Resistance exercise effects on aging skeletal muscle in rats

The purpose of this study was to determine whether a resistance exercise program could be initiated successfully at progressively older ages in rats. Forty female Sprague-Dawley rats, 7 to 10 in each age group (21, 24, 27, and 30 months, respectively), performed 60 manually resisted chin-ups (three sets of 10 repetitions each twice daily) for three months. Twenty controls, 5 in each age group, were followed for three months but not exercised. Before the experimental period began, the rats' left palmaris longus (PL) muscle was removed, weighed, frozen, sectioned, and stained. After the three-month period, the right PL muscle was removed and the same tissue preparation procedure was followed. Muscle fiber types I and II were identified on photomicrographs, and areas of each fiber type measured. No significant change in muscle wet weight or fiber size occurred in the controls. Significant increases (p less than .01) in type II muscle fiber area occurred for the 21-, 24-, and 30-month-old rats that exercised. No histological evidence of exercise-related harm was observed in tissues from exercised rats. Results indicate that resistance exercise can be introduced successfully to an aging or aged rat without doing harm. Studies are needed to determine whether similar results can be achieved for elderly humans.