Publications by authors named "Neil Maxwell"

54 Publications

Impact of Personal Cooling on Performance, Comfort and Heat Strain of Healthcare Workers in PPE, a Study From West Africa.

Front Public Health 2021 1;9:712481. Epub 2021 Sep 1.

Environmental Extremes Laboratory, University of Brighton, Eastbourne, United Kingdom.

Personal protective equipment (PPE) is an essential component of safely treating suspected or confirmed SARS-CoV-2 patients. PPE acts as a barrier to heat loss, therefore increasing the risk of thermal strain which may impact on cognitive function. Healthcare workers (HCWs) need to be able to prioritize and execute complex tasks effectively to ensure patient safety. This study evaluated pre-cooling and per-cooling methods on thermal strain, thermal comfort and cognitive function during simulated emergency management of an acutely unwell patient. This randomized controlled crossover trial was run at the Clinical Services Department of the Medical Research Unit The Gambia. Each participant attended two sessions (Cool and Control) in standard PPE. Cool involved pre-cooling with an ice slurry ingestion and per-cooling by wearing an ice-vest external to PPE. Twelve participants completed both sessions. There was a significant increase in tympanic temperature in Control sessions at both 1 and 2 h in PPE ( = 0.01). No significant increase was seen during Cool. Effect estimate of Cool was -0.2°C (95% CI -0.43; 0.01, = 0.06) post 1 h and -0.28°C (95% CI -0.57; 0.02, = 0.06) post 2 h on tympanic temperature. Cool improved thermal comfort ( < 0.001), thermal sensation ( < 0.001), and thirst ( = 0.04). No difference on cognitive function was demonstrated using multilevel modeling. Thermal strain in HCWs wearing PPE can be safely reduced using pre- and per-cooling methods external to PPE.
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http://dx.doi.org/10.3389/fpubh.2021.712481DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8440920PMC
September 2021

Exercise hyperthermia induces greater changes in gastrointestinal permeability than equivalent passive hyperthermia.

Physiol Rep 2021 Aug;9(16):e14945

Environmental Extremes Lab, Sport and Exercise Science and Medicine Research and Enterprise Group, University of Brighton, Eastbourne, East Sussex, UK.

Hyperthermia and exertional heat illness increase gastrointestinal (GI) permeability, although whether the latter is only via hyperthermia is unclear. The aim of this pilot study was to determine whether different changes in GI permeability, characterized by an increased plasma lactulose:rhamnose concentration ratio ([L:R]), occurred in exercise hyperthermia in comparison to equivalent passive hyperthermia. Six healthy adult male participants (age 25 ± 5 years, mass 77.0 ± 6.7 kg, height 181 ± 6 cm, peak oxygen uptake [ ] 48 ± 8 ml.kg .min ) underwent exercise under hot conditions (Ex-Heat) and passive heating during hot water immersion (HWI). Heart rate (HR), rectal temperature (T ), rating of perceived exertion (RPE), and whole-body sweat loss (WBSL) were recorded throughout the trials. The L:R ratio, peak HR, change in HR, and change in RPE were higher in Ex-Heat than HWI, despite no differences in trial duration, peak core temperature or WBSL. L:R was strongly correlated (p < 0.05) with HR peak (r = 0.626) and change in HR (r = 0.615) but no other variable. The greater L:R in Ex-Heat, despite equal T responses to HWI, indicates that increased cardiovascular strain occurred during exercise, and exacerbates hyperthermia-induced GI permeability at the same absolute temperature.
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http://dx.doi.org/10.14814/phy2.14945DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8374382PMC
August 2021

Thermoregulation is not impaired in breast cancer survivors during moderate-intensity exercise performed in warm and hot environments.

Physiol Rep 2021 Jul;9(14):e14968

Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.

This study aimed to assess how female breast cancer survivors (BCS) respond physiologically, hematologically, and perceptually to exercise under heat stress compared to females with no history of breast cancer (CON). Twenty-one females (9 BCS and 12 CON [age; 54 ± 7 years, stature; 167 ± 6 cm, body mass; 68.1 ± 7.62 kg, and body fat; 30.9 ± 3.8%]) completed a warm (25℃, 50% relative humidity, RH) and hot (35℃, 50%RH) trial in a repeated-measures crossover design. Trials consisted of 30 min of rest, 30 min of walking at 4 metabolic equivalents, and a 6-minute walk test (6MWT). Physiological measurements (core temperature (T ), skin temperature (T ), heart rate (HR), and sweat analysis) and perceptual rating scales (ratings of perceived exertion, thermal sensation [whole body and localized], and thermal comfort) were taken at 5- and 10-min intervals throughout, respectively. Venous blood samples were taken before and after to assess; IL-6, IL-10, CRP, IFN-γ, and TGF-β . All physiological markers were higher during the 35 versus 25℃ trial; T (~0.25℃, p = 0.002), T (~3.8℃, p < 0.001), HR (~12 beats·min , p = 0.023), and whole-body sweat rate (~0.4 L·hr , p < 0.001), with no difference observed between groups in either condition (p > 0.05). Both groups covered a greater 6MWT distance in 25 versus 35℃ (by ~200 m; p = 0.003). Nevertheless, the control group covered more distance than BCS, regardless of environmental temperature (by ~400 m, p = 0.03). Thermoregulation was not disadvantaged in BCS compared to controls during moderate-intensity exercise under heat stress. However, self-paced exercise performance was reduced for BCS regardless of environmental temperature.
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http://dx.doi.org/10.14814/phy2.14968DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8295682PMC
July 2021

Exercise heat acclimation and post-exercise hot water immersion improve resting and exercise responses to heat stress in the elderly.

J Sci Med Sport 2021 Aug 3;24(8):774-780. Epub 2021 Jun 3.

Environmental Extremes Laboratory, University of Brighton, United Kingdom.

Objectives: To investigate the efficacy of heat acclimation (HA) in the young (Y) and elderly (E) following exercise-HA, and the elderly utilising post-exercise hot water immersion HA (E).

Design: Cross-sectional study.

