Short-term hot water immersion results in substantial thermal strain and partial heat acclimation; comparisons with heat-exercise exposures

Greenfield, Andrew M.; Pereira, Felipe Gorini; Boyer, William R.; Apkarian, Marc R.; Kuennen, Matthew R.; Gillum, Trevor

doi:10.1016/j.jtherbio.2021.102898

Cited by 6 publications

(4 citation statements)

References 37 publications

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“…In that study, increases in local sweat rate were comparable between exercise‐ and spa‐based HA but sodium conservation was larger following exercise HA. The third is a recent investigation of the differences between 3 days of HWI or ExH, matched for time, in eight healthy males (Greenfield et al., 2021). No significant difference was evident between the two modes although the thermal load was larger with HWI.…”

Section: Introductionmentioning

confidence: 99%

A crossover control study of three methods of heat acclimation on the magnitude and kinetics of adaptation

Kissling

Akerman

Campbell

et al. 2022

Experimental Physiology

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New Findings What is the central question to the study?Are primary indices of heat adaptation (e.g., expansion of plasma volume and reduction in resting core temperature) differentially affected by the three major modes of short‐term heat acclimation, that is, exercise in the heat, hot water immersion and sauna? What it the main finding and its importance?The three modes elicited typical adaptations expected with short‐term heat acclimation, but these were not significantly different between modes. This comparison has not previously been made and highlights that individuals can expect similar adaptation to heat regardless of the mode used. Abstract Heat acclimation (HA) can improve heat tolerance and cardiovascular health. The mode of HA potentially impacts the magnitude and time course of adaptations, but almost no comparative data exist. We therefore investigated adaptive responses to three common modes of HA, particularly with respect to plasma volume. Within a crossover repeated‐measures design, 13 physically active participants (five female) undertook four, 5‐day HA regimes (60 min/day) in randomised order, separated by ≥4 weeks. Rectal temperature (Tre) was clamped at neutrality via 36.6°C (thermoneutral) water immersion (TWI; i.e., control condition), or raised by 1.5°C via heat stress in 40°C water, sauna (55°C, 52% relative humidity), or exercise in humid heat (40°C, 52% relative humidity; ExH). Adaptation magnitude was assessed as the pooled response across days 4–6, while kinetics was assessed via the 6‐day time series. Plasma volume expansion was similar in all heated conditions but only higher than TWI in exercise in the heat (ExH) (by 4%, P = 0.036). Approximately two‐thirds of the expansion was attained within the initial 24 h and was moderately related to that present on day 6, regardless of HA mode (r = 0.560–0.887). Expansion was mediated by conservation of both sodium and albumin content, with little evidence for these having differential roles between modes (P = 0.706 and 0.320, respectively). Resting Tre decreased by 0.1–0.3°C in all heated conditions, and systolic blood pressure decreased by 4 mmHg, but not differentially between conditions (P ≥ 0.137). In conclusion, HA mode did not substantially affect the magnitude or rate of adaptation in key resting markers of short‐term HA.

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Section: Introductionmentioning

confidence: 99%

A crossover control study of three methods of heat acclimation on the magnitude and kinetics of adaptation

Kissling

Akerman

Campbell

et al. 2022

Experimental Physiology

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“…Greenfield et al . [ 46 ] found that HWI resulted in substantial thermal strain and ‘partial’ heat acclimation for healthy participants. Only ‘partial’ acclimation could be attributed to the short exposure time which included three sessions of forty minutes in 40ºC, eliciting an average of only twenty minutes of core temperature ≥38.5ºC.…”

Section: Discussionmentioning

confidence: 99%

“…While this method utilised an exercise component, given the sedentary lifestyle of the elderly, future research involving an untrained, elderly population should investigate the HWI as a standalone intervention, like the method of Greenfield et al . [ 46 ]. Not all individuals are able to exercise, research investigating completely passive HWI protocols requires attention.…”

