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Age affects skeletal muscle adaptation to repeated exposures of stretch-shortening contractions.

Cutlip-RG; Baker-BA; Geronilla-KB; Kashon-ML; Murlasits-Z; Alway-SE
Med Sci Sports Exerc 2005 Jun; 37(Suppl 5):S318
Previous studies have shown that skeletal muscle is more susceptible to contraction-induced injury and recovers more slowly after the initial injury in aged animals. Purpose: To investigate if aging affects the ability of skeletal muscle to adapt to repeated exposures of maximal stretch-shortening cycles (SSCs). Methods: Dorsiflexor muscles of old (30 months, N= 5) and young (12 weeks, N = 6) Fischer 344 Brown Norway rats were exposed 3 times per week for 4.5 weeks to a protocol of 80 maximal stretch-shortening cycles (60 deg/s, 50 deg range of motion) per exposure in vivo. Performance was characterized by isometric performance, negative, positive, and net work, and stretch-shortening parameters (peak force and minimum force at each exposure interval (fourteen exposures). Results: The isometric force (p = 0.455), peak force (p = 0.761), and minimum force (p = 0.853) was not statistically different between groups at the start of the exposure. During the chronic exposure, those forces responded differently with age (p = 0.0003, 0.0081, and 0.0011 respectively) and were significantly different with age at the end of the exposure period (p <0.0001 for all parameters). Negative work and positive work were also not different between groups at the start of the exposure (p = 0.455 and 0.475, respectively). During the chronic exposure, both negative and positive work responded differently with age (p = 0.0044 and 0.0011, respectively) and resulted in significantly different magnitudes at the end of the exposure period (p <0.0011 for both parameters). There was also a significant increase in all performance parameters from the initial to the final exposure in the young animals (p <0.05), but a concomitant decrease in the old animals in all parameters (p <0.05) except negative work. Conclusions: A chronic exposure of SSCs results in a significant performance increase in young animals, and significant performance decrease in old animals. These findings indicate that aging impairs the ability of skeletal muscle to adapt to repetitive mechanical loading.
Age-factors; Muscles; Musculoskeletal-system; Skeletal-system; Injuries; Laboratory-animals; Animals; Animal-studies; Exposure-levels; Exposure-assessment; In-vivo-studies; Chronic-exposure
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Disease and Injury: Musculoskeletal Disorders of the Upper Extremities
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Medicine and Science in Sports and Exercise