The Navy SEAL Physical Fitness Guide 195
" Progressive symptoms of headache.
" Mental confusion or difficulty thinking.
" Visual disturbances.
" Lack of urination in excess of 8 hours.
" Excessive irregular breathing.
Other Factors that Hinder Performance at Altitude
Temperature
In general, temperature decreases 6.5° C for every 1,000 meter rise in elevation (or
11.7°F/ 3,280 ft.). At extreme altitudes (above 5,000 meters or 16,400 ft.), the combined
effects of hypoxia and hypothermia may make sustained aerobic activity extremely
difficult if not impossible.
Dry Air
Relative humidity falls as one ascends. Combined with the increased ventilatory
rate experienced at altitude, significant water loss can occur from the normally moist
respiratory passages. Cold temperatures will also cause an increase in urinary output and
together these two sources of water loss can result in rapid dehydration. Thirst cannot be
used as a “measuring stick” for hydration status and personnel must constantly replace
fluids with frequent water breaks.
Weight Loss
Most people who ascend to 13,000 feet (4,000 meters) or higher will experience a
weight loss of 3% to 5% in the first 2 weeks at altitude. Some of this loss is muscle mass
and appears to result from a decrease in the size of individual muscle fibers. There are
several reasons for this weight loss:
" Increased energy expenditure.
" Decreased appetite due to a direct effect of hypoxia and a decreased sense of
taste." Loss of body water.
" Acute Mountain Sickness - Please refer to The Navy SEAL Nutrition Guide
for dietary recommendations at altitude.