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Willmott AGB, James CA, Hayes M, Maxwell NS, Roberts J, Gibson OR. The reliability of a portable steam sauna pod for the whole-body passive heating of humans. J Therm Biol 2023; 118:103743. [PMID: 37979477 DOI: 10.1016/j.jtherbio.2023.103743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2023] [Revised: 10/16/2023] [Accepted: 10/17/2023] [Indexed: 11/20/2023]
Abstract
INTRODUCTION Passive heating is receiving increasing attention within human performance and health contexts. A low-cost, portable steam sauna pod may offer an additional tool for those seeking to manipulate physiological (cardiovascular, thermoregulatory and sudomotor) and perceptual responses for improving sporting or health profiles. This study aimed to 1) report the different levels of heat stress and determine the pods' inter-unit reliability, and 2) quantify the reliability of physiological and perceptual responses to passive heating. METHOD In part 1, five pods were assessed for temperature and relative humidity (RH) every 5 min across 70 min of heating for each of the 9 settings. In part 2, twelve males (age: 24 ± 4 years) completed two 60 min trials of passive heating (3 × 20 min at 44 °C/99% RH, separated by 1 week). Heart rate (HR), rectal (Trectal) and tympanic temperature (Ttympanic) were recorded every 5 min, thermal comfort (Tcomfort) and sensation (Tsensation) every 10 min, mean arterial pressure (MAP) at each break period and sweat rate (SR) after exiting the pod. RESULTS In part 1, setting 9 provided the highest temperature (44.3 ± 0.2 °C) and longest time RH remained stable at 99% (51±7 min). Inter-unit reliability data demonstrated agreement between pods for settings 5-9 (intra-class correlation [ICC] >0.9), but not for settings 1-4 (ICC <0.9). In part 2, between-visits, high correlations, and low typical error of measurement (TEM) and coefficient of variation (CV) were found for Trectal, HR, MAP, SR, and Tcomfort, but not for Ttympanic or Tsensation. A peak Trectal of 38.09 ± 0.30 °C, HR of 124 ± 15 b min-1 and a sweat loss of 0.73 ± 0.33 L were reported. No between-visit differences (p > 0.05) were observed for Trectal, Ttympanic, Tsensation or Tcomfort, however HR (+3 b.min-1) and MAP (+4 mmHg) were greater in visit 1 vs. 2 (p < 0.05). CONCLUSION Portable steam sauna pods generate reliable heat stress between-units. The highest setting (44 °C/99% RH) also provides reliable but modest adjustments in physiological and perceptual responses.
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Affiliation(s)
- A G B Willmott
- Cambridge Centre for Sport and Exercise Sciences (CCSES), Anglia Ruskin University, Cambridge, UK; Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.
| | - C A James
- Hong Kong Sports Institute (HKSI), Hong Kong; Department of Sport, Physical Education and Health, Hong Kong Baptist University. Kowloon Tong, Hong Kong
| | - M Hayes
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK
| | - N S Maxwell
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK
| | - J Roberts
- Cambridge Centre for Sport and Exercise Sciences (CCSES), Anglia Ruskin University, Cambridge, UK
| | - O R Gibson
- Centre for Physical Activity in Health and Disease (CHPAD), Division of Sport, Health and Exercise Sciences, Brunel University London, Uxbridge, UK
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Abstract
INTRODUCTION The aim of this study was to compare the effectiveness of exercise versus hot water immersion heat reacclimation (HRA) protocols. METHODS Twenty-four participants completed a heat stress test (HST; 33°C, 65% RH), which involved cycling at a power output equivalent to 1.5 W·kg-1 for 35 min whereby thermophysiological variables were measured. This was followed by a graded exercise test until exhaustion. HST1 was before a 10-d controlled hyperthermia (CH) heat acclimation (HA) protocol and HST2 immediately after. Participants completed HST3 after a 28-d decay period without heat exposure and were then separated into three groups to complete a 5-d HRA protocol: a control group (CH-CON, n = 8); a hot water immersion group (CH-HWI, n = 8), and a controlled hyperthermia group (CH-CH, n = 8). This was followed by HST4. RESULTS Compared with HST1, time to exhaustion and thermal comfort improved; resting rectal temperature (Tre), end of exercise Tre, and mean skin temperature (Tsk) were lower; and whole body sweat rate (WBSR) was greater in HST2 for all groups (P < 0.05). After a 28-d decay, only WBSR, time to exhaustion, and mean Tsk returned to pre-HA values. Of these decayed variables, only WBSR was reinstated after HRA; the improvement was observed in both the CH-CH and the CH-HWI groups (P < 0.05). CONCLUSION The data suggest that HRA protocol may not be necessary for cardiovascular and thermal adaptations within a 28-d decay period, as long as a 10-d CH-HA protocol has successfully induced these physiological adaptations. For sweat adaptations, a 5-d CH or HWI-HRA protocol can reinstate the lost adaptations.
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Affiliation(s)
- Nicola Gerrett
- Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, THE NETHERLANDS
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Osborne JO, Stewart IB, Borg DN, Beagley KW, Buhmann RL, Minett GM. Short-term heat acclimation preserves knee extensor torque but does not improve 20 km self-paced cycling performance in the heat. Eur J Appl Physiol 2021; 121:2761-2772. [PMID: 34148124 PMCID: PMC8416835 DOI: 10.1007/s00421-021-04744-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Accepted: 06/10/2021] [Indexed: 01/16/2023]
Abstract
Purpose This study investigated the effect of 5 days of heat acclimation training on neuromuscular function, intestinal damage, and 20 km cycling (20TT) performance in the heat. Methods Eight recreationally trained males completed two 5-day training blocks (cycling 60 min day−1 at 50% peak power output) in a counter-balanced, cross-over design, with a 20TT completed before and after each block. Training was conducted in hot (HA: 34.9 ± 0.7 °C, 53 ± 4% relative humidity) or temperate (CON: 22.2 ± 2.6 °C, 65 ± 8% relative humidity) environment. All 20TTs were completed in the heat (35.1 ± 0.5 °C, 51 ± 4% relative humidity). Neuromuscular assessment of knee extensors (5 × 5 s maximum voluntary contraction; MVC) was completed before and after each 20TT and on the first and last days of each training block. Results MVC torque was statistically higher after 5 days of HA training compared to CON (mean difference = 14 N m [95% confidence interval; 6, 23]; p < 0.001; d = 0.77). However, 20TT performance after 5 days of HA training was not statistically different to CON, with a between-conditions mean difference in the completion time of 68 s [95% confidence interval; − 9, 145] (p = 0.076; d = 0.35). Conclusion Short-term heat acclimation training may increase knee extensor strength without changes in central fatigue or intestinal damage. Nevertheless, it is insufficient to improve 20 km self-paced cycling performance in the heat compared to workload-matched training in a temperate environment. These data suggest that recreationally trained athletes gain no worthwhile performance advantage from short-term heat-training before competing in the heat. Supplementary Information The online version contains supplementary material available at 10.1007/s00421-021-04744-y.
