Temperature regulation during exercise in the heat: Insights for the aging athlete

Abstract

Objective: The purpose of this review is to evaluate the currently-available literature regarding the impact of both primary aging and age-related fitness on thermoregulatory function during exercise in the heat. In so doing, we aim to (1) characterize the influence of fitness in mitigating age-related declines in thermoregulation, (2) address the limitations of prior experimental approaches for investigating age-related thermoregulatory impairments, (3) examine to what extent aerobic fitness can be maintained in the aging athlete, and (4) begin to address the specific environmental conditions in which age-related impairments in thermoregulatory function may place highly active older adults at increased risk for heat-related illness and injury and/or limited performance.

Design: Mini-review.

Methods: Review and synthesis of available information.

Results: The earth's climate is warming, accompanied by a consequently greater frequency and severity of extreme heat events. At the same time, lifespan is increasing and people of all ages are staying increasingly active. Age-related impairments in thermoregulatory function are well-documented, leading to increased heat-related health risks and reduced exercise/athletic performance for older adults in hot environmental conditions. High aerobic fitness improves body temperature regulation during exercise via augmented sweating and improved cardiovascular function, including cardiac output and skin blood flow, in humans of all ages.

Conclusions: The masters athlete is better suited for exercise/heat-stress compared to his or her less fit peers. However, while age and thermoregulation in general has been studied extensively, research on the most fit older adults, including highly competitive athletes, is generally lacking.

Keywords: Body temperature; Exercise training; Heat stress; Skin blood flow; Sweating.

Figure 1.

Esophageal temperature (T_es) onset threshold for sweating responses (left y-axis) and the sweat rate (SR) thermosensitivity (i.e. slope of the increase in SR per °C rise in T_es; right y-axis) in older sedentary adults before (Pre) and after (Post) 18 weeks of exercise training (from Okazaki et al.). * P < 0.05 compared to pre-training.

Figure 2.

The onset threshold for increased skin blood flow (SkBF; Panel A^, ) and the magnitude of the SkBF response (Panel B^, ) before (Pre) and after (Post) exercise training. For each study, the comparative workload and environmental conditions are provided on the x-axis. Relative = participants exercised at the same relative intensity before and after exercise training; Absolute = participants exercised at the same absolute intensity before and after exercise training; RH = relative humidity; Tc = core temperature; %CVCmax = percentage of maximal cutaneous vascular conductance. * P < 0.05 compared to pre-training.

Figure 3.

Comparisons in core temperature responses during exercise-heat stress in older adults before (Pre) and after (Post) exercise training across studies^-. For each study, the comparative workload and environmental conditions are provided on the x-axis. Relative = participants exercised at the same relative intensity before and after exercise training; Absolute = participants exercised at the same absolute intensity before and after exercise training. * P < 0.05 compared to pre-training.

Figure 4.

The influences of aging and/or training volume and intensity on cardiovascular and thermoregulatory responses during exercise-heat stress. Aging may independently reduce heart rate (HR) and stroke volume (SV), and therefore cardiac output (CO), during exercise in athletes, resulting in impaired redistribution of blood to the cutaneous circulation during exercise-heat stress. Similarly, primary aging is associated with reduced sweat rates (SR). Reduced training volume and intensity in aging athletes likely contribute to such declines, although it is unclear to what magnitude. Although speculative, maintaining and/or increasing training volume and intensity throughout the aging process may prevent or slow the age-related declines in these responses in lifelong athletes, thereby improving thermoregulatory capacity and performance during exercise-heat stress.

Figure 5.

Adapted from Kenney 2020, depicts psychrometric limit lines for unacclimated young (solid line) and older (dashed line) women exercising at 30% $\stackrel{.}{\mathrm{V}}{\mathrm{O}}_{2\max }$. The white area between lines theoretically describes environments in which the older women are differentially adversely affected.