During soccer matches, players frequently adjust kicking effort to modulate ball velocity and meet specific tactical demands. Submaximal kicks are typically used for short passes, while maximal kicks are employed for long passes or goal attempts. In maximal kicks, the trunk plays a crucial role in generating a downward energy flow toward the pelvis and the kicking limb, which may avoid excessive effort and overload at the lower limb. However, how these contributions vary across different kicking effort levels remains unclear.

This study investigated the kinematic and kinetic adjustments at the trunk, hip, and knee joints of the kicking limb during instep kicks performed at three effort levels.

Forty-four amateur soccer players (age: 23.9 ± 4.8 years) performed kicks at maximal effort, 70-80% of maximal, and 50-60% of maximal. Three-dimensional motion capture was performed at 300 Hz, and ground reaction forces were recorded at 1200 Hz. Kinematic and kinetic data were processed using Visual 3D software. Statistical parametric mapping with repeated measures ANOVA was used to compare time series between effort levels.

The trunk exhibited distinct adjustments in the sagittal plane depending on the kicking effort. During maximal kicks, in the backswing and leg cocking phases, trunk flexion moments generated a downward energy flow toward the pelvis, accelerating its retroversion and contributing to the forward motion of the kicking limb toward the ball. Subsequently, part of this energy was redistributed to the thigh and shank during the acceleration phase, favoring increased final velocity. In contrast, during submaximal kicks, trunk extensor moments were predominant and generated an upward energy flow from the pelvis to the trunk, decelerating pelvic retroversion. In the transverse plane, in both maximal and submaximal kicks, trunk rotation moments generated a downward energy flow toward the pelvis, inducing pelvic rotation toward the support limb and assisting the forward displacement of the kicking limb. Additionally, hip and knee moments in the kicking limb increased with effort, optimizing energy transfer to the shank.

Trunk-generated moments and energy flows act as additional resources for advancing the kicking limb, with axial trunk moments being recruited at all effort levels and sagittal trunk moments being used exclusively during maximal kicks. These findings highlight the importance of trunk muscles in coordinating kicking performance.

Training programs should include exercises to strengthen trunk flexor and rotator muscles, especially for maximal kicks. Incorporating strength and power training for the trunk and lower limbs at different intensities may improve intermuscular coordination and kicking efficiency. Educating players about proximal-to-distal control of movement may enhance performance across different kicking efforts and avoid joint and muscle overloads.