Peripheral muscle function during repeated changes of direction in professional soccer players

Purposes To evaluate peripheral muscle function of the knee extensors during repeated changes of direction in professional soccer players by examining differences between competitive levels, periods of the season and playing positions, and to investigate the relationships between peripheral muscle function and physical activities during matches. Methods Knee extensor peripheral muscle function (twitch peak torque, PT) of 593 male soccer players from 13 European professional clubs competing at 3 different levels was evaluated 4 times during the season. The main outcomes were PTmax (maximal PT, muscle contractility), MPmax (maximal metabolic power exercise intensity) and PTdec (PT decline, muscle fatigability) obtained during intermittent runs of increasing intensity with multiple changes of direction interspersed with electrically evoked contractions. Relative total and sprint distances covered during a whole match and during short intervals were quantified from a sub-sample. Results PTmax and MPmax were higher for first than for second division (p < 0.047; d = 0.15-0.23) and Under-19 players (p < 0.007; d = 0.17-0.25). MPmax was lower (p < 0.016; d = 0.23-0.32) and PTdec was higher (p < 0.004; d = 0.26-0.39) in the pre-season compared to all the other time points. MPmax was higher for fullbacks than attackers and defenders (p < 0.041; d = 0.20-0.22). PTdec was higher for defenders than fullbacks, midfielders and wings (p < 0.029; d = 0.21-0.28). PTmax was associated with whole-match relative total distance (p = 0.004; d = 0.26). PTdec was associated with whole-match relative total distance and relative short-interval sprint distance (p < 0.050; d = 0.18-0.22). Conclusion The ability to sustain repeated change of direction efforts at high intensities while preserving peripheral muscle function should be considered an important determinant of soccer physical performance.