Method: Twenty-six participants (Y: n = 11 aged 22 ± 2 years, En = 8 aged 68 ± 3 years, E: n = 7 aged 73 ± 3 years) completed two pre-/post-tests, separated by five intervention days. Y and E exercised in hot conditions to raise rectal temperature (T) ≥38.5 °C within 60 min, with this increase maintained for a further 60 min. E completed 30 min of cycling in temperate conditions, then 30 min of HWI (40 °C), followed by 30 min seated blanket wrap. Pre- and post-testing comprised 30 min rest, followed by 30 min of cycling exercise (3.5 W·kg Ḣ and a six-minute walk test (6MWT), all in 35 °C, 50% RH.

Results: The HA protocols did not elicit different mean heart rate (HR), T, and duration T ≥ 38.5 °C (p > 0.05) between Y, E, and E groups. Resting T, peak skin temperature, systolic and mean arterial pressure, perceived exertion and thermal sensation decreased, and 6MWT distance increased pre- to post-HA (p < 0.05), with no difference between groups. Y also demonstrated a reduction in resting HR (p < 0.05). No change was observed in peak T or HR, vascular conductance, sweat rate, or thermal comfort in any group (p > 0.05).

Conclusions: Irrespective of age or intervention, HA induced thermoregulatory, perceptual and exercise performance improvements. Both exercise-HA (E), and post-exercise HWI (E) are considered viable interventions to prepare the elderly for heat stress.
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http://dx.doi.org/10.1016/j.jsams.2021.05.017DOI Listing
August 2021

Predicting middle-distance track and cross-country performances of national and international level adolescent runners.

Eur J Sport Sci 2021 Jan 18:1-9. Epub 2021 Jan 18.

School of Sport and Service Management, University of Brighton, UK.

This study evaluated the contribution of physiological data collected during laboratory testing in predicting race performances of trained junior middle-distance track (TK) and cross-country (XC) athletes. Participants performed a submaximal incremental ramp test, followed by an incremental test to exhaustion in a laboratory, with the results used to predict either 800 m TK, 1500 m TK or 4000-6000 m XC race performance. Twenty-eight participants (male (M), 15; female (F), 13) were analysed (age = 17 ± 2 years, height = 1.72 ± 0.08 m, body mass = 58.9 ± 8.9 kg). Performance times (min:s) for 800 m were: M, 1:56.55 ± 0:05.55 and F, 2:14.21 ± 0:03.89; 1500 m: M, 3:51.98 ± 0:07.35 and F 4:36.71 ± 0:16.58; XC: M (4900 ± 741 m), 16:00 ± 01:53; F (4628 ± 670 m), 17:41 ± 02:09. Stepwise regression analysis indicated significant contributions of speed at V̇O (V̇O), and heart rate maximum (HR) to the prediction of 800 m TK (() = 22.51,  < 0.001, adjusted = 0.72), V̇O for 1500 m TK (() = 36.65,  < 0.001, adjusted = 0.72) and V̇O allometrically scaled to body mass and speed at lactate threshold (sLT) for XC (() = 25.1,  < 0.001, adjusted = 0.72). Laboratory-based physiological measures can explain 72% of the variance in junior TK and XC events, although factors that explain performance alter depending on the race distance and tactics. The factors determining performance in TK and XC events are not interchangeable.
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http://dx.doi.org/10.1080/17461391.2020.1867650DOI Listing
January 2021

Heat acclimation attenuates the increased sensations of fatigue reported during acute exercise-heat stress.

Temperature (Austin) 2019 Sep 19;7(2):178-190. Epub 2019 Sep 19.

Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.

Athletes exercising in heat stress experience increased perceived fatigue acutely, however it is unknown whether heat acclimation (HA) reduces the magnitude of this perceptual response and whether different HA protocols influence the response. This study investigated sensations of fatigue following; acute exercise-heat stress; short- (5-sessions) and medium-term (10-sessions) HA; and between once- (ODHA) and twice-daily HA (TDHA) protocols. Twenty male participants (peak oxygen uptake: 3.75 ± 0.47 L·min-1) completed 10 sessions (60-min cycling at ~2 W·kg-1, 45°C/20% relative humidity) of ODHA (n = 10) or non-consecutive TDHA (n = 10). Sensations of fatigue (General, Physical, Emotional, Mental, Vigor and Total Fatigue) were assessed using the multi-dimensional fatigue scale inventory-short form pre and post session 1, 5 and 10. Heat adaptation was induced following ODHA and TDHA, with reductions in resting rectal temperature and heart rate, and increased plasma volume and sweat rate (P < 0.05). General, Physical and Total Fatigue increased from pre-to-post for session 1 within both groups (P < 0.05). Increases in General, Physical and Total Fatigue were attenuated in session 5 and 10 vs. session 1 of ODHA (P < 0.05). This change only occurred at session 10 of TDHA (P < 0.05). Whilst comparative heat adaptations followed ODHA and TDHA, perceived fatigue is prolonged within TDHA.

Abbreviations: ∆: Change; ANOVA: Analysis of variance; HA: Heat acclimation; HR: Heart rate; IL-6: Interleukin-6; MFS-SF: Multi-dimensional fatigue symptom inventory-short form (MFSI-SF); MTHA: Medium-term heat acclimation; Na: Sodium; ODHA: Once daily heat acclimation; PV: Plasma volume; RH: Relative humidity; RPE: Rating of perceived exertion; SD: Standard deviation; SE: Standard error of the slope coefficient or intercept; : Standard error of the estimate for the regression equation; STHA: Short-term heat acclimation; TDHA: Twice daily heat acclimation; TC: Thermal Comfort; T: Rectal temperature; TSS: Thermal sensation; V̇O: Peak oxygen uptake; WBSL: whole-body sweat loss.
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http://dx.doi.org/10.1080/23328940.2019.1664370DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7518764PMC
September 2019

Editorial: Heat Acclimation for Special Populations.

Front Physiol 2020 29;11:895. Epub 2020 Jul 29.

School of Science and Technology, Nottingham Trent University, Nottingham, United Kingdom.

