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

2013 ◽  
Vol 305 (6) ◽  
pp. R619-R629 ◽  
Author(s):  
Joanie Larose ◽  
Heather E. Wright ◽  
Jill Stapleton ◽  
Ronald J. Sigal ◽  
Pierre Boulay ◽  
...  
Keyword(s):  
Heat Loss ◽  
Heat Storage ◽  
Intermittent Exercise ◽  
Heat Content ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Middle Aged ◽  
Young Males ◽  
Body Heat ◽  
Older Males

Studies in young adults show that a greater proportion of heat is gained shortly following the start of exercise and that temporal changes in whole body heat loss during intermittent exercise have a pronounced effect on body heat storage. The consequences of short-duration intermittent exercise on heat storage with aging are unclear. We compared evaporative heat loss (H E) and changes in body heat content (ΔHb) between young (20–30 yr), middle-aged (40–45 yr), and older males (60–70 yr) of similar body mass and surface area, during successive exercise (4 × 15 min) and recovery periods (4 × 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35°C/20% relative humidity). H E was lower in older males vs. young males during each exercise (Ex1: 283 ± 10 vs. 332 ± 11 kJ, Ex2: 334 ± 10 vs. 379 ± 5 kJ, Ex3: 347 ± 11 vs. 392 ± 5 kJ, and Ex4: 347 ± 10 vs. 387 ± 5 kJ, all P < 0.02), whereas H E in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 ± 13, Ex2: 355 ± 13, Ex3: 371 ± 13, and Ex4: 365 ± 8 kJ). H E was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ΔHb in older (267 ± 33 kJ; P = 0.016) and middle-aged adults (245 ± 16 kJ; P = 0.073) relative to younger counterparts (164 ± 20 kJ). As a result of a reduced capacity to dissipate heat during exercise, which was not compensated by a sufficiently greater rate of heat loss during recovery, both older and middle-aged males had a progressively greater rate of heat storage compared with young males over 2 h of intermittent exercise.

Exercise-rest cycles do not alter local and whole body heat loss responses

2011 ◽  
Vol 300 (4) ◽  
pp. R958-R968 ◽  
Author(s):  
Daniel Gagnon ◽  
Glen P. Kenny
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Intermittent Exercise ◽  
Sweat Rate ◽  
Heat Content ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Esophageal Temperature ◽  
Direct Calorimetry ◽  
Body Heat

Previous studies have suggested that greater core temperatures during intermittent exercise (Ex) are due to attenuated sweating [upper back sweat rate (SR)] and skin blood flow (SkBF) responses. We evaluated the hypothesis that heat loss is not altered during exercise-rest cycles (ER). Ten male participants randomly performed four 120-min trials: 1) 60-min Ex and 60-min recovery (60ER); 2) 3 × 20-min Ex separated by 20-min recoveries (20ER); 3) 6 × 10-min Ex separated by 10-min recoveries (10ER), or 4) 12 × 5-min Ex separated by 5-min recoveries (5ER). Exercise was performed at a workload of 130 W at 35°C. Whole body heat exchange was determined by direct calorimetry. Core temperature, SR (by ventilated capsule), and SkBF (by laser-doppler) were measured continuously. Evaporative heat loss (EHL) progressively increased with each ER, such that it was significantly greater ( P ≤ 0.05) at the end of the last compared with the first Ex for 5ER (299 ± 39 vs. 440 ± 41 W), 10ER (425 ± 51 vs. 519 ± 45 W), and 20ER (515 ± 63 vs. 575 ± 74 W). The slope of the EHL response against esophageal temperature significantly increased from the first to the last Ex within the 10ER (376 ± 56 vs. 445 ± 89 W/°C, P ≤ 0.05) and 20ER (535 ± 85 vs. 588 ± 28 W/°C, P ≤ 0.05) conditions, but not during 5ER (296 ± 96 W/°C vs. 278 ± 95 W/°C, P = 0.237). In contrast, the slope of the SkBF response against esophageal temperature did not significantly change from the first to the last Ex (5ER: 51 ± 23 vs. 54 ± 19%/°C, P = 0.848; 10ER: 53 ± 8 vs. 56 ± 21%/°C, P = 0.786; 20ER: 44 ± 20 vs. 50 ± 27%/°C, P = 0.432). Overall, no differences in body heat content and core temperature were observed. These results suggest that altered local and whole body heat loss responses do not explain the previously observed greater core temperatures during intermittent exercise.

