Isometric force and maximal shortening velocity of single muscle
fibers from elite master runners.
Widrick, Jeffrey J., Scott W. Trappe, Cindy A. Blaser, 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 3:0091C, 1996.
Single chemically permeabilized gastrocnemius fibers, obtained from 6
elite endurance trained master runners (RUN group) and 5 age-matched
sedentary controls (SED group), were mounted between a force
transducer and position motor, studied under conditions of maximal
and sub-maximal Ca2+-activation, and subsequently electrophoresed on
5% polyacrylamide gels to determine myosin heavy chain (MHC)
composition. For the SED group, peak isometric tension (Po) averaged
143 +/- 3, 156 +/- 4, and 170 +/- 4 kN x m-2 and maximal shortening
velocity (Vo) averaged 0.43 +/- 0.01, 1.90 +/- 0.08, and 5.59 +/-
0.40 fiber lengths x s-1 for fibers expressing type I, IIa, and IIx
MHC, respectively (all comparisons, P < 0.05). Hill plot
analysis of relative forces during submaximal Ca2+-activation
indicated no SED verses RUN differences in either Ca2+ sensitivity or
the cooperativity of Ca2+ activation. However, at maximal Ca2+
-activation, RUN type I and IIa fibers produced 15% less peak absolute
force in comparison to SED fibers (P < 0.05). This reduction in
fiber force was a direct result of the smaller diameter of the RUN
fibers (P < 0.05) since Po, peak elastic modulus (Eo), and Po/Eo
were not different between SED and RUN groups. RUN type I fibers also
displayed a mean Vo that was 19% higher than the average Vo of the
SED type I fibers (P < 0.05). In separate experiments,
quantification of relative myosin light chain (MLC) isoform content
revealed a 28% greater ratio of MLC3/MLC2 in single type I fibers
obtained from the RUN group (P < 0.05), suggesting that the
elevated Vo of the RUN type I fibers was related to a greater
expression of MLC3. In conclusion, the single fibers obtained from
the elite master runners displayed specific morphological and
contractile properties that may enhance the performance of these
athletes during prolonged muscular activity.
Received 16 October 1995; accepted in final form 15 March 1996.
APS Manuscript Number C627-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96