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http://dx.doi.org/10.3389/fphys.2020.00895DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7438765PMC
July 2020

Heat acclimation improves sweat gland function and lowers sweat sodium concentration in an adult with cystic fibrosis.

J Cyst Fibros 2021 05 2;20(3):485-488. Epub 2020 Aug 2.

Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.

We present novel data concerning the time-course of adaptations and potential benefits of heat acclimation for people with cystic fibrosis (pwCF), who are at greater risk of exertional heat illness. A 25-year-old male (genotype: delta-F508 and RH117, forced expiratory volume in 1-second: 77% predicted and baseline sweat [Na]: 70 mmol·L  ), who had previously experienced muscle cramping during exercise in ambient heat, underwent 10-sessions of heat acclimation (90-min at 40°C and in 40% relative humidity). Adaptations included; lower resting core temperature (-0.40°C) and heart rate (-6 beats·min), plasma volume expansion (+6.0%) and, importantly, increased sweat loss (+370 mL) and sweat gland activity (+12 glands·cm) with decreased sweat [Na] (-18 mmol·L  ). Adaptations were maintained for at least 7-days, with no evidence of cramping during follow-up exercise-heat stress testing. These data suggest pwCF may benefit from heat acclimation to induce sudomotor function improvements, particularly reductions in sweat [Na], however, further research is required.
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http://dx.doi.org/10.1016/j.jcf.2020.07.013DOI Listing
May 2021

Validity of a wearable sweat rate monitor and routine sweat analysis techniques using heat acclimation.

J Therm Biol 2020 May 29;90:102577. Epub 2020 Mar 29.

Environmental Extremes Laboratory, University of Brighton, Eastbourne, BN20 7SR, UK.

Introduction: the aim of this study was to assess the validity of a novel wearable sweat rate monitor against an array of sweat analysis techniques which determine sudomotor function when exercising moderately under heat stress. Construct validity was determined utilising a 5-day short-term heat acclimation (STHA) intervention.

Methods: Nineteen healthy individuals (age: 41 ± 23 years, body mass: 74.0 ± 12.2 kg, height: 174.9 ± 6.9 cm) [male; n = 15, female; n = 4] completed nine trials over a three-week period, in a controlled chamber set to 35 °C, 50% relative humidity for all sessions. The pre and post-trials were separated by five consecutive controlled hyperthermia HA sessions. Sweat analysis was compared from pre and post-trial, whereby whole body sweat rate (WBSR) was assessed via pre and post nude body mass. Local sweat rate (LSR) was determined via technical absorbent patches (TA) (weighed pre and post) and a novel wearable KuduSmart® (SMART) monitor which was placed on the left arm during the 30-min of exercise. Tegaderm patches, used to measure sweat sodium chloride conductivity (SC), and TA patches were placed on the back, chest and forearm for the 30-min cycling.

Results: Sudomotor function significantly adapted via STHA (p < 0.05); demonstrated by a WBSR increase of 24%, LSR increase via the TA method (back: 26%, chest: 45% and arm: 48%) and LSR increase by the SMART monitor (35%). Finally, SC decreased (back: -21%, chest: -25% and arm: -24%, p < 0.05).

Conclusion: All sweat techniques were sensitive to sudomotor function adaptation following STHA, reinforcing their validity. The real time data given by the wearable KuduSmart® monitor provides coaches and athletes instant comparable sudomotor function feedback to traditional routinely used sweat analysis techniques.
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http://dx.doi.org/10.1016/j.jtherbio.2020.102577DOI Listing
May 2020

A protocol for an observational cohort study of heat strain and its effect on fetal wellbeing in pregnant farmers in The Gambia.

Wellcome Open Res 2020 31;5:32. Epub 2020 Mar 31.

Environmental Extremes Laboratory, University of Brighton, Brighton, UK.

Climate change predictions indicate that global temperatures are likely to exceed those seen in the last 200,000 years, rising by around 4°C above pre-industrial levels by 2100 (without effective mitigation of current emission rates). In regions of the world set to experience extreme temperatures, women often work outside in agriculture even during pregnancy. The implications of heat strain in pregnancy on maternal health and pregnancy outcome are not well understood. This protocol describes a study to assess the physiological response of pregnant women to environmental heat stress and the immediate effect this has on fetal wellbeing. The study will be performed in West Kiang district, The Gambia; a semi-arid zone in West Africa with daily maximum temperatures ranging from approximately 32 to 40°C. We will recruit 125 pregnant women of all ages who perform agricultural work during their pregnancy. Participants will be followed every two months until delivery. At each study visit fetal growth will be measured by ultrasound scan. During the course of their working day we will take the following measurements: continuous maternal physiological measurements (heart rate, respiratory rate, chest skin temperature and tri-axis accelerometer data); intermittent maternal tympanic core temperature, four point skin temperature, blood pressure; intermittent fetal heart rate and, if eligible, umbilical artery doppler; intermittent environmental measurements of air temperature, humidity, solar radiation and wind speed. Venous blood and urine will be collected at beginning and end of day for biomarkers of heat strain or fetal distress and hydration status.
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http://dx.doi.org/10.12688/wellcomeopenres.15731.2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7141168PMC
March 2020

Heat alleviation strategies for athletic performance: A review and practitioner guidelines.

Temperature (Austin) 2020 12;7(1):3-36. Epub 2019 Oct 12.

Environmental Extremes Laboratory, School of Sport and Service Management, University of Brighton, Eastbourne, UK.

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. : 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; T: Core temperature; TDHA: Twice-daily heat acclimation; TS: Thermal sensation; T: Skin temperature; V̇O: Maximal oxygen uptake; WGBT: Wet bulb globe temperature.
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http://dx.doi.org/10.1080/23328940.2019.1666624DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7053966PMC
October 2019

Reliability of a wearable sweat rate monitor and routine sweat analysis techniques under heat stress in females.

J Therm Biol 2019 Jan 18;79:209-217. Epub 2018 Dec 18.

Environmental Extremes Laboratory, University of Brighton, Eastbourne BN20 7SR, UK.

