Physical performance and metabolic changes induced by combined prolonged exercise and different energy intakes in humans

Abstract

The purpose of this study was to evaluate the effects on physical performance of three levels of energy intake during a 5-day period of prolonged physical exercise and relative sleep deprivation. A group of 27 male soldiers were randomly assigned to three groups receiving either 1800 kcal · 24 h⁻¹ (7560 kJ, LC), 3200 kcal · 24h⁻¹ (13440 kJ, MC) or 4200 kcal-24h⁻¹ (17640 kJ, HC). They took part in a 5-day combat course (CC) of heavy and continuous physical activities, with less than 4 h sleep per day. Performance capacity was tested just before and at the end of CC. Maximal oxygen uptake ($\dot V$O_2max) was determined during an exhausting incremental exercise test on a cycle ergometer. Anaerobic performance was measured from the time during which exercise could be maintained at supra maximal loads on a cycle ergometer. After CC, the subjects receiving LC exhibited a 14% decrease in power output at exhaustion in the incremental exercise test [from 325 (SEM 8) to 278 (SEM 9) W,P < 0.001] and a significant decrease in$\dot V$O_2max of 8% [from 3.74 (SEM 0.06) to 3.45 (SEM 0.05) l · min⁻¹,P<0.05]. The remaining two experimental groups demonstrated the same mechanical and metabolic performances on days 1 and 5. Anaerobic performance was not influenced by energy intake and the field course. Blood samples were obtained at rest on days 1 and 5. At the end of CC, the data demonstrated a significant decrease in blood glucose concentrated ion (P<0.01) for LC diet only. Plasma free fatty acid, blood glycerol and β-OH butyrate were significantly increased in all groups, from day 1, but the values observed for LC were higher than those for the MC and HC diets. The concentrations of the anabolic hormones, insulin and testosterone, decreased in the three groups, the lowest values being observed in the LG group (P < 0.05). In conclusion, we found that only a severe energy deficit decreased physical performance during submaximal exercise. A moderate deficit between energy intake and expenditure did not affect performance. Supramaximal exercise did not appear to be influenced by energy intake and CC.