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First published online April 26, 2005
Journal of Experimental Biology 208, 1635-1644 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01548

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Exercise-induced maximal metabolic rate scales with muscle aerobic capacity

Ewald R. Weibel and Hans Hoppeler^*

Institute of Anatomy, University of Bern, Baltzerstrasse 2 3000 Bern 9, Switzerland

View larger version (21K): [in a new window]   Fig. 1. Oxygen consumption in mammals carrying different loads. From Taylor et al. (1980).

View larger version (61K): [in a new window]   Fig. 2. (A) The distribution of oxygen consumption at rest and at O2max. (B) Model of pathway for oxygen from the lung to muscle.

View larger version (24K): [in a new window]   Fig. 3. O2max plotted against body mass Mb for the 34 mammalian species separated into athletic (open triangles) and non-athletic (filled triangles) species. The heavy line represents the allometric regression for all animals with a slope of 0.872±0.029 (95% confidence limits 0.813, 0.932. F=890, d.f.=1,32, P<0.00001). The mass exponent of the allometric regression of athletic species (thin solid line) is 0.942 (95% confidence limits 0.889, 0.995, F=1609, d.f.=1,?; that of non-athletic species (broken line) is 0.849 (95% CL 0.799, 0.900; F=1231, d.f.=1,21), P<0.00001 for both. The slope of athletic species is significantly larger than that for the non-athletic species (F=38.3, P<0.00001). Data from Weibel et al. (2004). For reference, the curve for BMR or O2bas (blue line) is plotted after Kleiber (1947).

View larger version (21K): [in a new window]   Fig. 4. O2max (triangles) and morphometric estimate of total volume of muscle mitochondria V(mt) (circles) in 11 species based on whole body sampling. The slope is 0.962 for O2max (95% CL=0.829-1.096; F=265, d.f.=1,9, P<0.00001), and 0.956 for V(mt) (95% CL=0.846-1.066; F=388, d.f.=1,9, P<0.00001); the two regressions are identical (r2=0.168, d.f.=1, P=0.683). Numbers at the bottom identify species: 1, woodmouse; 2, mole rat; 3, white rat; 4, guinea pig; 5, agouti; 6, fox; 7, goat; 8, dog; 9, pronghorn; 10, horse; 11, steer. From Weibel et al. (2004).

View larger version (155K): [in a new window]   Fig. 5. Light micrograph of capillary network in muscle (A) with arrow pointing to an erythrocyte in stained plasma. Electron micrograph (B) shows path for oxygen from capillary erythrocyte to mitochondria in muscle cell. From Weibel and Hoppeler (2004).

View larger version (21K): [in a new window]   Fig. 6. O2max (triangles) and morphometric estimate of total volume of muscle capillaries V(c) (squares) in 11 species based on whole body sampling. The slope is 0.962 for O2max (95% CL=0.829-1.096; F=265, d.f.=1,9, P<0.00001), and 0.984 for V(c) (95% CL= 0.909-1.056; F=916, d.f.=1,9, P<0.00001); the two regressions are identical. Numbers at the bottom identify species, as in Fig. 4. From Weibel et al. (2004).

View larger version (18K): [in a new window]   Fig. 7. O2max plotted as function of total muscle mitochondrial volume V(mt) (squares) and capillary erythrocyte volume (V(ec) (squares) in 11 species. The exponent for the regression to V(mt) is 1.009; 95% CL=0.949,1.068, F=1463, d.f.=1,9, P<0.00001; that for V(ec) is 0.975; 95% CL=0.893,1.074, F=604, d.f.=1,9, P<0.00001. Numbers at right identify species, as in Fig. 4.

View larger version (140K): [in a new window]   Fig. 8. Electron micrograph of muscle mitochondrion shows the packing of inner mitochondrial membranes where oxidative phosphorylation takes place.

View larger version (17K): [in a new window]   Fig. 9. Allometric plot of resting (circles) and maximal heart frequencies (triangles) in mammalian species. From Weibel and Hoppeler (2004).