Abstract
BACKGROUND: The purpose of this study was to determine whether muscle viscoelastic properties, muscle activation and thigh rotational velocity and rotational acceleration are significantly associated with high ball speed during instep soccer kick by prepubescent male athletes. METHODOLOGY: This study included 31 prepubescent male soccer players. Maximal ball speed during the instep kick was measured using a radar gun. Viscoelastic properties such as tone, elasticity, and stiffness of the superficial abdominal and leg muscles were measured at rest using myotonometry. The activation of the rectus abdominis (RA) and rectus femoris (RF), as well as the thigh's three-dimensional rotational velocity and acceleration, were evaluated using surface electromyography and an inertial measurement unit. RESULTS: Significant negative correlations were found between the maximum ball speed and the hamstring medialis (HM) and gastrocnemius medialis (GM) elasticity (r = -0.656 and -0.680; power > 0.95; p < 0.05 for all). Significant positive correlations existed between maximum ball speed and RA-RF activation (r = 0.494 and 0.579), maximum thigh rotational velocity in the sagittal plane (r = 0.619), and maximum thigh rotational acceleration in the sagittal (r = 0.435) and horizontal (r = 0.380) planes (power > 0.95; p < 0.05 for all). The multiple linear regression analysis demonstrated that significant parameters for maximum ball speed were HM (B = -36.84) and GM (B = -26.83) elasticity along with thigh rotational velocity in sagittal plane (B = 0.01) (adjusted R(2) = 0.56, delta R(2) = 0.17). CONCLUSIONS: The elasticity of the GM and HM muscles, the activation levels of the RA and RF muscles, and the rotational velocity-acceleration of the thigh in the sagittal and horizontal planes were significant factors associated with high ball speed during the instep kick. To enhance ball speed during the instep kick, training methods that focus on improving the elasticity of the GM and HM muscles, as well as increasing activation of the core and rectus femoris, should be prioritized for prepubescent male soccer players.