The Navy SEAL Physical Fitness Guide 187
Adapting to a hot environment can take one to three weeks; for physically fit
individuals, 75% of acclimation occurs during the first week of heat exposure. During this
time, sustained physical activity is more difficult and onset of fatigue occurs with minimal
physical exertion. Acclimation involves two parts:
" Cardiovascular adaptations: Changes that gradually lead to a lower
heart rate for a given workload or intensity of exercise This is the most rapid
change during acclimation to heat." Sweating: Sweating begins earlier with exertion; sweat rate is higher and
can be sustained for longer periods of time. Sweat also becomes more dilute
thus saving essential body electrolytes.Maximizing Acclimation
Maintain Aerobic Fitness
A solid base of endurance training established before you enter a hot environment
will ease the cardiovascular strain encountered during acclimation. Pre-acclimation
endurance training must be rigorous enough to raise core temperatures for acclimation to
be most beneficial. Aerobically fit individuals will retain heat acclimation longer once
removed from a hot environment than less fit personnel. Remember: Aerobic fitness will
help speed the acclimation process but is not a substitute for it.
Exercise in a Hot Environment
Any form of physical exercise will hasten acclimation. However, the intensity will
be lower than what you are used to. Refer to your local medical officer for guidance. If the
environmental conditions permit, gradually increase the intensity of exercise until you
reach the desired workload or level of training.
Maintain Adequate Hydration
Acclimation results in an earlier onset of sweating as well as an increase in the
sweating rate. These changes translate to an increased need for fluids. Acclimated
personnel may produce as much as 8 to 10 liters (8.5 to 10.5 quarts) of sweat per day. Thirst
cannot be used as a “measuring stick” for proper hydration. When training in hot
environments, a minimum of 10 to 12 quarts of water per day should be consumed, but not
more than 5 cups per hour. Drinking at frequent intervals will decrease the risk of a
potentially fatal heat stroke.
Maintaining Acclimation
Heat acclimation cannot be maintained unless there is repeated heat exposure and even if
repeated exposure is maintained, other factors may cause a loss of acclimation. Factors that
lead to loss of heat acclimation include:
" Sleep loss.
" Alcohol.