Kinetics and kinematics of initial sprint acceleration performance in Division I collegiate American football players.

This study collected the first direct measurements of the kinetic and kinematic variables associated with initial acceleration performance in American football players. 123 male NCAA Division I American football players performed one-to-two maximal sprints of 20-30-meters. Kinetics were derived from a linear motorised encoder and individual linear sprint force-velocity-power (FVP) profiles were calculated utilising a validated field method. Kinematics were derived from video images recorded in slow-motion. The first three steps, including the initial push-off, were used for analysis at the instants of toe-off and touchdown. Large to nearly perfect, significant relationships were obtained between maximal power and 10-meter time. The spatiotemporal variables with the strongest relationships to maximal power were contact time, takeoff and step velocity, and normalised flight length. At toe-off, the swing leg hip angle, stance leg thigh angle, and CM-toe distance had large relationships with maximal power. At touchdown, the shank angles of both the stance and swing leg and the stance leg knee angle had large relationships. Maximal power associated with force output in the horizontal direction may considered a key performance indicator for initial acceleration in American football and certain technical underpinnings are associated with higher levels of maximal power during initial sprint acceleration.