Running is a composite of specific tasks including weight support, forward propulsion, and leg swing. The purpose of this study was to deduce the energetic costs of these tasks by studying the reductions in metabolic rate in response to strategic combinations of assistive devices.

Ten healthy, fit, adults volunteered. I measured metabolic rate via expired gas analysis during standing, running at 3.0 m/s normally, and with combinations of assistive devices. The first assistive device provided weight support (WS) via a pelvic harness, the second assisted forward propulsion using an aiding horizontal force (AHF) at the waist, and the third provided leg swing assist (LSA) via forward pulling forces on the feet. Guided by previous experiments, I tested 12 trials combining 4 levels of body weight (100, 75, 50 and 25%), AHF of 10% of effective body weight, and LSA of 2% of normal body weight.

With WS alone, I found a linear decrease in metabolic rate that was less than directly proportional to body weight. By extrapolating the WS only data to zero weight, I deduced that weight support comprises 65% of the net cost of running. Combining WS with AHF further reduced the metabolic rate during running. The difference between the WS and the (WS + AHF) conditions indicated that forward propulsion comprises ~39% of the net cost of running. Additionally providing LSA caused a consistent absolute decrease in the metabolic rate at each WS level, equal to ~7% of the net cost of normal running.

By extrapolating the data for all three assistive devices (WS + AHF + LSA) to zero body weight, I deduced that these methods eliminated all but 12.9% of the net cost of normal running. This remainder may reflect the metabolic costs of braking, arm swing, balance, increased ventilation and increased cardiac work. However, by another method of calculating, the sum of WS, forward propulsion, and leg swing costs is 111%. This indicating that my methods of easuring the metabolic cost of individual running tasks led to an over-estimation of the total cost of running.