Effect of velocity and SF/SL ratio on external work and gait movement waveforms.

Ten normal adult subjects were tested under a wide range of combinations of stride length and stride frequency. Both longitudinal and vertical accelerations of the body increased with velocity, while stride frequency to stride length ratio (SF/SL) had little effect. The peak-to-peak amplitude of the forward velocity (V) decreased with SF/SL, but at constant SF/SL remained essentially unchanged throughout the speed range from 0.4 to 1.4 m/s. The external work of locomotion related as a paraboloid of revolution to V and SF/SL with minimum work being 0.32 J/kg-m at V = 0.52 m/s and SF/SL = 0.76. The efficiency of transfer between potential and kinetic energies related as a paraboloid of revolution to V and SF/SL with maximum efficiency being 0.58 (58 percent at V = 0.98 m/s and SF/SL = 0.43). Latent work, herein defined as work divided by efficiency, related as a paraboloid of revolution to V and SF/SL being minimum at V = 0.7 m/s and SF/SL = 0.65. At any given velocity, latent work tended to be least in the SF/SL range of 0.6 to 0.7. The latter finding may suggest why people tend to walk at a nearly constant SF/SL ratio over a broad range of velocities.