Objective: The aims of this study were firstly to determine if knee extensor and flexor muscle contralateral strength imbalances were present in soccer players and secondly to establish the influence of playing positions on contralateral strength imbalances. Methods: The knee extensor and flexor muscle concentric strength of 20 volunteer recreational soccer players were tested using leg extensor and leg curl devices respectively. The load-velocity relationships were established for knee extensor and flexor muscles on the dominant lower limb (DL) and the non-dominant lower limb (NDL). Results: Regardless of playing position, participants presented significant strength imbalances between the DL and the NDL for knee extensor and flexor muscles at 40% and 60% of maximal strength. When playing position was taken into consideration, axial players had a greater knee extensor muscle contralateral strength imbalance than side players, while side players had a greater knee flexor muscle contralateral strength imbalance than axial players. All of the strength imbalances were observed at intensities specific to soccer game actions (jumps, sprints, and shots). The playing position has probably an influence on the contralateral strength imbalance of the knee flexor and extensor muscles.
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