Introduction: The aim of the study was to evaluate the reliability of five different sweat analysis techniques which measure; whole body sweat rate [WBSR], local sweat rate [LSR] (via technical absorbent [TA] method and KuduSmart monitor), sweat conductivity [SC] and sweat gland activation [SGA] in a female population when exercising moderately under heat stress.

Methods: Fourteen females (age; 26 ± 7 years, body mass; 66.5 ± 7.6 kg, height; 167.1 ± 6.4 cm) completed a preliminary threshold walking test (to determine exercise intensity) and two main trials, separated by 2 days. Main trials consisted of 30-min seated rest in the environmental chamber (35 °C, 50% relative humidity) in an upper body sauna-suit, before its removal, and walking at a moderate intensity (4 metabolic equivalents) for 30-min (speeds ranged from 4.8 to 6.5 km h). WBSR was measured via nude mass pre and post exercise. The TA and Tegaderm patches (for sweat sodium chloride) were placed on the back, forearm and chest for the entire 60-min, replicated for all participants for both trials. SGA was assessed following the 60-min trial and the KuduSmart® monitor was placed on the left arm for the 30-min of exercise.

Results: WBSR, LSR methods and SC demonstrated no difference between trials (p > 0.05), good agreement (within limits), strong correlations (r ≥ 0.88) and low typical error of measurements [TEM] (< 0.04 L min, 0.13 mg min cm and 8 mmol L, respectively). SGA method showed moderate intra-class correlation (r = 0.80), with high TEM (5 glands) and large limits of agreement.

Conclusion: Sudomotor function is reliable, as demonstrated by good reliability, small TEM and strong correlations. The use of these sweat techniques is appropriate and practical in females who are exercising at moderate intensity under heat stress, and so, may aid future interventions. SGA shows larger variation and should be used with caution.
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http://dx.doi.org/10.1016/j.jtherbio.2018.12.019DOI Listing
January 2019

Once- and twice-daily heat acclimation confer similar heat adaptations, inflammatory responses and exercise tolerance improvements.

Physiol Rep 2018 12;6(24):e13936

Environmental Extremes Laboratory, University of Brighton, Brighton, Eastbourne, United Kingdom.

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 (TTTF : 22°C/40% RH) and hot conditions (TTTF : 38°C/20% RH), before and after 10-sessions (60 min of cycling at ~2 W·kg ) 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 ], 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 ·°C ]). TTTF increased (P < 0.001) following ODHA (+25 ± 4%) and TDHA (+24 ± 10%), but not ODTEMP (+5 ± 14%) or TDTEMP (+5 ± 17%). TTTF 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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http://dx.doi.org/10.14814/phy2.13936DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6302546PMC
December 2018

A comparison of two global positioning system devices for team-sport running protocols.

J Biomech 2019 01 5;83:324-328. Epub 2018 Dec 5.

University of Brighton, Environmental Extremes Laboratory, Eastbourne BN20 7SN, UK.

The comparability and reliability of global positioning system (GPS) devices during running protocols associated with team-sports was investigated. Fourteen moderately-trained males completed 690 m of straight-line movements, a 570 m change of direction (COD) course and a 642.5 m team-sport simulated circuit (TSSC); on two occasions. Participants wore a FieldWiz GPS device and a Catapult MinimaxX S4 10-Hz GPS device. Typical error of measurement (TE) and coefficient of variation (CV%) were calculated between GPS devices, for the variables of total distance and peak speed. Reliability comparisons were made within FieldWiz GPS devices, between sessions. Small TE were observed between FieldWiz and Catapult GPS devices for total distance and peak speed during straight-line (16.9 m [2%], 1.2 km·h [4%]), COD (31.8 m [6%], 0.4 km·h [2%]) and TSSC protocols (12.9 m [2%], 0.5 km·h [2%]), respectively, with no significant mean bias (p > 0.05). Small TE were also observed for the FieldWiz GPS device between sessions (p > 0.05) for straight-line (9.6 m [1%], 0.2 km·h [1%]), COD (12.8 m [2%], 0.2 km·h [1%]) and TSSC protocols (6.9 m [1%], 0.6 km·h [2%]), respectively. Data from the FieldWiz GPS device appears comparable to established devices and reliable across a range of movement patterns associated with team-sports.
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http://dx.doi.org/10.1016/j.jbiomech.2018.11.044DOI Listing
January 2019

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 13;5(2):162-174. Epub 2018 Mar 13.

Environmental Extremes Laboratory, University of Brighton, Eastbourne, UK.

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 then 15-mins at 1 W.kg) under four experimental conditions; temperate (TEMP, 22°C/45%), hot (HOT, 45°C/20%) and, temperate (TEMP, 22°C/45%) and hot (HOT, 45°C/20%) whilst wearing an upper-body "sauna suit". Core temperature changes were higher (<0.05) in TEMP (+1.7±0.4°C.hr), HOT (+1.9±0.5°C.hr) and HOT (+2.3±0.5°C.hr) than TEMP (+1.3±0.3°C.hr). Skin temperature was higher (<0.05) in HOT (36.53±0.93°C) and HOT (37.68±0.68°C) than TEMP (33.50±1.77°C) and TEMP (33.41±0.70°C). Sweat rate was greater (<0.05) in TEMP (0.89±0.24 L.hr), HOT (1.14±0.48 L.hr) and HOT (1.51±0.52 L.hr) than TEMP (0.56±0.27 L.hr). Peak heart rate was higher (<0.05) in TEMP (155±23 b.min), HOT (163±18 b.min) and HOT (171±18 b.min) than TEMP (151±20 b.min). Thermal sensation and perceived exertion were greater (<0.05) in TEMP (5.8±0.5 and 14±1), HOT (6.4±0.5 and 15±1) and HOT (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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http://dx.doi.org/10.1080/23328940.2018.1426949DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6205027PMC
March 2018

Altitude training in endurance running: perceptions of elite athletes and support staff.

J Sports Sci 2019 Jan 22;37(2):163-172. Epub 2018 Jun 22.

a Centre for Sport and Exercise Science and Medicine (SESAME) , University of Brighton , Eastbourne , UK.

