Transition from upright to greater forward lean posture predicts faster acceleration during the run-to-sprint transition

Background: Forward body lean and greater horizontal ground reaction force have been associated with being able to accelerate during running. However, kinematic features which may predict acceleration during the run-to-sprint transition have not been determined. The purpose of this study was to identify kinematic features which are predictive of greater acceleration during the run-to-sprint transition. Methods: Forty-seven healthy adults completed straight line running along a 30 m track by running in at ~4 m.s-1. A minimum of 20 trials were completed, with 25% triggering a light to signal the participant to accelerate as fast as possible. Step characteristics (velocity, length, duration, cadence) and kinematics (neck, trunk, hip, knee and ankle angles and excursions) were determined using a radar gun and inertial measurement units, respectively. ANOVA was used to determine the step-to-step differences and a multiple linear regression was used to determine the relationship between kinematics and acceleration. Results: There was an initial increase in trunk flexion angle during early acceleration (p < 0.001) with knee joint excursion significantly lower (p < 0.001) during loading and propulsion compared to the run-in steps. Greater acceleration was predicted using a stepwise linear regression by five variables including less neck flexion excursion and trunk flexion angle during swing of the 1st step, greater trunk flexion angle and extension excursion of the neck during propulsion of the 2nd step and greater hip flexion angle at foot strike of the 3rd step (r2 = 0.804, p < 0.001). Significance: Faster acceleration was observed when participants transitioned from an upright posture to greater forward trunk lean in the early phase of acceleration. This may be encouraged as a training strategy to improve acceleration in fields sports with the observation that the greatest increase in running velocity occurs over the first 5 m during the run-to-sprint transition