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Affiliation(s)
- John O Osborne
- School of Sport Sciences, UiT The Arctic University of Norway, Tromsø, Norway. .,School of Exercise and Nutrition Sciences, Queensland University of Technology (QUT), Brisbane, Australia. .,Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Australia.
| | - Ian B Stewart
- School of Exercise and Nutrition Sciences, Queensland University of Technology (QUT), Brisbane, Australia.,Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Australia
| | - David N Borg
- School of Exercise and Nutrition Sciences, Queensland University of Technology (QUT), Brisbane, Australia.,Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Australia.,The Hopkins Centre, Menzies Health Institute Queensland, Griffith University, Brisbane, Australia
| | - Kenneth W Beagley
- Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Australia.,School of Biomedical Sciences, Queensland University of Technology (QUT), Brisbane, Australia
| | - Robert L Buhmann
- School of Health and Sport Sciences, University of the Sunshine Coast, Maroochydore, Australia
| | - Geoffrey M Minett
- School of Exercise and Nutrition Sciences, Queensland University of Technology (QUT), Brisbane, Australia.,Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, Australia
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Callovini A, Fornasiero A, Savoldelli A, Stella F, Low DA, Pellegrini B, Schena F, Bortolan L. Effects of three-exercise sessions in the heat on endurance cycling performance. J Therm Biol 2021; 98:102925. [PMID: 34016347 DOI: 10.1016/j.jtherbio.2021.102925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 03/22/2021] [Accepted: 03/27/2021] [Indexed: 11/16/2022]
Abstract
PURPOSE To investigate the effects of a very short-term acclimation protocol (VSTAP) on performance, physiological and perceptual responses to exercise in the heat. METHODS 12 trained male cyclists (age 31.2 ± 7; weight 71.3 ± 7 kg, VO2max: 58.4 ± 3.7 mL/kg/min) randomly performed two Time to Exhaustion Tests (TTE) at 75% of normothermic peak power output (PPO), one in normothermia (N,18°C-50% RH) and one in the heat (H,35°C-50% RH), before and after a VSTAP intervention, consisting of 3 days-90 min exercise (10min at 30% of PPO+80 min at 50% of PPO) in H (≈4.5h of heat exposure). Performance time of TTEs and physiological and perceptual variables of both TTEs and training sessions (T1, T2 and T3) were evaluated. RESULTS Magnitude Based Inferences (MBI) revealed 92/6/1% and 62/27/11% chances of positive/trivial/negative effects of VSTAP of improving performance in H (+17%) and in N (+9%), respectively. Heart Rate (HR) decreased from T1 to T3 (p < 0.001) and T2 to T3 (p < 0.001), whereas Tympanic Temperature (TyT) decreased from T1 to T2 (p = 0.047) and from T1 to T3 (p = 0.007). Furthermore, despite the increased tolerance to target Power Output (PO) throughout training sessions, RPE decreased from T1 to T3 (p = 0.032). CONCLUSIONS The VSTAP determined meaningful physiological (i.e. decreased HR and TyT) and perceptual (i.e. decreased RPE) adaptations to submaximal exercise. Furthermore, showing good chances to improve performance in the heat, it represents a valid acclimation strategy to be implemented when no longer acclimation period is possible. Finally, no cross-over effect of the VSTAP on performance in temperate conditions was detected.
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Affiliation(s)
- Alexa Callovini
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy; Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
| | - Alessandro Fornasiero
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy; Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
| | - Aldo Savoldelli
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy; Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
| | - Federico Stella
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy.
| | - David A Low
- Liverpool John Moores University, Research Institute for Sport and Exercise Sciences (RISES), Liverpool, United Kingdom.
| | - Barbara Pellegrini
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy; Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
| | - Federico Schena
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy; Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
| | - Lorenzo Bortolan
- CeRiSM, Sport Mountain and Health Research Centre, University of Verona, Rovereto, Italy; Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy.
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Greenfield AM, Pereira FG, Boyer WR, Apkarian MR, Kuennen MR, Gillum TL. Short-term hot water immersion results in substantial thermal strain and partial heat acclimation; comparisons with heat-exercise exposures. J Therm Biol 2021; 97:102898. [PMID: 33863451 DOI: 10.1016/j.jtherbio.2021.102898] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 01/30/2021] [Accepted: 02/19/2021] [Indexed: 10/22/2022]
Abstract
OBJECTIVE To examine the effectiveness of hot water immersion (HWI) as a heat acclimation strategy in comparison to time and temperature matched, exercise-heat acclimation (EHA). METHODS 8 males performed heat stress tests (HST) (45 min of cycling at 50% of VO2max in 40 °C, 40% RH) before and after heat acclimation sessions. Acclimation sessions were either three consecutive bouts of HWI (40 min of submersion at 40 °C) or EHA (40 min of cycling at 50% VO2max in 40 °C, 40% RH). RESULTS Average change in tympanic temperature (TTympanic) was significantly higher following HWI (2.1 °C ± 0.4) compared to EHA (1.5 °C ± 0.4) (P < 0.05). Decreases in peak heart rate (HR) (HWI: -10 bpm ± 8; EHA: -6 ± 7), average HR (-7 bpm ± 6; -3 ± 4), and average core temperature (-0.4 °C ± 0.3; -0.2 ± 0.4) were evident following acclimation (P < 0.05), but not different between interventions (P > 0.05). Peak rate of perceived exertion (RPEPeak) decreased for HWI and EHA (P < 0.05). Peak thermal sensation (TSPeak) decreased following HWI (P < 0.05) but was not different between interventions (P > 0.05). Plasma volume increased in both intervention groups (HWI: 5.9% ± 5.1; EHA: 5.4% ± 3.7) but was not statistically different (P > 0.05). CONCLUSION HWI induced significantly greater thermal strain compared to EHA at equivalent temperatures during time-matched exposures. However, the greater degree of thermal strain did not result in between intervention differences for cardiovascular, thermoregulatory, or perceptual variables. Findings suggest three HWI sessions may be a potential means to lower HR, TCore, and perceptual strain during exercise in the heat.
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Affiliation(s)
- Andrew M Greenfield
- Department of Kinesiology, California Baptist University, 8432 Magnolia Ave, Riverside, CA, 92504, USA.
| | - Felipe Gorini Pereira
- Department of Kinesiology, California Baptist University, 8432 Magnolia Ave, Riverside, CA, 92504, USA.
| | - William R Boyer
- Department of Kinesiology, California Baptist University, 8432 Magnolia Ave, Riverside, CA, 92504, USA.
| | - Marc R Apkarian
- Department of Kinesiology and Health Science, Biola University, 13800 Biola Ave, La Mirada, CA, 90639, USA.
| | - Matthew R Kuennen
- Department of Exercise Science, High Point University, 1 N. University Parkway, High Point, NC, 27268, USA.
| | - Trevor L Gillum
- Department of Kinesiology, California Baptist University, 8432 Magnolia Ave, Riverside, CA, 92504, USA.
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Perceptual and Physiological Responses to Carbohydrate and Menthol Mouth-Swilling Solutions: A Repeated Measures Cross-Over Preliminary Trial. BEVERAGES 2021. [DOI: 10.3390/beverages7010009] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Carbohydrate and menthol mouth-swilling have been used to enhance exercise performance in the heat. However, these strategies differ in mechanism and subjective experience. Participants (n = 12) sat for 60 min in hot conditions (35 °C; 15 ± 2%) following a 15 min control period, during which the participants undertook three 15 min testing blocks. A randomised swill (carbohydrate; menthol; water) was administered per testing block (one swill every three minutes within each block). Heart rate, tympanic temperature, thermal comfort, thermal sensation and thirst were recorded every three minutes. Data were analysed by ANOVA, with carbohydrate intake controlled for via ANCOVA. Small elevations in heart rate were observed after carbohydrate (ES: 0.22 ± 90% CI: −0.09–0.52) and water swilling (0.26; −0.04–0.54). Menthol showed small improvements in thermal comfort relative to carbohydrate (−0.33; −0.63–0.03) and water (−0.40; from −0.70 to −0.10), and induced moderate reductions in thermal sensation (−0.71; from −1.01 to −0.40 and −0.66; from −0.97 to −0.35, respectively). Menthol reduced thirst by a small to moderate extent. These effects persisted when controlling for dietary carbohydrate intake. Carbohydrate and water may elevate heart rate, whereas menthol elicits small improvements in thermal comfort, moderately improves thermal sensation and may mitigate thirst; these effects persist when dietary carbohydrate intake is controlled for.
