Heat Balance and Cumulative Heat Storage during Intermittent Bouts of Exercise

Kenny, Glenn P.; Dorman, Lucy E.; Webb, Paul W.; Ducharme, Michel B.; Gagnon, Daniel; Reardon, Francis D.; Hardcastle, Stephen G.; Jay, Ollie

doi:10.1249/mss.0b013e31818c97a9

Cited by 41 publications

(44 citation statements)

References 27 publications

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“…6). This response appears to be a consistent finding with intermittent exercise (10,11). Moreover, the local heat loss responses of SkBF and sweating did not differ between conditions at any of the time points compared; further supporting that intermittent exercise does not alter the body's capacity to dissipate heat.…”

Section: Whole Body and Local Heat Loss Responsessupporting

confidence: 76%

“…The rate at which total heat loss decreases during a given recovery period of intermittent exercise has been shown to remain relatively constant across multiple exercise-rest cycles and to be similar to the rate observed following a single bout of exercise (10). As such, the same rationale explained above for exercise can be applied for the recovery period, with the overall negative change in body heat content dependent on the number of recovery cycles.…”

Section: Changes In Body Heat Contentmentioning

confidence: 61%

“…These results suggest that progressive increases in evaporative heat loss, consistently observed during intermittent exercise (10,11), might be attributed to more than a "priming effect" associated with progressively greater core temperatures at the start of each exercise bout. It is possible that intermittent exercise may provide favorable peripheral and/or central adaptations in thermoeffector activity, and future studies should consider further examining this hypothesis.…”

Section: Thermal Sensitivities Of the Evaporative Heat Loss And Foreamentioning

confidence: 72%

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

Gagnon

Kenny

2011

American Journal of Physiology-Regulatory, Integrative and Comp

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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 ϫ 20-min Ex separated by 20-min recoveries (20ER); 3) 6 ϫ 10-min Ex separated by 10-min recoveries (10ER), or 4) 12 ϫ 5-min Ex separated by 5-min recoveries (5ER In contrast, the slope of the SkBF response against esophageal temperature did not significantly change from the first to the last Ex (5ER: 51 Ϯ 23 vs. 54 Ϯ 19%/°C, P ϭ 0.848; 10ER: 53 Ϯ 8 vs. 56 Ϯ 21%/°C, P ϭ 0.786; 20ER: 44 Ϯ 20 vs. 50 Ϯ 27%/°C, P ϭ 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. calorimetry; core temperature; heat stress; skin blood flow; sweat rate INTERMITTENT EXERCISE IS TYPICAL of many occupational and military activities. In most cases, the intermittent aspect of these activities is inherent to the task(s) being performed. However, intermittent exercise is also used by many health and safety industries (1, 18), as well as the US military (24), as a strategy to minimize the risk of exertional heat strain when these activities are performed in hot and/or humid environments.The benefit of exercise-rest cycles is to decrease the timeweighted average rate of metabolic heat production for a given task, which, when combined with sufficient recovery periods, should maintain core temperature below 38°C (1, 18). However, studies examining differences in core temperature between continuous and intermittent exercise have yielded conflicting results. In general, when the exercise periods are of long duration and/or performed under compensable conditions, continuous and intermittent exercise result in similar increases in core temperature (2,3,5,(13)(14)(15)22). In contrast, greater increases in core temperature have been reported during intermittent exercise consisting of short exercise-rest cycles performed under both compensable (4, 17) and uncompensable (13) conditions. Although the specific reason(s) for these discrepancies is unclear, studies that report greater core temperatures during intermittent exercise have consistently attributed this response to altered heat loss responses (4,13,17).It is surprising to note, however, that there exists relatively limited research that directly compares the control of heat loss responses between intermittent and continuous exercise, as most studies only examine core temperature responses. Ekblom et al. (4) attributed a greater increase in core temperature during intermittent exercise to a lower overall loss of body weight (i.e., evaporative heat loss), while Kraning and Gonzalez (13) implied reduced sk...

