In ongoing decompression sickness studies at the USAF School of Aerospace Medicine, an exercise regimen is used in which extra-vehicular activity (EVA) is simulated. A ground based study was undertaken in order to assess, for the protocol, the currently accepted value of energy expenditure (150-200 kcal/hr) which was based on very limited data. Six male and five female subjects performed an hour of exercise comprised of 3 tasks analogous to actual tasks perfomed by astronauts during EVA.Metabolic data were collected using an open-loop oxygen consumption meter during rest and exercise. Values for the males were 119.4-193-3 kcal/hr (χ̄=147.95 kcal/hr, sd=24.51), while values for the females were significantly lower, 91.5-114.5 kcal/hr (χ̄=104.6 kcal/hr, sd=8.9). Gender differences in energy expenditure during performance disappeared when the values were expressed in terms of added energy cost, body weight or lean-body mass.