Effect of aerobic fitness on the relation between age and whole‐body heat exchange during exercise‐heat stress: a retrospective analysis

Abstract

New Findings What is the central question of this study?Does higher aerobic fitness, indexed by peak oxygen uptake (V̇O2normalpeak), attenuate the age‐related decline in thermoregulatory function during exercise in the heat? What is the main finding and its importance?When assessed in aerobically fit and less fit adults (V̇O2normalpeak: ∼30 vs. ∼50 ml kg−1 min−1) aged 18–66 years, a steeper decline in whole‐body total heat loss (evaporative + dry heat exchange) was observed with increasing age in less aerobically fit adults. These outcomes indicate that increased aerobic fitness may attenuate the age‐related decline in thermoregulatory function during exercise‐heat stress. Abstract Ageing is associated with decrements in cutaneous vasodilatation and sweating that attenuate whole‐body total heat loss (evaporative + dry heat exchange) during exercise‐heat stress. However, it remains uncertain whether increased aerobic fitness, as indexed by peak oxygen uptake (V̇O2normalpeak), slows that age‐related decline. To evaluate this possibility, we conducted a retrospective analysis of data from aerobically fit (n = 38; V̇O2normalpeak: (mean (SD)) 49 (4) ml kg−1 min−1) and less fit (n = 35; V̇O2normalpeak: 32 (3) ml kg−1 min−1) adults spanning a broad age range (18–65 vs. 18–66 years). Participants performed three, 30 min bouts of cycling at metabolic heat productions of 150, 200 and 250 W m−2, each separated by 15 min recovery, in dry heat (40˚C, ∼15% relative humidity). Metabolic heat production and whole‐body total heat loss were measured using indirect and direct calorimetry, respectively. Total heat loss (mean (95% CI)) declined at a rate of 5 (2, 8), 6 (3, 8) and 5 (3, 10) W m−2 per decade during exercise at metabolic heat productions of 150, 200 and 250 W m−2, respectively, in less aerobically fit individuals (all P ≤ 0.002), due primarily to reductions in evaporative heat loss. In contrast, no significant associations between age and total heat loss were observed in aerobically fit individuals (all P ≥ 0.146). As such, the slope of the age‐related reduction in total heat loss was steeper in less fit compared to fit individuals across all three exercise bouts (all P ≤ 0.029). These outcomes indicate that increased aerobic fitness attenuates the age‐related decline in exercise thermoregulation.

Aerobic fitness as a parameter of importance for labour loss in the heat

“…If typical age related reductions in VȮ 2max is observed, the differences are amplified. 25 While based on the above, an increased work capacity in the heat in fitter individuals may be obvious, what is not clear is whether with increasing heat stress there is a difference in the relative decrease in physical work capacity with heat, between workers of different aerobic fitness. Since our recent work modelled the PWC response to heat for an average group of workers, 1 the aim of this paper was to model the effect of individual VȮ 2max on the human PWC response to heat stress.…”

“…Finally, it is worth noting that aerobic fitness has also been identified as a key parameter in explaining negative ageing effects on thermoregulation. 14,[23][24][25] For example, if maximal oxygen consumption (VȮ 2max ) is maintained through regular training, there is minimal thermoregulatory differences between young and older groups. If typical age related reductions in VȮ 2max is observed, the differences are amplified.…”

Risk factors for, and prediction of, exertional heat illness in Thoroughbred racehorses at British racecourses

“…An increase in EHI up to 4 years of age may be explained by a lower level of fitness in the younger horses and an increasing workload as horses develop. In humans it is reported that age related thermoregulatory diminishments are less in fitter individuals 63,64 . The older horses could therefore, benefit from being more highly trained than the younger horses.…”

Revisiting regional variation in the age‐related reduction in sweat rate during passive heat stress

“…Third, despite possessing a lower peak oxygen consumption (V̇O 2peak ) than their younger counterparts (Table 1), the older men in the current study would still be considered as relatively well‐trained, with a V̇O 2peak in the 95th percentile of age‐ and sex‐specific normative values (Hoffmann et al, 2019). Increased aerobic fitness, as indexed by V̇O 2peak , can attenuate age‐related reductions in evaporative heat loss during exercise‐heat stress (Notley et al, 2020a), which in turn may have reduced age‐related reductions in sweat rate and the magnitude of regional variation in that decrement compared to less aerobically fit older adults. Fourth, we assessed the older and young adults in different seasons.…”