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Ashworth ET, Cotter JD, Kilding AE. Methods for improving thermal tolerance in military personnel prior to deployment. Mil Med Res 2020; 7:58. [PMID: 33248459 PMCID: PMC7700709 DOI: 10.1186/s40779-020-00287-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 11/10/2020] [Indexed: 12/16/2022] Open
Abstract
Acute exposure to heat, such as that experienced by people arriving into a hotter or more humid environment, can compromise physical and cognitive performance as well as health. In military contexts heat stress is exacerbated by the combination of protective clothing, carried loads, and unique activity profiles, making them susceptible to heat illnesses. As the operational environment is dynamic and unpredictable, strategies to minimize the effects of heat should be planned and conducted prior to deployment. This review explores how heat acclimation (HA) prior to deployment may attenuate the effects of heat by initiating physiological and behavioural adaptations to more efficiently and effectively protect thermal homeostasis, thereby improving performance and reducing heat illness risk. HA usually requires access to heat chamber facilities and takes weeks to conduct, which can often make it impractical and infeasible, especially if there are other training requirements and expectations. Recent research in athletic populations has produced protocols that are more feasible and accessible by reducing the time taken to induce adaptations, as well as exploring new methods such as passive HA. These protocols use shorter HA periods or minimise additional training requirements respectively, while still invoking key physiological adaptations, such as lowered core temperature, reduced heart rate and increased sweat rate at a given intensity. For deployments of special units at short notice (< 1 day) it might be optimal to use heat re-acclimation to maintain an elevated baseline of heat tolerance for long periods in anticipation of such an event. Methods practical for military groups are yet to be fully understood, therefore further investigation into the effectiveness of HA methods is required to establish the most effective and feasible approach to implement them within military groups.
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Affiliation(s)
- Edward Tom Ashworth
- Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, 17 Antares Place, Rosedale, Auckland, 0632 New Zealand
| | - James David Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, Otago 9016 New Zealand
| | - Andrew Edward Kilding
- Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, 17 Antares Place, Rosedale, Auckland, 0632 New Zealand
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Ko Y, Kang J, Seol SH, Lee JY. Effectiveness of skin-heating using a water-perfused suit as passive and post-exercise heat acclimation strategies. J Therm Biol 2020; 93:102703. [PMID: 33077124 DOI: 10.1016/j.jtherbio.2020.102703] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2020] [Revised: 08/14/2020] [Accepted: 08/15/2020] [Indexed: 11/26/2022]
Abstract
The purpose of the present study was to evaluate the effectiveness of passive and post-exercise heat acclimation strategies through directly heating the skin with a water-perfused suit. Nineteen young males participated in the heat acclimation (HA) protocols for 10 days, which were conducted at an air temperature of 33oC with 60%RH. The exercise-only condition (N = 6) conducted 1-h treadmill walking (6 km·h-1) followed by 1-h rest. The post-exercise passive-heating condition (N = 6) wore the suit (inflow water temperature 44.2oC) for 1-h after 1-h walking. The passive-heating condition (N = 7) donned the suit for 2 h. Heat tolerance tests (leg immersion in 42oC water for 60 min) were conducted before and after the training to evaluate changes due to the 10-day intervention. Reflecting that suit-wearing for 10 days as both passive and post-exercise HA strategies can effectively induce adaptive changes, significant interaction effects appeared in: increase or decrease in mean skin temperature (P < 0.05) and elevation in whole-body sweat rate (P < 0.05). Reduction in rectal temperature (P < 0.05) and blood pressure (P < 0.05) were found most prominently in the passive-heating condition. These results indicate that this new method of heat acclimation training, donning a skin-heating water-perfused suit, can generate thermoregulatory benefits. The passive HA intervention could be applied to individuals for whom doing exercise regularly are not feasible.
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Affiliation(s)
- Yelin Ko
- College of Human Ecology, Seoul National University, South Korea
| | - Juho Kang
- College of Human Ecology, Seoul National University, South Korea; Department of Physical Education, Seoul National University, South Korea
| | - Seon-Hong Seol
- College of Human Ecology, Seoul National University, South Korea
| | - Joo-Young Lee
- College of Human Ecology, Seoul National University, South Korea; Research Institute of Human Ecology, Seoul National University, South Korea.
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Foster J, Hodder SG, Lloyd AB, Havenith G. Individual Responses to Heat Stress: Implications for Hyperthermia and Physical Work Capacity. Front Physiol 2020; 11:541483. [PMID: 33013476 PMCID: PMC7516259 DOI: 10.3389/fphys.2020.541483] [Citation(s) in RCA: 55] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 08/18/2020] [Indexed: 12/11/2022] Open
Abstract
Background Extreme heat events are increasing in frequency, severity, and duration. It is well known that heat stress can have a negative impact on occupational health and productivity, particularly during physical work. However, there are no up-to-date reviews on how vulnerability to heat changes as a function of individual characteristics in relation to the risk of hyperthermia and work capacity loss. The objective of this narrative review is to examine the role of individual characteristics on the human heat stress response, specifically in relation to hyperthermia risk and productivity loss in hot workplaces. Finally, we aim to generate practical guidance for industrial hygienists considering our findings. Factors included in the analysis were body mass, body surface area to mass ratio, body fat, aerobic fitness and training, heat adaptation, aging, sex, and chronic health conditions. Findings We found the relevance of any factor to be dynamic, based on the work-type (fixed pace or relative to fitness level), work intensity (low, moderate, or heavy work), climate type (humidity, clothing vapor resistance), and variable of interest (risk of hyperthermia or likelihood of productivity loss). Heat adaptation, high aerobic fitness, and having a large body mass are the most protective factors during heat exposure. Primary detrimental factors include low fitness, low body mass, and lack of heat adaptation. Aging beyond 50 years, being female, and diabetes are less impactful negative factors, since their independent effect is quite small in well matched participants. Skin surface area to mass ratio, body composition, hypertension, and cardiovascular disease are not strong independent predictors of the heat stress response. Conclusion Understanding how individual factors impact responses to heat stress is necessary for the prediction of heat wave impacts on occupational health and work capacity. The recommendations provided in this report could be utilized to help curtail hyperthermia risk and productivity losses induced by heat.