Section: Discussionmentioning

confidence: 99%

Short-term heat acclimation protocols for an aging population: Systematic review

et al. 2023

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Introduction Elderly and sedentary individuals are particularly vulnerable to heat related illness. Short-term heat acclimation (STHA) can decrease both the physical and mental stress imposed on individuals performing tasks in the heat. However, the feasibility and efficacy of STHA protocols in an older population remains unclear despite this population being particularly vulnerable to heat illness. The aim of this systematic review was to investigate the feasibility and efficacy of STHA protocols (≤twelve days, ≥four days) undertaken by participants over fifty years of age. Methods Academic Search Premier, CINAHL Complete, MEDLINE, APA PsycInfo, and SPORTDiscus were searched for peer reviewed articles. The search terms were; (heat* or therm*) N3 (adapt* or acclimati*) AND old* or elder* or senior* or geriatric* or aging or ageing. Only studies using primary empirical data and which included participants ≥50 years of age were eligible. Extracted data includes participant demographics (sample size, gender, age, height, weight, BMI and V.O2max), acclimation protocol details (acclimation activity, frequency, duration and outcome measures taken) and feasibility and efficacy outcomes. Results Twelve eligible studies were included in the systematic review. A total of 179 participants took part in experimentation, 96 of which were over 50 years old. Age ranged from 50 to 76. All twelve of the studies involved exercise on a cycle ergometer. Ten out of twelve protocols used a percentage of V.O2max or V.O2peak to determine the target workload, which ranged from 30% to 70%. One study-controlled workload at 6METs and one implemented an incremental cycling protocol until Tre was reached +0.9°C. Ten studies used an environmental chamber. One study compared hot water immersion (HWI) to an environmental chamber while the remaining study used a hot water perfused suit. Eight studies reported a decrease in core temperature following STHA. Five studies demonstrated post-exercise changes in sweat rates and four studies showed decreases in mean skin temperature. The differences reported in physiological markers suggest that STHA is viable in an older population. Conclusion There remains limited data on STHA in the elderly. However, the twelve studies examined suggest that STHA is feasible and efficacious in elderly individuals and may provide preventative protection to heat exposures. Current STHA protocols require specialised equipment and do not cater for individuals unable to exercise. Passive HWI may provide a pragmatic and affordable solution, however further information in this area is required.

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“…While researchers have access to various heating methods in laboratory settings, the application of heating treatment in home conditions for many potential users would only be possible via hot baths ( Kjertakov and Petersen, 2022 ). Head-out submersion in ∼40°C water is the most described hot water immersion method in the passive heating literature ( Gerrett et al, 2021 ; Greenfield et al, 2021 ; Hashiguchi et al, 2002 ; Lee et al, 2012 ; Lovell et al, 2008 ; Naumann et al, 2017 ), which typically induces a magnitude of hyperthermia (≥39°C) similar to that in the studies by Ihsan et al (2020) and Racinais et al (2017) previously cited. However, the 40°C water immersion treatment may not be the best alternative to the heating methods used in the latter two studies mainly because it usually causes unbearable discomfort after only 30–40 min from the onset of immersion with a resultant termination of the treatment ( Greenfield et al, 2021 ; Naumann et al, 2017 ).…”

Section: Introductionmentioning

confidence: 99%

Hot water immersion as a potential substitute for strength training during the COVID-19 pandemic

Kjertakov

Chandrasiri²,

Petersen³

2023

Front. Physiol.

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Short-term hot water immersion results in substantial thermal strain and partial heat acclimation; comparisons with heat-exercise exposures

Cited by 6 publications

References 37 publications

A crossover control study of three methods of heat acclimation on the magnitude and kinetics of adaptation

A crossover control study of three methods of heat acclimation on the magnitude and kinetics of adaptation

Short-term heat acclimation protocols for an aging population: Systematic review

Hot water immersion as a potential substitute for strength training during the COVID-19 pandemic

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