Cross-adaptation from heat stress to hypoxia: A systematic review and exploratory meta-analysis.

Cross-adaptation (CA) refers to the successful induction of physiological adaptation under one environmental stressor (e.g., heat), to enable subsequent benefit in another (e.g., hypoxia). This systematic review and exploratory meta-analysis investigated the effect of heat acclimation (HA) on physiological, perceptual and physical performance outcome measures during rest, and submaximal and maximal intensity exercise in hypoxia. Database searches in Scopus and MEDLINE were performed. Studies were included when they met the Population, Intervention, Comparison, and Outcome criteria, were of English-language, peer-reviewed, full-text original articles, using human participants. Risk of bias and study quality were assessed using the COnsensus based Standards for the selection of health status Measurement INstruments checklist. Nine studies were included, totalling 79 participants (100 % recreationally trained males). The most common method of HA included fixed-intensity exercise comprising 9 ± 3 sessions, 89 ± 24-min in duration and occurred within 39 ± 2 °C and 32 ± 13 % relative humidity. CA induced a moderate, beneficial effect on physiological measures at rest (oxygen saturation: g = 0.60) and during submaximal exercise (heart rate: g = -0.65, core temperature: g = -0.68 and skin temperature: g = -0.72). A small effect was found for ventilation (g = 0.24) and performance measures (peak power: g = 0.32 and time trial time: g = -0.43) during maximal intensity exercise. No effect was observed for perceptual outcome measures. CA may be appropriate for individuals, such as occupational or military workers, whose access to altitude exposure prior to undertaking submaximal activity in hypoxic conditions is restricted. Methodological variances exist within the current literature, and females and well-trained individuals have yet to be investigated. Future research should focus on these cohorts and explore the mechanistic underpinnings of CA.

Profile of Athletes With a Vision Impairment: Exploring Demographics and Ocular Pathologies of Athletes in Three Paralympic Sports.

OBJECTIVE: This study aimed to explore the profile of athletes with a vision impairment who compete in three Paralympic sports (goalball, vision impairment judo, and blind football). DESIGN: Descriptive and association analyses of the vision impairment athletes' profile were conducted. RESULTS: The typical athlete profile was a male (65.1%), aged 26-34 yrs (39.7%), from Europe (38.8%), representing a country with a high income (46.1%), and was diagnosed with a retinal-related ocular pathology (38.9%). In all three sports, the ages of the athletes were similar. In goalball, most athletes were from Europe, represented countries with a high income, and were diagnosed with retinal-, globe-, or neurological-related pathologies. In vision impairment judo, the majority of athletes were from Asia, represented countries with an upper middle income, and were diagnosed with retinal-, global-, or neurological-related pathologies. In blind football, most athletes were from Europe, represented countries with an upper middle income, and were diagnosed with retinal-, neurological-related ocular pathologies, or glaucoma. CONCLUSIONS: The homogeneity of the athletes' profile suggests that an effort is needed to target other parts of the vision impairment population to take part in vision impairment sports. Differences in the athletes' profiles across the sports provide information that may be useful for sport-specific talent identification.

Impact of Running With and Without a Guide on Short Distance Running Performance for Athletes With a Vision Impairment.

OBJECTIVE: This study aimed to investigate the difference of running with or without a guide on running performance (100, 200, and 400 m) for athletes with a vision impairment. DESIGN: Data including athletes' and guides' sex, age, and race times were extracted from 11 elite competitions. RESULTS: Male athletes predominantly ran without a guide (100 m = 91.4%, 200 m = 88.1%, 400 m = 84.8%), whereas female athletes mainly ran with a guide (100 m = 60.5%, 200 m = 80.0%, 400 m = 72.0%). No significant difference in 100-m race times was found between male athletes with or without a guide ( P = 0.647). For the 200 m ( P = 0.001) and 400 m ( P = 0.030), race times were significantly slower for male athletes running with a guide (mean rank 200 m = 36.80, 400 m = 33.57) compared to without a guide (mean rank 200 m = 19.43, 400 m = 21.69). Conversely, 100- ( P = 0.015), 200- ( P = 0.025), and 400-m ( P = 0.029) race times were significantly faster for female athletes with (mean rank 100 m = 18.25, 200 m = 13.71, 400 m = 11.00) compared with without a guide (mean rank 100 m = 27.74, 200 m = 22.67, 400 m = 21.69). CONCLUSIONS: Running with a guide affects vision impairment athletes' race times. The influence of running with a guide, and the gender mix of vision impairment athlete and guide, should be considered in any research with the aim of establishing a new classification system for vision impairment athletes.

