Alterations in muscle contractile properties and fiber composition ofter weight-lifting exercise in cats

Abstract

To determine if weight-lifting exercise alters the contractile properties of muscle, eight cats were trained to lift weights with their right forelimb to receive a food reward. After 10 to 61 weeks of training and lifting (0.45 to 1.52 kg), the palmaris longus (PLM) and flexor carpi radialis (FCR) muscles were prepared for physiological examination for 6 trained and 16 control cats. This report demonstrated that exercise-induced hypertrophy resulted in a significant increase in the isometric twitch (35% FCR, 32% PLM) and tetanic (23% FCR, 41% PLM) tensions for both exercised muscles. In addition, there was a significant increase of the time to peak tension (22% FCR, 34% PLM) and half-relaxation time (45% FCR, 78% PLM) of an isometric twitch and a slowing of the rate of tension development (39% FCR, 32% PLM) of the exercised muscles. Even though the overall effect of weight-lifting exercise was to slow the contractile properties of the muscles for most cats, the histochemical profiles of the trained muscles showed a significant increase in fast-twitch glycolytic fibers (from 45 to 58%) and a decrease in the proportion of fast-twitch oxidative glycolytic fibers (from 29 to 20%) for the PLM. No significant change was observed in the proportion of slow-twitch oxidative fibers in this muscle or in the fiber proportions of the FCR. It appears that light to moderate weight-lifting exercise alters the contractile properties of the muscle independent of the muscle fiber populations demonstrated by histochemistry.