Fig. 2. Net metabolic rate for running as a percentage of normal body weight from the rolling trolley method (half-solid squares), the fixed pulley method (open circles), the Farley and McMahon (Farley and McMahon, 1992) data (solid line), and normal running (open square). Net metabolic rate decreased substantially when we reduced body weight. The dashed line indicates an extrapolation to zero weight. Lines are linear least squares regressions. Rolling trolley: (%NNMR) = 0.73 x %BW + 26.18; R²=0.88; and fixed pulley: %NNMR = 0.81 x %BW + 19.36; R²=0.84; where %NNMR is the percentage of normal net metabolic rate and %BW is the percentage of normal body weight. Error bars are s.e.m. Within the rolling trolley and fixed pulley methods, metabolic rates were all significantly different from each other (P<0.0001). However, at a given percentage of body weight, there was no significant difference between rolling and fixed trolley methods (P>0.08). Statistics were calculated on absolute values.