FIBROSIS AND INTERCELLULAR COLLAGEN CONNECTIONS FROM 4 WEEKS OF MUSCLE STRAINS

The effect of repeated cycles of muscle strain was studied in the sole us muscle of female rats, Muscle strains were repeated 3x/week for 1 m onth using two different strain protocols. Striking changes, including marked variability in fiber size, evidence of degeneration and regene ration, and an expanded extracellular matrix were pronounced in the fa st-stretched muscles, Using scanning electron microscopy, fibrosis was confirmed in the fast-stretched muscles but not in the slow-stretched muscles. However, the slow-stretched muscles did contain struts of co nnective tissue joining adjacent myofibers, Therefore, repeated muscle strains at high strain rates produced morphological changes similar t o many myopathies, including fibrosis, whereas adaptation occurred in response to the same number of strains at slow strain rates, Such dive rse tissue responses have relevance to the understanding of the mechan isms of skeletal muscle dysfunction in cumulative trauma disorders and in the design of preventive actions and treatments. (C) 1996 John Wil ey & Sons, Inc.