The reliability of a portable steam sauna pod for the whole-body passive heating of humans.

INTRODUCTION: Passive heating is receiving increasing attention within human performance and health contexts. A low-cost, portable steam sauna pod may offer an additional tool for those seeking to manipulate physiological (cardiovascular, thermoregulatory and sudomotor) and perceptual responses for improving sporting or health profiles. This study aimed to 1) report the different levels of heat stress and determine the pods' inter-unit reliability, and 2) quantify the reliability of physiological and perceptual responses to passive heating. METHOD: In part 1, five pods were assessed for temperature and relative humidity (RH) every 5 min across 70 min of heating for each of the 9 settings. In part 2, twelve males (age: 24 ± 4 years) completed two 60 min trials of passive heating (3 × 20 min at 44 °C/99% RH, separated by 1 week). Heart rate (HR), rectal (Trectal) and tympanic temperature (Ttympanic) were recorded every 5 min, thermal comfort (Tcomfort) and sensation (Tsensation) every 10 min, mean arterial pressure (MAP) at each break period and sweat rate (SR) after exiting the pod. RESULTS: In part 1, setting 9 provided the highest temperature (44.3 ± 0.2 °C) and longest time RH remained stable at 99% (51±7 min). Inter-unit reliability data demonstrated agreement between pods for settings 5-9 (intra-class correlation [ICC] >0.9), but not for settings 1-4 (ICC <0.9). In part 2, between-visits, high correlations, and low typical error of measurement (TEM) and coefficient of variation (CV) were found for Trectal, HR, MAP, SR, and Tcomfort, but not for Ttympanic or Tsensation. A peak Trectal of 38.09 ± 0.30 °C, HR of 124 ± 15 b min-1 and a sweat loss of 0.73 ± 0.33 L were reported. No between-visit differences (p > 0.05) were observed for Trectal, Ttympanic, Tsensation or Tcomfort, however HR (+3 b.min-1) and MAP (+4 mmHg) were greater in visit 1 vs. 2 (p < 0.05). CONCLUSION: Portable steam sauna pods generate reliable heat stress between-units. The highest setting (44 °C/99% RH) also provides reliable but modest adjustments in physiological and perceptual responses.

Resource-efficient frequency conversion for quantum networks via sequential four-wave mixing.

We report a resource-efficient scheme in which a single pump laser was used to achieve frequency conversion by Bragg-scattering four-wave mixing in a photonic crystal fiber. We demonstrate bidirectional conversion of coherent light between Sr+2P1/2→2D3/2 emission wavelength at 1092 nm and the telecommunication C band with conversion efficiencies of 4.2% and 37% for up- and down-conversion, respectively. We discuss how the scheme may be viably scaled to meet the temporal, spectral, and polarization stability requirements of a hybrid light-matter quantum network.

Menthol as an Ergogenic Aid for the Tokyo 2021 Olympic Games: An Expert-Led Consensus Statement Using the Modified Delphi Method.

INTRODUCTION: Menthol topical application and mouth rinsing are ergogenic in hot environments, improving performance and perception, with differing effects on body temperature regulation. Consequently, athletes and federations are beginning to explore the possible benefits to elite sport performance for the Tokyo 2021 Olympics, which will take place in hot (~ 31 °C), humid (70% RH) conditions. There is no clear consensus on safe and effective menthol use for athletes, practitioners, or researchers. The present study addressed this shortfall by producing expert-led consensus recommendations. METHOD: Fourteen contributors were recruited following ethical approval. A three-step modified Delphi method was used for voting on 96 statements generated following literature consultation; 192 statements total (96/96 topical application/mouth rinsing). Round 1 contributors voted to "agree" or "disagree" with statements; 80% agreement was required to accept statements. In round 2, contributors voted to "support" or "change" their round 1 unaccepted statements, with knowledge of the extant voting from round 1. Round 3 contributors met to discuss voting against key remaining statements. RESULTS: Forty-seven statements reached consensus in round 1 (30/17 topical application/rinsing); 14 proved redundant. Six statements reached consensus in round 2 (2/4 topical application/rinsing); 116 statements proved redundant. Nine further statements were agreed in round 3 (6/3 topical application/rinsing) with caveats. DISCUSSION: Consensus was reached on 62 statements in total (38/24 topical application/rinsing), enabling the development of guidance on safe menthol administration, with a view to enhancing performance and perception in the heat without impairing body temperature regulation.

