The Influence of Trunk Inclination on the Countermovement Jump Take-Off Velocity in Older Women

INTRODUCTION: The physiological age-related functional ability decrements in older adults are more evident during high velocity coordinated movements (1) such as vertical jumps. The Countermovement Jump (CMJ) test is one of the most commonly used protocols to evaluate maximal vertical jump height and overall lower limbs power in older adults. It has been suggested that due to forward trunk inclination in the CMJ takeoff , knee extension is delayed to avoid forward rotation of the body and subsequent loss of balance throughout the completion of the takeoff phase (2). Therefore, forward trunk inclination at the CMJ takeoff might influence subsequent takeoff velocity, thus having an impact on the estimation of maximal jump height and lower limbs power. This study aimed at investigating the influence of trunk inclination on the CMJ takeoff velocity in older women. METHODS: Sixteen old women (age: 73±6.6 yrs; body mass: 57.1±7.2 kg; height 160±0.0 cm; BMI 23.0±3.2 kg/m2) were assessed during CMJ testing session. During the execution, takeoff velocity and forward trunk inclination were recorded by a wearable inertial measurement unit (Sensorize, Rome, Italy) positioned on the trunk at L5 level (3). A polynomial least square fit with the highest adjusted R² was selected for the assessment of nonlinear relationship between trunk inclination performance and Take Off Velocity at the jump. Root mean square error (RMSE) was also calculated. Significance level was set at P-value of 0.05. RESULTS: A very strong significant (P=0.0001) 2nd order curvilinear relationship (R²=0.96; RMSE=0.03) between trunk inclination (10.1±7.9°) and takeoff velocity (1.1±0.2 m/s) was found. To clarify the relationship between takeoff velocity and forward trunk inclination , the following equation was developed: takeoff velocity =-0.0032(trunk inclination2) + 0.0839(trunk inclination) + 0.7115 CONCLUSION: The correct kinematic execution of jumps has been mainly defined by the relative angular joint motion of the hip, knee and ankle, and muscle moments patterns (2). Accordingly, in older women, the forward trunk inclination influences the correct execution of the CMJ and takeoff velocity, and consequently the estimation of maximal jump height. For these reasons, to maximize takeoff velocity, it was identified that forward trunk inclination should range between 8° and 18°. References 1) Cortis et al., J. Strength Cond. Res. 2011 2) Vanrenterghem et al., J. Strength Cond. Res. 2008 3) Strath et al., Med Sci Sports Exerc. 2012