Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men. Widrick, Jeffrey J., Scott W. Trappe, David L. Costill, and Robert H. Fitts. Department of Biology, Marquette University, Milwaukee, WI 53201, and Human Performance Laboratory, Ball State University, Muncie, IN, 47306
APStracts 3:0092C, 1996.
Gastrocnemius muscle fiber bundles were obtained by needle biopsy from 5 middle-aged sedentary men (SED group) and 6 age-matched endurance trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and position motor, subjected to a series of isotonic contractions at maximal Ca2+-activation (15 C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain (MHC) composition. The Hill equation was fit to the data obtained for each individual fiber (R2 ( 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber MHC expression as follows: peak force, no differences; peak tension (force/fiber cross-sectional area), IIx > IIa > I; maximal shortening velocity (Vmax, defined as the y -intercept of the force-velocity relationship), IIx = IIa > I; a/Po, IIx > IIa > I. Consequently, type IIx fibers produced 2 times more peak power than type IIa fibers while IIa fibers produced 5 times more peak power than type I fibers. Type I and IIa fibers from the RUN group were smaller in diameter and produced less peak force in comparison to the type I and IIa fibers from the SED group. The absolute peak power output of RUN type I and IIa fibers was 13% and 27% less, respectively, than peak power of similarly typed SED fibers. However, both type I and type IIa Vmax and a/Po were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus, the reduced absolute peak power output of the type I and IIa fibers obtained from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance trained athletes. 

Received 16 October 1995; accepted in final form 15 March 1996.
APS Manuscript Number C628-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96