Metabolic heat production during fatigue from voluntary repetitive
isometric contractions in humans.
Saugen, E., and N. K. V[phi]llestad.
Department of Physiology, National Institute of Occupational
Health, N-0033 Oslo, Norway
APStracts 3:0210A, 1996.
The effect of repetitive isometric knee extensions on the energy cost
of contraction was examined. The rate of temperature rise (dT/dt) was
determined in test contractions at 30 % and 50 % of maximal voluntary
contraction (MVC) force before and during 30 % MVC repetitive
isometric exercise (RIE) to exhaustion, and regularly in a 30 min
post exercise recovery period (n=9). Pulmonary oxygen uptake (VO2)
and muscle temperature (Tm) was determined at regular intervals.
During 30 % MVC test contractions dT/dt was 5.6 +/- 0.6 mK.s-1 in
unfatigued muscle, increasing linearly by 68 % during exercise. In
the 50 % MVC test contractions dT/dt rose by 84 % from 9.8 +/- 1.1
mK.s-1. dT/dt determined during test contractions at both force
levels did not decrease significantly through the 30 min post
exercise recovery period. The rise in dT/dt was paralleled by a 76 %
increase in VO2. In contrast, Tm rose initially and then leveled off.
The present data indicate that RIE induced a gradual rise in the rate
of energy turnover associated with isometric force production.
Neither increased Tm nor recruitment of less economic type II fibers
can fully explain the increased energy cost. We suggest that
energetic changes may occur at the cellular level and argue that this
may be associated with the changes in muscle mechanics occurring
during fatigue from submaximal voluntary RIE.
Received 29 August 1995; accepted in final form 8 April 1996.
APS Manuscript Number A943-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96