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Performance of plantar flexor muscles with eccentric and isometric contractions in intact rats.

Willems MET; Stauber WT
Med Sci Sports Exerc 2000 Jul; 32(7):1293-1299
To examine the changes in performance of active plantar flexor muscles of rats by controlled dorsiflexion (i.e., stretching of muscles) at two angular velocities. Repeated stretches (30) at two velocities of ankle rotation [slow stretch (0.87 rads x s(-1) (i.e., 50 degrees x (s-1))), fast stretch (10.47 rad x s(-1) (i.e., 600 degrees x s-1))] were superimposed on maximally active muscles from an ankle position of 1.57 rad to 0.70 rad (i.e., from 90 degrees to 40 degrees). Repeated isometric contractions (30) of the same duration (1,900 ms) and rest interval (3 min) were performed at 1.13 rad (i.e., 65 degrees). Performance was assessed by measuring the isometric torque at ankle positions of 1.57 and 0.70 rad, work during concentric contractions [range of motion 1.22 rad (i.e., 70 degrees)], and the time to produce 50% of the maximal isometric torque. Thirty isometric contractions resulted in a linear reduction in torque (total deficit of 13.8% at 1.57 rad), whereas for slow and fast stretches, half of the total, nonlinear deficit at 1.57 rad (about 30%) was completed after six stretches. Increases in half contraction times were larger for stretches than for isometric contractions. Reductions in isometric torque were greater at an ankle position of 1.57 rad than at 0.70 rad. One hour of rest after the repeated stretches and isometric contractions did not restore muscle performance. Isometric contractions of skeletal muscle can create a torque deficit which is much less than that after stretches. Repeated fast and slow stretches resulted in similar torque deficits which did not recover after a rest period of 1 h.
Musculoskeletal system disorders; Muscle tension; Muscle stress; Injuries; Skeletal stress; Skeletal disorders; Animals; Animal studies; Laboratory animals; Author Keywords: skeletal muscle; muscle injury; muscle force; velocity; ankle; dynamometer
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Journal Article
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Disease and Injury: Musculoskeletal Disorders of the Upper Extremities
Source Name
Medicine and Science in Sports and Exercise
Performing Organization
West Virginia University, Morgantown, West Virginia
Page last reviewed: April 9, 2021
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