ISB XXth Congress - ASB 29th Annual Meeting, July 31- August 5, 2005, Cleveland, Ohio. Cleveland, OH: International Society of Biomechanics, 2005 Jul; :355
INTRODUCTION: Inverted pendulum models, operationalized in ballistic walking studies and passive dynamic robots, have been used to describe normal gait in the absence of active mechanisms, leading some clinicians to minimize the importance of joint powers. We hypothesized that a telescoping action, associated with joint powers, would improve the fidelity of a simple inverted pendulum model applied to normal gait, as measured by its ability to predict horizontal and vertical ground reaction forces (Fh, Fv, respectively). Unlike previous studies, we made direct comparisons between model predictions and actual gait data for a sample of normal subjects. RESULTS AND DISCUSSION: Pendulum compression averaged 1.7 cm over the first 20% of single support, length changes were variable at mid single support, and extension occurred over the last 20% of single support. Ground reaction forces were predicted best when this telescoping action was included. RMS errors for Fh increased from 2.1%BW to 8.0%BW when telescoping was removed, as the predicted force diverged from actual values in early and late single support. RMS errors for Fv increased from 6.8%BW to 22%BW, and the double peak pattern was lost, when telescoping was removed. Peaks in Fh and Fv were significantly different for all comparisons (actual vs. telescoping, actual vs. no telescoping, telescoping vs. no telescoping), but this was not true for a local minimum in Fv near 50% single support. In every case, deviations from actual data were worse when telescoping was removed, and these deviations were greatest during lower extremity power bursts calculated for these subjects. We conclude that telescoping contributes to Fh and Fv during single support, and reflects changes in hip, knee, and ankle angles modulated by joint powers. We expect these findings to be amplified in a companion study of pathological gait, now underway. We also plan to explore correlations between radial powers (F - r) and joint power bursts.
ISB XXth Congress - ASB 29th Annual Meeting, July 31- August 5, 2005, Cleveland, Ohio