This study sought to establish perceptions of elite endurance athletes on the role and worth of altitude training. Elite British endurance runners were surveyed to identify the altitude and hypoxic training methods utilised, along with reasons for use, and any situational, cultural and behaviour factors influencing these. Prior to the 2012 Olympics Games, 39 athletes and 20 support staff (coaches/practitioners) completed an internet-based survey to establish differences between current practices and the accepted "best-practice". Almost all of the athletes (98%) and support staff (95%) surveyed had utilised altitude and hypoxic training, or had advised it to athletes. 75% of athletes believed altitude and hypoxia to be a "very important" factor in their training regime, with 50% of support staff believing the same. Athletes and support staff were in agreement of the methods of altitude training utilised (i.e. 'hypoxic dose' and strategy), with camps lasting 3-4 weeks at 1,500-2,500 m being the most popular. Athletes and support staff are utilising altitude and hypoxic training methods in a manner agreeing with research-based suggestions. The survey identified a number of specific challenges and priorities, which could provide scope to optimise future altitude training methods for endurance performance in these elite groups.
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http://dx.doi.org/10.1080/02640414.2018.1488383DOI Listing
January 2019

Defining the determinants of endurance running performance in the heat.

Temperature (Austin) 2017 25;4(3):314-329. Epub 2017 May 25.

Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne, UK.

In cool conditions, physiologic markers accurately predict endurance performance, but it is unclear whether thermal strain and perceived thermal strain modify the strength of these relationships. This study examined the relationships between traditional determinants of endurance performance and time to complete a 5-km time trial in the heat. Seventeen club runners completed graded exercise tests (GXT) in hot (GXTHOT; 32°C, 60% RH, 27.2°C WBGT) and cool conditions (GXTCOOL; 13°C, 50% RH, 9.3°C WBGT) to determine maximal oxygen uptake (V̇O), running economy (RE), velocity at V̇O (vV̇O), and running speeds corresponding to the lactate threshold (LT, 2 mmol.l) and lactate turnpoint (LTP, 4 mmol.l). Simultaneous multiple linear regression was used to predict 5 km time, using these determinants, indicating neither GXTHOT (R = 0.72) nor GXTCOOL (R = 0.86) predicted performance in the heat as strongly has previously been reported in cool conditions. vV̇O was the strongest individual predictor of performance, both when assessed in GXT ( = -0.83) and GXT ( = -0.90). The GXTs revealed the following correlations for individual predictors in GXT; V̇O = -0.7, RE = 0.36, LT = -0.77, LTP = -0.78 and in GXT; V̇O = -0.67, RE = 0.62, LT = -0.79, LTP = -0.8. These data indicate (i) GXT does not predict 5 km running performance in the heat as strongly as a GXT, (ii) as in cool conditions, vV̇O may best predict running performance in the heat.
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http://dx.doi.org/10.1080/23328940.2017.1333189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5605161PMC
May 2017

Sauna exposure immediately prior to short-term heat acclimation accelerates phenotypic adaptation in females.

J Sci Med Sport 2018 Feb 4;21(2):190-195. Epub 2017 Jul 4.

Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, UK.

Objectives: Investigate whether a sauna exposure prior to short-term heat acclimation (HA) accelerates phenotypic adaptation in females.

Design: Randomised, repeated measures, cross-over trial.

Methods: Nine females performed two 5-d HA interventions (controlled hyperthermia T≥38.5°C), separated by 7-wk, during the follicular phase of the menstrual cycle confirmed by plasma concentrations of 17-β estradiol and progesterone. Prior to each 90-min HA session participants sat for 20-min in either a temperate environment (20°C, 40% RH; HA) wearing shorts and sports bra or a hot environment (50°C, 30% RH) wearing a sauna suit to replicate sauna conditions (HA). Participants performed a running heat tolerance test (RHTT) 24-h pre and 24-h post HA.

Results: Mean heart rate (HR) (85±4 vs. 68±5 bpm, p≤0.001), sweat rate (0.4±0.2 vs. 0.0±0.0Lh, p≤0.001), and thermal sensation (6±0 vs. 5±1, p=0.050) were higher during the sauna compared to temperate exposure. Resting rectal temperature (T) (-0.28±0.16°C), peak T (-0.42±0.22°C), resting HR (-10±4 bpm), peak HR (-12±7 bpm), T at sweating onset (-0.29±0.17°C) (p≤0.001), thermal sensation (-0.5±0.5; p=0.002), and perceived exertion (-3±2; p≤0.001) reduced during the RHTT, following HA; but not HA. Plasma volume expansion was greater following HA (HA, 9±7%; HA, 1±5%; p=0.013). Sweat rate (p≤0.001) increased and sweat NaCl (p=0.006) reduced during the RHTT following HA and HA.

Conclusions: This novel strategy initiated HA with an attenuation of thermoregulatory, cardiovascular, and perceptual strain in females due to a measurably greater strain in the sauna compared to temperate exposure when adopted prior to STHA.
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http://dx.doi.org/10.1016/j.jsams.2017.06.024DOI Listing
February 2018

Short-Term Heat Acclimation and Precooling, Independently and Combined, Improve 5-km Time Trial Performance in the Heat.

J Strength Cond Res 2018 May;32(5):1366-1375

Environmental Extremes Laboratory, Center for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne, United Kingdom.

