EFFECT OF ENDURANCE TRAINING ON MYOCARDIAL MYOSIN ADENOSINE-TRIPHOSPHATASE ACTIVITY OF THE DOG

Endurance exercise training has been found to enhance the functional capacity of the myocardium in several animal models. The sub-cellular phenomena accompanying the augmented function are yet to be explained. The present study sought to determine if the myosin ATPase activity of cardiac muscle increased as a result of endurance conditioning. Five beagles trained by running on a motor driven treadmill (T) and five control (NT) animals were studied. Following 10 weeks of training the T group had a significantly (P<.05) lower heart rate than the NT while performing the same submaximal exercise and the gastrocnemius cytochrome oxidase activity was significantly greater (PC.005) in the T than in the NT. These two mea-surements established that the exercised animals were physicaly trained. Myosin was isolated from the left ventricular myocardium and activated in a medium containing K-EDTA. No significant (P<.05) difference in maximum myosin ATPase activity was observed between the NT and T groups in cardiac muscle. It was concluded that cardiac muscle myosin ATPase activity was not affected by 10 weeks of endurance conditioning induced by treadmill running in dogs. © 1979 The American College of Sports Medicine.