Abstract
PurposeGiven the pressing impact of global warming and its detrimental effect on the health of older populations, understanding age-related changes in thermoregulatory function is essential. Age differences in regional sweat distribution have been observed previously, but given the typically small measurement areas assessed, the development of whole body sweat maps for older individuals is required. Therefore, this study investigated age-related differences in regional sweat distribution in a hot environment (32 °C/50%RH) in young and older adults, using a body mapping approach.MethodsTechnical absorbent pads were applied to the skin of 14 young (age 24 ± 2 years) and 14 older (68 ± 5 years) males to measure regional sweat rate (RSR) at rest (30 min) and during exercise (30 min), at a fixed heat production (200 W m−2). Gastrointestinal (Tgi) and skin temperature (Tsk), heart rate, thermal sensation, and thermal comfort were also measured.ResultsWhole body sweat maps showed that despite equal heat production, healthy older males had significantly lower gross sweat loss (GSL) than the young and significantly lower RSR at almost all body regions at rest and at the hands, legs, ankles, and feet during exercise. The lower sweat loss in the older group coincided with a greater increase in Tgi and a consistently higher Tsk at the legs, despite subjectively feeling slightly cooler than younger individuals.ConclusionThese findings support the evidence of age-related deterioration in both autonomic and subjective responses in the heat and highlight the lower extremities as the most affected body region.
Highlights
Communicated by Narihiko Kondo.Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Under thermoneutral, resting conditions, heat balance is subtly maintained via vasomotor adjustments, whereby heat is dissipated at a similar rate to heat production (Parsons 2014)
As the gross sweat loss (GSL) in the two trials were slightly different, a correction was applied to standardise regional sweat rate (RSR) for this variation (Smith and Havenith 2011). This correction is based on the assumption that for a specific condition, there was a relation between RSR and GSL
The main findings of this study were that despite equal heat production, healthy older individuals had (1) significantly lower GSLs than the young group and (2) significantly lower RSR at almost all body regions during rest and at the hands, legs, ankles, and feet during exercise—accepting the hypothesis
Summary
Under thermoneutral, resting conditions, heat balance is subtly maintained via vasomotor adjustments, whereby heat is dissipated at a similar rate to heat production (Parsons 2014). During exercise and exposure to high environmental temperatures, the challenge of maintaining heat balance is greater, as the requirement for heat dissipation becomes essential to prevent overheating (Smith and Johnson 2016). Under these conditions, evaporation of sweat becomes the primary avenue of heat loss from the body, triggered by an increase in both core temperature (Tcore) and skin temperature (Tsk). Understanding the mechanisms that underpin and alter the human sweat response is important to maintain human function
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