 times larger than standard deviations between individuals. In addition, at either level, we observed different correlations between load and recovery. Conclusions: The results suggest that the process of load and recovery in athletes is non-ergodic, which has important implications for the sports field. Recommendations for training programs of individual athletes may be suboptimal, or even erroneous, when guided by group-level outcomes. The utilization of individual-level data is key to ensure the optimal balance of individual load and recovery.
Originele taal-2English
TijdschriftInternational journal of sports physiology and performance
StatusAccepted/In press - 2021

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