Interrelationships between mechanical power, energy transfers, and walking and running economy.

The interrelationships between aerobic demand, kinematic and kinetic-based estimates of mechanical power output and energy transfer, and total body angular impulse (summation of net joint moments integrated with respect to time over a stride) were quantified for walking at 1.69 m.s-1 and running at 3.35 m.s-1 to assess the ability of these various biomechanical expressions to explain interin-dividual differences in walking and running economy. Fourteen healthy men participated in the walking study and 16 recreational male runners were subjects for the running analysis. Each subject performed treadmill locomotion for determination of aerobic demand and overground locomotion from which biomechanical measures were quantified. It was expected that mechanical power and angular impulse expressions would correlate positively with aerobic demand while energy transfer expressions would correlate negatively. Correlations between aerobic demand and power estimates primarily were positive, but explained no more than 32% of the variability in walking or running VO2 (center of mass model: 0.22 < r < 0.57; segment-based model: -0.02 < r < 0.20; kinetic model: -0.07 < r < 0.22). Total body angular impulse also correlated positively with aerobic demand (0.32 < r < 0.42). Energy transfer expressions from the various analytical models showed no consistent relationship with aerobic demand, either in terms of magnitude or direction (-0.26 < r < 0.48). It was concluded that mechanical power, energy transfer, and angular impulse expressions frequently used in analyses of gait explain only a small proportion of normal interindividual variability in the aerobic demand at a given speed of walking or running.