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Affiliation(s)
- Josh Foster
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Simon G Hodder
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - Alex B Lloyd
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
| | - George Havenith
- Environmental Ergonomics Research Centre, Loughborough University, Loughborough, United Kingdom
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Benjamin CL, Sekiguchi Y, Fry LA, Casa DJ. Performance Changes Following Heat Acclimation and the Factors That Influence These Changes: Meta-Analysis and Meta-Regression. Front Physiol 2019; 10:1448. [PMID: 31827444 PMCID: PMC6890862 DOI: 10.3389/fphys.2019.01448] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 11/08/2019] [Indexed: 11/17/2022] Open
Abstract
Heat acclimation (HA) is the process of intentional and consistent exercise in the heat that results in positive physiological adaptations, which can improve exercise performance both in the heat and thermoneutral conditions. Previous research has indicated the many performance benefits of HA, however, a meta-analysis examining the magnitude of different types of performance improvement is absent. Additionally, there are several methodological discrepancies in the literature that could lead to increased variability in performance improvement following HA and no previous study has examined the impact of moderators on performance improvement following HA. Therefore, the aim of this study was two-fold; (1) to perform a meta-analysis to examine the magnitude of changes in performance following HA in maximal oxygen consumption (VO2max), time to exhaustion, time trial, mean power, and peak power tests; (2) to determine the impact of moderators on results of these performance tests. Thirty-five studies met the inclusion/exclusion criteria with 23 studies that assessed VO2max (n = 204), 24 studies that assessed time to exhaustion (n = 232), 10 studies that performed time trials (n = 101), 7 studies that assessed mean power (n = 67), and 10 papers that assessed peak power (n = 88). Data are reported as Hedge's g effect size (ES), and 95% confidence intervals (95% CI). Statistical significance was set to p < 0.05, a priori. The magnitude of change following HA was analyzed, with time to exhaustion demonstrating the largest performance enhancement (ES [95% CI], 0.86 [0.71, 1.01]), followed by time trial (0.49 [0.26, 0.71]), mean power (0.37 [0.05, 0.68]), VO2max (0.30 [0.07, 0.53]), and peak power (0.29 [0.09, 0.48]) (p < 0.05). When all of the covariates were analyzed as individual models, induction method, fitness level, heat index in time to exhaustion (coefficient [95% CI]; induction method, -0.69 [-1.01, -0.37], p < 0.001; fitness level, 0.04 [0.02, 0.06], p < 0.001; heat index, 0.04 [0.02, 0.07], p < 0.0001) and induction length in mean power (coefficient [95% CI]; induction length 0.15 [0.05, 0.25], p = 0.002) significantly impacted the magnitude of change. Sport scientists and researchers can use the findings from this meta-analysis to customize HA induction. For time to exhaustion improvements, HA implementation should focus on induction method and baseline fitness, while the training and recovery balance could lead to optimal time trial performance.
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Affiliation(s)
- Courteney Leigh Benjamin
- Department of Kinesiology, Korey Stringer Institute, University of Connecticut, Storrs, CT, United States
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Gibson OR, James CA, Mee JA, Willmott AG, Turner G, Hayes M, Maxwell NS. Heat alleviation strategies for athletic performance: A review and practitioner guidelines. Temperature (Austin) 2019; 7:3-36. [PMID: 32166103 PMCID: PMC7053966 DOI: 10.1080/23328940.2019.1666624] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Revised: 09/06/2019] [Accepted: 09/08/2019] [Indexed: 12/19/2022] Open
Abstract
International competition inevitably presents logistical challenges for athletes. Events such as the Tokyo 2020 Olympic Games require further consideration given historical climate data suggest athletes will experience significant heat stress. Given the expected climate, athletes face major challenges to health and performance. With this in mind, heat alleviation strategies should be a fundamental consideration. This review provides a focused perspective of the relevant literature describing how practitioners can structure male and female athlete preparations for performance in hot, humid conditions. Whilst scientific literature commonly describes experimental work, with a primary focus on maximizing magnitudes of adaptive responses, this may sacrifice ecological validity, particularly for athletes whom must balance logistical considerations aligned with integrating environmental preparation around training, tapering and travel plans. Additionally, opportunities for sophisticated interventions may not be possible in the constrained environment of the athlete village or event arenas. This review therefore takes knowledge gained from robust experimental work, interprets it and provides direction on how practitioners/coaches can optimize their athletes' heat alleviation strategies. This review identifies two distinct heat alleviation themes that should be considered to form an individualized strategy for the athlete to enhance thermoregulatory/performance physiology. First, chronic heat alleviation techniques are outlined, these describe interventions such as heat acclimation, which are implemented pre, during and post-training to prepare for the increased heat stress. Second, acute heat alleviation techniques that are implemented immediately prior to, and sometimes during the event are discussed. Abbreviations: CWI: Cold water immersion; HA: Heat acclimation; HR: Heart rate; HSP: Heat shock protein; HWI: Hot water immersion; LTHA: Long-term heat acclimation; MTHA: Medium-term heat acclimation; ODHA: Once-daily heat acclimation; RH: Relative humidity; RPE: Rating of perceived exertion; STHA: Short-term heat acclimation; TCORE: Core temperature; TDHA: Twice-daily heat acclimation; TS: Thermal sensation; TSKIN: Skin temperature; V̇O2max: Maximal oxygen uptake; WGBT: Wet bulb globe temperature.
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Affiliation(s)
- Oliver R. Gibson
- Centre for Human Performance, Exercise and Rehabilitation (CHPER), Division of Sport, Health and Exercise Sciences, Brunel University London, Uxbridge, UK
| | - Carl A. James
- Institut Sukan Negara (National Sports Institute), Kuala Lumpur, Malaysia
| | - Jessica A. Mee
- School of Sport and Exercise Sciences, University of Worcester, Worcester, UK
| | - Ashley G.B. Willmott
- Cambridge Centre for Sport and Exercise Sciences, Anglia Ruskin University, Cambridge, UK
| | - Gareth Turner
- Bisham Abbey National High-Performance Centre, English Institute of Sport, EIS Performance Centre, Marlow, UK
| | - Mark Hayes
- Environmental Extremes Laboratory, School of Sport and Service Management, University of Brighton, Eastbourne, UK
| | - Neil S. Maxwell
- Environmental Extremes Laboratory, School of Sport and Service Management, University of Brighton, Eastbourne, UK
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Kirby NV, Lucas SJE, Lucas RAI. Nine-, but Not Four-Days Heat Acclimation Improves Self-Paced Endurance Performance in Females. Front Physiol 2019; 10:539. [PMID: 31156449 PMCID: PMC6532023 DOI: 10.3389/fphys.2019.00539] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 04/16/2019] [Indexed: 11/13/2022] Open
Abstract
Although emerging as a cost and time efficient way to prepare for competition in the heat, recent evidence indicates that "short-term" heat acclimation (<7 days) may not be sufficient for females to adapt to repeated heat stress. Furthermore, self-paced performance following either short-term, or longer (>7 days) heat acclimation has not been examined in a female cohort. Therefore, the aim of this study was to investigate self-paced endurance performance in hot conditions following 4- and 9-days of a high-intensity isothermic heat acclimation protocol in a female cohort. Eight female endurance athletes (mean ± SD, age 27 ± 5 years, mass 61 ± 5 kg, VO2peak 47 ± 6 ml⋅kg⋅min-1) performed 15-min self-paced cycling time trials in hot conditions (35°C, 30%RH) before (HTT1), and after 4-days (HTT2), and 9-days (HTT3) isothermic heat acclimation (HA, with power output manipulated to increase and maintain rectal temperature (T rec) at ∼38.5°C for 90-min cycling in 40°C, 30%RH) with permissive dehydration. There were no significant changes in distance cycled (p = 0.47), mean power output (p = 0.55) or cycling speed (p = 0.44) following 4-days HA (i.e., from HTT1 to HTT2). Distance cycled (+3.2%, p = 0.01; +1.8%, p = 0.04), mean power output (+8.1%, p = 0.01; +4.8%, p = 0.05) and cycling speed (+3.0%, p = 0.01; +1.6%, p = 0.05) were significantly greater in HTT3 than in HTT1 and HTT2, respectively. There was an increase in the number of active sweat glands per cm2 in HTT3 as compared to HTT1 (+32%; p = 0.02) and HTT2 (+22%; p < 0.01), whereas thermal sensation immediately before HTT3 decreased ("Slightly Warm," p = 0.03) compared to ratings taken before HTT1 ("Warm") in 35°C, 30%RH. Four-days HA was insufficient to improve performance in the heat in females as observed following 9-days HA.
