Age-related changes in hydration status during intermittent exercise in the heat

Aging is associated with a progressive decrease in thermoregulatory and cardiovascular function. When combined, these age-related changes are thought to decrease the body\u2019s ability to maintain core temperature at safe levels, during heat exposure. This can be exacerbated by reductions in hydration. However, the differences in hydration between young and older individuals during exercise in the heat and how this may affect core temperature are unclear. PURPOSE: To examine the effects of intermittent exercise in a hot/dry environment on the changes in hydration status in healthy young, middle-aged, and older males. METHODS: Five young (Mean\ub1SD; Y: 27.6\ub14.4 yrs), five middle-aged (M: 45.2\ub13.0 yrs), and five older (O: 61.2\ub14.3 yrs) healthy males, matched for weight and body composition, performed four successive bouts of 15-min cycling at a constant rate of metabolic heat production (400 W) in dry heat (35\ub0C, 20% relative humidity). Each exercise bout was separated by 15 minutes of rest with a final rest period of 60 minutes. Rectal temperature (Tre) was measured continuously. Blood and urine samples were obtained prior to exercise (PRE) and following the final recovery for the analysis of hematological parameters (e.g., hemoglobin, hematocrit) and osmolality, and urine specific gravity (USG), respectively. RESULTS: The change in Tre from PRE to the end of exercise (Y: 0.36\ub10.15, M: 0.55\ub10.21, O: 0.58\ub10.23\ub0C) and final recovery was similar between age groups. Similar hydration status measures, including changes in weight (Y: -1.2\ub10.1, M: -1.2\ub10.2, O: -1.2\ub10.1 kg), plasma (Y: -6.1\ub12.8, M: -7.8\ub12.5, O: -7.1\ub14.0%) and blood volumes (Y: -2.8\ub12.4, M: -3.8\ub11.5, O: - 4.0\ub11.8%), plasma osmolality (Y: +4.5\ub15.7, M: +3.7\ub12.6, O: +3.8\ub12.5 mOsm/kgH2O), and USG (Y: +0.006\ub10.007, M: +0.007\ub10.005, O: +0.005\ub10.007), were observed between groups. CONCLUSION: Preliminary data indicate that young, middle-aged, and older male adults show similar changes in hydration status following intermittent exercise in the heat. Support: Workplace Safety and Insurance Board of Ontario and Canada Foundation for Innovation-Leaders Opportunity FundPeer reviewed: NoNRC publication: N