Accession Number:

ADA151023

Title:

Exercise-Heat Strain during Hypohydration: Interaction with Heat Acclimation and Aerobic Fitness,

Descriptive Note:

Corporate Author:

ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA

Personal Author(s):

• Sawka,M. N.
• Pandolf,K. B.

Report Date:

1985-01-01

Pagination or Media Count:

29.0

Abstract:

During military operations in hot environments, the combined metabolic and environmental heat stress must be dissipated by the soldier to enable sustained physical exercise performance. The primary factors influencing a soldiers thermoregulatory responses during exercise-heat stress are acclimlation state, aerobic fitness and hydration level. During physical exercise in the heat, sweat output often exceeds water intake, resulting in hypohydration, which is defined as a body water deficit. Hypohydration causes a greater heat storage and reduces physical exercise performance relative to euhydration levels. The greater heat storage is attributed to a decreased sweating rate as well as a decreased cutaneous blood flow. The greater the level of hypohydration, the greater the magnitude of cardiovascular and thermoregulatory strain and reduced physical exercise performance. Rectal temperature and heart rate responses are elevated above euhydration levels by about 0.15 C and 4 bmin for each percent decrease in body weight during exercise-heat stress, respectively. Likewise, sweating rates are decreased by about 29sq mh for each percent decrease in body weight. When hypohydrated, heat acclimation decreases thermoregulatory and cardiovascular strain in a comfortable environment, but only decreases cardiovascular strain in hot environments during exercise. Originator supplied keywords include dehydration hypohydration heat acclimation aerobic fitness core temperature voluntary dehydration sweating rate heart rate.

Descriptors:

• *PHYSICAL FITNESS
• *DEHYDRATION
• *HEAT STRESS(PHYSIOLOGY)
• *EXERCISE(PHYSIOLOGY)
• *ACCLIMATIZATION
• ARMY PERSONNEL
• PERFORMANCE(HUMAN)
• TEMPERATURE CONTROL
• BODY FLUIDS
• HEART RATE
• AEROBIC PROCESSES
• BLOOD CIRCULATION
• BODY TEMPERATURE
• PERSPIRATION
• SWEAT COOLING

Subject Categories:

• Personnel Management and Labor Relations
• Stress Physiology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE