MYOCARDIAL HYPERTROPHY IS THE PRIMARY CARDIOVASCULAR ADAPTATION TO ENDURANCE TRAINING IN SEDENTARY MEN 804

Abstract

In sedentary individuals at sea level, maximal aerobic power is determined primarily by the ability to deliver and accommodate blood flow to skeletal muscle. In order to determine the relative importance of central and/or peripheral adaptations in the cardiovascular system in response to endurance training, we measured cardiac mass (magnetic resonance imaging, MRI) and maximal vascular conductance (Gmax) before and after 3 months of training(running/cycling/swimming, 3-4 days/wk) in 5 sedentary healthy men (27± 6yrs). Maximal leg blood flow was measured by mercury strain-gauge plethysmography during reactive hyperemia produced by ischemic exercise to fatigue. Gmax in the lower leg was calculated from blood flow and mean arterial cuff pressure from the branchial artery. Results: VO2max increased by 12% (43 ± 4.6, to 48 ± 6.5 ml/kg/min; p<0.004), while both resting (95 ± 10, to 78 ± 10) and submaximal (171 ± 15, to 146 ± 14) heart rates decreased 16% and 15% respectively. There was no change in body weight (78 ± 4.8, to 77± 4.5 kg; p=0.15). LV mass increased by 7% (204 ± 29, to 219± 13g; p<0.005), with no increase in Gmax [0.396 ±.089, to 0.394 ± 0.076 (ml/min/100g) (mmHg)-1; p=0.07].Conclusion: Cardiac hypertrophy appears to be the initial primary mechanism for increasing VO2max and oxygen delivery in healthy sedentary subjects following three months of moderate endurance training.