James, CA, Richardson, AJ, Watt, PW, Willmott, AGB, Gibson, OR, and Maxwell, NS. Short-term heat acclimation and precooling, independently and combined, improve 5-km time trial performance in the heat. J Strength Cond Res 32(5): 1366-1375, 2018-Following heat acclimation (HA), endurance running performance remains impaired in hot vs. temperate conditions. Combining HA with precooling (PC) demonstrates no additive benefit in intermittent sprint, or continuous cycling exercise protocols, during which heat strain may be less severe compared to endurance running. This study investigated the effect of short-term HA (STHA) combined with mixed methods PC, on endurance running performance and directly compared PC and HA. Nine amateur trained runners completed 5-km treadmill time trials (TTs) in the heat (32° C, 60% relative humidity) under 4 conditions; no intervention (CON), PC, short-term HA (5 days-HA) and STHA with PC (HA + PC). Mean (±SD) performance times were; CON 1,476 (173) seconds, PC 1,421 (146) seconds, HA 1,378 (116) seconds and HA + PC 1,373 (121) seconds. This equated to the following improvements versus CON; PC -3.7%, HA -6.6% and HA + PC -7.0%. Statistical differences were only observed between HA and CON (p = 0.004, d = 0.68, 95% CI [-0.27 to 1.63]) however, similar effect sizes were observed for HA + PC vs. CON (d = 0.70, 95% CI [-0.25 to 1.65]), with smaller effects between PC vs. CON (d = 0.34, 95% CI [-0.59 to 1.27]), HA vs. PC (d = 0.33, 95% CI [-0.60 to 1.26]) and HA + PC vs. PC (d = 0.36, 95% CI [-0.57 to 1.29]). Pilot testing revealed a TT typical error of 16 seconds (1.2%). Precooling offered no further benefit to performance in the acclimated individual, despite modest alleviation of physiological strain. Maintenance of running speed in HA + PC, despite reduced physiological strain, may indicate an inappropriate pacing strategy therefore, further familiarization is recommended to optimize a combined strategy. Finally, these data indicate HA, achieved through cycle training, yields a larger ergogenic effect than PC on 5-km running performance in the heat, although PC remains beneficial when HA is not possible.
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http://dx.doi.org/10.1519/JSC.0000000000001979DOI Listing
May 2018

Cross-Adaptation: Heat and Cold Adaptation to Improve Physiological and Cellular Responses to Hypoxia.

Sports Med 2017 Sep;47(9):1751-1768

Welkin Human Performance Laboratories, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Denton Road, Eastbourne, UK.

To prepare for extremes of heat, cold or low partial pressures of oxygen (O), 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 O 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 O 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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http://dx.doi.org/10.1007/s40279-017-0717-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5554481PMC
September 2017

Females exposed to 24 h of sleep deprivation do not experience greater physiological strain, but do perceive heat illness symptoms more severely, during exercise-heat stress.

J Sports Sci 2018 Feb 24;36(3):348-355. Epub 2017 Mar 24.

a Centre for Sport and Exercise Science and Medicine (SESAME), Environmental Extremes Laboratory , University of Brighton , Eastbourne , UK.

There is limited and inconclusive evidence surrounding the physiological and perceptual responses to heat stress while sleep deprived, especially for females. This study aimed to quantify the effect of 24 h sleep deprivation on physiological strain and perceptual markers of heat-related illness in females. Nine females completed two 30-min heat stress tests (HST) separated by 48 h in 39°C, 41% relative humidity at a metabolic heat production of 10 W · kg. The non-sleep deprived HST was followed by the sleep deprivation (SDHST) trial for all participants during the follicular phase of the menstrual cycle. Physiological and perceptual measures were recorded at 5 min intervals during the HSTs. On the cessation of the HSTs, heat illness symptom index (HISI) was completed. HISI scores increased after sleep deprivation by 28 ± 16 versus 20 ± 16 (P = 0.01). Peak (39.40 ± 0.35°C vs. 39.35 ± 0.33°C) and change in rectal temperature (1.91 ± 0.21 vs. 1.93 ± 0.34°C), and whole body sweat rate (1.08 ± 0.31 vs. 1.15 ± 0.36 L · h) did not differ (P > 0.05) between tests. No difference was observed in peak, nor rise in: heart rate, mean skin temperature, perceived exertion or thermal sensation during the HSTs. Twenty-four hours sleep deprivation increased perceptual symptoms associated with heat-related illness; however, no thermoregulatory alterations were observed.
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http://dx.doi.org/10.1080/02640414.2017.1306652DOI Listing
February 2018

Short-term heat acclimation improves the determinants of endurance performance and 5-km running performance in the heat.

Appl Physiol Nutr Metab 2017 Mar 18;42(3):285-294. Epub 2016 Nov 18.

a Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne BN20 7UR, UK.

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), 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 (vV̇O; 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·min (7.3(4.0)%) and CON +1.9(3.7) mL·kg·min (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, vV̇O). 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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http://dx.doi.org/10.1139/apnm-2016-0349DOI Listing
March 2017

CAERvest® - a novel endothermic hypothermic device for core temperature cooling: safety and efficacy testing.

Int J Occup Saf Ergon 2018 Mar 2;24(1):118-128. Epub 2017 Feb 2.

a Centre for Sport and Exercise Science and Medicine (SeSAME), Environmental Extremes Laboratory , University of Brighton , UK.

Introduction: Cooling of the body is used to treat hyperthermic individuals with heatstroke or to depress core temperature below normal for neuroprotection. A novel, chemically activated, unpowered cooling device, CAERvest®, was investigated for safety and efficacy.

Methods: Eight healthy male participants (body mass 79.9 ± 1.9 kg and body fat percentage 16.1 ± 3.8%) visited the laboratory (20 °C, 40% relative humidity) on four occasions. Following 30-min rest, physiological and perceptual measures were recorded. Participants were then fitted with the CAERvest® proof of concept (PoC) or prototype 1 (P1), 2 (P2) or 3 (P3) for 60 min. Temperature, cardiovascular and perceptual measures were recorded every 5 min. After cooling, the CAERvest® was removed and the torso checked for cold-related injuries.

Results: Temperature measures significantly (p < 0.05) reduced pre to post in all trials. Larger reductions in core and skin temperatures were observed for PoC (-0.36 ± 0.18 and -1.55 ± 0.97 °C) and P3 (-0.36 ± 0.22 and -2.47 ± 0.82 °C), compared with P1 and P2. No signs of cold-related injury were observed at any stage.