Do older adults experience greater thermal strain during heat waves?

2014 ◽  
Vol 39 (3) ◽  
pp. 292-298 ◽  
Author(s):  
Jill M. Stapleton ◽  
Joanie Larose ◽  
Christina Simpson ◽  
Andreas D. Flouris ◽  
Ronald J. Sigal ◽  
...  
Keyword(s):  
Older Adults ◽  
Heat Loss ◽  
Heat Waves ◽  
Thermal Strain ◽  
Heat Content ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Older Individuals ◽  
Dry Heat ◽  
Body Heat

Heat waves are the cause of many preventable deaths around the world, especially among older adults and in countries with more temperate climates. In the present study, we examined the effects of age on whole-body heat loss and heat storage during passive exposure to environmental conditions representative of the upper temperature extremes experienced in Canada. Direct and indirect calorimetry measured whole-body evaporative heat loss and dry heat exchange, as well as the change in body heat content. Twelve younger (21 ± 3 years) and 12 older (65 ± 5 years) adults with similar body weight (younger: 72.0 ± 4.4 kg; older: 80.1 ± 4.2 kg) and body surface area (younger: 1.8 ± 0.1 m2; older: 2.0 ± 0.1 m2) rested for 2 h in a hot–dry [36.5 °C, 20% relative humidity (RH)] or hot–humid (36.5 °C, 60% RH) environment. In both conditions, evaporative heat loss was not significantly different between groups (dry: p = 0.758; humid: p = 0.814). However, the rate of dry heat gain was significantly greater (by approx. 10 W) for older adults relative to younger adults during the hot–dry (p = 0.032) and hot–humid exposure (p = 0.019). Consequently, the cumulative change in body heat content after 2 h of rest was significantly greater in older adults in the hot–dry (older: 212 ± 25 kJ; younger: 131 ± 27 kJ, p = 0.018) as well as the hot–humid condition (older: 426 ± 37 kJ; younger: 317 ± 45 kJ, p = 0.037). These findings demonstrate that older individuals store more heat during short exposures to dry and humid heat, suggesting that they may experience increased levels of thermal strain in such conditions than people of younger age.

Effect of heating rate on evaporative heat loss in the microwave-exposed mouse

1982 ◽  
Vol 53 (2) ◽  
pp. 316-323 ◽  
Author(s):  
C. J. Gordon
Keyword(s):  
Body Temperature ◽  
Heat Loss ◽  
Heat Dissipation ◽  
Dew Point ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Heat Absorption ◽  
Deep Body Temperature ◽  
The Difference ◽  
Body Heat

Male CBA/J mice were administered heat loads of 0–28 J X g-1 at specific absorption rates (SARs) of either 47 or 93 W X kg-1 by exposure to 2,450-MHz microwave radiation at an ambient temperature of 30 degrees C while evaporative heat loss (EHL) was continuously monitored with dew-point hygrometry. At an SAR of 47 W X kg-1 a threshold heat load of 10.5 J X g-1 had to be exceeded before EHL increased. An approximate doubling of SAR to 93 W X kg-1 reduced the threshold to 5.2 J X g-1. Above threshold the slopes of the regression lines were 1.15 and 0.929 for the low- and high-SAR groups, respectively. Thus the difference in threshold and not slope attributes to the significant increase in EHL when mice are exposed at a high SAR (P less than 0.02). In separate experiments a SAR of 47 W X kg-1 raised the deep body temperature of anesthetized mice at a rate of 0.026 degrees C X s-1, whereas 93 W X kg-1 raised temperature at 0.049 degrees C X s-1. Hence the sensitivity of the EHL mode of heat dissipation is directly proportional to the rate of heat absorption and to the rate of rise in body temperature. These data contradict the notion that mammals have control over whole-body heat exchange only (i.e., thermoregulation) but instead indicate that the EHL system is highly responsive to the rate of heat absorption (i.e., temperature regulation).

scholarly journals Aging impairs heat loss, but when does it matter?

