Biomechanical comparison of stimulated and nonstimulated skeletal muscle pulled to failure

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Abstract

We compared the biomechanical properties of passive and stimulated muscle rapidly lengthened to failure in an experimental animal model. The mechanical parameters compared were force to tear, change in length to tear, site of failure, and energy absorbed by the muscle-tendon unit before failure. Paired comparisons were made between 1) muscles stimulated at 64 Hz (tetanic stimulation) and passive (no stimulation) muscles, 2) muscles stimulated at 16 Hz (wave-summated stimulation) and passive muscles, and 3) muscles stimulated at 64 Hz and at 16 Hz. Both tetanically stimulated and wave-summation contracted muscles required a greater force to tear (at 64 Hz, 12.86 N more, P less than 0.0004; and at 16 Hz, 17.79 N more, P less than 0.003) than their nonstimulated controls, while there was no statistical difference in failure force between muscles stimulated at 16 Hz and 64 Hz. The energy absorbed was statistically greater for the stimulated muscles than for the passive muscles in Groups 1 and 2 (at 64 Hz, 100% more, P less than 0.0003; and 16 Hz, 88% more, P less than 0.0002). In Group 3, the tetanically contracted muscle-tendon units absorbed 18% more energy than the wave-summated stimulated muscles (P less than 0.01). All muscles tore at the distal musculotendinous junction, and there was no difference in the length increase at tear between muscles in each group. These findings may lead to enhanced understanding of the mechanism and physiology of muscle strain injuries.

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The variation in isometric tension with sarcomere length in vertebrate muscle fibres

A M Gordon, A HUXLEY, F. Julian (1966)

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Myofibrillar damage following intense eccentric exercise in man.

B Ekblom, J Fridén, M Sjöström (1983)

Muscle soreness that has a delayed onset is a common feature among both athletes and untrained individuals who engage in unusual exercises. This study was designed to provide additional morphological data to assess the relevance and significance of our previous findings that the sore muscles contain fibers with disorganized myofibrillar material. Muscle biopsies were obtained from 12 males (mean age 25 +/- 7 years), who suffered from severe soreness in their thigh muscles 18--72 h following eccentric bicycle exercise. Their strength performance were tested in parallel. Knee extensor strength was decreased at all angular velocities soon after exercise but gradually increased over the subsequent days although slower at the fastest contractions. Disturbances of the cross-striated band pattern were constantly observed. They originated from the myofibrillar Z-band, which showed marked streaming, broadening and, at places, total disruption. The disturbances were found in every second to every third fiber up to 3 days after exercise and in one tenth of the fibers 6 days following the exercise. Type 2 fibers were predominantly affected. Thus, the eccentric exercise gives rise to muscles soreness and influences, on mechanical basis and selectively with regard to fiber type, the fine structure of the contractile apparatus.