Conclusion: This study demonstrates that the CAERvest® is an effective device for reducing body temperature in healthy normothermic individuals without presence of cold injury. Further research in healthy and clinical populations is warranted.
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http://dx.doi.org/10.1080/10803548.2016.1273640DOI Listing
March 2018

Short-term heat acclimation prior to a multi-day desert ultra-marathon improves physiological and psychological responses without compromising immune status.

J Sports Sci 2017 Nov 9;35(22):2249-2256. Epub 2016 Dec 9.

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.

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, 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 T was evident after STHA, with reductions in perceived Physical (P = 0.04) and General (P = 0.04) fatigue. Exercising T 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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http://dx.doi.org/10.1080/02640414.2016.1265142DOI Listing
November 2017

Hsp72 and Hsp90α mRNA transcription is characterised by large, sustained changes in core temperature during heat acclimation.

Cell Stress Chaperones 2016 11 11;21(6):1021-1035. Epub 2016 Aug 11.

Athlete Health and Performance Research Centre, ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.

Increased intracellular heat shock protein-72 (Hsp72) and heat shock protein-90α (Hsp90α) have been implicated as important components of acquired thermotolerance, providing cytoprotection during stress. This experiment determined the physiological responses characterising increases in Hsp72 and Hsp90α mRNA on the first and tenth day of 90-min heat acclimation (in 40.2 °C, 41.0 % relative humidity (RH)) or equivalent normothermic training (in 20 °C, 29 % RH). Pearson's product-moment correlation and stepwise multiple regression were performed to determine relationships between physiological [e.g. (T, sweat rate (SR) and heart rate (HR)] and training variables (exercise duration, exercise intensity, work done), and the leukocyte Hsp72 and Hsp90α mRNA responses via reverse transcription quantitative polymerase chain reaction (RT-QPCR) (n = 15). Significant (p < 0.05) correlations existed between increased Hsp72 and Hsp90α mRNA (r = 0.879). Increased core temperature was the most important criteria for gene transcription with ΔT (r = 0.714), SR (r = 0.709), T (r = 0.682), area under the curve where T ≥ 38.5 °C (AUC38.5 °C; r = 0.678), peak T (r = 0.661), duration T ≥ 38.5 °C (r = 0.650) and ΔHR (r = 0.511) each demonstrating a significant (p < 0.05) correlation with the increase in Hsp72 mRNA. The T AUC38.5 °C (r = 0.729), ΔT (r = 0.691), peak T (r = 0.680), T (r = 0.678), SR (r = 0.660), duration T ≥ 38.5 °C (r = 0.629), the rate of change in T (r = 0.600) and ΔHR (r = 0.531) were the strongest correlate with the increase in Hsp90α mRNA. Multiple regression improved the model for Hsp90α mRNA only, when T AUC38.5 °C and SR were combined. Training variables showed insignificant (p > 0.05) weak (r < 0.300) relationships with Hsp72 and Hsp90α mRNA. Hsp72 and Hsp90α mRNA correlates were comparable on the first and tenth day. When transcription of the related Hsp72 and Hsp90α mRNA is important, protocols should rapidly induce large, prolonged changes in core temperature.
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http://dx.doi.org/10.1007/s12192-016-0726-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5083671PMC
November 2016

Ischaemic preconditioning does not alter the determinants of endurance running performance in the heat.

Eur J Appl Physiol 2016 Sep 12;116(9):1735-45. Epub 2016 Jul 12.

Environmental Extremes Laboratory, Centre for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Welkin Laboratories, Denton Road, Eastbourne, BN20 7SN, UK.

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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http://dx.doi.org/10.1007/s00421-016-3430-yDOI Listing
September 2016

Power Relative to Body Mass Best Predicts Change in Core Temperature During Exercise-Heat Stress.

J Strength Cond Res 2017 Feb;31(2):403-414

1Center for Human Performance, Exercise and Rehabilitation (CHPER), Brunel University London, Uxbridge, United Kingdom; and 2Center for Sport and Exercise Science and Medicine (SESAME), University of Brighton, Eastbourne, United Kingdom.

Gibson, OR, Willmott, AGB, James, CA, Hayes, M, and Maxwell, NS. Power relative to body mass best predicts change in core temperature during exercise-heat stress. J Strength Cond Res 31(2): 403-414, 2017-Controlling internal temperature is crucial when prescribing exercise-heat stress, particularly during interventions designed to induce thermoregulatory adaptations. This study aimed to determine the relationship between the rate of rectal temperature (Trec) increase, and various methods for prescribing exercise-heat stress, to identify the most efficient method of prescribing isothermic heat acclimation (HA) training. Thirty-five men cycled in hot conditions (40° C, 39% R.H.) for 29 ± 2 minutes. Subjects exercised at 60 ± 9% V[Combining Dot Above]O2peak, with methods for prescribing exercise retrospectively observed for each participant. Pearson product moment correlations were calculated for each prescriptive variable against the rate of change in Trec (° C·h), with stepwise multiple regressions performed on statistically significant variables (p ≤ 0.05). Linear regression identified the predicted intensity required to increase Trec by 1.0-2.0° C between 20- and 45-minute periods and the duration taken to increase Trec by 1.5° C in response to incremental intensities to guide prescription. Significant (p ≤ 0.05) relationships with the rate of change in Trec were observed for prescriptions based on relative power (W·kg; r = 0.764), power (%Powermax; r = 0.679), rating of perceived exertion (RPE) (r = 0.577), V[Combining Dot Above]O2 (%V[Combining Dot Above]O2peak; r = 0.562), heart rate (HR) (%HRmax; r = 0.534), and thermal sensation (r = 0.311). Stepwise multiple regressions observed relative power and RPE as variables to improve the model (r = 0.791), with no improvement after inclusion of any anthropometric variable. Prescription of exercise under heat stress using power (W·kg or %Powermax) has the strongest relationship with the rate of change in Trec with no additional requirement to correct for body composition within a normal range. Practitioners should therefore prescribe exercise intensity using relative power during isothermic HA training to increase Trec efficiently and maximize adaptation.
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http://dx.doi.org/10.1519/JSC.0000000000001521DOI Listing
February 2017

Physiological and psychological responses in Fire Instructors to heat exposures.