2015 ◽  
Vol 118 (3) ◽  
pp. 299-309 ◽  
Author(s):  
Jill M. Stapleton ◽  
Martin P. Poirier ◽  
Andreas D. Flouris ◽  
Pierre Boulay ◽  
Ronald J. Sigal ◽  
...  
Keyword(s):  
Aerobic Exercise ◽  
Surface Area ◽  
Heat Loss ◽  
Body Surface Area ◽  
Body Surface ◽  
Aerobic Fitness ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Middle Aged ◽  
Direct Calorimetry

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.

Human heat balance during postexercise recovery: separating metabolic and nonthermal effects

2008 ◽  
Vol 294 (5) ◽  
pp. R1586-R1592 ◽  
Author(s):  
Ollie Jay ◽  
Daniel Gagnon ◽  
Michel B. DuCharme ◽  
Paul Webb ◽  
Francis D. Reardon ◽  
...  
Keyword(s):  
Heat Loss ◽  
Core Temperature ◽  
Heat Production ◽  
Heat Balance ◽  
Heat Content ◽  
Total Heat ◽  
Whole Body ◽  
Active Recovery ◽  
Total Heat Loss ◽  
Body Heat

Previous studies report greater postexercise heat loss responses during active recovery relative to inactive recovery despite similar core temperatures between conditions. Differences have been ascribed to nonthermal factors influencing heat loss response control since elevations in metabolism during active recovery are assumed to be insufficient to change core temperature and modify heat loss responses. However, from a heat balance perspective, different rates of total heat loss with corresponding rates of metabolism are possible at any core temperature. Seven male volunteers cycled at 75% of V̇o2peak in the Snellen whole body air calorimeter regulated at 25.0°C, 30% relative humidity (RH), for 15 min followed by 30 min of active (AR) or inactive (IR) recovery. Relative to IR, a greater rate of metabolic heat production (Ṁ − Ẇ) during AR was paralleled by a greater rate of total heat loss (ḢL) and a greater local sweat rate, despite similar esophageal temperatures between conditions. At end-recovery, rate of body heat storage, that is, [(Ṁ − Ẇ) − ḢL] approached zero similarly in both conditions, with Ṁ − Ẇ and ḢL elevated during AR by 91 ± 26 W and 93 ± 25 W, respectively. Despite a higher Ṁ − Ẇ during AR, change in body heat content from calorimetry was similar between conditions due to a slower relative decrease in ḢL during AR, suggesting an influence of nonthermal factors. In conclusion, different levels of heat loss are possible at similar core temperatures during recovery modes of different metabolic rates. Evidence for nonthermal influences upon heat loss responses must therefore be sought after accounting for differences in heat production.

The Hexoskin physiological monitoring shirt does not impair whole-body heat loss during exercise in hot-dry conditions

2019 ◽  
Vol 44 (3) ◽  
pp. 332-335 ◽  
Author(s):  
Andrew W. D’Souza ◽  
Sean R. Notley ◽  
Erin K. Brown ◽  
Martin P. Poirier ◽  
Glen P. Kenny
Keyword(s):  
Heat Loss ◽  
Heat Dissipation ◽  
Heat Storage ◽  
Whole Body ◽  
Moderate Intensity ◽  
Physiological Strain ◽  
Direct Calorimetry ◽  
Dry Conditions ◽  
Similar Body ◽  
Body Heat

Using direct calorimetry, we determined if the Hexoskin shirt (Carré Technologies Inc., Que., Canada), a wearable device for monitoring physiological strain, would compromise whole-body heat loss and exacerbate body heat storage during moderate-intensity activity in hot-dry conditions. The shirt did not impair heat dissipation and resulted in similar body heat storage when worn alone relative to a semi-nude condition (214 vs. 211 kJ) or when worn underneath a work uniform compared with a cotton undershirt (307 vs. 318 kJ).

