Journal of Applied Physiology, Vol 73, Issue 5 2105-2111, Copyright © 1992 by American Physiological Society

ARTICLES

Force-velocity shifts with repetitive isometric and isotonic contractions of canine gastrocnemius in situ

B. T. Ameredes, W. F. Brechue, G. M. Andrew and W. N. Stainsby
Department of Physiology, University of Florida, Gainesville 32610.

The force-velocity (F-V) relationships of canine gastrocnemius-plantaris muscles at optimal muscle length in situ were studied before and after 10 min of repetitive isometric or isotonic tetanic contractions induced by electrical stimulation of the sciatic nerve (200-ms trains, 50 impulses/s, 1 contraction/s). F-V relationships and maximal velocity of shortening (Vmax) were determined by curve fitting with the Hill equation. Mean Vmax before fatigue was 3.8 +/- 0.2 (SE) average fiber lengths/s; mean maximal isometric tension (Po) was 508 +/- 15 g/g. With a significant decrease of force development during isometric contractions (-27 +/- 4%, P < 0.01, n = 5), Vmax was unchanged. However, with repetitive isotonic contractions at a low load (P/Po = 0.25, n = 5), a significant decrease in Vmax was observed (-21 +/- 2%, P < 0.01), whereas Po was unchanged. Isotonic contractions at an intermediate load (P/Po = 0.5, n = 4) resulted in significant decreases in both Vmax (-26 +/- 6%, P < 0.05) and Po (-12 +/- 2%, P < 0.01). These results show that repeated contractions of canine skeletal muscle produce specific changes in the F-V relationship that are dependent on the type of contractions being performed and indicate that decreases in other contractile properties, such as velocity development and shortening, can occur independently of changes in isometric tension.

This article has been cited by other articles:

				A. N. Devrome and B. R. MacIntosh The biphasic force-velocity relationship in whole rat skeletal muscle in situ J Appl Physiol, June 1, 2007; 102(6): 2294 - 2300. [Abstract] [Full Text] [PDF]

				S. Medler Comparative trends in shortening velocity and force production in skeletal muscles Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2002; 283(2): R368 - R378. [Abstract] [Full Text] [PDF]

				B. T. Ameredes, W.-Z. Zhan, Y. S. Prakash, R. Vandenboom, and G. C. Sieck Power fatigue of the rat diaphragm muscle J Appl Physiol, December 1, 2000; 89(6): 2215 - 2219. [Abstract] [Full Text] [PDF]

				J. F. Watchko, M. J. Daood, B. Wieringa, and A. P. Koretsky Myofibrillar or mitochondrial creatine kinase deficiency alone does not impair mouse diaphragm isotonic function J Appl Physiol, March 1, 2000; 88(3): 973 - 980. [Abstract] [Full Text] [PDF]

				B. T. Ameredes, J. F. Watchko, M. J. Daood, J. F. Rosas, M. P. Donahoe, and R. M. Rogers Growth hormone restores aged diaphragm myosin composition and performance after chronic undernutrition J Appl Physiol, October 1, 1999; 87(4): 1253 - 1259. [Abstract] [Full Text] [PDF]

				J. F. Watchko, M. J. Daood, G. C. Sieck, J. J. Labella, B. T. Ameredes, A. P. Koretsky, and B. Wieringa Combined myofibrillar and mitochondrial creatine kinase deficiency impairs mouse diaphragm isotonic function J Appl Physiol, May 1, 1997; 82(5): 1416 - 1423. [Abstract] [Full Text] [PDF]