The Effect of a Hydroxytyrosol-Rich, Olive-Derived Phytocomplex on Aerobic Exercise and Acute Recovery.

There is current scientific interest in naturally sourced phenolic compounds and their potential benefits to health, as well as the effective role polyphenols may provide in an exercise setting. This study investigated the chronic effects of supplementation with a biodynamic and organic olive fruit water phytocomplex (OliPhenolia® [OliP]), rich in hydroxytyrosol (HT), on submaximal and exhaustive exercise performance and respiratory markers of recovery. Twenty-nine recreationally active participants (42 ± 2 yrs; 71.1 ± 2.1 kg; 1.76 ± 0.02 m) consumed 2 × 28 mL∙d−1 of OliP or a taste- and appearance-matched placebo (PL) over 16 consecutive days. Participants completed a demanding, aerobic exercise protocol at ~75% maximal oxygen uptake (V˙O2max) for 65 min 24 h before sub- and maximal performance exercise tests prior to and following the 16-day consumption period. OliP reduced the time constant (τ) (p = 0.005) at the onset of exercise, running economy (p = 0.015) at lactate threshold 1 (LT1), as well as the rating of perceived exertion (p = 0.003) at lactate turnpoint (LT2). Additionally, OliP led to modest improvements in acute recovery based upon a shorter time to achieve 50% of the end of exercise V˙O2 value (p = 0.02). Whilst OliP increased time to exhaustion (+4.1 ± 1.8%), this was not significantly different to PL (p > 0.05). Phenolic compounds present in OliP, including HT and related metabolites, may provide benefits for aerobic exercise and acute recovery in recreationally active individuals. Further research is needed to determine whether dose-response or adjunct use of OliP alongside longer-term training programs can further modulate exercise-associated adaptations in recreationally active individuals, or indeed support athletic performance.

The Impact of a Natural Olive-Derived Phytocomplex (OliPhenolia®) on Exercise-Induced Oxidative Stress in Healthy Adults.

The role of natural polyphenols in reducing oxidative stress and/or supporting antioxidant mechanisms, particularly relating to exercise, is of high interest. The aim of this study was to investigate OliPhenolia® (OliP), a biodynamic and organic olive fruit water phytocomplex, rich in hydroxytyrosol (HT), for the first time within an exercise domain. HT bioavailability from OliP was assessed in fifteen healthy volunteers in a randomized, double-blind, placebo controlled cross-over design (age: 30 ± 2 yrs; body mass: 76.7 ± 3.9 kg; height: 1.77 ± 0.02 m), followed by a separate randomized, double-blinded, cohort trial investigating the short-term impact of OliP consumption (2 × 28 mL∙d−1 of OliP or placebo (PL) for 16-days) on markers of oxidative stress in twenty-nine recreationally active participants (42 ± 2 yrs; 71.1 ± 2.1 kg; 1.76 ± 0.02 m). In response to a single 28 mL OliP bolus, plasma HT peaked at 1 h (38.31 ± 4.76 ng∙mL−1), remaining significantly elevated (p < 0.001) until 4 h. Plasma malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH) and HT were assessed at rest and immediately following exercise (50 min at ~75% V˙O2max then 10 min intermittent efforts) and at 1 and 24 h post-exercise, before and after the 16-day supplementation protocol. Plasma HT under resting conditions was not detected pre-intervention, but increased to 6.3 ± 1.6 ng·mL−1 following OliP only (p < 0.001). OliP demonstrated modest antioxidant effects based on reduced SOD activity post-exercise (p = 0.016) and at 24 h (p ≤ 0.046), and increased GSH immediately post-exercise (p = 0.009) compared with PL. No differences were reported for MDA and CAT activity in response to the exercise protocol between conditions. The phenolic compounds within OliP, including HT, may have specific antioxidant benefits supporting acute exercise recovery. Further research is warranted to explore the impact of OliP following longer-term exercise training, and clinical domains pertinent to reduced oxidative stress.

Increased air temperature decreases high-speed, but not total distance, in international field hockey.

