Observations on a Mobile Arctic Force. The Health, Physical Fitness and Nutrition of Exercise "Musk Ox", February-May 1945

Human performance research for military operations in extreme cold environments

OBJECTIVES

Soldier performance in the Arctic depends on planning and training, protective equipment, and human physiological limits. The purpose of this review was to highlight the span of current research on enhancing soldier effectiveness in extreme cold and austere environments.

METHODS

The practices of seasoned soldiers who train in the Arctic and cold-dwelling natives inform performance strategies. We provide examples of research and technology that build on these concepts.

RESULTS

Examples of current performance research include evaluation of equipment and tactics such as the bioenergetics of load carriage over snow in Norwegian exercises; Canadian field monitoring of hand temperatures and freezing cold injuries for better protection of manual dexterity; and Dutch predictive modeling of cold-wet work tolerances. Healthy young men can respond to cold with a substantial thermogenic response based on US and Canadian studies on brown adipose tissue and other mechanisms of non-shivering thermogenesis; the potential advantage of greater fat insulation is offset in obese unfit subjects by a smaller thermogenic response. Current physiological studies are addressing previously unanswered problems of cold acclimation procedures, thermogenic enhancement and regulation, and modulation of sympathetic activation, all of which may further enhance cold survival and expand the performance envelope.

CONCLUSION

There is an inseparable behavioral component to soldier performance in the Arctic, and even the best equipment does not benefit soldiers who have not trained in the actual environment. Training inexperienced soldiers to performance limits may be helped with personal monitoring technologies and predictive models.

Development and biomedical testing of military operational rations

This article gives a brief history of military nutrition research in this century and reviews recent advances made through field testing. Although modern rations are nutritionally complete, ration developers are challenged to improve palatability to promote increased intakes in field training and combat settings. The principal goal for military nutritionists is to identify the optimal macronutrient mix and specific ration components that sustain a soldier's performance in the face of operational stressors such as sleep deprivation, intense physical activity, climatic extremes, and hypobaric hypoxia. Energy expenditures during typical field-training exercises average approximately 4000 kcal/day, whereas energy intakes are usually 3000 kcal/day or less when operational rations are consumed. One way to ameliorate the effects of this shortfall is to provide soldiers with a carbohydrate beverage supplement.

Megadosage of ascorbic acid in an Antarctic expedition

1. No difference in health was observed between men on megadosage of ascorbic acid and controls during the year of an Antarctic expedition. 2. All men appeared to have a satisfactory intake of ascorbic acid throughout the year. 3. There was a statistically significant decrease in excretion of ascorbic acid by men on megadosage over the year, and by the controls. 4. The decline in excretion by the control group may be explained by dietary change, but the decline in those on megadosage may be due to altered handling of ascorbic acid by the body. 5. No complications due to megadosage of ascorbic acid were observed.

Food intake in Antarctica

1. Body-weight, skinfold thickness and food intake were measured at regular intervals in twenty-five young men while on an Antarctic expedition.

2. The mean calorie intake over the year was 3600 kcal/man per day; 12.1% of these calories were supplied by protein, 39.8% by fat, and 48.1% by carbohydrate.

3. The calorie intake was equivalent to that which would be expected in a moderately active worker living in a temperate climate. The chemical composition of the diets did not differ from average values for young men in the United Kingdom.

4. There was a significant fall in food intake during the winter months, when the outside temperatures were greatly reduced and there was polar night. During this period the men were largely confined to the limits of the base hut and the levels of physical activity showed a marked fall.

5. During the year there was a gain in body-weight of 2.7 kg. Of this gain 2.5 kg occurred in the first 2 months.

6. Skinfold thickness followed the trend of the body-weights except for the April-May increment which was unaccompanied by a weight change. This dissociation could not be explained.

ELECTROLYTE METABOLISM IN THE RAT EXPOSED TO A LOW ENVIRONMENTAL TEMPERATURE

Some aspects of electrolyte metabolism in the rat exposed to a low environmental temperature have been examined. The first day of exposure at 2 °C. was accompanied by a loss of chloride. Continued exposure to cold resulted in a retention of sodium, and to a lesser extent, of potassium. Exposure to cold for 45 days (at 2 °C.) caused a sustained elevation of concentration of sodium in the plasma, with a transient increase in potassium and no change in the chloride concentration. Prolonged exposure to cold resulted in an increased blood volume and total body water content. These observations suggest that the rats acclimatized to cold have a larger proportion of actively metabolizing tissues than do comparable animals at room temperature.

ELECTROLYTE METABOLISM IN THE RAT EXPOSED TO A LOW ENVIRONMENTAL TEMPERATURE

Some aspects of electrolyte metabolism in the rat exposed to a low environmental temperature have been examined. The first day of exposure at 2 °C. was accompanied by a loss of chloride. Continued exposure to cold resulted in a retention of sodium, and to a lesser extent, of potassium. Exposure to cold for 45 days (at 2 °C.) caused a sustained elevation of concentration of sodium in the plasma, with a transient increase in potassium and no change in the chloride concentration. Prolonged exposure to cold resulted in an increased blood volume and total body water content. These observations suggest that the rats acclimatized to cold have a larger proportion of actively metabolizing tissues than do comparable animals at room temperature.