Increased age and reduced physical activity level worsen thermoregulatory pacing behaviour in men during walking exercise in the heat.

Older adults are vulnerable to heat-related morbidity and mortality due to reduced thermoregulatory function associated with aging. The aim of this study was to examine the relationship between age and thermoregulatory behaviour during walking exercise in Control (22 °C; 40% relative humidity [RH]) and Hot (35 °C, 40% RH) conditions. Thirty-six healthy males (age 46 ± 20 (range 19-86) years; stature 177 ± 7 cm; body mass 75.7 ± 11.3 kg; BMI 24.2 ± 2.9 kg m^-2; Ʃskinfolds 33.3 ± 10.5 mm; mean ± SD) each completed two experimental trials, one in Control and one in Hot conditions. Each trial consisted of three bouts of 10 min walking at a rating of perceived exertion (RPE) of 13, interspersed with 5 min of seated rest. Thermoregulatory behaviour was assessed as the ratio between distance walked in the Control and Hot trials. Participants walked 3.8% less in the Hot (2.63 ± 0.46 km) than in the Control (2.73 ± 0.4 km) condition (t(36) = -2.38, p = 0.023, d = 0.26). Regression analysis demonstrated that age was the primary predictor of thermoregulatory pacing behaviour, explaining 23% of the variance (Std β = -0.475, p = 0.003). Including physical activity levels (PASE) increased the variance accounted to 32% (age Std β = -0.396, p = 0.011; PASE Std β = 0.319, p = 0.038). In conclusion, thermoregulatory pacing behaviour was impaired with increased age and reduced physical activity when undertaking walking exercise at a perceived exertion of 'somewhat hard' in hot ambient conditions.