Energy expenditures in 12 male and 7 female untrained adult subjects were measured with Max Planck respirometers while walking in the laboratory at speeds of 24.4, 48.8, 73.2 and 97.6 meters/ min. The results were collated with those of other investigators, and the following conclusions were drawn:

1. During level walking, the energy expenditure is a linear function of the square of the speed. The relation is: \(\dot E_w = 29 + 0.0053v^2 \), where \(\dot E_w \) is energy expenditure in cal/min/kg, and v is speed in meters/min. 2. The energy expenditure per unit distance walked is derived from the above equation and is shown to be a hyperbola having a minimal value of 0.78 cal/meter/kg at a speed of 74 meters/min. 3. A given subject adopts a “natural” speed of walking that corresponds to a minimal value of the energy expenditure expressed as cal/ meter/kg.