Performance Capacity and Effects of Caloric Restriction With Hard Physical Work on Young Men

Abstract

The effect of caloric deficits was studied on performance capacity under the following conditions: a) 3100 Cal/day for the entire experiment (control group of 6 men); b) 580 Cal/day for 12 days (6 men); c) 1010 Cal/day for 24 days (13 men). Except for the control group, all men ate a diet of pure carbohydrate and 4.5 gm of NaCl daily during the period of caloric restriction. Assigned work requiring 1200 Cal/ day was performed by each subject in both experiments. The 580 Cal/day prevented ketosis and demonstrable liver damage but failed to maintain adequate work blood sugar levels. The capacity to preform both aerobic and anaerobic work tasks was well maintained but pulmonary ventilation during work, the O₂ debt and pulse rate responses to a fixed task indicated some deterioration. The 1010 Cal/day maintained satisfactory work blood sugar levels and there was no evidence of poor physiological response to the stress of work. No important change occurred in grip strength or in the maximal oxygen intake per kilogram of body weight or fat free tissue in either experiment. But the total maximal oxygen intake declined slowly in both experiments. Data from the Minnesota experiment on 6 months of semistarvation were pooled with the current observations to show that a marked deterioration in both maximal oxygen intake and strength as measured by the hand dynamometer took place between a weight loss of 10 and 16%. It is concluded that when sufficient calories and NaCl in the presence of an adequate vitamin intake are provided to prevent ketosis, dehydration and hypoglycemia under conditions of moderate energy output, performance capacity is well maintained up to a weight loss of 10% of the original body weight. Submitted on December 19, 1956