Space suit bioenergetics: cost of transport during walking and running

Space suits significantly affect the metabolic cost of human movement during extravehicular activity, a key component of future human missions to the Moon and Mars. We hypothesized that space suit legs act as springs during running, thereby lowering cost of transport relative to space-suited walking.

We transformed data from suited and unsuited energetics studies into a common format and developed a regression equation for specific resistance, S, (energy per weight per distance) based on the Froude number (a nondimensional parameter associated with gait transitions), surface slope, gravity, and space suit pressure. Acceptance criteria for regression factors included significance and a reduction in residual variance. We divided suited data into two groups, running and walking or slow running, and performed a group means hypothesis test and categorical regression of metabolic rate per unit weight and S, measures of time- and distance-associated metabolic efficiency, respectively.

The regression on S achieved an adjusted R2 of 0.83; all factors were significant (P < 0.0005). No additional evaluated factors met the acceptance criteria. The categorical regression, but not the hypothesis test, suggested that the running group had reduced efficiency per unit time; both tests suggested that the running group had increased efficiency per unit distance.

The regression model largely explained variations in S across studies. Several findings suggest that gas-pressure space suit legs function as springs during running, including the finding of higher efficiency per unit distance during running, despite the presumed increased work against space suit joint torques at higher velocities.