Fig. 3. Net metabolic rate for running with added mass and weight (solid squares), with added mass at normal body weight (half-solid squares), and with normal weight and mass (open square). Net metabolic rate increased slightly more than in direct proportion to added mass and weight. Net metabolic rate increased only slightly when we added mass alone. Error bars are s.e.m. (W kg^–1). Metabolic rates at all levels of added mass and weight were significantly different from each other and from normal (P<0.004). For the added mass alone trials, the only significant difference was between 110% added mass and normal (P=0.005). Statistics were calculated on absolute values.