Journal of Applied Physiology, Vol 71, Issue 1 204-209, Copyright © 1991 by American Physiological Society
Skeletal muscle relaxation rate after fasting or hypocaloric feeding
M. L. Nishio and K. N. Jeejeebhoy
Department of Physiology, University of Toronto, Ontario, Canada.
The effect of malnutrition on skeletal muscle relaxation is not entirely
clear; some studies indicate no change and others a slowing of the
relaxation rate. We investigated whether these different results were due
to type of malnutrition, muscle fiber type composition, or the index used
to express relaxation rate. The effect of a 2-day fast (16% body wt loss)
or 1 wk of hypocaloric feeding (22.6% wt loss) on relaxation rates of
soleus and extensor digitorum longus (EDL) muscles was studied in situ with
the use of anesthetized adult Wistar rats. Relaxation rates were assessed
for twitch contractions using half-relaxation times and exponential phase
half-times and for tetanic contractions using exponential phase half-times.
The rate of relaxation was unaffected by fasting, whereas hypocaloric
feeding reduced relaxation rates after twitch and tetanic contractions in
both soleus and EDL muscles. We conclude that slowing of skeletal muscle
relaxation rate occurs after 1 wk of hypocaloric feeding but not after 2
days of fasting. The slowing is independent of muscle fiber composition,
type of contraction, or the index used to express relaxation rate.