Body heat storage during intermittent work in hot–dry and warm–wet environments

2012 ◽  
Vol 37 (5) ◽  
pp. 840-849 ◽  
Author(s):  
Jill M. Stapleton ◽  
Heather E. Wright ◽  
Stephen G. Hardcastle ◽  
Glen P. Kenny
Keyword(s):  
Heat Exchange ◽  
Intermittent Exercise ◽  
Heat Content ◽  
Heat Rate ◽  
High Heat ◽  
Threshold Limit Value ◽  
Whole Body ◽  
Exercise Protocol ◽  
Body Heat ◽  
Intermittent Work

We examined heat balance using an American Conference of Governmental Industrial Hygienists threshold limit value allocated exercise protocol in hot–dry (HD; 46 °C, 10% relative humidity (RH)) and warm–wet (WW; 33 °C, 60% RH) environments of equivalent WBGT (29 °C) for different clothing ensembles. Whole-body heat exchange and changes in body heat content (ΔHb) were measured using simultaneous direct whole-body and indirect calorimetry. Eight males performed six 15-min cycling periods at a constant rate of metabolic heat production (360 W) interspersed by 5-min rest periods for six experimental trials: HD and WW environments for a seminude control (CON), modified work uniform (MWU, moisture permeable top and work pants), and standard work uniform (SWU, work coveralls and cotton undergarments). Whole-body evaporative and dry heat exchange, rectal temperature (Tre), and heart rate were measured continuously. The cumulative ΔHb during the 2 h intermittent exercise protocol was similar between HD and WW environments for each of the clothing ensembles (CON, 387 ± 55 vs. 435 ± 49 kJ; MWU, 485 ± 58 vs. 531 ± 61 kJ; SWU, 585 ± 74 vs. 660 ± 54 kJ, respectively). Similarly, no differences in Tre (CON, 37.67 ± 0.07 vs. 37.48 ± 0.08 °C; MWU, 37.73 ± 0.08 vs. 37.53 ± 0.09 °C; SWU, 38.01 ± 0.09 vs. 37.94 ± 0.05 °C) or heat rate (CON, 93 ± 3 vs. 84 ± 3 beats·min–1; MWU, 102 ± 5 vs. 95 ± 9 beats·min–1; SWU, 119 ± 8 vs. 110 ± 9 beats·min–1) were observed at the end of the 2 h intermittent exercise protocol in HD vs. WW environments, respectively. We showed similar levels of thermal and cardiovascular strain for intermittent work performed in high heat stress conditions of varying environmental conditions but similar WBGT.

scholarly journals Age-related differences in heat loss capacity occur under both dry and humid heat stress conditions

2014 ◽  
Vol 117 (1) ◽  
pp. 69-79 ◽  
Author(s):  
Joanie Larose ◽  
Pierre Boulay ◽  
Heather E. Wright-Beatty ◽  
Ronald J. Sigal ◽  
Stephen Hardcastle ◽  
...  
Keyword(s):  
Heat Stress ◽  
Relative Humidity ◽  
Heat Loss ◽  
Heat Dissipation ◽  
Heat Storage ◽  
Intermittent Exercise ◽  
Age Groups ◽  
Evaporative Heat Loss ◽  
Age Group ◽  
Age Related

