Abstract
BackgroundThis investigation characterized the time-history pattern of the free moment (FM) during walking and, additionally, assessed whether walking with either an internally or externally rotated foot position altered the FM's time-history.MethodsForce plate and foot kinematic data were acquired simultaneously for 11 healthy subjects (6 males, 5 females) while walking at their self-selected comfortable speed in 3 foot rotation conditions (normal, internal and external). The FM was calculated and normalized by the product of each participant's body weight and height prior to extraction of peak FM, occurrence of peak FM in stance and net relative impulse. Differences in these values across foot rotation conditions were assessed using separate one-way, repeated measures analysis of variance and subsequent pair-wise comparisons.ResultsThe average FM pattern during normal walking exhibits a biphasic shape: resisting inward rotation during approximately the first half of stance and outward rotation during the latter part of stance. While no differences in peak FM or net relative impulse were observed between the internal foot rotation condition and normal walking, the external foot rotation condition resulted in significantly greater peak FM and relative net impulse in comparison to normal walking.ConclusionThe differences in selected FM variables between normal walking and the external foot rotation condition are attributable to individual subject response to walking with an externally rotated foot. In this condition, some subjects displayed a FM pattern that was similar to that recorded during normal walking, while others displayed markedly larger FM patterns that are comparable in magnitude to those reported for running. The larger FM values in these latter subjects are speculated to be a result of excessive transverse plane body movements. Whilst further investigation is warranted regarding the FM time-history characteristics during walking, our results indicate that the FM may provide useful information in assessment of gait.
Highlights
This investigation characterized the time-history pattern of the free moment (FM) during walking and, assessed whether walking with either an internally or externally rotated foot position altered the FM's time-history
Results of the analysis of variance (ANOVA) performed on selected FM variables reveal that peak free moment (PFM) and IMP were significantly affected by foot rotation condition
No differences were found between the NORM and INT conditions in (p > 0.05 for both PFM and IMP), nor was a significant main effect detected in OPFM across the three foot rotation conditions (INT 70 ± 9%, NORM 69 ± 3%, EXT 77 ± 9%, p > 0.05)
Summary
This investigation characterized the time-history pattern of the free moment (FM) during walking and, assessed whether walking with either an internally or externally rotated foot position altered the FM's time-history. Attention has been drawn to the clinical usefulness of the FM by Milner et al [9], who were able to discriminate retrospectively, based on FM indices, between a group of healthy runners and a group of female runners with a history of tibial stress fractures. Based on the results of Milner et al [9], it can be speculated that the FM might serve as an indicator for the amount of torsional loading experienced during ambulation While this supposition has yet to be validated, there are two related points that make it appealing: one, cortical bone is not able to sustain large amounts of torsional loading [10,11], and, two, considerable torsional loading is experienced during ambulation, during the push off phase of walking [12]. The question that naturally arises is whether an elevated FM during walking a potential cause of tibial stress fractures?
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