The Navy SEAL Physical Fitness Guide - Uniformed Services ...

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