A previous hamstring injury affects kicking mechanics in soccer players

BACKGROUND: Although the kicking skill is influenced by limb dominance and sex, how a previous hamstring injury affects kicking has not been studied in detail. Thus, the objective of this study was to evaluate the effect of sex and limb dominance on kicking in limbs with and without a previous hamstring injury. METHODS: Forty-five professional players (males: N.= 19, previously injured players 4, age 21.16 +/- 2.00 years; females: N.= 19, previously injured players =10, age= 22.15 +/- 4.50 years) performed 5 kicks each with their preferred and non-preferred limb at a target 7m away, which were recorded with a three-dimensional motion capture system. Kinematic and kinetic variables were extracted for the backswing, leg cocking, leg acceleration and follow through phases. RESULTS: A shorter backswing (20.20 +/- 3.49% vs. 25.64 +/- 4.57%), and differences in knee flexion angle (58 +/- 10 degrees vs. 72 +/- 14 degrees) and hip flexion velocity (8 +/- 0 rad/s vs. 10 +/- 2 rad/s) were observed in previously injured. non-preferred limb kicks for females. A lower peak hip linear velocity (3.50 +/- 0.84 m/s vs. 4.10 +/- 0.45 m/s) was observed in previously injured, preferred limb kicks of females. These differences occurred in the backswing and leg-cocking phases where the hamstring muscles were the most active. A variation in the functioning of the hamstring muscles and that of the gluteus maximus and iliopsoas in the case of a previous injury could account for the differences observed in the kicking pattern. CONCLUSIONS: Therefore, the effects of a previous hamstring injury must be considered while designing rehabilitation programs to re-educate kicking movement.