Effect of added mass on human unipedal hopping.

Although hopping is considered a children's activity, it can be used to provide insight into the neuromuscular and biomechanical performance of adults. This study investigated whether mass added during unipedal hopping altered the vertical stiffness, hopping period, and angular kinematics of the lower extremity of adults. Measures of two-dimensional kinematics and vertical force were made from 10 healthy men during hopping at a preferred period under three conditions: Body Mass, Body Mass+10%, and Body Mass+20%. Adding mass significantly increased hopping period and hip flexion without significantly affecting vertical stiffness, ankle dorsiflexion, or knee flexion. Overall, the findings agreed with predictions based on a simple-mass spring model. The results indicate unique kinetic and kinematic responses to increased mass during hopping may have potential application in neuromuscular assessment and training for the lower extremities.