This study investigated the effect of heat stress on locomotor activity within international field hockey at team, positional and playing-quarter levels. Analysis was conducted on 71 matches played by the Malaysia national men's team against 24 opponents. Fixtures were assigned to match conditions, based on air temperature [COOL (14 ± 3°C), WARM (24 ± 1°C), HOT (27 ± 1°C), or VHOT (32 ± 2°C), p < 0.001]. Relationships between locomotor metrics and air temperature (AIR), absolute and relative humidity, and wet bulb globe temperature (WBGT) were investigated further using correlation and regression analyses. Increased AIR and WBGT revealed similar correlations (p < 0.01) with intensity metrics; high-speed running (AIR r = -0.51, WBGT r = -0.45), average speed (AIR r = -0.48, WBGT r = -0.46), decelerations (AIR r = -0.41, WBGT r = -0.41), sprinting efforts (AIR r = -0.40, WBGT r = -0.36), and sprinting distance (AIR r = -0.37, WBGT r = -0.29). In comparison to COOL, HOT, and VHOT matches demonstrated reduced high-speed running intensity (-14-17%; p < 0.001), average speed (-5-6%; p < 0.001), sprinting efforts (-17%; p = 0.010) and decelerations per min (-12%; p = 0.008). Interactions were found between match conditions and playing quarter for average speed (+4-7%; p = 0.002) and sprinting distance (+16-36%; p < 0.001), both of which were higher in the fourth quarter in COOL versus WARM, HOT and VHOT. There was an interaction for "low-speed" (p < 0.001), but not for "high-speed" running (p = 0.076) demonstrating the modulating effect of air temperature (particularly >25°C) on pacing within international hockey. These are the first data demonstrating the effect of air temperature on locomotor activity within international men's hockey, notably that increased air temperature impairs high-intensity activities by 5-15%. Higher air temperatures compromise high-speed running distances between matches in hockey.

Volume and Intensity of Locomotor Activity in International Men's Field Hockey Matches Over a 2-Year Period.

The locomotor demands of international men's field hockey matches were investigated across positions (DEF, MID, FWD) and playing quarters. Volume (i.e., total values) and intensity (i.e., relative to playing time) data were collected using 10-Hz GPS/100-Hz accelerometer units from the #11 world-ranked (WR) team, during 71 matches, against 24 opponents [WR 12 ± 11 (range, 1-60)]. Mean ± SD team total distance (TD) was 4,861 ± 871 m, with 25% (1,193 ± 329 m) "high-speed running" (>14.5 km h-1) and 8% (402 ± 144 m) "sprinting" (>19.0 km h-1). Reduced TD (range, -3 to 4%) and average speed (range, -3.4 to 4.7%) occurred through subsequent quarters, vs. Q1 (p < 0.05). A "large" negative relationship (r = -0.64) was found between playing duration and average speed. Positional differences (p < 0.05) were identified for all volume metrics including; playing duration (DEF, 45:50 ± 8:00 min; MID, 37:37 ± 7:12 min; FWD, 33:32 ± 6:22 min), TD (DEF, 5,223 ± 851 m; MID, 4,945 ± 827 m; FWD, 4,453 ± 741 m), sprinting distance (DEF, 315 ± 121 m; MID, 437 ± 144 m; FWD, 445 ± 129 m), and acceleration efforts (>2 m s-2; DEF, 48 ± 12; MID, 51 ± 11; FWD, 50 ± 14). Intensity variables similarly revealed positional differences (p < 0.05) but with a different pattern between positions; average speed (DEF, 115 ± 10 m min-1; MID, 132 ± 10 m min-1; FWD, 134 ± 15 m min-1), sprinting (DEF, 7 ± 3 m min-1; MID, 12 ± 4 m min-1; FWD, 14 ± 4 m min-1), and accelerations (DEF, 1.1 ± 0.3 n min-1; MID, 1.4 ± 0.2 n min-1; FWD, 1.5 ± 0.3 n min-1). Physical outputs reduced across playing quarters, despite unlimited substitutions, demonstrating the importance of optimizing physical preparation prior to international competition. Volume and intensity data highlight specific positional requirements, with forwards displaying shorter playing durations but greater high-intensity activities than defenders.

The Impact of Decaffeinated Green Tea Extract on Fat Oxidation, Body Composition and Cardio-Metabolic Health in Overweight, Recreationally Active Individuals.

