The relationship between performance and trunk movement during change of direction

The purpose of this study was to obtain the trunk kinematics data during a change-of-direction task and to determine the relationship between trunk kinematics and the change-ofdirection performance. The design of this investigation was a descriptive laboratory study. Twelve healthy male collegiate soccer players (age: 21.3 ± 1.0 yrs, body mass: 67.7 ± 6.7 kg, and height: 1.75 ± 0.05 m) participated in this study. Participants performed a shuttle run cutting task with a 180 degree pivot as quickly as possible. The shuttle run cutting time, ground contact time during a change-of-direction, and trunk inclination angle were measured. The shuttle run cutting time tends to correlate positively with ground contact time. During the change-ofdirection task, the trunk forward inclination angle gradually increased during the first 50% of the stance phase and decreased subsequently whereas the trunk flexed, maintaining a left inclination during the first 40% of the stance phase and changing exponentially in the opposite direction. Forward angular displacement of the trunk between foot-contact and maximum trunk inclination correlated positively with the shuttle run cutting time (r = 0.61, p < 0.05) and ground contact time (r = 0.65, p < 0.05). These findings suggest that the change-of-direction performance could be related to the small angular displacement of the trunk during a change of direction. Moreover, it was considered that there might be optimal inclination angles related to change-of-direction performance. Therefore, coaches in field sports should check body posture and trunk movements during changes of direction.