Journal of Applied Physiology, Vol 54, Issue 5 1209-1215, Copyright © 1983 by American Physiological Society
Force and duration of muscle twitch contractions in humans at pressures up to 70 bar
D. J. Harris and P. B. Bennett
The contraction peak force (CPF) and contraction time (CT) of the soleus
Hoffmann (H) reflex and motor (M) response muscle twitch were measured in
three subjects during the 686-m seawater Atlantis III simulated dive at
Duke University. The mean CPF of both H and M twitches was observed to be
40-60% larger during compression than in predive control studies (P less
than 0.001 for M response). This effect was sustained during the first 300
m of decompression, while postdive values were normal. Rate of contraction,
as measured by changes in CT, was slowed significantly but only during
compression (by 23% in the H reflex at 66.4 bar, P less than 0.001). These
marked effects in CPF and CT cannot be explained by the small increases
observed in the muscle action potential latency and duration, or other
neuronal mechanisms. It is concluded that the twitch contraction of
skeletal muscle is significantly slowed and augmented at pressure due to
changes in excitation-contraction coupling or in the contractile process
itself. These findings may be of importance in interpreting the etiology of
many neuromuscular signs of the high-pressure neurological syndrome.
