Effect of velocity-based loading on acceleration kinetics and kinematics during sled towing

Abstract

Sled towing (ST) provides an external load in the form of a sled towed via a shoulder or waist harness and cord, behind the athlete. Loading strategies have varied greatly between studies and despite many investigations there is little agreement on the optimum sled loading to develop the acceleration phase. The aim of this study was to investigate the kinetics and kinematics of velocity-based ST during the acceleration phase of sprinting. Twelve academy rugby league players performed a series of 6 m sprints in different conditions; uninhibited, 10%, 15% and 20% velocity decrement 12 (VDec). Sagittal plane kinematics and kinetic measures were examined using one-way repeated measures analysis of variance. Results indicated that ST affected trunk, knee and ankle joint kinematics (p < 0.05). Peak knee flexion increased as sled loads increased (p < 0.05), which may enable athletes to lower their centre of mass and increase their horizontal force application. Net horizontal and propulsive impulse measures were greater in all sled conditions (p < 0.05), which increased significantly as sled loadings were heavier. In conclusion, this study highlights the effects of differential loads to help coaches understand acute kinetics and kinematic changes in order to improve the planning of sprint training.