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Affiliation(s)
- Nathalie V. Kirby
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
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13
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Watkins ER, Hayes M, Watt P, Richardson AJ. Heat tolerance of Fire Service Instructors. J Therm Biol 2019; 82:1-9. [DOI: 10.1016/j.jtherbio.2019.03.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2019] [Revised: 02/21/2019] [Accepted: 03/12/2019] [Indexed: 12/19/2022]
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14
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Alhadad SB, Tan PMS, Lee JKW. Efficacy of Heat Mitigation Strategies on Core Temperature and Endurance Exercise: A Meta-Analysis. Front Physiol 2019; 10:71. [PMID: 30842739 PMCID: PMC6391927 DOI: 10.3389/fphys.2019.00071] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2018] [Accepted: 01/21/2019] [Indexed: 11/26/2022] Open
Abstract
Background: A majority of high profile international sporting events, including the coming 2020 Tokyo Olympics, are held in warm and humid conditions. When exercising in the heat, the rapid rise of body core temperature (Tc) often results in an impairment of exercise capacity and performance. As such, heat mitigation strategies such as aerobic fitness (AF), heat acclimation/acclimatization (HA), pre-exercise cooling (PC) and fluid ingestion (FI) can be introduced to counteract the debilitating effects of heat strain. We performed a meta-analysis to evaluate the effectiveness of these mitigation strategies using magnitude-based inferences. Methods: A computer-based literature search was performed up to 24 July 2018 using the electronic databases: PubMed, SPORTDiscus and Google Scholar. After applying a set of inclusion and exclusion criteria, a total of 118 studies were selected for evaluation. Each study was assessed according to the intervention's ability to lower Tc before exercise, attenuate the rise of Tc during exercise, extend Tc at the end of exercise and improve endurance. Weighted averages of Hedges' g were calculated for each strategy. Results: PC (g = 1.01) was most effective in lowering Tc before exercise, followed by HA (g = 0.72), AF (g = 0.65), and FI (g = 0.11). FI (g = 0.70) was most effective in attenuating the rate of rise of Tc, followed by HA (g = 0.35), AF (g = −0.03) and PC (g = −0.46). In extending Tc at the end of exercise, AF (g = 1.11) was most influential, followed by HA (g = −0.28), PC (g = −0.29) and FI (g = −0.50). In combination, AF (g = 0.45) was most effective at favorably altering Tc, followed by HA (g = 0.42), PC (g = 0.11) and FI (g = 0.09). AF (1.01) was also found to be most effective in improving endurance, followed by HA (0.19), FI (−0.16) and PC (−0.20). Conclusion: AF was found to be the most effective in terms of a strategy's ability to favorably alter Tc, followed by HA, PC and lastly, FI. Interestingly, a similar ranking was observed in improving endurance, with AF being the most effective, followed by HA, FI, and PC. Knowledge gained from this meta-analysis will be useful in allowing athletes, coaches and sport scientists to make informed decisions when employing heat mitigation strategies during competitions in hot environments.
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Affiliation(s)
- Sharifah Badriyah Alhadad
- NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore, Singapore.,Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.,Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore
| | - Pearl M S Tan
- Defence Medical & Environmental Research Institute, DSO National Laboratories, Singapore, Singapore
| | - Jason K W Lee
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.,Defence Medical & Environmental Research Institute, DSO National Laboratories, Singapore, Singapore.,Department of Orthopaedic Surgery, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
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15
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Willmott AGB, Hayes M, James CA, Dekerle J, Gibson OR, Maxwell NS. Once- and twice-daily heat acclimation confer similar heat adaptations, inflammatory responses and exercise tolerance improvements. Physiol Rep 2018; 6:e13936. [PMID: 30575321 PMCID: PMC6302546 DOI: 10.14814/phy2.13936] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Accepted: 11/08/2018] [Indexed: 11/29/2022] Open
Abstract
This experiment aimed to investigate the efficacy of twice-daily, nonconsecutive heat acclimation (TDHA) in comparison to once-daily heat acclimation (ODHA) and work matched once- or twice-daily temperate exercise (ODTEMP, TDTEMP) for inducing heat adaptations, improved exercise tolerance, and cytokine (immune) responses. Forty males, matched biophysically and for aerobic capacity, were assigned to ODHA, TDHA, ODTEMP, or TDTEMP. Participants completed a cycling-graded exercise test, heat acclimation state test, and a time to task failure (TTTF) at 80% peak power output in temperate (TTTFTEMP : 22°C/40% RH) and hot conditions (TTTFHOT : 38°C/20% RH), before and after 10-sessions (60 min of cycling at ~2 W·kg-1 ) in 45°C/20% RH (ODHA and TDHA) or 22°C/40% RH (ODTEMP or TDTEMP). Plasma IL-6, TNF-α, and cortisol were measured pre- and postsessions 1, 5, and 10. ODHA and TDHA induced equivalent heat adaptations (P < 0.05) (resting rectal temperature [-0.28 ± 0.22, -0.28 ± 0.19°C], heart rate [-10 ± 3, -10 ± 4 b·min-1 ], and plasma volume expansion [+10.1 ± 5.6, +8.5 ± 3.1%]) and improved heat acclimation state (sweat set point [-0.22 ± 0.18, -0.22 ± 0.14°C] and gain [+0.14 ± 0.10, +0.15 ± 0.07 g·sec-1 ·°C-1 ]). TTTFHOT increased (P < 0.001) following ODHA (+25 ± 4%) and TDHA (+24 ± 10%), but not ODTEMP (+5 ± 14%) or TDTEMP (+5 ± 17%). TTTFTEMP did not improve (P > 0.05) following ODHA (+14 ± 4%), TDHA (14 ± 8%), ODTEMP (9 ± 10%) or TDTEMP (8 ± 13%). Acute (P < 0.05) but no chronic (P > 0.05) increases were observed in IL-6, TNF-α, or cortisol during ODHA and TDHA, or ODTEMP and TDTEMP. Once- and twice-daily heat acclimation conferred similar magnitudes of heat adaptation and exercise tolerance improvements, without differentially altering immune function, thus nonconsecutive TDHA provides an effective, logistically flexible method of HA, benefitting individuals preparing for exercise-heat stress.
