Peak oxygen uptake during running and arm cranking normalized to total and regional skeletal muscle mass measured by magnetic resonance imaging

The purposes of our study were to determine the peak oxygen uptake ( V̇O_2peak) per total or regional skeletal muscle (SM) mass using magnetic resonance imaging (MRI) and to investigate the relationships between SM mass and V̇O_2peak during running and arm cranking. Eight male college swimmers aged 18–22 years [mean (SD) age 20.0 (1.3) years] were recruited to participate in this study. V̇O₂ during running and arm cranking were measured using an automated breath-by-breath mass spectrometry system. Contiguous MRI slices were obtained from the first vertebra cervicale to the malleolus lateralis (1.0-cm slice thickness, 0-cm inter-slice gap), resulting in a total of approximately 156 images for each subject. The absolute V̇O_2peak and the V̇O_2peak per body mass during running and arm cranking were 3.6 (0.6) l.min^-1, 54.4 (5.9) ml.min^-1.kg^-1 and 2.5 (0.5) l.min^-1, 36.9 (5.3) ml.min^-1.kg^-1, respectively. The absolute V̇O_2peak was higher ( P <0.05) during running than during arm cranking, but not the V̇O_2peak per regional area SM mass. The lower body SM mass was correlated to the V̇O_2peak during running ( r =0.95, P <0.001). All measurements and calculated values were expressed as the mean (SD) for the eight subjects. To eliminate the influence of body mass and fat-free mass (FFM), a regression analysis was performed on the mass-residuals of the V̇O_2peak during running and the lower body SM mass. The residuals of lower body SM mass were correlated to the residuals of V̇O_2peak during running, with respect to body mass ( r =0.90, P <0.001) and FFM ( r =0.82, P <0.05). These results suggest that the MRI-measured lower body SM mass was closely associated to the absolute V̇O_2peak during running, independently of body mass or FFM, and that the V̇O_2peak per regional SM mass corresponded, regardless of the type of exercise (upper or lower body).