Effect of jumping on growing bones : forces during different landings

Graduation date: 2006In order to develop a stimulating yet effective school-based program which elicits\ud a positive bone growth response, we need to understand the forces acting on the bones of\ud children during various high-impact activities. One activity found to promote bone\ud growth is drop landings from a height. We determined whether there are other jumping\ud activities that exhibit similar loading properties to those of a drop landing and identified\ud the effects of number of feet used, continuity, and direction on loading.\ud Twenty-one healthy children (11 boys, 10 girls; age 7-9 years) were recruited from\ud the local population. After warming up, each child performed five trials of 13 types of\ud jumps as motion capture and ground reaction force data were collected. One type of\ud jump was a drop landing from a 61 cm-high platform. The other 12 types were performed\ud from the ground and comprised all possible combinations of three factors: direction\ud (vertical as high as possible, forward a distance of 80% body height, sideways a distance\ud of 55% body height), feet used (1-footed hops, 2-footed jumps), and continuity (discrete, \ud continuous). The average peak force and peak loading rate at the hip of the dominant\ud limb over five trials were computed and normalized to body weight for analysis. Three-way\ud ANOVA identified loading differences across direction, feet used, and continuity\ud among the 12 jump types. Paired t-tests with a Bonferroni correction compared the\ud loading for each activity to that of the drop landings.\ud In general, peak forces and loading rates during landing were greater for hops than\ud for jumps, greater for discrete than for continuous hops/jumps, and greater for forward\ud than for vertical hops/jumps. However, peak forces did not differ between sideways hops\ud and jumps, nor did peak loading rates differ between vertical hops and jumps. Peak\ud forces during the drop landings exceeded those during all other jumping activities except\ud the discrete forward hop, which had peak forces similar to the drop landing. Although\ud discrete forward hops had greater peak loading rates than the other 11 activities from the\ud ground, the rates were less than those during the drop landings. Likely, the need to arrest\ud the body's large forward momentum using a single limb upon landing of the discrete\ud forward hop elevated loading over the other 11 conditions and made it comparable to that\ud of the drop landing.\ud Knowing what factors influence impact forces and loading rates on the hip,\ud specifically that discrete forward hops have high forces similar to those for drop landings,\ud will aid in developing a stimulating and effective jumping program for improved bone\ud development in children