Abstract

Exercises that produce high forces and velocities are necessary to activate large, fast-twitch motor units.  If these motor units are not activated during training, then do not receive a training effect. The purpose of this study was to examine the difference in force and velocity measures while performing partial ballistic step-ups and ballistic quarter squats at loads ranging from less than body mass to loads in excess of a 1RM. Participants reported to the lab on four separate testing sessions, each separated by 48 hours. The four sessions consisted of two full ROM one-repetition maximum (1RM) sessions and two ballistic partial (squat and step-up) testing sessions. During the first session, subjects completed a one-repetition maximum in the back squat, followed by the second session 1 RM step-up exercise. A successful repetition for both the squat and step-up was completed when the subject lifted the load from a position where their thigh was parallel to the ground. After 1RM testing, participants attended two testing sessions: one for the partial squat and the second for the partial step-up. For both of these conditions, subjects began in a partial squat position (knees at 125-135 degrees) and jumped maximally.  During these sessions peak force as well as mean barbell velocity and peak barbell velocity were measured using a force plate and linear position transducer, respectively.