This study examined the progression of impairments in heat dissipation as a function of age and environmental conditions. Sixty men ( n = 12 per group; 20–30, 40–44, 45–49, 50–54, and 55–70 yr) performed four intermittent exercise/recovery cycles for a duration of 2 h in dry (35°C, 20% relative humidity) and humid (35°C, 60% relative humidity) conditions. Evaporative heat loss and metabolic heat production were measured by direct and indirect calorimetry, respectively. Body heat storage was measured as the temporal summation of heat production and heat loss during the sessions. Evaporative heat loss was reduced during exercise in the humid vs. dry condition in age groups 20–30 (−17%), 40–44 (−18%), 45–49 (−21%), 50–54 (−25%), and 55–70 yr (−20%). HE fell short of being significantly different between groups in the dry condition, but was greater in age group 20–30 yr (279 ± 10 W) compared with age groups 45–49 (248 ± 8 W), 50–54 (242 ± 6 W), and 55–70 yr (240 ± 7 W) in the humid condition. As a result of a reduced rate of heat dissipation predominantly during exercise, age groups 40–70 yr stored between 60–85 and 13–38% more heat than age group 20–30 yr in the dry and humid conditions, respectively. These age-related differences in heat dissipation and heat storage were not paralleled by significant differences in local sweating and skin blood flow, or by differences in core temperature between groups. From a whole body perspective, combined heat and humidity impeded heat dissipation to a similar extent across age groups, but, more importantly, intermittent exercise in dry and humid heat stress conditions created a greater thermoregulatory challenge for middle-aged and older adults.

Blunted Effects of Elevated Serum Osmolality on Whole‐body Heat Loss and Rectal Temperature in Middle‐aged‐to‐older Men Exercising in Dry Heat

2020 ◽  
Vol 34 (S1) ◽  
pp. 1-1
Author(s):  
Robert D. Meade ◽  
Sean R. Notley ◽  
Andrew W. D'Souza ◽  
Maura M. Rutherford ◽  
Emileigh R. Binet ◽  
...  
Keyword(s):  
Heat Loss ◽  
Rectal Temperature ◽  
Elevated Serum ◽  
Older Men ◽  
Serum Osmolality ◽  
Whole Body ◽  
Middle Aged ◽  
Dry Heat ◽  
Body Heat

Is there evidence for nonthermal modulation of whole body heat loss during intermittent exercise?

2010 ◽  
Vol 299 (1) ◽  
pp. R119-R128 ◽  
Author(s):  
Glen P. Kenny ◽  
Daniel Gagnon
Keyword(s):  
Heat Loss ◽  
Intermittent Exercise ◽  
Progressive Increase ◽  
Cycle Ergometer ◽  
Lower Limbs ◽  
Whole Body ◽  
Evaporative Heat Loss ◽  
Active Recovery ◽  
Mean Body Temperature ◽  
Passive Recovery

This study compared the effect of active, passive, and inactive recoveries on whole body evaporative and dry heat loss responses during intermittent exercise at an air temperature of 30°C and a relative humidity of 20%. Nine males performed three 15-min bouts of upright seated cycling at a fixed external workload of 150 W. The exercise bouts were separated by three 15-min recoveries during which participants 1) performed loadless pedaling (active recovery), 2) had their lower limbs passively compressed with inflatable sleeves (passive recovery), or 3) remained upright seated on the cycle ergometer (inactive recovery). Combined direct and indirect calorimetry was employed to measure rates of whole body evaporative heat loss (EHL) and metabolic heat production (M-W). Mean body temperature (Tb) was calculated from esophageal and mean skin temperatures, and mean arterial pressure (MAP) was measured continuously. Active and passive recoveries both reversed the reduction in MAP associated with inactive recovery ( P ≤ 0.05). This response was paralleled by greater levels of EHL during active (207 ± 53 W) and passive recoveries (203 ± 55 W) compared with the inactive condition (168 ± 53 W, P ≤ 0.05). However, the greater rate of EHL during active recovery was paralleled by a greater M-W (194 ± 16 W) compared with inactive recovery (149 ± 27 W, P ≤ 0.001). In contrast, M-W during passive recovery (139 ± 20 W) was not significantly different from the inactive condition ( P = 0.468). Furthermore, there were no differences in Tb between inactive and passive conditions during the recovery periods ( P = 0.820). As such, passive recovery resulted in greater levels of EHL for a given change in Tb compared with inactive recovery ( P ≤ 0.05). These results strongly suggest that the progressive increase in core temperature during successive exercise/rest cycles is primarily the result of a baroreflex-mediated attenuation of postexercise whole body evaporative heat loss.

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