Metabolic Rate, Blood Sugar and the Utilization of Carbohydrate

The many observations on blood sugar in exercise have revealed widely different conditions. Thus one may have extreme hypoglycemia as found by Levine, Burgess and Derick (1) in some marathon runners, or at the other extreme, hyperglycemia as in football players (2). A moderate decrease in the concentration of sugar in the blood (B. S.) has been found by Christiansen (3) in exercise of one hour’s duration; in recovery following exercise both Rakestraw (4) and Christiansen report moderate increases. We have found that when exercise is carried on for many hours without emotional stress the value of B. S. may not vary much from the resting level until a terminal hypoglycemia develops (5). It seems probable that such a state reflects the exhaustion of glycogen reserves; if so it should be associated with a decreasing respiratory quotient. With this possibility in mind we have undertaken a series of experiments designed to study the relation between metabolic rate (M. R.), respiratory quotient (R. Q.), carbohydrate reserve,l and blood sugar (B. S.). The experimental procedure has been described in part elsewhere (6). In these experiments two rates of work were employed with alternation of rate each half-hour. The work was carried on for several hours, tiz., long enough to reduce materially the reserve of carbohydrate. During each half-hour blood was obtained from the finger while work proceeded and sugar was determined by the Folin-Malmros method (7). At the same time expired air was collected and analyzed in the usual manner. Since the rate of work did not exceed the oxygen transport capacity the rate of oxygen intake is a measure of the M. R. Our ablest subject was Y, aged 19, a skilled runner who has finished near the front in marathons. In three experiments he ran for 6 hours alternating at rates of 9.3 and 11.3 km. per hour with an energy output on these occasions averaging 3400 Cals. The second of’these experiments