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Affiliation(s)
- Ashley G. B. Willmott
- Environmental Extremes LaboratoryUniversity of BrightonBrightonEastbourneUnited Kingdom
| | - Mark Hayes
- Environmental Extremes LaboratoryUniversity of BrightonBrightonEastbourneUnited Kingdom
| | - Carl A. James
- Environmental Extremes LaboratoryUniversity of BrightonBrightonEastbourneUnited Kingdom
- Institut Sukan Negara (National Sports Institute)National Sports ComplexKuala LumpurMalaysia
| | - Jeanne Dekerle
- Environmental Extremes LaboratoryUniversity of BrightonBrightonEastbourneUnited Kingdom
| | - Oliver R. Gibson
- Centre for Human Performance, Exercise and Rehabilitation (CHPER)Brunel University LondonUxbridgeUnited Kingdom
| | - Neil S. Maxwell
- Environmental Extremes LaboratoryUniversity of BrightonBrightonEastbourneUnited Kingdom
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16
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Gibson OR, Taylor L, Watt PW, Maxwell NS. Cross-Adaptation: Heat and Cold Adaptation to Improve Physiological and Cellular Responses to Hypoxia. Sports Med 2018; 47:1751-1768. [PMID: 28389828 PMCID: PMC5554481 DOI: 10.1007/s40279-017-0717-z] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
To prepare for extremes of heat, cold or low partial pressures of oxygen (O2), humans can undertake a period of acclimation or acclimatization to induce environment-specific adaptations, e.g. heat acclimation (HA), cold acclimation (CA), or altitude training. While these strategies are effective, they are not always feasible due to logistical impracticalities. Cross-adaptation is a term used to describe the phenomenon whereby alternative environmental interventions, e.g. HA or CA, may be a beneficial alternative to altitude interventions, providing physiological stress and inducing adaptations observable at altitude. HA can attenuate physiological strain at rest and during moderate-intensity exercise at altitude via adaptations allied to improved O2 delivery to metabolically active tissue, likely following increases in plasma volume and reductions in body temperature. CA appears to improve physiological responses to altitude by attenuating the autonomic response to altitude. While no cross-acclimation-derived exercise performance/capacity data have been measured following CA, post-HA improvements in performance underpinned by aerobic metabolism, and therefore dependent on O2 delivery at altitude, are likely. At a cellular level, heat shock protein responses to altitude are attenuated by prior HA, suggesting that an attenuation of the cellular stress response and therefore a reduced disruption to homeostasis at altitude has occurred. This process is known as cross-tolerance. The effects of CA on markers of cross-tolerance is an area requiring further investigation. Because much of the evidence relating to cross-adaptation to altitude has examined the benefits at moderate to high altitudes, future research examining responses at lower altitudes should be conducted, given that these environments are more frequently visited by athletes and workers. Mechanistic work to identify the specific physiological and cellular pathways responsible for cross-adaptation between heat and altitude, and between cold and altitude, is warranted, as is exploration of benefits across different populations and physical activity profiles.
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Affiliation(s)
- Oliver R Gibson
- Centre for Human Performance, Exercise and Rehabilitation (CHPER), Brunel University London, Uxbridge, UK. .,Welkin Human Performance Laboratories, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Denton Road, Eastbourne, UK.
| | - Lee Taylor
- Athlete Health and Performance Research Centre, ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.,School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Peter W Watt
- Welkin Human Performance Laboratories, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Denton Road, Eastbourne, UK
| | - Neil S Maxwell
- Welkin Human Performance Laboratories, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Denton Road, Eastbourne, UK
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17
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Abstract
Background Although the acquisition of heat acclimation (HA) is well-documented, less is known about HA decay (HAD) and heat re-acclimation (HRA). The available literature suggests 1 day of HA is lost following 2 days of HAD. Understanding this relationship has the potential to impact upon the manner in which athletes prepare for major competitions, as a HA regimen may be disruptive during final preparations (i.e., taper). Objective The aim of this systematic review and meta-analysis was to determine the rate of HAD and HRA in three of the main physiological adaptations occurring during HA: heart rate (HR), core temperature (Tc), and sweat rate (SR). Data Sources Data for this systematic review were retrieved from Scopus and critical review of the cited references. Study Selection Studies were included when they met the following criteria: HA, HAD, and HRA (when available) were quantified in terms of exposure and duration. HA had to be for at least 5 days and HAD for at least 7 days for longitudinal studies. HR, Tc, or SR had to be monitored in human participants. Study Appraisal The level of bias in each study was assessed using the McMaster critical review form. Multiple linear regression techniques were used to determine the dependency of HAD in HR, Tc, and SR from the number of HA and HAD days, daily HA exposure duration, and intensity. Results Twelve studies met the criteria and were systematically reviewed. HAD was quantified as a percentage change relative to HA (0% = HA, 100% = unacclimated state). Adaptations in end-exercise HR decreased by 2.3% (P < 0.001) for every day of HAD. For end-exercise Tc, the daily decrease was 2.6% (P < 0.01). The adaptations in Tc during the HA period were more sustainable when the daily heat exposure duration was increased and heat exposure intensity decreased. The decay in SR was not related to the number of decay days. However, protracted HA-regimens seem to induce longer-lasting adaptations in SR. High heat exposure intensities during HA seem to evoke more sustained adaptations in SR than lower heat stress. Only eight studies investigated HRA. HRA was 8–12 times faster than HAD at inducing adaptations in HR and Tc, but no differences could be established for SR. Limitations The available studies lacked standardization in the protocols for HA and HAD. Conclusions HAD and HRA differ considerably between physiological systems. Five or more HA days are sufficient to cause adaptations in HR and Tc; however, extending the daily heat exposure duration enhances Tc adaptations. For every decay day, ~ 2.5% of the adaptations in HR and Tc are lost. For SR, longer HA periods are related to better adaptations. High heat exposure intensities seem beneficial for adaptations in SR, but not in Tc. HRA induces adaptations in HR and Tc at a faster rate than HA. HRA may thus provide a practical and less disruptive means of maintaining and optimizing HA prior to competition.
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Affiliation(s)
- Hein A M Daanen
- Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Amsterdam Movement Sciences, Vrije Universiteit Amsterdam, Van der Boechorststraat 7, 1081BT, Amsterdam, The Netherlands.
| | - Sebastien Racinais
- Athlete Health and Performance Research Centre, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
| | - Julien D Périard
- Athlete Health and Performance Research Centre, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
- Research Institute for Sport and Exercise, University of Canberra, Canberra, ACT, Australia
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18
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Pryor JL, Johnson EC, Roberts WO, Pryor RR. Application of evidence-based recommendations for heat acclimation: Individual and team sport perspectives. Temperature (Austin) 2018; 6:37-49. [PMID: 30906810 DOI: 10.1080/23328940.2018.1516537] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Revised: 06/28/2018] [Accepted: 06/28/2018] [Indexed: 01/18/2023] Open
Abstract
Heat acclimation or acclimatization (HA) occurs with repeated exposure to heat inducing adaptations that enhance thermoregulatory mechanisms and heat tolerance leading to improved exercise performance in warm-to-hot conditions. HA is an essential heat safety and performance enhancement strategy in preparation for competitions in warm-to-hot conditions for both individual and team sports. Yet, some data indicate HA is an underutilized pre-competition intervention in athletes despite the well-known benefits; possibly due to a lack of practical information provided to athletes and coaches. Therefore, the aim of this review is to provide actionable evidence-based implementation strategies and protocols to induce and sustain HA. We propose the following suggestions to circumvent potential implementation barriers: 1) incorporate multiple induction methods during the initial acclimation period, 2) complete HA 1-3 weeks before competition in the heat to avoid training and logistical conflicts during the taper period, and 3) minimize adaptation decay through intermittent exercise-heat exposure or re-acclimating immediately prior to competition with 2-4 consecutive days of exercise-heat training. Use of these strategies may be desirable or necessary to optimize HA induction and retention around existing training or logistical requirements.
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Affiliation(s)
- J Luke Pryor
- Department of Kinesiology, California State University, Fresno, CA, USA
| | - Evan C Johnson
- Division of Kinesiology & Health, University of Wyoming, Laramie, WY, USA
| | - William O Roberts
- Department of Family Medicine and Community Health, University of Minnesota, Minneapolis, MN, USA
| | - Riana R Pryor
- Department of Kinesiology, California State University, Fresno, CA, USA
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19
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Casadio JR, Kilding AE, Cotter JD, Laursen PB. From Lab to Real World: Heat Acclimation Considerations for Elite Athletes. Sports Med 2018; 47:1467-1476. [PMID: 28035584 DOI: 10.1007/s40279-016-0668-9] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
As major sporting events are often held in hot environments, increased interest in ways of optimally heat acclimating athletes to maximise performance has emerged. Heat acclimation involves repeated exercise sessions in hot conditions that induce physiological and thermoregulatory adaptations that attenuate heat-induced performance impairments. Current evidence-based guidelines for heat acclimation are clear, but the application of these recommendations is not always aligned with the time commitments and training priorities of elite athletes. Alternative forms of heat acclimation investigated include hot water immersion and sauna bathing, yet uncertainty remains around the efficacy of these methods for reducing heat-induced performance impairments, as well as how this form of heat stress may add to an athlete's overall training load. An understanding of how to optimally prescribe and periodise heat acclimation based on the performance determinants of a given event is limited, as is knowledge of how heat acclimation may affect the quality of concurrent training sessions. Finally, differences in individual athlete responses to heat acclimation need to be considered. This article addresses alternative methods of heat acclimation and heat exposure, explores gaps in literature around understanding the real world application of heat acclimation for athletes, and highlights specific athlete considerations for practitioners.
