Physical and mental performance of soldiers on high- and low-energy diets during prolonged heavy exercise combined with sleep deprivation.

Abstract

A group of 24 men was studied during a period of heavy, sustained work lasting for 107 hours, during which time they had less than 2 hours sleep. Nine men received a diet providing 33·49 MJ (8000 kcal) and 15 a diet providing 6·30 MJ (1500kcal) per day. The subjects were assessed by objective measurements of simulated military tasks and by subjective assessments using self-rated (Borg perceived exertion and Standford sleepiness scales) and observer-rated scales. Although the high energy group tended to feel slightly more alert there were no differences between the group in the tests of military performance. After 4 days of sustained activity all subjects were judged to be ineffective as soldiers. The high-energy diet was well tolerated. The average loss of body-fat in the high-energy group was 1·3 kg compared with 3·1 kg in the other group, suggesting that even the high-energy group was in energy deficit. These results suggest that the major factor influencing performance in these experiments was sleep deprivation, and that the decline in performance as assessed by observers, could not be prevented by giving a high-energy diet alone.