The physiological effects of a midshift feed of sucrose

Abstract

Four well-trained subjects worked for fifty minutes of every hour for six hours on a bicycle ergometer at loads requiring about 30 per cent and 50 per cent of the subjects maximal aerobic capacity. Subjects were studied when they received only water and again when they were fed 100 g and 200 g sucrose at the beginning of the fourth hour of work. The physiological responses of the men given the mid-shift feed of sucrose were compared with those obtained when no sucrose was fed . The respiratory quotients of men who received no sucrose during six hours at the two work loads, showed a continuous decrease in carbohydrate metabolism from 70 per cent in the first hour to 30 per cent at the end of the sixth hour. This decrease in carbohydrate metabolism and corresponding increase in fat metabolism was accompanied by a continuous rise in oxygen uptake and heart r ate . Physiologically, these subjects exhibited relatively more strain and were mechanically less efficient at t he end of Lh0 work period than they were at the start. When the same subjects received a mid-shift feed of 100 g or 200 g sucrose at the end of the third hour of the work period , they displayed a significant increase in carbohydrate metabolism as shown by the higher respiratory quotient. This was associated with a lower rate of oxygen consumption and heart rate than in the fasting state. Subjects were mechanically more efficient at the higher work load and also showed less circulatory strain as evidenced by the lower heart rate and higher stroke volume. The best results were obtained when 100 g sucrose was administered as a mid-shift feed, the extra ·benefit obtained with a feed of 200 g being small. Subjects working at the higher rate benefited more than men working at the lower rate.