Effect of Velocity-Based Loading on Acceleration Kinetics and Kinematics During Sled Towing

Sled towing(ST) provides an external load in the form of a sled towedusing 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 onthe optimum sled loading to develop the acceleration phase.The aim of this study was to investigate the kinetics andkinematics of velocity-based ST during the accelerationphase of sprinting. Twelve academy rugby league playersperformed a series of 6-m sprints in different conditions;uninhibited, 10, 15, and 20% velocity decrement (VDec).Sagittal plane kinematics and kinetic measures were examinedusing 1-way repeated-measures analysis of variance.Results indicated that ST affected trunk, knee, and ankleAU5 joint kinematics (p < 0.05). Peak knee flexion increased assled loads increased (p < 0.05), which may enable athletesto lower their center of mass and increase their horizontalforce application. Net horizontal and propulsive impulsemeasures were greater in all sled conditions (p < 0.05),which increased significantly because sled loadings wereheavier. In conclusion, this study highlights the effects ofdifferential loads to help coaches understand acute kineticsand kinematic changes to improve the planning of sprinttraining