Comparison of vertical ground reaction forces at impact while vertical jumping using soft and pretensed landing mechanics

The authors compared the effects of soft and pretensed landing mechanics on ground reaction forces (GRFs) at impact while performing repetitive manual vertical jumps. They found that the GRFs at impact after a maximal vertical jump were greater for jumps using a pretensed landing than a soft landing in preparation for a maximal repetitive jump. The time of impact and slope of impact loading exhibited during pretensed and soft landings were found to be similar due to a large variability in the landing technique employed by average jumpers. A faster propulsive phase was found for the second jump using a pretensed landing than a soft landing. Greater GRFs were applied to the floor during the propulsive phase of the repetitive jump as a result of the storage of elastic energy in the muscle for the pretensed landing than the soft landing. Pretensed landings during repetitive jumping increased the impact and propulsive GRFs while reducing the propulsion time without affecting the flight time or vertical height. Therefore, pretensed landings may be desirable for faster repetitive maximal jumps but the increased impact forces may increase the potential for fatigue fractures