Intermittent sprint performance in the heat is not altered by augmenting thermal perception via L-menthol or capsaicin mouth rinses.

PURPOSE: Cooling sensations elicited by mouth rinsing with L-menthol have been reported as ergogenic. Presently, responses to L-menthol mouth rinsing during intermittent sprint performance (ISP) in the heat are unknown and the impact of increased thermal perception on ISP via capsaicin has also not been quantified. This experiment aimed to identify whether eliciting cooling/warming sensations via L-menthol/capsaicin would alter ISP in the heat. METHOD: Fourteen participants (mass = 72 ± 9 kg, [Formula: see text] = 3.30 ± 0.90 L min-1), undertook four experimental trials, involving 40 min of ISP in hot conditions (40.2 ± 0.6 °C, 42 ± 2% R.H.) with mouth rinsing (25 mL, 6 s) at the protocol onset, and every 10 min thereafter. Cooling (0.01% L-menthol; MEN), warming (0.2% capsaicin; CAP), placebo (0.3 sham-CHO; PLA), and control (water; CON) mouth rinses were utilized. Performance was quantified via power (PP) and work done (WD) during sprints. Heart rate (HR), core (Trec) and skin (Tskin) temperature, perceived exertion (RPE), thermal sensation (Tsens), and comfort (Tcom) were measured at 10 min intervals. Sweat rate (whole-body sweat rate) was calculated from ∆mass. RESULT: PP reduced over time (P < 0.05); however, no change was observed between trials for PP or WD (P > 0.05). Tcom increased over time and was lower in MEN (2.7 ± 1.1; P < 0.05) with no difference between CAP (3.1 ± 1.2), PLA (3.2 ± 1.3) and CON (3.1 ± 1.3). RPE, Tsens HR, Trec, and Tskin increased over time (P < 0.05) with no between trial differences (P > 0.05). CONCLUSION: Despite improved thermal comfort via L-menthol, ISP did not improve. Capsaicin did not alter thermal perception or ISP. The reduction in ISP over time in hot conditions is not influenced by thermal perception.

The time course of endogenous erythropoietin, IL-6, and TNFα in response to acute hypoxic exposures.

Erythropoietin (EPO) rapidly decreases on return to sea level (SL) after chronic altitude exposure. Acute hypoxia may provide an additional stimulus to prevent the decline in EPO. Proinflammatory cytokines, interleukin-6 (IL-6), and tumor necrosis factor alpha (TNFα) have been shown to inhibit EPO production. Optimal normobaric hypoxic exposure has not been established; therefore, investigation of methods eliciting the greatest response in EPO to limit physiological stress is required. Eight men (age 27 ± 4 years, body mass 77.5 ± 9.0 kg, height 179 ± 6 cm) performed four passive exposures to different normobaric hypoxic severities [FiO2 : 0.209 (SL), FiO2 : ~0.135 (3600 m), FiO2 : ~0.125 (4200 m) and FiO2 : ~0.115 (4800 m)] in a hypoxic chamber for 2 h. Venous blood was drawn pre-exposure and then at 1, 2, 4, 6, and 8 h to determine EPO concentration ([EPO]), IL-6, and TNFα. During 4200 and 4800 m, [EPO] increased from 5.9 ± 1.5 to 8.1 ± 1.5 mU/mL (P = 0.009) and 6.0 ± 1.4 to 8.9 ± 2.0 mU/mL (P = 0.037), respectively, with [EPO] increase peaking at 4 h (2 h post-exposure). There were no differences in IL-6 or TNFα during or post-exposure. Increased [EPO] was found 2 h post hypoxic exposure as result of 2 h of normobaric hypoxia ≥4200 m. There was no dose-response relationship in [EPO] between simulated hypoxia severities.

