An Examination of the Influence of Age on Behavioural Thermoregulation Responses During Heat Exposure

Millyard, Alison (2023) An Examination of the Influence of Age on Behavioural Thermoregulation Responses During Heat Exposure. Doctoral thesis, Plymouth Marjon University.

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Abstract

Heat wave events are increasing in frequency and severity, resulting in many heat-related deaths in older adults. This thesis aimed to develop an understanding of how increasing age impacts thermoregulatory behaviour while exercising during heat exposure. The thesis also looked to identify what, if any, factors influence this relationship. The first study examined the relationship between age and behavioural thermoregulation during walking exercise in 35°C. Thermoregulatory behaviour was assessed by having participants walk at a self-selected speed that elicited an RPE of 13 in 22°C and 35°C conditions. The multiple regression model did not significantly predict thermoregulatory behaviour (p = 0.406, R2 = 0.156). None of the variables added statistical significance to the prediction (p > 0.05). For the male participants, the multiple regression model did significantly predict thermoregulatory behaviour (p = 0.038, R2 = 0.469). Age added statistical significance to the prediction (p = 0.005). Men age ≥60 years were less able to implement thermoregulatory behaviours than men aged <60 years (p <0.05). For the female participants, the multiple regression model did not significantly predict thermoregulatory behaviour (p = 0.906, R2 = 0.184). None of the variables added statistical significance to the prediction, p > 0.05. The second study identified factors that influence the diminished ability to reduce exercise intensity in 35°C conditions in older men. No significant differences were evident between men aged 18-35 and ≥60 years in their anthropometry, physical activity and fitness, whole body sweat rate, cardiovascular, or thermal perceptual responses. The older men did not reduce walking speed when exposed to 35°C temperatures, but the young men did. Factors influencing thermoregulatory behaviour in men aged ≥60 years need to be identified as they offer potential intervention strategies to reduce heat stress and heat-related illness risk. By using pre-warming and radiant heat lamps, the final study investigated the influence of skin and rectal temperature thermoregulatory behaviour in exercising men aged >65 years. Young and older men cycle at a fixed RPE of 13 for 30 min. Trials included a stable ambient control (22°C), changing ambient temperature (22 - 35°C), a pre-warmed stable ambient (rectal elevated 1°C, 22°C ambient), and a pre-warmed changing ambient (rectal elevated by 1°C, 22 - 35°C ambient). Young men implemented thermoregulatory behaviour in response to changing ambient conditions, whereas older men did not (thermoregulatory behaviour scores: Young CHC 1.09 ± 0.12, W+CHC 1.08 ± 0.16. Older CHC 0.94 ± 0.09, W+CHC 0.97 ± 0.07). This was despite similar skin and rectal temperature, and thermal perception responses between the two age groups. Older men are unable to adjust exercise intensity in response to changing ambient conditions, thus skin temperature is a less effective driver of thermoregulatory behaviours in older men than young men. The primary outcome of this thesis is that older (≥60 years) men do not voluntarily implement thermoregulatory behaviours while exercising in 35°C conditions, whereas younger men do. No physiological or perceptual factors could be identified to explain this inability to implement thermoregulatory behaviours. This has public health implications, as older adults, particularly men, are unable, or unwilling to voluntarily reduce their heat exposure during heat wave events. This will increase their risk of heat-related illness putting strain on health and emergency services. Public health messaging should move to educate adults aged ≥60 years of their insensitivity to heat exposure, the reduced likelihood of them implementing necessary behavioural thermoregulation strategies, and the implications if they do not voluntarily adopt cooling strategies.

Item Type:	Thesis (Doctoral)
Depositing User:	Ms Raisa Burton
Date Deposited:	20 Feb 2025 11:54
Last Modified:	20 Feb 2025 11:54
URI:	https://marjon.repository.guildhe.ac.uk/id/eprint/17941

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