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Affiliation(s)
- Julia R Casadio
- Sports Performance Research Institute New Zealand (SPRINZ), School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand.
- High Performance Sport New Zealand, PO Box 302 563, North Harbour, Auckland, 0751, New Zealand.
| | - Andrew E Kilding
- Sports Performance Research Institute New Zealand (SPRINZ), School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand
| | - James D Cotter
- School of Physical Education, Sport and Exercise Sciences, University of Otago, Dunedin, New Zealand
| | - Paul B Laursen
- Sports Performance Research Institute New Zealand (SPRINZ), School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand
- High Performance Sport New Zealand, PO Box 302 563, North Harbour, Auckland, 0751, New Zealand
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20
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Willmott AGB, Gibson OR, James CA, Hayes M, Maxwell NS. Physiological and perceptual responses to exercising in restrictive heat loss attire with use of an upper-body sauna suit in temperate and hot conditions. Temperature (Austin) 2018; 5:162-174. [PMID: 30377634 DOI: 10.1080/23328940.2018.1426949] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 01/08/2018] [Indexed: 10/18/2022] Open
Abstract
The aim of this experiment was to quantify physiological and perceptual responses to exercise with and without restrictive heat loss attire in hot and temperate conditions. Ten moderately-trained individuals (mass; 69.44±7.50 kg, body fat; 19.7±7.6%) cycled for 30-mins (15-mins at 2 W.kg-1 then 15-mins at 1 W.kg-1) under four experimental conditions; temperate (TEMP, 22°C/45%), hot (HOT, 45°C/20%) and, temperate (TEMPSUIT, 22°C/45%) and hot (HOTSUIT, 45°C/20%) whilst wearing an upper-body "sauna suit". Core temperature changes were higher (P<0.05) in TEMPSUIT (+1.7±0.4°C.hr-1), HOT (+1.9±0.5°C.hr-1) and HOTSUIT (+2.3±0.5°C.hr-1) than TEMP (+1.3±0.3°C.hr-1). Skin temperature was higher (P<0.05) in HOT (36.53±0.93°C) and HOTSUIT (37.68±0.68°C) than TEMP (33.50±1.77°C) and TEMPSUIT (33.41±0.70°C). Sweat rate was greater (P<0.05) in TEMPSUIT (0.89±0.24 L.hr-1), HOT (1.14±0.48 L.hr-1) and HOTSUIT (1.51±0.52 L.hr-1) than TEMP (0.56±0.27 L.hr-1). Peak heart rate was higher (P<0.05) in TEMPSUIT (155±23 b.min-1), HOT (163±18 b.min-1) and HOTSUIT (171±18 b.min-1) than TEMP (151±20 b.min-1). Thermal sensation and perceived exertion were greater (P<0.05) in TEMPSUIT (5.8±0.5 and 14±1), HOT (6.4±0.5 and 15±1) and HOTSUIT (7.1±0.5 and 16±1) than TEMP (5.3±0.5 and 14±1). Exercising in an upper-body sauna suit within temperate conditions induces a greater physiological strain and evokes larger sweat losses compared to exercising in the same conditions, without restricting heat loss. In hot conditions, wearing a sauna suit increases physiological and perceptual strain further, which may accelerate the stimuli for heat adaptation and improve HA efficiency.
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Affiliation(s)
| | - Oliver R Gibson
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.,Centre for Human Performance, Exercise and Rehabilitation, Brunel University London, Uxbridge, UK
| | - Carl A James
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.,National Sports Institute, Institut Sukan Negara, National Sport Complex, Bukit Jalil, 57000 Kuala Lumpur, Malaysia
| | - Mark Hayes
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK
| | - Neil S Maxwell
- Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK
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21
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Timpmann S, Hackney AC, Tamm M, Kreegipuu K, Unt E, Ööpik V. Influence of Rhodiola rosea on the heat acclimation process in young healthy men. Appl Physiol Nutr Metab 2017; 43:63-70. [PMID: 28873320 DOI: 10.1139/apnm-2017-0372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The adaptogen Rhodiola rosea (RR) may mitigate stress responses and have beneficial effects on endurance capacity (EC) and mental performance. Heat acclimation (HA) improves EC in the heat, but the potential impact of RR on the HA process is unknown. Therefore, our intent was to determine if RR has a positive impact on HA. Twenty male subjects (age, 22.5 ± 3.0 years) completed 2 EC tests involving walking (6 km·h-1) until volitional exhaustion in a climate chamber (air temperature, 42 °C; relative humidity, 18%) before (H1) and after (H2) an 8-day HA period. One group (SHR; n = 10) ingested standardised extract SHR-5 of RR (a single daily dose of 432 mg), while a second group (PLC; n = 10) administered a placebo prior to each HA session. Efficacy of HA was evaluated on the basis of changes that occurred from H1 to H2 in the time to exhaustion (TTE), exercise heart rate (HR), core and skin temperatures (Tc, Tsk), stress hormones, ratings of perceived exertion (RPE) and fatigue (RPF), and thermal sensation (TS). HA significantly increased TTE (133.1 ± 44.1 min in H1; 233.4 ± 59.8 min in H2; p < 0.0001) and decreased (p < 0.0001) HR, Tc, Tsk, stress hormones as well as RPE, RPF, and TS. However, the magnitude of all these changes was similar (p > 0.05) in the SHR and PLC groups. These results suggest that the use of RR during HA has no beneficial performance, physiological, or perceptual effects in young healthy males.
