Kinetic mechanisms to alter walking speed.

A mechanism to modulate speed during human walking has not yet been proposed in the literature, even though changing walking speed is likely a necessary attribute of everyday ambulation. To understand how joint kinetics modulate walking speed 12 normal adults walked Fast (1.4m/s), Slow (1.0m/s), Accel (1.0-1.4m/s) and Decel (1.4-1.0m/s) trials while full body 3D kinematics and kinetics were collected. Reduced sagittal ankle plantarflexor moments were observed in Accel trials during early single limb stance (p<0.001) and increased sagittal plantarflexor moments were seen in Decel trials during early single limb stance (p<0.001) compared to steady speed walking. Modulating the sagittal ankle moment altered the center of pressure location and either attenuated (Accel) or accentuated (Decel) the early stance braking impulse to accelerate or decelerate the center of mass. The onset of walking speed changes occurred at approximately 15% of the gait cycle and did not support the concept of "controlled falling". Sagittal ankle push-off power appears a consequence of increased walking speed, but not the causative factor to increase walking speed.