Combined active and passive heat exposure induced heat acclimation in a soccer referee before 2014 FIFA World Cup.

INTRODUCTION: The 2014 FIFA World Cup was held in Brazil, where the climatic conditions presented a significant thermoregulatory and perceptual challenge to those unfamiliar with the heat and humidity. CASE PRESENTATION: This case report documents the adaptation induced by a novel mixed methods (isothermic and passive) heat acclimation (HA) regime for a northern European professional soccer match official prior to the tournament. The intervention involved 13 HA sessions over an 18 day period comprising five isothermic HA sessions whereby intermittent running was used to target and maintain tympanic temperature (Tytemp) at 38 °C for 90 min, and seven passive HA sessions of 48 °C water bathing for 30 min. The athlete performed a heat stress test (HST) (35 min running at four incremental intensities in 30 °C) and a repeated high-intensity running test (as many 30 s self-paced efforts as possible, to a maximum of 20, with 30 s passive recovery) before and after the intervention. The mixed methods HA regime increased plasma volume (+7.1 %), and sweat loss (+0.9 L h(-1)), reduced exercising Tytemp (-0.6 °C), and mean body temperature (-0.5 °C). High-intensity running performance improved after HA (+29 %), as did the perception of thermal comfort during exercise (-0.3 units). CONCLUSION: This data evidences the effectiveness of a practical, mixed methods HA strategy, remotely implemented around training and competition, at inducing the heat acclimation phenotype in a high-level soccer match official.

The effects of single versus twice daily short term heat acclimation on heat strain and 3000m running performance in hot, humid conditions.

Endurance performances are impaired under conditions of elevated heat stress. Short term heat acclimation (STHA) over 4-6 days can evoke rapid adaptation, which mitigate decrements in performance and alleviate heat strain. This study investigated the efficacy of twice daily heat acclimation (TDHA) compared to single session per day heat acclimation (SDHA) and normothermic training, at inducing heat acclimation phenotype and its impact upon running performance in hot, humid conditions. Twenty one, moderately trained males were matched and assigned to three groups; SDHA (mean±SD) (peak oxygen consumption [V̇O2peak] 45.8±6.1mLkg(-1)min(-1), body mass 81.3±16.0kg, stature 182±3cm), TDHA (46.1±7.0mLkg(-1)min(-1), 80.1±11.9kg, 178±4cm) or control (CON) (47.1±3.5mLkg(-1)min(-1), 78.6±16.7kg, 178±4cm). Interventions consisted of 45min cycling at 50% V̇O2peak, once daily for 4d (SDHA) and twice daily for 2d (TDHA), in 35°C, 60% relative humidity (RH), and once daily for 4 days (CON) in 21°C, 40% RH. Participants completed a pre- and post-intervention 5km treadmill run trial in 30°C, 60% RH, where the first 2km were fixed at 40% V̇O2peak and the final 3km was self-paced. No statistically significant interaction effects occurred within- or between-groups over the 2-4 days intervention. While within-group differences were found in physiological and perceptual measures during the fixed intensity trial post-intervention, they did not statistically differ between-groups. Similarly, TDHA (-36±34s [+3.5%]) and SDHA (-26±28s [+2.8%]) groups improved 3km performances (p=0.35), but did not differ from CON (-6±44s [+0.6%]). This is the first study to investigate the effects of HA twice daily and compare it with traditional single session per day STHA. These STHA protocols may have the ability to induce partial adaptive responses to heat stress and possibly enhance performance in environmentally challenging conditions, however, future development is warranted to optimise the administration to provide a potent stimuli for heat adaptation in athletic and military personnel within a rapid regime.

Leukocyte Hsp72 mRNA transcription does not differ between males and females during heat acclimation.

