Effects of electrolyte and nutrient solutions on performance and metabolic balance.

Three commercial sport drinks, solutions of their individual minerals and glucose, and water were used to maintain water balances in six men during 4 h of physical activity in a 35 degrees C room. Each solution was provided for 5 consecutive days to each man during the 12-wk study. Complete mineral and water balances (including sweat losses) were conducted. Oxygen consumption and carbon dioxide production were measured during two levels of sub-maximal and during a maximal treadmill performance test. All of the solutions, including water, were equally effective in maintaining water and mineral balances, and moderate physical performance while the men were consuming an adequate all liquid diet. All of the solutions containing carbohydrates increased respiratory exchange ratios. These increases were significant during maximal performance for only two of the commercial products. These two products also produced the higher values for most of the performance evaluations, although they were not generally significantly different from values obtained while other solutions or water were consumed. The major benefit of these commercial sport drinks are their prevention of hypohydration due to an increase in voluntary fluid intakes.

Nutrition in adverse environments, 3. The metabolic effects of a restricted food intake on men working in a tropical environment.

As part of a research programme concerned with the need to lighten the load carried by soldiers engaged in long foot patrols, a field experiment was undertaken in West Malaysia. For 12 d a group of 15 men consumed 7.4 MJ/d (1770 kcal/d) whilst a control group of 14 men ate 12.9 MJ/d (3080 kcal/d); both groups expended on average about 15.8 MJ/d (3770 kcal/d). The low-energy group incurred an energy deficit of 98 MJ (23 410 kcal) with a weight loss of 3.9 kg, whereas corresponding figures for the control group were 37 MJ (8840 kcal) and 2.4 kg. Before, during and after the energy deprivation phase, assessment was made of work capacity (estimated VO2 max), vigilance and military skills but no difference was found between the groups.

Nutrition and the responses to extreme environments.

The calorie requirements of adequately clothed men living and working in a cold environment are not increased, except for the 2-5 percent increase in matabolic rate due to the "hobbling" effect of the heavy clothing. The energy requirements in the cold, as in a temperate environment, are primarily a function of body weight and level of physical activity. The discrepancies between studies of persons living in a hot environment are explainable and are primarily due to the level of protection from the heat. The increased requirements are probably due to the increased heat load imposed on the body by solar radiation and the extreme heat. The increased requirements, in all likelihood, are a combination of increased action by blood in heat transport, increased ventilation and heart rate, and increased action of the sweat glands plus the increase in metabolic rate due partially to elevation in body temperature. In view of some strong new evidence, the energy requirements are increased for individuals living and working in extremely hot environments. There is no evidence showing that modification of macro nutrient composition of the diet will enhance either heat tolerance or cold adaptation in humans. Recent studies indicate that high carbohydrate diets will improve tolerance during high altitude exposure.

Changes in pulmonary volumes with relocation to 1,600 m following acute translocation to 4,300 m.

In studies of 12 volunteer subjects, VC and ERV significantly decreased during a 3-d sojourn at 4,300 m while VE, VT, TLC, FRC and RV were elevated. Acid-base parameters showed typical changes associated with translocation to high altitude. Thus, PaO2, PaCO2 and SaO2 were immediately reduced upon translocation to 4,300 m, while the compensatory reduction in arterial HCO3- concentration was delayed temporarily by 24 h; pH, however, remained essentially unchanged throughout the sojourn. Upon relocation to 1,600 m, there was a gradual return to VC, ERV, TLC and RV to prealtitude values. FRC, on the other hand, remained elevated as did VE and VT through the third day of relocation to 1,600 m. PaCO2 and arterial HCO3- concentration showed a slight delay in returning to prealtitude values upon relocation, while the remainder of the acid-base measurements returned to prealtitude values within 24 h. The conclusion drawn from these results indicates a physiological adjustment period as long as 3 d may be required for individuals returning from a 72-h sojourn to high altitude (4,300 m).

Effects of a glucose meal on human pulmonary function at 1600-m and 4300-m altitudes.

The effects of a high-glucose meal on pulmonary function were observed in seven healthy males at medium (1,600 m) and high (4,300 m) altitude. Thirty minutes after the ingestion of 410 kcal (109.9 g cerelose) of glucose, peak serum glucose values were noted with a subsequent decrease over 3 h to below fasting levels at both elevations. At the same time, triglyceride levels continued to decline from 104.2 to 83.3 mg at 1,600 m and 103.7 to 80.5 mg/100 ml at 4,300 m, with differences being significant after 2 h. Both V-E and V-T increased in response to translocation to altitude; however, only V-T increased by 10.9% and 13.3% at 0.5 h for 1,600 m and 4,300 m, respectively. The V-o-2 increased during glucose elevation at 4300 m, while P-A-O2 remained essentially unchanged except for differences associated with translocation to altitude. A 13.9% increase was noted in D-L-CO followign glucose ingestion at 4,300 m along with a decreased triglyceride levels. The elevated D-L-CO values suggest an increase in gas exchange at the alveolar-capillary (A-c) level following the ingestion of a glucose meal for individuals transported to high altitude.

Protein metabolism during intensive physical training in the young adult.

Two groups of men consumed two levels of protein (1.4 and 2.8 g/kg body weight) during a 40-day experimental period. Physical activity and the sweat rates were fairly high during the entire experimental phase. Urinary nitrogen excretions remained fairly constant for both groups during the training and heavy physical activity periods. Nitrogen balances were positive exclusive or inclusive of the daily sweat nitrogen losses showing nitrogen retention. The essentially unchanged blood hemoglobin and serum protein levels showed that the control group was receiving an adequate protein intake to maintain nitrogen equilibrium, under conditions of fairly heavy physical acitvity. Although others may have suggested some compensatory reductions in the urinary excretion of nitrogen under conditions of profuse sweating, our data have not supported these conclusions. It appears that sweat losses of nutrients become relevant in determining requirements and will increase in importance as sweat rates are increased. The data again demonstrate that the nutrient losses during profuse sweating consitute an error that could seriously invalidate the accuracy of metabolic balance studies. In this study, although the men did increase body protein stores and muscle mass with high-protein diets, the additional body protein did not enhance physiological work performance. It is suggested that in this sutdy 100 g of protein/day was adequate for men performing fairly heavy work.