This study investigated the effect of decaffeinated green tea extract (dGTE), with or without antioxidant nutrients, on fat oxidation, body composition and cardio-metabolic health measures in overweight individuals engaged in regular exercise. Twenty-seven participants (20 females, 7 males; body mass: 77.5 ± 10.5 kg; body mass index: 27.4 ± 3.0 kg·m2; peak oxygen uptake (O2peak): 30.2 ± 5.8 mL·kg-1·min-1) were randomly assigned, in a double-blinded manner, either: dGTE (400 mg·d-1 (-)-epigallocatechin-3-gallate (EGCG), n = 9); a novel dGTE+ (400 mg·d-1 EGCG, quercetin (50 mg·d-1) and α-lipoic acid (LA, 150 mg·d-1), n = 9); or placebo (PL, n = 9) for 8 weeks, whilst maintaining standardised, aerobic exercise. Fat oxidation ('FATMAX' and steady state exercise protocols), body composition, cardio-metabolic and blood measures (serum glucose, insulin, leptin, adiponectin, glycerol, free fatty acids, total cholesterol, high [HDL-c] and low-density lipoprotein cholesterol [LDL-c], triglycerides, liver enzymes and bilirubin) were assessed at baseline, week 4 and 8. Following 8 weeks of dGTE+, maximal fat oxidation (MFO) significantly improved from 154.4 ± 20.6 to 224.6 ± 23.2 mg·min-1 (p = 0.009), along with a 22.5% increase in the exercise intensity at which fat oxidation was deemed negligible (FATMIN; 67.6 ± 3.6%O2peak, p = 0.003). Steady state exercise substrate utilisation also improved for dGTE+ only, with respiratory exchange ratio reducing from 0.94 ± 0.01 at week 4, to 0.89 ± 0.01 at week 8 (p = 0.004). This corresponded with a significant increase in the contribution of fat to energy expenditure for dGTE+ from 21.0 ± 4.1% at week 4, to 34.6 ± 4.7% at week 8 (p = 0.006). LDL-c was also lower (normalised fold change of -0.09 ± 0.06) for dGTE+ by week 8 (p = 0.038). No other significant effects were found in any group. Eight weeks of dGTE+ improved MFO and substrate utilisation during exercise, and lowered LDL-c. However, body composition and cardio-metabolic markers in healthy, overweight individuals who maintained regular physical activity were largely unaffected by dGTE.

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

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 - 1), 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-1), plasma volume expansion (+6.0%) and, importantly, increased sweat loss (+370 mL) and sweat gland activity (+12 glands·cm2) with decreased sweat [Na+] (-18 mmol·L - 1). 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.

Assessing the impact of a mushroom-derived food ingredient on vitamin D levels in healthy volunteers.

BACKGROUND: Prevalence of vitamin D insufficiency/deficiency has been noted in athletic populations, although less is known about recreationally active individuals. Biofortification of natural food sources (e.g. UV radiated mushrooms) may support vitamin D status and is therefore of current scientific and commercial interest. The aim of this study was to assess the impact of a mushroom-derived food ingredient on vitamin D status in recreationally active, healthy volunteers. METHODS: Twenty-eight participants were randomly assigned to either: 25 µg (1000 IU) encapsulated natural mushroom-derived vitamin D2; matched-dose encapsulated vitamin D3 or placebo (PL) for 12 weeks. Venous blood samples were collected at baseline, week 6 and 12 for analysis of serum 25(OH)D2 and 25(OH)D3 using liquid chromatography mass spectrometry. Habitual dietary intake and activity were monitored across the intervention. RESULTS: Vitamin D status (25(OH)DTOTAL) was significantly increased with vitamin D3 supplementation from 46.1 ± 5.3 nmol·L- 1 to 88.0 ± 8.6 nmol·L- 1 (p < 0.0001) across the intervention, coupled with an expected rise in 25(OH)D3 concentrations from 38.8 ± 5.2 nmol·L- 1 to 82.0 ± 7.9 nmol·L- 1 (p < 0.0001). In contrast, D2 supplementation increased 25(OH)D2 by + 347% (7.0 ± 1.1 nmol·L- 1 to 31.4 ± 2.1 nmol·L- 1, p < 0.0001), but resulted in a - 42% reduction in 25(OH)D3 by week 6 (p = 0.001). A net + 14% increase in 25(OH)DTOTAL was established with D2 supplementation by week 12 (p > 0.05), which was not statistically different to D3. Vitamin D status was maintained with PL, following an initial - 15% reduction by week 6 (p ≤ 0.046 compared to both supplement groups). CONCLUSIONS: The use of a UV radiated mushroom food ingredient was effective in maintaining 25(OH)DTOTAL in healthy, recreationally active volunteers. This may offer an adjunct strategy in supporting vitamin D intake. However, consistent with the literature, the use of vitamin D3 supplementation likely offers benefits when acute elevation in vitamin D status is warranted.

