Journal of Applied Physiology
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J Appl Physiol 83: 40-45, 1997;
8750-7587/97 $5.00
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Journal of Applied Physiology
Vol. 83, No. 1, pp. 40-45, July 1997
EXERCISE AND MUSCLE

Neuromuscular factors contributing to in vivo eccentric moment generation

Sandra Webber and Dean Kriellaars

School of Medical Rehabilitation, University of Manitoba, Winnipeg, Manitoba, Canada R3E 0W3

Received 9 April 1996; accepted in final form 7 March 1997.

Webber, Sandra, and Dean Kriellaars. Neuromuscular factors contributing to in vivo eccentric moment generation. J. Appl. Physiol. 83(1): 40-45, 1997.---Muscle series elasticity and its contribution to eccentric moment generation was examined in humans. While subjects [male, n = 30; age 26.3 ± 4.8 (SD) yr; body mass 78.8 ± 13.1 kg] performed an isometric contraction of the knee extensors at 60° of knee flexion, a quick stretch was imposed with a 12°-step displacement at 100°/s. The test was performed at 10 isometric activation levels ranging from 1.7 to 95.2% of maximal voluntary contraction (MVC). A strong linear relationship was observed between the peak imposed eccentric moment derived from quick stretch and the isometric activation level (y = 1.44x + 7.08; r = 0.99). This increase in the eccentric moment is consistent with an actomyosin-dependent elasticity located in series with the contractile element of muscle. By extrapolating the linear relationship to 100% MVC, the predicted maximum eccentric moment was found to be 151% MVC, consistent with in vitro data. A maximal voluntary, knee extensor strength test was also performed (5-95°, 3 repetitions, ±50, 100, 150, 200, and 250°/s). The predicted maximum eccentric moment was 206% of the angle- and velocity-matched, maximal voluntary eccentric moments. This was attributed to a potent neural regulatory mechanism that limits the recruitment and/or discharge of motor units during maximal voluntary eccentric contractions.

actomyosin; cross bridge; series elasticity; strength

0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society




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