Purpose: Thermotolerance is an acquired state of increased cytoprotection achieved following single or repeated exposures to heat stress, in part characterized by changes in the intracellular 72 kda heat shock protein (HSP72; HSPA1A). Females have demonstrated reduced exercise induced HSP72 in comparison to males. This study examined sex differences in heat shock protein 72 messenger ribonucleic acid (Hsp72 mRNA) transcription during heat acclimation (HA) to identify whether sex differences were a result of differential gene transcription. Methods: Ten participants (5M, 5F) performed 10, 90 min controlled hyperthermia [rectal temperature (Tre) ≥ 38.5°C] HA sessions over 12 d. Leukocyte Hsp72 mRNA was measured pre and post D1, D5, and D10, via Reverse transcription polymerase chain reaction (RT-QPCR). Results: HA was evidenced by a reduction in resting Tre (-0.4 ± 0.5°C) and resting heart rate [(HR); -13 ± 7 beats.min-1] following HA (p ≤ 0.05). During HA no difference (p > 0.05) was observed in ΔTre between males (D1 = 1.5 ± 0.2°C; D5 = 1.6 ± 0.4°C; D10 = 1.8 ± 0.3°C) and females (D1 = 1.5 ± 0.5°C; D5 = 1.4 ± 0.2°C; D10 = 1.8 ± 0.3°C). This was also true of mean Tre demonstrating equality of thermal stimuli for mRNA transcription and HA. There were no differences (p > 0.05) in Hsp72 mRNA expression between HA sessions or between males (D1 = +1.8 ± 1.5-fold; D5 = +2.0 ± 1.0 fold; D10 = +1.1 ± 0.4-fold) and females (D1 = +2.6 ± 1.8-fold; D5 = +1.8 ± 1.4-fold; D10 = +0.9 ± 1.9-fold). Conclusions: This experiment demonstrates that there is no difference in Hsp72 mRNA increases during HA between sexes when controlled hyperthermia HA is utilised. Gender specific differences in exercise-induced HSP72 reported elsewhere likely result from post-transcriptional events.

Physiological responses to incremental exercise in the heat following internal and external precooling.

Twelve males completed three incremental, discontinuous treadmill tests in the heat [31.9(1.0) °C, 61.9(8.9)%] to determine speed at two fixed blood lactate concentrations (2 and 3.5 mmol/L), running economy (RE), and maximum oxygen uptake ( V ˙ O 2 m a x ). Trials involved 20 min of either internal cooling (ICE, 7.5 g/kg ice slurry ingestion) or mixed-methods external cooling (EXT, cold towels, forearm immersion, ice vest, and cooling shorts), alongside no intervention (CON). Following precooling, participants ran 0.3 km/h faster at 2 mmol/L and 0.2 km/h faster at 3.5 mmol/L (P = 0.04, partial η(2) = 0.27). Statistical differences were observed vs CON for ICE (P = 0.03, d = 0.15), but not EXT (P = 0.12, d = 0.15). There was no effect of cooling on RE (P = 0.81, partial η(2) = 0.02), nor on V ˙ O 2 m a x (P = 0.69, partial η(2) = 0.04). An effect for cooling on physiological strain index was observed (P < 0.01, partial η(2) = 0.41), with differences vs CON for EXT (P = 0.02, d = 0.36), but not ICE (P = 0.06, d = 0.36). Precooling reduced thermal sensation (P < 0.01, partial η(2) = 0.66) in both cooling groups (P < 0.01). Results indicate ICE and EXT provide similar physiological responses for exercise up to 30 min duration in the heat. Differing thermoregulatory responses are suggestive of specific event characteristics determining the choice of cooling. Precooling appears to reduce blood lactate accumulation and reduce thermoregulatory and perceptual strain during incremental exercise.

A comparison of males and females' temporal patterning to short- and long-term heat acclimation.

