title: Maximum aerobic performance in lines of Mus selected for high wheel-running activity: effects of selection, oxygen availability and the mini-muscle phenotype.
abstract: We compared maximum aerobic capacity during forced exercise (VO2max) in hypoxia (PO2=14% O2), normoxia (21%) and hyperoxia (30%) of lines of house mice selectively bred for high voluntary wheel running (S lines) with their four unselected control (C) lines. We also tested for pleiotropic effects of the ;mighty mini-muscle' allele, a Mendelian recessive that causes a 50% reduction in hind limb muscle but a doubling of mass-specific aerobic enzyme activity, among other pleiotropic effects. VO2max of female mice was measured during forced exercise on a motorized treadmill enclosed in a metabolic chamber that allowed altered PO2. Individual variation in VO2max was highly repeatable within each PO2, and values were also significantly correlated across PO2. Analysis of covariance showed that S mice had higher body-mass-adjusted VO2max than C at all PO2, ranging from +10.7% in hypoxia to +20.8% in hyperoxia. VO2max of S lines increased practically linearly with PO2, whereas that of C lines plateaued from normoxia to hyperoxia, and respiratory exchange ratio (=CO2 production/VO2max) was lower for S lines. These results suggest that the physiological underpinnings of VO2max differ between the S and C lines. Apparently, at least in S lines, peripheral tissues may sustain higher rates of oxidative metabolism if central organs provide more O2. Although the existence of central limitations in S lines cannot be excluded based solely on the present data, we have previously reported that both S and C lines can attain considerably higher VO2max during cold exposure in a He-O2 atmosphere, suggesting that limitations on VO2max depend on interactions between the central and peripheral organs involved. In addition, mini-muscle individuals had higher VO2max than did those with normal muscles, suggesting that the former might have higher hypoxia tolerance. This would imply that the mini-muscle phenotype could be a good model to test how exercise performance and hypoxia tolerance could evolve in a correlated fashion, as previous researchers have suggested.
authors.affiliation: Department of Biology, University of California, Riverside, CA 92521, USA. enrico.rezende@ebd.csic.es
authors.forename: Enrico L
authors.initials: EL
authors.lastname: Rezende
authors.forename: Theodore
authors.initials: T
authors.lastname: Garland
authors.forename: Mark A
authors.initials: MA
authors.lastname: Chappell
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Malisch
authors.forename: Fernando R
authors.initials: FR
authors.lastname: Gomes
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D005075:Biological Evolution; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D051379:Mice / Q000502:physiology*; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012641:Selection, Genetic