Force-time analysis of the countermovement jump as an indicator of fatigue status in professional academy footballers

Abstract

Purpose: A by-product of the greater financial rewards in elite football is that teams have tended to increase the volume and frequency of their physical training. To reduce the risk of injury and overtraining in players, football coaches need accurate, easy-to-use, and time-efficient monitoring tools for measuring the physical condition of the player. Vertical jump tests are commonly used to determine the player’s neuromuscular fatigue status. However, it is suspected that some skilled players can modify their jumping technique to maintain jump height even when fatigued. Therefore, variables from a jump test other than jump height might be more sensitive indicators of the player’s fatigue state. The aim of this study was to identify the jump metrics that are most sensitive to the delayed neuromuscular fatigue induced by a competitive football match. Methods: This study used a quasi-experiment design with a linear regression analysis of the individual player. Twenty male elite academy footballers performed countermovement jump tests the day before and two days after a competitive match for 20 consecutive weeks during the competition season. After exclusion, data from eight participants were used for the analysis. Seven jump variables related to jump height and jumping technique were selected for analysis. The physical match load variables, very high-speed running and high-intensity decelerations, were plotted separately against the change in each jump variable due to the match. Following an initial visual analysis, a linear regression fit to the data was used to determine the strength of the relationships. Results: Jump height and other countermovement jump variables showed no significant findings when assessing the change from pre- to post-match and there were no universally consistent relationships between the change in a jump variable and the physical match load on a player. Multiple individual differences were observed in the strength of the associations and the direction of these relationships between the jump variables and match load. Conclusion: The absence of statistically significant changes of the countermovement jump variables used in the study suggest that they are not sufficiently sensitive measures to indicate neuromuscular fatigue. However, large individual differences suggest that coaches could utilise countermovement jump monitoring to inform on the altered movement strategy used in the presence of neuromuscular fatigue on an individual level.