Humoral nature of the hypoglycemic factor of muscular work.

The striated muscle mass of the body, by virtue of its weight alone, constitutes the major quantitative factor in the bodily conversion of foodstuffs to CO2, water and energy. The flow of gluconeogenic precursors to the liver, the hepatic manufacture of sugar and the release of glucose in the satisfaction of the ever-changing needs of total muscular activity of the body represent a complex of regulation which is taken for granted but is understood inadequately in detail. Outside of an occasional epinephrine-induced hyperglycemia, the stability of the blood sugar gives no indication of the changing ebb and flow of foodstuff which attends the wide range of activity from the sedentary, basal muscle tone of deep sleep to the mild, moderate or severe exertions which characterize the normal course of events. The minute by minute alterations in oxygen consumption and the difficulties experienced in making a truly basal metabolic rate measurement are common clinical experiences. This variability in oxygen consumption must be reflected in equivalent variation in the rate of substrate metabolism.