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comparison, and studies conducted under military conditions are necessary. In this chapter, findings from this laboratory documenting specific and nonspecific immune changes during 7 days of continuous Norwegian Ranger training will be summarized. Results of studies involving neuroendocrine modulators of immune functions will also be given.

The Ranger Training Course of the Norwegian Military Academy

The cadets of the Norwegian Military Academy take part in a Ranger training course lasting for 7 days as a part of their training program. During this course, cadets engage in continuous, physical, military activities of moderate intensity, day and night, such as marching with a rucksack, digging, and climbing. In a typical training course, activities have been found to correspond to an average of 32 percent of maximum oxygen uptake (O2max) around the clock or about 8,500 kcal/24 h. This estimate is derived from continuous heart rate recordings, data on maximum heart rate and O2max, and workload calculations and assumes a linear relationship between mean heart rate and the workload. However, increased heart rate due to dehydration or psychological stress, for example, may lead to an overestimation of the workload.

The energy supplied to each cadet during the actual training course was 0 kcal on days 1 and 2; about 700 and 950 kcal on days 3 and 4, respectively; 0 kcal on day 5; about 1,300 kcal on day 6; and 0 kcal on day 7. In one course, one group was given an extra 1,200 kcal per day per cadet in order to study the influence of reducing the calorie deficiency from about 95 to about 80 percent. No drugs, minerals, or vitamins were allowed.

Cadets were allowed no formal sleep time during the training course but got short periods of sleep between activities. On the basis of continuous heart rate recordings of individuals in a similar training course, total sleep time for Norwegian Ranger cadets was estimated to be less than 3 hours.

Immune Changes During Norwegian Ranger Training

Changes in Parameters of Immune Function
Leukocyte Numbers

The total number of blood leukocytes in cadets increased during the Norwegian Ranger training course. Maximum numbers were observed in the first blood test administered to cadets, after 12 to 18 hours of activities, and submaximal numbers were observed on the following days (Bøyum et al., 1996). Of the various blood cells, granulocytes increased about two- to threefold, with maximum numbers reached after 1 to 2 days. Monocytes increased more gradually up to twofold, with maximum numbers reached after 4



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