Effect of Exercise Conditioning on the Intrinsic Contractile State of Cat Myocardium

SUMMARY Fourteen adult cats were exercised on a motor-driven treadmill 5 days each week for 6 weeks to determine the effect of exercise conditioning on the intrinsic contractile state of the myocardium. The exercise program was sufficient to produce a cardiovascular training effect manifested by slower exercising heart rates and resting heart rates after atropine by the end of the 6th week. The mechanical function of the isolated right ventricular papillary muscle from exercised cats was compared with that of 17 sedentary adult cats. There were no significant differences between exercised and control cats in heart weight-body weight ratios, resting and active length-tension relations, maximal rate of isometric force development at the peak of the length-tension curve (!.„,.,), time to peak force at Lm.x, maximal force development with paired stimulation and norepinephrine, or force-velocity relations. These results indicate that the intrinsic contractile state of feline myocardium is unaffected b