Home Current Issue Previous Issues Published Ahead-of-Print Collections For Authors Journal Info
Skip Navigation LinksHome > November 2002 - Volume 34 - Issue 11 > Fiber recruitment affects oxidative recovery measurements of...
Medicine & Science in Sports & Exercise:
BASIC SCIENCES: Original Investigations

Fiber recruitment affects oxidative recovery measurements of human muscle in vivo

CROWTHER, GREGORY J.; GRONKA, RODNEY K.

Collapse Box

Abstract

CROWTHER, G. J., and R. K. GRONKA. Fiber recruitment affects oxidative recovery measurements of human muscle in vivo. Med. Sci. Sports Exerc., Vol. 34, No. 11, pp. 1733–1737, 2002.

Purpose: Fast-twitch and slow-twitch muscle fibers are known to have distinct metabolic properties. However, it has not been clearly established whether such heterogeneity within mixed-fiber muscles can influence measurements of energy metabolism in vivo. We therefore tested the hypothesis that differences in muscle fiber recruitment can cause differences in whole-muscle oxidative recovery from exercise.

Methods: We used 31P magnetic resonance spectroscopy to measure oxidative ATP synthesis in the ankle dorsiflexor muscles of eight healthy volunteers under a variety of recruitment conditions. Oxidative ATP synthesis after isometric exercise was quantified as the rate constant kPCr, the reciprocal of the time constant of PCr recovery.

Results: kPCr was 37% higher after low-force ramp contractions (which primarily recruit slow-twitch fibers) than after ballistic contractions to the same peak force (which recruit both fast- and slow-twitch fibers). kPCr was also 24% higher after low-force ramp contractions than after high-force ramp contractions, presumably reflecting the recruitment of fast-twitch fibers at high forces.

Conclusion: Our results indicate that the muscle fibers recruited first in voluntary contractions have a higher oxidative capacity than those recruited last. Such metabolic differences among fibers can confound whole-muscle measurements and thus need to be taken into account when studying voluntary exercise.

© 2002 Lippincott Williams & Wilkins, Inc.

Login

Article Tools

Share

Search for Similar Articles
You may search for similar articles that contain these same keywords or you may modify the keyword list to augment your search.

Connect With Us