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Muscle fiber type distribution and nonlinear VO2-power output relationship in cycling

PEDERSEN, PREBEN K.; BAK SØRENSEN, JES; JENSEN, KURT; JOHANSEN, LARS; LEVIN, KLAUS

Medicine & Science in Sports & Exercise: April 2002 - Volume 34 - Issue 4 - p 655-661
BASIC SCIENCES: Original Investigations

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.

Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, DENMARK; Team Danmark’s Testcenter, University of Southern Denmark, Odense, DENMARK; and Odense University Hospital, DENMARK

Submitted for publication January 2001.

Accepted for publication September 2001.

© 2002 American College of Sports Medicine