Jumping for distance: control of the external force in squat jumps.

PURPOSE

It was investigated whether control in jumps for distance is related to control in jumps for height.

METHODS

Five male subjects performed maximum squat jumps in the following conditions: VJ (vertical jump), LJ (long jump), and two conditions with inclination angles of the body relative to the horizontal of 75 and 65 degrees, respectively. An inverse dynamics analysis was performed using measured kinematics and ground reaction forces. In addition, jumps were simulated with a forward dynamic model of the musculoskeletal system, comprising four segments and six muscles. First, VJ was simulated by finding the optimal stimulation pattern, i.e., the pattern resulting in a maximum height of the mass center of the body (MCB). Subsequently, LJ was simulated using a "rotation-extension" strategy, i.e., by applying the optimal stimulation pattern for VJ to the system after imposing an initial angular velocity.

RESULTS

In the experiments, no significant differences were found among jumps with different inclination angles in the magnitude of the peak ground reaction force. The same was true for the magnitude of the velocity of MCB and the distance of MCB from the center of pressure at the instance of take-off. As the inclination angle became smaller, i.e., jumps were directed more forward, the net knee joint moment increased whereas net hip and ankle moments decreased. Also, the peak angular velocity in the hip joint was higher and the joint was more extended at take-off. The opposite was true for the knee joint. In the simulation study, using the "rotation-extension" strategy for simulating VJ, these adaptations in kinematics and net joint moments were reproduced satisfactorily.

CONCLUSION

By virtue of the stabilizing effect of intrinsic muscle properties, a jump for distance may be achieved using control of a vertical jump according to a "rotation-extension" strategy.