Heat balance and cumulative heat storage during exercise performed in the heat in physically active younger and middle-aged men

Abstract

On separate days, eight physically active younger (22 +/- 2 years) and eight highly trained middle-aged (45 +/- 4 years) men matched for physical fitness and body composition performed 90 min of semi-recumbent cycling at a constant rate of heat production (290 W) followed by 60 min of seated recovery in either a temperate (T, 30 degrees C), warm (W, 35 degrees C) or hot (H, 40 degrees C) ambient condition. Rectal temperature (T (re)) was measured continuously, while the rate of whole-body heat loss (H (L)), as well as changes in body heat content (H (b)) was measured simultaneously using direct whole-body and indirect calorimetry. No difference in H (L) was observed between age groups for all ambient conditions. Accordingly, the average H (b) during the 90-min exercise was similar for the younger (+193 +/- 52, 212 +/- 82 and +211 +/- 44 kJ for T, W and H, respectively) and middle-aged men (+192 +/- 119, +225 +/- 76 and +217 +/- 130 kJ for T, W and H, respectively). This was paralleled by a similar increase in T (re) of 0.40 +/- 0.20, 0.36 +/- 0.14 and 0.34 +/- 0.23 degrees C for T, W and H, respectively in the younger men and 0.37 +/- 0.23, 0.32 +/- 0.19 and 0.28 +/- 0.14 degrees C for T, W and H, respectively in the middle-aged men. After 60 min of recovery, H (b) was similar for the younger and the middle-aged men, respectively (-45 +/- 52 and -38 +/- 31 kJ for T; -57 +/- 78 and -40 +/- 25 kJ for W; and -32 +/- 71 and 11 +/- 96 kJ for H). End recovery T (re) remained elevated to similar levels in both the younger and middle-aged men, respectively, for each of the ambient conditions (0.24 +/- 019 and 0.18 +/- 0.18 degrees C for T; 0.25 +/- 0.11 and 0.24 +/- 0.14 degrees C for W and 0.33 +/- 0.21 and 0.33 +/- 0.13 degrees C for H). We conclude that highly trained middle-aged men demonstrate a similar capacity for heat dissipation when compared with physically active younger men.

Whole body heat loss is reduced in older males during short bouts of intermittent exercise

“…The change in body heat content was, however, similar during R2, R3, and R4 in all age groups. This study was the first to show that in accordance with results obtained in young adults (21)(22)(23), even older adults have a compromised ability to dissipate heat during postexercise recovery, irrespective of the age-related impairments in thermoregulatory function observed during exercise. Hellon et al (12) and Lind et al (26) previously reported that sweat loss during the postexercise recovery periods tended to be greater in middle-aged adults relative to young adults.…”

“…Again, it is well established that core and skin temperature measurements underestimate changes in mean body temperature (17)(18)(19) and that these measurements do not accurately represent the magnitude of residual heat storage especially in the early stages (non-steady-state period) of exercise (2,19). As demonstrated by a growing number of recent studies (6,8,21,23), the use of whole body calorimetry is the optimal way to assess changes in whole body heat loss capacity and heat storage to eliminate the potential confounding effects of regional variations in local heat loss responses and heat distribution when studying independent groups. In fact, had we only relied on measurements of local sweating and skin blood flow, as well as core/skin temperature, our conclusions would have been markedly different, that is, the capacity to dissipate heat appears unaffected by advancing age.…”

“…A growing number of recent studies have demonstrated a consistent and rapid attenuation of local and/or whole body heat loss at the onset of recovery in young adults (21)(22)(23). Kenny et al (21) demonstrated that the attenuation in heat loss occurring at the start of recovery was the same for each recovery period in young adults who engaged in three 30-min bouts of cycling separated by 15-min inactive recovery periods at an ambient air temperature of 30°C/30% RH.…”

“…evaporative heat loss; aging; calorimetry; thermal transients A NUMBER OF STUDIES HAVE EXAMINED age-related differences in thermoregulatory control during prolonged exercise (range 30 -90 min) in the heat [range: 30 -49°C/20 -60% relative humidity (RH)] (4, 11-13, 20, 23, 26, 29, 33, 34). Some studies reported no differences in thermoregulatory function (4,20,23,29,33), whereas others found significant age-related impairments in heat loss capacity (e.g., reduced local sweating rate/onset/sensitivity and/or greater increments in core and skin temperatures) (11-13, 26, 34). It is possible that these discrepancies reflect that in some studies, older adults were able to achieve heat balance, while in other studies, heat load exceeded their physiological maximal sweating capacity; hence, differences in local sweat rate and/or core temperature were evident.…”

Body temperature regulation: Sasang typology-based perspective

“…The HC of the body was defined as the energy required to increase the body temperature by 1 °C. Since the HC of fat (1.88 kJ/kg/°C) is lower than that in fat-free tissues (3.72 kJ/kg/°C), 37 200 kJ of H load after 90 minutes of intensive exercise 38 induces a temperature increment of 0.83 °C in a body of 70 kg weight with 15% fat, whereas the increment is 0.90 °C in the same weight of body with 30% fat.…”