Sex differences in thermophysiological responses of elderly to low-intensity exercise during uncompensable heat strain.

PURPOSE: The rising frequency of extreme heat events poses an escalating threat of heat-related illnesses and fatalities, placing an additional strain on global healthcare systems. Whether the risk of heat-related issues is sex specific, particularly among the elderly, remains uncertain. METHODS: 16 men and 15 women of similar age (69 ± 5 years) were exposed to an air temperature of 39.1 ± 0.3 °C and a relative humidity (RH) of 25.1 ± 1.9%, during 20 min of seated rest and at least 40 min of low-intensity (10 W) cycling exercise. RH was gradually increased by 2% every 5 min starting at minute 30. We measured sweat rate, heart rate, thermal sensation, and the rise in gastrointestinal temperature (Tgi) and skin temperature (Tsk). RESULTS: Tgi consistently increased from minute 30 to 60, with no significant difference between females and males (0.012 ± 0.004 °C/min vs. 0.011 ± 0.005 °C/min; p = 0.64). Similarly, Tsk increase did not differ between females and males (0.044 ± 0.007 °C/min vs. 0.038 ± 0.011 °C/min; p = 0.07). Females exhibited lower sweat rates than males (0.29 ± 0.06 vs. 0.45 ± 0.14 mg/m2/min; p < 0.001) in particular at relative humidities exceeding 30%. No sex differences in heart rate and thermal sensation were observed. CONCLUSION: Elderly females exhibit significantly lower sweat rates than their male counterparts during low-intensity exercise at ambient temperatures of 39 °C when humidity exceeds 30%. However, both elderly males and females demonstrate a comparable rise in core temperature, skin temperature, and mean body temperature, indicating similar health-related risks associated with heat exposure.

Size, weight, and expectations.

The size-weight illusion is well-known: if two equally heavy objects differ in size, the large one feels lighter than the small one. Most explanations for this illusion assume that because the information about the relevant attribute (weight itself) is unreliable, information about an irrelevant but correlated attribute (size) is used as well. If such reasoning is correct, one would expect that the illusion can be inverted: if size information is unreliable, weight information will be used to judge size. We explored whether such a weight-size illusion exists by asking participants to lift Styrofoam balls that were coated with glow in the dark paint. The balls (2 sizes, 3 weights) were lifted using a pulley system in complete darkness at 2 distances. Participants reported the size using free magnitude estimation. The visual size information was indeed unreliable: balls that were presented at a 20% larger distance were judged 15% smaller. Nevertheless, the judgments of size were not systematically affected by the 20% weight change (differences < 0.5%). We conclude that because the weight-size illusion does not exist, the mechanism behind the size-weight illusion is specific for judging heaviness.