PEDERSEN, P. K., J. B. SØRENSEN, K. JENSEN, L. JOHANSEN, and K. LEVIN. Muscle fiber type distribution and nonlinear V̇O2-power output relationship in cycling. Med. Sci. Sports Exerc., Vol. 34, No. 4, pp. 655–661, 2002.
Purpose: We examined whether reported deviations from linearity of the oxygen uptake (V̇O2)-to-power output (W) relationship during intense cycling exercise correlated with the percentage Type II fibers in the exercising muscle.
Methods: Twelve trained young men with known fiber type distribution in the vastus lateralis muscle performed step-increment exercise (40 W·3 min−1) to exhaustion.
Results: V̇O2 increased linearly with W up to about 50% V̇O2max with a regression equation of V̇O2 (mL·min−1) = 661 + 9.73 W and a correlation coefficient (r) of 1.000. Subsequent V̇O2 values were all greater than corresponding linear estimates (P < 0.001 or 0.0001). Peak exercise excess V̇O2 (measured minus estimated V̇O2 assuming linearity) averaged (SD) 434 (192) mL O2·min−1 or 10.3 (4.7) % V̇O2max. A comprehensive curvilinearity index defined as the sum of measured minus estimated V̇O2 at the four highest completed exercise trials averaged 973 (460) mL O2·min−1 or 21.5 (9.4) % V̇O2max. Correlations between percentage Type II fibers and either of the two expressions of curvilinearity were nonsignificant. Delta [H+] (arterialized capillary blood) from basal level to peak exercise correlated with the submaximal curvilinearity index (r = 0.59–0.64;P < 0.05) but not with peak excess V̇O2. There was a trend toward a correlation between delta La and curvilinearity index in % V̇O2max (r = 0.52;P < 0.10) but not with any of the other curvilinearity expressions. The relative ventilatory activity expressed as V̇E-to-V̇O2 ratio tended to correlate with peak excess V̇O2 (P < 0.10) but not with curvilinearity index. Signals from motion sensors indicate that coactivation of upper-body musculature coincided with deviation from linearity in the V̇O2-W relationship.
Conclusion: V̇O2 during step-increment cycling increases linearly with power output up to about 50% V̇O2max and then curvilinearly. The degree of curvilinearity is not related to muscle fiber type distribution in the vastus lateralis, and only marginally and insignificantly related (P < 0.10) to the relative degree of hyperventilation or to lactate response. Acidosis, on the other hand, correlated significantly with curvilinearity index. The inclusion of isometrically working, upper-body muscular groups during high-intensity cycling may also contribute to the overshoot in oxygen cost.