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Affiliation(s)
- Saima Timpmann
- a Institute of Sport Sciences and Physiotherapy; Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia
| | - Anthony C Hackney
- b Department of Exercise and Sport Science; Department of Nutrition, School of Public Health, University of North Carolina, Chapel Hill, NC 27599, USA
| | - Maria Tamm
- c Institute of Psychology; Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia
| | - Kairi Kreegipuu
- c Institute of Psychology; Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia
| | - Eve Unt
- d Department of Cardiology; Department of Sports Medicine and Rehabilitation, University of Tartu; Sports Medicine and Rehabilitation Clinic, Tartu University Hospital, 50406 Tartu, Estonia
| | - Vahur Ööpik
- a Institute of Sport Sciences and Physiotherapy; Estonian Centre of Behavioral and Health Sciences, University of Tartu, 50090 Tartu, Estonia
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22
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James CA, Richardson AJ, Watt PW, Willmott AG, Gibson OR, Maxwell NS. Short-term heat acclimation improves the determinants of endurance performance and 5-km running performance in the heat. Appl Physiol Nutr Metab 2017; 42:285-294. [DOI: 10.1139/apnm-2016-0349] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study investigated the effect of 5 days of controlled short-term heat acclimation (STHA) on the determinants of endurance performance and 5-km performance in runners, relative to the impairment afforded by moderate heat stress. A control group (CON), matched for total work and power output (2.7 W·kg−1), differentiated thermal and exercise contributions of STHA on exercise performance. Seventeen participants (10 STHA, 7 CON) completed graded exercise tests (GXTs) in cool (13 °C, 50% relative humidity (RH), pre-training) and hot conditions (32 °C, 60% RH, pre- and post-training), as well as 5-km time trials (TTs) in the heat, pre- and post-training. STHA reduced resting (p = 0.01) and exercising (p = 0.04) core temperature alongside a smaller change in thermal sensation (p = 0.04). Both groups improved the lactate threshold (LT, p = 0.021), lactate turnpoint (LTP, p = 0.005) and velocity at maximal oxygen consumption (vV̇O2max; p = 0.031) similarly. Statistical differences between training methods were observed in TT performance (STHA, −6.2(5.5)%; CON, −0.6(1.7)%, p = 0.029) and total running time during the GXT (STHA, +20.8(12.7)%; CON, +9.8(1.2)%, p = 0.006). There were large mean differences in change in maximal oxygen consumption between STHA +4.0(2.2) mL·kg−1·min−1 (7.3(4.0)%) and CON +1.9(3.7) mL·kg−1·min−1 (3.8(7.2)%). Running economy (RE) deteriorated following both training programmes (p = 0.008). Similarly, RE was impaired in the cool GXT, relative to the hot GXT (p = 0.004). STHA improved endurance running performance in comparison with work-matched normothermic training, despite equality of adaptation for typical determinants of performance (LT, LTP, vV̇O2max). Accordingly, these data highlight the ergogenic effect of STHA, potentially via greater improvements in maximal oxygen consumption and specific thermoregulatory and associated thermal perception adaptations absent in normothermic training.
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Affiliation(s)
- Carl A. James
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
- National Sports Institute of Malaysia, Institut Sukan Negara, Bukit Jalil Stadium, Kuala Lumpur 57000, Malaysia
| | - Alan J. Richardson
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
| | - Peter W. Watt
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
| | - Ashley G.B. Willmott
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
| | - Oliver R. Gibson
- Centre for Human Performance, Exercise and Rehabilitation (CHPER), Brunel University London UB8 3PH, UK
| | - Neil S. Maxwell
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK
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23
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Willmott AGB, Hayes M, Waldock KAM, Relf RL, Watkins ER, James CA, Gibson OR, Smeeton NJ, Richardson AJ, Watt PW, Maxwell NS. Short-term heat acclimation prior to a multi-day desert ultra-marathon improves physiological and psychological responses without compromising immune status. J Sports Sci 2016; 35:2249-2256. [PMID: 27935427 DOI: 10.1080/02640414.2016.1265142] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Multistage, ultra-endurance events in hot, humid conditions necessitate thermal adaptation, often achieved through short term heat acclimation (STHA), to improve performance by reducing thermoregulatory strain and perceptions of heat stress. This study investigated the physiological, perceptual and immunological responses to STHA prior to the Marathon des Sables. Eight athletes (age 42 ± 4 years and body mass 81.9 ± 15.0 kg) completed 4 days of controlled hyperthermia STHA (60 min·day‒1, 45°C and 30% relative humidity). Pre, during and post sessions, physiological and perceptual measures were recorded. Immunological measures were recorded pre-post sessions 1 and 4. STHA improved thermal comfort (P = 0.02), sensation (P = 0.03) and perceived exertion (P = 0.04). A dissociated relationship between perceptual fatigue and Tre was evident after STHA, with reductions in perceived Physical (P = 0.04) and General (P = 0.04) fatigue. Exercising Tre and HR did not change (P > 0.05) however, sweat rate increased 14% (P = 0.02). No changes were found in white blood cell counts or content (P > 0.05). Four days of STHA facilitates effective perceptual adaptations, without compromising immune status prior to an ultra-endurance race in heat stress. A greater physiological strain is required to confer optimal physiological adaptations.
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Affiliation(s)
- Ashley G B Willmott
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Mark Hayes
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Kirsty A M Waldock
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Rebecca L Relf
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Emily R Watkins
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Carl A James
- b National Sports Institute (Institut Sukan Negara) , National Sport Complex , Kuala Lumpur , Malaysia
| | - Oliver R Gibson
- c Centre for Human Performance, Exercise and Rehabilitation , Brunel University London , London , UK
| | - Nicholas J Smeeton
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Alan J Richardson
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Peter W Watt
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
| | - Neil S Maxwell
- a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), Sport and Exercise Science Consultancy Unit (SESCU) , University of Brighton , Eastbourne , UK
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24
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James CA, Willmott AGB, Richardson AJ, Watt PW, Maxwell NS. Ischaemic preconditioning does not alter the determinants of endurance running performance in the heat. Eur J Appl Physiol 2016; 116:1735-45. [PMID: 27406142 DOI: 10.1007/s00421-016-3430-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Accepted: 07/05/2016] [Indexed: 11/26/2022]
Abstract
PURPOSE Ischaemic preconditioning (IP) has been shown to be ergogenic for endurance performance in normothermic conditions and alleviate physiological strain under hypoxia, potentially through haemodynamic and/or metabolic mechanisms. Exertional hyperthermia is characterised by competition for blood flow between the muscles and skin, an enhanced metabolic strain and impaired endurance performance. This study investigated the effect of IP on the determinants of endurance performance, through an incremental exercise test in the heat. METHOD Eleven males completed two graded exercise tests in the heat (32 °C, 62 % RH) until volitional exhaustion, preceded by IP (4 × 5 min 220 mmHg bilateral upper leg occlusion) or a control (CON) condition (4 × 5-min 50 mmHg bilateral). RESULT IP did not improve running speeds at fixed blood lactate concentrations of 2 and 4 mMol L(-1) (p = 0.828), or affect blood glucose concentration throughout the trial [mean (±SD); CON 5.03 (0.94) mMol L(-1), IP 5.47 (1.38) mMol L(-1), p = 0.260). There was no difference in [Formula: see text]O2max [CON 55.5 (3.7) mL kg(-1) min(-1), IP 56.0 (2.6) mL kg(-1) min(-1), p = 0.436], average running economy [CON 222.3 (18.0) mL kg(-1) km(-1), IP 218.9 (16.5) mL kg(-1) km(-1), p = 0.125], or total running time during graded exercise [CON 347 (42) s, IP 379 (68) s, p = 0.166]. The IP procedure did not change muscle temperature [CON ∆ = 0.55 (0.57) °C, IP ∆ = 0.78 (0.85) °C, p = 0.568], but did reduce T CORE during exercise (~-0.1 °C, p = 0.001). CONCLUSION The novel application of IP prior to exercise in the heat does not enhance the determinants of endurance performance. For events where IP appears ergogenic, muscle warming strategies are unnecessary as IP does not influence deep muscle temperature.
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Affiliation(s)
- Carl A James
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Welkin Laboratories, Denton Road, Eastbourne, BN20 7SN, UK.
| | - Ashley G B Willmott
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Welkin Laboratories, Denton Road, Eastbourne, BN20 7SN, UK
| | - Alan J Richardson
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Welkin Laboratories, Denton Road, Eastbourne, BN20 7SN, UK
| | - Peter W Watt
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Welkin Laboratories, Denton Road, Eastbourne, BN20 7SN, UK
| | - Neil S Maxwell
- Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Welkin Laboratories, Denton Road, Eastbourne, BN20 7SN, UK
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25
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Tyler CJ, Reeve T, Hodges GJ, Cheung SS. The Effects of Heat Adaptation on Physiology, Perception and Exercise Performance in the Heat: A Meta-Analysis. Sports Med 2016; 46:1699-1724. [DOI: 10.1007/s40279-016-0538-5] [Citation(s) in RCA: 167] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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