Effects of graded duration of stretch on normal and dystrophic skeletal muscle.

Daily passive stretch for six weeks ranging from 30 minutes to 24 hours per day was studied in the patagialis (PAT) muscle of normal and dystrophic chickens. Significant increases in wet weight, cross-sectional area, and mean fiber cross-sectional area occurred in both normal and dystrophic PAT in response to stretch of all daily durations tested. More than 50% of the growth occurring in response to continuous stretch was elicited by as little as 30 minutes of stretch per day. Oxidative enzyme capacity increased proportionately with increasing durations of stretch in the normal PAT. Similarly, increasing duration of stretch progressively retarded the onset of histopathological signs in the dystrophic PAT. We conclude that daily stretching for as little as 30 minutes per day is a powerful inducer of growth in normal and dystrophic muscle and that the progress of the histopathology in dystrophic muscle is delayed in proportion to the daily duration of stretch.