Non-linear relationship between heat production and force during
voluntary contractions in man .
Saugen, E., and N. K. Vollestad.
Department of Physiology, National Institute of Occupational
Health, N-0033 Oslo, Norway
APStracts 2:0349A, 1995.
The rate of temperature rise (dT/dt) in the vastus lateralis muscle of
seven subjects was measured at 4-5 locations in each muscle during
voluntary isometric contractions ranging from 10-90% of maximal
voluntary contraction force (MVC). dT/dt increased from 3.1 +/- 1.1
mK/s at 10% MVC to 14.5 +/- 1.3 mK/s at 90% MVC. In the typical
subject the increase in dT/dt with force was markedly higher between
30-70% MVC than in the upper and lower force ranges. The estimated
ratio between heat rate in active muscle and force was 6 times higher
at 10% MVC than at 90% MVC, indicating a markedly increasing economy
of contraction with increasing force. The lower contraction economy
at low forces may be explained by an increased rate of energy
turnover associated with force generation and relaxation when motor
-units are contracting at low firing rates. Hence, we argue that
recruitment and rate coding may have a profound affect on the economy
of contraction at different force levels.
Received 25 April 1995; accepted in final form 28 July 1995.
APS Manuscript Number A446-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.