Journal of Applied Physiology, Vol 72, Issue 6 2278-2284, Copyright © 1992 by American Physiological Society
Dependence of muscle fatigue on stimulation protocol: effect of hypocaloric diet
C. J. Barclay and D. S. Loiselle
Department of Physiology, School of Medicine, University of Auckland, New Zealand.
This study tested the hypothesis that the decreased resistance of skeletal
muscles to fatigue after a period of inadequate nutrition is a consequence
of the type of fatigue test employed. Rats (n = 8) were fed hypocalorically
for 10 days, resulting in a 33.5 +/- 3.0% (SE) reduction in body weight.
The fatigue resistance of muscles was assessed with use of isolated soleus
muscles at a temperature of 25 degrees C. Fatigue resistance was determined
from the decline in isometric force during a series of tetanic
contractions. Two contrasting contraction protocols were devised to test
the susceptibility of muscles to fatigue. One protocol was designed to
require high rates of energy supply and hence force a dependence on
glycolytic energy supply pathways. The second protocol required much lower
rates of energy supply that could be entirely met by oxidative energy
supply processes. During the high energy demand (glycolytic) protocol, the
force produced by muscles from a control group of rats decreased to 78.7
+/- 0.8% (n = 12 muscles) of the initial value. Hypocaloric feeding
significantly reduced the resistance of muscles to fatigue: force declined
to 61.3 +/- 3.5% (n = 16 muscles) during the contraction protocol. In
contrast, when fatigue was quantified using the low energy demand
(oxidative) contraction protocol, the effect of nutritional status on
fatigue resistance was entirely abolished. This result supports the
hypothesis that resistance to fatigue is critically dependent on the
fatigue test employed.
