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The purpose of this study was to examine the effect of changing the midsole density of athletic shoes on impact forces upon landing during a non-rhythmic athletic activity. Previous studies showed that changing the density of the midsole had neither a positive or negative effect on running, which is a repetitive rhythmic athletic activity. This investigation examined the influence of variations in athletic shoe midsole density on vertical ground reaction forces, loading rates, peak joint moments, and examined which specific kinematic variables were affected upon landing after a non-rhythmic vertical jump. Subjects included 20 female, NCAA volleyball athletes (mean=21.1; sd=2.84 years). Each subject was tested in three different athletic shoe conditions: control midsole, soft midsole, and hard midsole. For each of the athletic shoe midsole conditions, the subjects performed 10 volleyball approaches and spike jumps; landing onto two force platforms to measure impact forces. Kinematic data was collected simultaneously with the kinetic data using a six camera Motion Analysis system. Data was collected for each subject for a total of 30 trials (10 trials X 3 midsole conditions). A one-way repeated measures analysis of variance was used to compare the three different shoe conditions (significance; p = .05). Results indicated that variations in midsole density do not significantly affect impact forces or loading rates upon landing. Kinematic variables failed to sufficiently explain this result. It is possible that athletes may use neuromuscular adaptations to account for changes in midsole density during impact. More research is needed to determine if changes in muscle activity are used as a possible strategy during landing to affect impact forces. Further research is needed on the effects of athletic shoe midsole density during landings from non-rhythmic athletic activities. |
