Aging impairs heat loss, but when does it matter?

Abstract

Aging is associated with an attenuated physiological ability to dissipate heat. However, it remains unclear if age-related impairments in heat dissipation only occur above a certain level of heat stress and whether this response is altered by aerobic fitness. Therefore, we examined changes in whole body evaporative heat loss (HE) as determined using whole body direct calorimetry in young (n = 10; 21 ± 1 yr), untrained middle-aged (n = 10; 48 ± 5 yr), and older (n = 10; 65 ± 3 yr) males matched for body surface area. We also studied a group of trained middle-aged males (n = 10; 49 ± 5 yr) matched for body surface area with all groups and for aerobic fitness with the young group. Participants performed intermittent aerobic exercise (30-min exercise bouts separated by 15-min rest) in the heat (40°C and 15% relative humidity) at progressively greater fixed rates of heat production equal to 300 (Ex1), 400 (Ex2), and 500 (Ex3) W. Results showed that HE was significantly lower in middle-aged untrained (Ex2: 426 ± 34; and Ex3: 497 ± 17 W) and older (Ex2: 424 ± 38; and Ex3: 485 ± 44 W) compared with young (Ex2: 472 ± 42; and Ex3: 558 ± 51 W) and middle-aged trained (474 ± 21; Ex3: 552 ± 23 W) males at the end of Ex2 and Ex3 (P < 0.05). No differences among groups were observed during recovery. We conclude that impairments in HE in older and middle-aged untrained males occur at exercise-induced heat loads of ≥400 W when performed in a hot environment. These impairments in untrained middle-aged males can be minimized through regular aerobic exercise training.

Increasing age is a major risk factor for susceptibility to heat stress during physical activity

“…In fact, our findings are consistent with their results such that we only found a difference in WBHL between our groups with the lowest (<20%) and highest (>30%) body fat percentage. In addition, while Stapleton et al (2015) reported greater fitness to dampen the age-related decrease in WBHL, these differences generally were observed at a rate of metabolic heat production exceeding that used in the present study (i.e., ≥400 W). Therefore, while aging appears to be the major predictor of WBHL in otherwise healthy adults, the impact of body fat and cardiorespiratory fitness cannot be entirely discounted.…”

“…To date, research has demonstrated several factors -primarily age, cardiorespiratory fitness, and body fat -to influence wholebody heat loss (WBHL) and therefore alter susceptibility to heat stress in otherwise healthy adults (Larose et al 2013b;Stapleton et al 2015;Dervis et al 2016). Specifically, recent reports depict impairments in WBHL in physically active adults as young as 40 years of age (Larose et al 2013a(Larose et al , 2013b, although these studies isolated aging from other factors (i.e., participants were matched for body morphology and fitness).…”

“…Specifically, recent reports depict impairments in WBHL in physically active adults as young as 40 years of age (Larose et al 2013a(Larose et al , 2013b, although these studies isolated aging from other factors (i.e., participants were matched for body morphology and fitness). Cardiorespiratory fitness has yielded contradictory evidence in smaller studies (Jay 2014); however, it was found to have a critical role in attenuating the agerelated decrements in WBHL (Stapleton et al 2015). Furthermore, increased body fat has been shown to independently diminish heat dissipation (Dervis et al 2016).…”

Body Temperature Regulation During Exercise and Hyperthermia in Diabetics

“…A recent study indicated that the age-related decline in aerobic fitness was associated with the decreased whole-body evaporative heat loss during exercise in the heat [100]. Moreover, a group of trained middleaged males (~48 years) exhibited greater whole-body heat loss than an untrained group during exercise [100].…”

Age, human performance, and physical employment standards

“…Indeed, while all age groups in this study stored almost double the amount of heat when ambient humidity was increased from dry (ϳ20%) to moderately humid (60%), the middle-aged and older adults still demonstrated disproportionately greater heat storage (by ϳ38%). In addition, these differences are dependent upon metabolic heat load (i.e., intensity of physical activity or work) such that marked reductions in the physiological capacity to dissipate heat were observed at a metabolic heat load ≥400 W and ≥325 W for older males and females, respectively (Stapleton et al 2015a(Stapleton et al , 2015b. The authors also noted that the age-related impairments were influenced by fitness such that middle-aged adults with high fitness showed high heat loss (i.e., compared with their younger counterparts), while middle-aged adults with low fitness showed low heat loss (i.e., compared with their older counterparts) (Stapleton et al 2015a(Stapleton et al , 2015b.…”