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

WILLEMS, MARK E. T.; STAUBER, WILLIAM T.

Medicine & Science in Sports & Exercise: July 2000 - Volume 32 - Issue 7 - p 1293-1299
Applied Sciences: Physical Fitness And Performance

WILLEMS, M. E. T., and W. T. STAUBER. Performance of plantar flexor muscles with eccentric and isometric contractions in intact rats. Med. Sci. Sports Exerc., Vol. 32, No. 7, pp. 1293–1299, 2000.

Purpose 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.

Methods Repeated stretches (30) at two velocities of ankle rotation [slow stretch (0.87 rad·s1 (i.e., 50°·s1)), fast stretch (10.47 rad·s1 (i.e., 600°·s1))] were superimposed on maximally active muscles from an ankle position of 1.57 rad to 0.70 rad (i.e., from 90° to 40°). Repeated isometric contractions (30) of the same duration (1900 ms) and rest interval (3 min) were performed at 1.13 rad (i.e., 65°). 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°)], and the time to produce 50% of the maximal isometric torque.

Results 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.

Conclusions 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.

Department of Physiology, West Virginia University, Morgantown, WV 26506

Submitted for publication January 1999.

Accepted for publication October 1999.

Address for correspondence: William T. Stauber, Ph.D., FACSM, Department of Physiology, West Virginia University, PO Box 9229, Morgantown, WV 26506-9229; E-mail: wstauber@wvu.edu.

© 2000 Lippincott Williams & Wilkins, Inc.