J Therm Biol 2016 May 22;58:106-14. Epub 2016 Apr 22.

Centre for Sport and Exercise Science and Medicine (SESAME), Environmental Extremes Laboratory, University of Brighton, Hillbrow, Denton Road, Eastbourne BN20 7SR, UK. Electronic address:

Aim: Fire Service Instructors (FSI) are exposed to many repeated periods of high environmental temperatures when training firefighters. Such repeated exposures will impose significant strains on the function of instructors. We aimed to measure the effects of a training programme including repeated exposures to heat, termed "Wears" in the fire service, on the physiological, psychological some immunological markers of Fire Service Instructors.

Methods: Six FSI and six physiologically matched controls completed blood and cardiovascular tests pre and post a 4wk heat instruction training block, controls completed the tests only. FSI were given a 7wk period of no heat exposure prior to starting the training. Physiological and perceptual measures were taken pre and post the first and last Wear of the 4wk training protocol.

Results: There were acute effects of a Wear on core temperature and physiological strain index, as well as measures of fatigue. The acute exposure to heat during a Wear led to a consistent decrease in CRP (-10% to -40%), increased IL6 concentrations 33-45%) as well as increased RPE and TSS. Over the training programme significantly lower quantities of white cells, particularly neutrophils, leukocytes and monocytes were found in the FSI group. Between the start and the end of the 4 week training programme the FSI showed a significantly greater physiological strain index (PSI) to the Wears, which nearly doubled from 2.5 to 4.7 (p<0.05).

Conclusion: Physiological and psychological measures indicate that FSI may be experiencing symptoms and changes to their health consistent with an overtraining type condition.
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http://dx.doi.org/10.1016/j.jtherbio.2016.04.008DOI Listing
May 2016

Heat acclimation attenuates physiological strain and the HSP72, but not HSP90α, mRNA response to acute normobaric hypoxia.

J Appl Physiol (1985) 2015 Oct 23;119(8):889-99. Epub 2015 Jul 23.

Centre for Sport and Exercise Science and Medicine (SESAME), Environmental Extremes Laboratory, University of Brighton, Welkin Human Performance Laboratories, Eastbourne, United Kingdom;

Heat acclimation (HA) attenuates physiological strain in hot conditions via phenotypic and cellular adaptation. The aim of this study was to determine whether HA reduced physiological strain, and heat shock protein (HSP) 72 and HSP90α mRNA responses in acute normobaric hypoxia. Sixteen male participants completed ten 90-min sessions of isothermic HA (40°C/40% relative humidity) or exercise training [control (CON); 20°C/40% relative humidity]. HA or CON were preceded (HYP1) and proceeded (HYP2) by a 30-min normobaric hypoxic exposure [inspired O2 fraction = 0.12; 10-min rest, 10-min cycling at 40% peak O2 uptake (V̇O2 peak), 10-min cycling at 65% V̇O2 peak]. HA induced greater rectal temperatures, sweat rate, and heart rates (HR) than CON during the training sessions. HA, but not CON, reduced resting rectal temperatures and resting HR and increased sweat rate and plasma volume. Hemoglobin mass did not change following HA nor CON. HSP72 and HSP90α mRNA increased in response to each HA session, but did not change with CON. HR during HYP2 was lower and O2 saturation higher at 65% V̇O2 peak following HA, but not CON. O2 uptake/HR was greater at rest and 65% V̇O2 peak in HYP2 following HA, but was unchanged after CON. At rest, the respiratory exchange ratio was reduced during HYP2 following HA, but not CON. The increase in HSP72 mRNA during HYP1 did not occur in HYP2 following HA. In CON, HSP72 mRNA expression was unchanged during HYP1 and HYP2. In HA and CON, increases in HSP90α mRNA during HYP1 were maintained in HYP2. HA reduces physiological strain, and the transcription of HSP72, but not HSP90α mRNA in acute normobaric hypoxia.
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http://dx.doi.org/10.1152/japplphysiol.00332.2015DOI Listing
October 2015

Effect of Practical Precooling on Neuromuscular Function and 5-km Time-Trial Performance in Hot, Humid Conditions Among Well-Trained Male Runners.

J Strength Cond Res 2015 Jul;29(7):1925-36

1School of Sport and Service Management, University of Brighton, Eastbourne, United Kingdom; and 2English Institute of Sport, Bisham Abbey National Sports Centre, Marlow, United Kingdom.

This study investigated whether torso and thigh precooling during a warm-up effects neuromuscular function and 5-km time-trial performance in hot, humid conditions. Eight well-trained male runners completed 3 randomized time-trials in 32.2 ± 0.8° C and 48.6 ± 6.7% relative humidity. A 30-minute warm-up was completed with no cooling (Control), precooling by an ice vest (Vest), or ice packs covering the thighs (Packs). Before the warm-up and after the time-trial, supramaximal femoral nerve stimulation was delivered during and following maximal isometric contractions. Core and skin temperature, heart rate, and perceptual ratings were recorded before and during the warm-up and time-trial. Overall performance time was improved in Packs compared with Control (1,407 ± 80 seconds vs. 1,492 ± 88 seconds; p ≤ 0.05) but not in Vest (1,444 ± 71 seconds; p > 0.05). In Packs, a higher exercise intensity (p ≤ 0.05) and less cumulative time (p < 0.01) were evident during the last kilometer compared with Control. Maximum voluntary force, voluntary activation, muscle contractility, and membrane excitability were not different after exercise or between conditions. Ten minutes after the warm-up, skin temperature was lower in Vest and Packs compared with Control (p < 0.01). Thermal strain and body heat content change was lower in Vest and Packs, respectively (p ≤ 0.05). Findings indicate that torso and thigh precooling during a warm-up reduces thermoregulatory strain. However, thigh opposed to torso precooling provides greater performance improvements. Neuromuscular function did not aid performance, indicating that transient changes in afferent feedback and muscle recruitment may enhance endurance trial performance.
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http://dx.doi.org/10.1519/JSC.0000000000000840DOI Listing
July 2015
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