Frequency of intensive, prolonged exercise as a determinant of relative coronary circumference index.

This study determined the effects of 10 weeks of intensive swimming 0, 1, 5, and 10 times per week on relative coronary circumference index (RCCI), which was calculated as the ratio of cardiac ventricular weight to the sum of the circumferences of the right and left main coronary arteries. Sixty-nine Wistar rats swam continuously for 30 to 51 min per session while carrying 1.0% to 1.25% of their individual body weights. Hearts were prepared using routine histological methods and were analyzed for RCCI, coronary circumference, heart mass, and regressed heart mass. Data were analyzed for linear, quadratic, and cubic trends relative to exercise frequency. Mean values for wet weight RCCI were 98.82, 99.16, 91.04, and 90.21 mg per planimeter unit for groups exercising 0, 1, 5, and 10 times weekly (P less than 0.01 for linear trend). Regressed mean ventricular dry weights exhibited expected significant linear increases of 4.89%, 5.66%, and 6.12% over sedentary control rats. The RCCI was clearly shown to undergo a significant linearly graded decrease with increasing frequencies of exercise.