Work capacity determinants and physiologic cost of weight-supported work in obesity

Abstract

Selected cardiopulmonary responses of 14 obese and 14 normal, healthy, sedentary males were compared with specific reference to: a) the "physiological cost" of performing identical intensities of external work on the bicycle ergometer; and b) the capacity of the oxygen transport systems during "maximal" work. The obese subject''s energy expenditure per unit of work load on the bicycle ergometer was markedly increased. The greater "relative intensity" of moderate work in the obese was reflected in a higher level of anaerobic work, elevated blood pressure, heart rate, and pulmonary ventilation, and an exaggerated alveolar-arterial PO2 difference. The maximum quantity of oxidative energy available for muscular work was severly reduced in obesity. Excessive fatness contributed to this decrement in work capacity directly, through its presence as an inert, noncontributory load, and indirectly, through its apparent interference with over-all maximum circulatory-respiratory function. Interference with alveolar-arterial exchange of O2 or CO2 during moderate and severe work was not of sufficient magnitude to warrant the implication of ineffective pulmonary function as a major limitation to maximum oxygen transport in the majority of obese subjects.