Control of propulsion and body lift during the first two stances of sprint running: a simulation study

The aim of this study was to relate the contribution of lower limb joint moments and individual muscle forces to the specific biomechanical demands and more specific the body center of mass (COM) vertical and horizontal acceleration during the initial two steps of sprint running. Sprint start performance of seven well-trained sprinters (2 men and 5 women) was recorded using an opto-electronic motion analysis system consisting of 12 MX3 cameras (250 Hz) and two Kistler force plates (1000 Hz). Subject-specific torque driven simulations were conducted in Opensim to quantify the contributions of the individual joints to forward and upward acceleration of the body COM, referred to as body propulsion and rise respectively. The contribution of individual muscles to progression and body rise was calculated using subject specific muscle driven simulations. The ankle joint is the major contributor to propulsion and body rise during the first two stances. This contribution even increased from the first to the second stance. The muscle driven simulations identified the biarticular M. Gastrocnemius to be the main muscle contributing to propulsion from the second stance onwards. The contribution of the hip and knee joint depends highly on the position of the athlete with the knee contributing primarily to body rise during the first stance and with the hip contributing to propulsion and body rise, to lift the athlete from the bended starting position . In conclusion, even a small increase in ankle power generation seems to affect the body center of mass acceleration, whereas increases in hip and knee power generation is less efficient in affecting the body center of mass accelerations during the first stance.