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Section: Whole Body and Local Heat Loss Responsessupporting

confidence: 76%

Section: Changes In Body Heat Contentmentioning

confidence: 61%

Section: Thermal Sensitivities Of the Evaporative Heat Loss And Foreamentioning

confidence: 72%

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

Gagnon

Kenny

2011

American Journal of Physiology-Regulatory, Integrative and Comp

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“…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. What these studies did not examine, however, is whether age-related impairments in heat loss capacity occur during exercise of short duration (i.e., 15 min) when the rate of heat storage has been shown to be the greatest (21).At the onset of exercise, the rate of metabolic heat production increases immediately and is not initially offset by an increase in the rate of heat loss, thus, giving rise to a pronounced increase in body heat storage in the first 15 min of exercise (21,35). If as previously suggested (11, 12), older adults have a delayed onset and/or reduced responsiveness of local sweating response, older individuals would likely store more heat during this period of thermal imbalance than young adults.…”

mentioning

confidence: 99%

“…At the onset of exercise, the rate of metabolic heat production increases immediately and is not initially offset by an increase in the rate of heat loss, thus, giving rise to a pronounced increase in body heat storage in the first 15 min of exercise (21,35). If as previously suggested (11, 12), older adults have a delayed onset and/or reduced responsiveness of local sweating response, older individuals would likely store more heat during this period of thermal imbalance than young adults.…”

mentioning

confidence: 99%

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

Larose

Wright

Stapleton

et al. 2013

American Journal of Physiology-Regulatory, Integrative and Comp

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Hardcastle S, Kenny GP. Whole body heat loss is reduced in older males during short bouts of intermittent exercise. Am J Physiol Regul Integr Comp Physiol 305: R619 -R629, 2013. First published July 24, 2013 doi:10.1152/ajpregu.00157.2013.-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 (HE) and changes in body heat content (⌬Hb) 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 ϫ 15 min) and recovery periods (4 ϫ 15 min) at a fixed rate of heat production (400 W) and under fixed environmental conditions (35°C/20% relative humidity). HE was lower in older males vs. young males during each exercise (Ex1: 283 Ϯ 10 vs. 332 Ϯ 11 kJ, Ex2: 334 Ϯ 10 vs. 379 Ϯ 5 kJ, Ex3: 347 Ϯ 11 vs. 392 Ϯ 5 kJ, and Ex4: 347 Ϯ 10 vs. 387 Ϯ 5 kJ, all P Ͻ 0.02), whereas HE in middle-aged males was intermediate to that measured in young and older adults (Ex1: 314 Ϯ 13, Ex2: 355 Ϯ 13, Ex3: 371 Ϯ 13, and Ex4: 365 Ϯ 8 kJ). HE was not significantly different between groups during the recovery periods. The net effect over 2 h was a greater ⌬Hb in older (267 Ϯ 33 kJ; P ϭ 0.016) and middle-aged adults (245 Ϯ 16 kJ; P ϭ 0.073) relative to younger counterparts (164 Ϯ 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. 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. What these studies did not examine, however, is whether age-related impairments in heat loss capacity occur during exercise of short duration (i.e., 15 min) when the rate of heat storage has been shown to be the greatest (21).At the onset of exercise, the rate of metabolic heat production increases immediately and is not i...

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Work–rest regimens for work in hot environments: A scoping review

Deshayes,

Hsouna,

Braham

et al. 2024

American J Industrial Med

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BackgroundTo limit exposures to occupational heat stress, leading occupational health and safety organizations recommend work–rest regimens to prevent core temperature from exceeding 38°C or increasing by ≥1°C. This scoping review aims to map existing knowledge of the effects of work–rest regimens in hot environments and to propose recommendations for future research based on identified gaps.MethodsWe performed a search of 10 databases to retrieve studies focused on work–rest regimens under hot conditions.ResultsForty‐nine articles were included, of which 35 were experimental studies. Most studies were conducted in laboratory settings, in North America (71%), on healthy young adults, with 94% of the 642 participants being males. Most studies (66%) employed a protocol duration ≤240 min (222 ± 162 min, range: 37–660) and the time‐weighted average wet‐bulb globe temperature was 27 ± 4°C (range: 18–34). The work–rest regimens implemented were those proposed by the American Conference of Governmental and Industrial Hygiene (20%), National Institute of Occupational Safety and Health (11%), or the Australian Army (3%). The remaining studies (66%) did not mention how the work–rest regimens were derived. Most studies (89%) focused on physical tasks only. Most studies (94%) reported core temperature, whereas only 22% reported physical and/or mental performance outcomes, respectively. Of the 35 experimental studies included, 77% indicated that core temperature exceeded 38°C.ConclusionsAlthough work–rest regimens are widely used, few studies have investigated their physiological effectiveness. These studies were mainly short in duration, involved mostly healthy young males, and rarely considered the effect of work–rest regimens beyond heat strain during physical exertion.

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Heat Balance and Cumulative Heat Storage during Intermittent Bouts of Exercise

Cited by 41 publications

References 27 publications

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

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

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

Work–rest regimens for work in hot environments: A scoping review

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