HEMODYNAMIC RELATIONSHIPS OF ANAEROBIC METABOLISM AND PLASMA FREE FATTY ACIDS DURING PROLONGED, STRENUOUS EXERCISE IN TRAINED AND UNTRAINED SUBJECTS*

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Abstract
Responses to prolonged strenuous exercise were compared in 15 sedentary subjects and in 11 physically conditioned men, walking on a treadmill at 3 mph and 18% grade. Fatigue and dyspnea forced the sedentary group to stop after an average of 23 minutes, whereas the physically active men showed little evidence of fatigue after an hour. In spite of greater stroke volume in the latter group, cardiac outputs in the 2 groups were equal during exercise. Stroke volume fell 11 to 16% and heart rate rose during exercise. VO2 was equal in the 2 groups (1.1 L/min/M2). Anaerobiosis, as estimated by excess lactate, was several times greater in the sedentary subjects. Excess lactate in the physically active subjects rose slightly at the onset of exercise and fell to a low plateau for up to 80 minutes. Changes in free fatty acids and glucose were similar in the 2 groups. These studies indicate that increased endurance for exercise in trained persons is at least in part a circulatory or metabolic adaptation associated with skeletal muscle hypertrophy and not dependent on increased cardiac output.