Inter-limb step asymmetry in closed and open skill sprint accelerations in soccer players

Purpose. Inter-limb differences may decrease sports performance. There is a need to understand the comparison of asymmetries between open and closed skill tasks. The study investigated inter-limb step asymmetry responses to closed and open skill acceleration sprint running tasks. Methods. 3D motion analysis kinematic data of step characteristics were collected from 20 male soccer players (mean ± SD: 21 ± 1.9 years, 78.7 ± 7.7 kg, 1.78 ± 0.06 m) for bilaterally located lower-limb markers during the initial 20 m of closed and open skill acceleration sprint running trials. Step velocity, step length, step frequency, flight time, contact time, and flight distance were calculated. In the closed skill conditions, players knew the final sprint distance before initiation. In the open skill conditions, players were informed of the final sprint distance (20 or 40 m) immediately after run initiation. Results. Significant asymmetries (0.10-10.3%, p < 0.05) in step characteristics were observed during closed skill acceleration sprint performances. Positive correlations (r: 0.51-0.77, p < 0.05) were evidenced between asymmetry scores in the closed skill and in the open skill 20-m and 40-m conditions. Asymmetry scores were not associated with sprint performance (r: From -0.13 to 0.30, p > 0.05), suggesting that asymmetry may be functional or dysfunctional. Conclusions. Skilled soccer players can regulate step characteristic asymmetries across closed and open skill tasks. Symmetry should not be assumed when assessing open and closed skill acceleration sprint performance in soccer players. Practitioners should be aware of these asymmetries when implementing programmes.