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

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.

The physiological and perceptual responses of stand-up paddle board exercise in a laboratory- and field-setting.

This study quantified the physiological and perceptual responses of stand-up paddle boarding (SUP) during a range of stroke rates in a laboratory- and field-setting. Ten participants (eight male, two female; mean ± standard deviation [SD] age: 23 ± 3 years; body mass: 70.5 ± 9.1 kg; height: 170 ± 9 cm; body mass index [BMI]: 24.3 ± 1.5 kg m2) completed a SUP ⩒O2peak trial, and two SUP trials in both a laboratory- and field-setting (5-min at 10, 20 and 30 strokes min-1 per stage). Energy expenditure (EE), metabolic equivalents (METs), heart rate (HR) and rating of perceived exertion (RPE) were recorded throughout. In the laboratory-setting, mean ± SD EE and METs increased (P < .001) linearly when SUP at 10 (3.3 ± 1.0 kcal min-1, 2.7 ± 0.5), 20 (5.5 ± 0.9 kcal min-1, 4.4 ± 0.7) and 30 strokes min-1 (7.6 ± 1.6 kcal min-1, 6.1 ± 1.2), respectively. During these efforts, mean ± SD percentage of maximal HR were 56 ± 5%, 69 ± 6% and 84 ± 8%, respectively. In the field-setting, mean ± SD EE and METs also increased (P < .001) linearly when SUP at 10 (3.6 ± 0.9 kcal min-1, 2.7 ± 0.9), 20 (4.3 ± 1.8 kcal min-1, 3.5 ± 1.0) and 30 strokes min-1 (6.3 ± 2.1 kcal min-1, 4.6 ± 1.4). During the three conditions, mean ± SD percentage of maximal HR were 58 ± 8%, 65 ± 7% and 73 ± 9%. SUP at ≥20 strokes min-1 in the laboratory- and field-setting meet the criteria for moderate-intensity exercise (3.0-5.9 METs). These findings may now be included in the latest Compendium of Physical Activities guidelines and offer the potential to improve cardiorespiratory fitness if SUP is undertaken regularly by young, healthy adults.

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

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; SEE : Standard error of the estimate for the regression equation; STHA: Short-term heat acclimation; TDHA: Twice daily heat acclimation; TC: Thermal Comfort; Tre: Rectal temperature; TSS: Thermal sensation; V̇O2peak: Peak oxygen uptake; WBSL: whole-body sweat loss.

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

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-1 [4%]), COD (31.8 m [6%], 0.4 km·h-1 [2%]) and TSSC protocols (12.9 m [2%], 0.5 km·h-1 [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 [1%]), COD (12.8 m [2%], 0.2 km·h-1 [1%]) and TSSC protocols (6.9 m [1%], 0.6 km·h-1 [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.

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

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.

Physiological and perceptual responses to exercising in restrictive heat loss attire with use of an upper-body sauna suit in temperate and hot conditions.

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.

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

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.

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

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.

Defining the determinants of endurance running performance in the heat.

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 (V̇O2max), running economy (RE), velocity at V̇O2max (vV̇O2max), and running speeds corresponding to the lactate threshold (LT, 2 mmol.l-1) and lactate turnpoint (LTP, 4 mmol.l-1). Simultaneous multiple linear regression was used to predict 5 km time, using these determinants, indicating neither GXTHOT (R2 = 0.72) nor GXTCOOL (R2 = 0.86) predicted performance in the heat as strongly has previously been reported in cool conditions. vV̇O2max was the strongest individual predictor of performance, both when assessed in GXTHOT (r = -0.83) and GXTCOOL (r = -0.90). The GXTs revealed the following correlations for individual predictors in GXTHOT; V̇O2maxr = -0.7, RE r = 0.36, LT r = -0.77, LTP r = -0.78 and in GXTCOOL; V̇O2maxr = -0.67, RE r = 0.62, LT r = -0.79, LTP r = -0.8. These data indicate (i) GXTHOT does not predict 5 km running performance in the heat as strongly as a GXTCOOL, (ii) as in cool conditions, vV̇O2max may best predict running performance in the heat.

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

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.