Exercise during growth may significantly contribute to the enhancement of peak bone mass reached at young adulthood. Unfortunately, longitudinal studies have produced very inconsistent results. Running, as an example for a commonly used exercise stimulus, can have positive as well as negligible or deterimental effects on growing bnoe. Recent cross-sectional, as well as longitudinal studies, have suggested that high-impact exercise is osteogenically more effective than lower-impact aerobic exercise (Courteix et al., 1998). It is eifficult, however, to extrapolate from these studies as the exercise related mechanical milieu was not quantified. From a mechanical point of view, high-impact exercise is ill-defined. The efficacy of high-impact exercise has often been attributed to the presumed increase in bone strain magnitude and strain rate, as well as to altered strain distributions. This, ohwever, has not been verified. Here, we asked the following question: Compared to high-speed treadmill running, does high-impact jumping significantly elevate mechanical parameters previously proposed to drive adaptation, including strain magnitude and distribution (Rubin and Lanyon, 1987), strain rate (Mosley and Lanyon, 1998), and strain gradients (Judex et al., 1997)?
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