The current study assessed sex differences in thermoregulatory and physiological adaptation to short-term (STHA) and long-term heat acclimation (LTHA). Sixteen (eight males; eight females) participants performed three running heat tolerance tests (RHTT), preceding HA (RHTT1), following 5 days HA (RHTT2) and 10 days HA (RHTT3). The RHTT involved 30-min running (9 km/h, 2% gradient) in 40 °C, 40% relative humidity. Following STHA, resting rectal temperature (Trrest ) (males: -0.24 ± 0.16 °C, P ≤ 0.001; females: -0.02 ± 0.08 °C, P = 0.597), peak rectal temperature (Trpeak ) (males: -0.39 ± 0.36 °C, P ≤ 0.001; females -0.07 ± 0.18 °C, P = 0.504), and peak heart rate (males: -14 ± 12 beats/min, P ≤ 0.001; females: -5 ± 3 beats/min, P = 0.164) reduced in males, but not females. Following STHA, sweat rate relative to body surface area (SRBSA ) increased (428 ± 269 g/h/m(2) , P = 0.029) in females, but not males (-11 ± 286 g/h/m(2) , P = 0.029). Following LTHA, Trrest (males: -0.04 ± 0.15 °C, P = 0.459; females: -0.22 ± 0.12 °C, P ≤ 0.01) and Trpeak (males: -0.05 ± 0.26 °C, P = 0.590; females: -0.41 ± 0.24 °C, P ≤ 0.01) reduced in females, but not males. Following LTHA, SRBSA increased in males (308 ± 346 g/h/m(2) , P = 0.029), but not females (44 ± 373 g/h/m(2) , P = 0.733). Males and females responded to STHA; however, females required LTHA to establish thermoregulatory and cardiovascular stability. HA protocols should be designed to target sex differences in thermoregulation for optimal adaptation.

Isothermic and fixed-intensity heat acclimation methods elicit equal increases in Hsp72 mRNA.

Thermotolerance, to which heat shock protein-72 (Hsp72) contributes, is an acquired state achieved following heat acclimation (HA), eliciting cellular adaption and protection against thermal stress. Optimal HA methods achieving the greatest heat shock response (HSR) are equivocal; therefore, investigation of methods provoking the greatest sustained HSR is required to optimize cellular adaptation. Twenty-four males performed short-term HA (STHA; five sessions) and long-term HA (LTHA; STHA plus further five sessions) utilizing fixed-intensity (FIXED; workload = 50% V ˙ O 2 p e a k ), continuous isothermic HA [ISOCONT ; target rectal temperature (Trec ) = 38.5 °C], or progressive isothermic HA (ISOPROG ; target Trec = 38.5 °C for STHA then target Trec = 39.0 °C for LTHA). Leukocyte Hsp72 mRNA was measured pre- and post day 1, day 5, and day 10 of HA via reverse transcription quantitative polymerase chain reaction to determine the HSR. Hsp72 mRNA increased (P < 0.05) pre- to post day 1, pre- to post day 5, and pre to post day 10 in FIXED, ISOCONT , and ISOPROG , but no differences were observed between methods (P > 0.05). The equal Hsp72 mRNA increases occurring from consistent, reduced, or increased endogenous strain following STHA and LTHA suggest that transcription occurs following attainment of sufficient endogenous criteria. These data give confidence that all reported HA methods increase Hsp72 mRNA and are capable of eliciting adaptations toward thermotolerance.

Simulated hypoxia does not further improve aerobic capacity during sprint interval training.

AIM: The aim of this study was to investigate the use of hypoxic sprint interval training (SIT) for the improvement of aerobic capacity. METHOD: Twenty-seven participants (mean±SD), age 21±1 yrs, body mass 72.4±9.7 kg and height 175±7 cm, completed an V̇O2peak Incremental Exercise Test and time to exhaustion (TTE) trial (80% V̇O2peak) pre and post SIT. Participants were randomly assigned to either, control (CONT), normoxic (NORM) or hypoxic (FiO2: 0.15) (HYP) conditions. SIT involved 30 s sprints interspersed with 4 min rest. The number of sprints progressed from four to seven over six sessions separated by 1-2 days rest. Two-way mixed design ANOVA was performed to determine changes between conditions. RESULTS: V̇O2peak improved (P<0.05) pre to post SIT in NORM (11.2±10.8%) and HYP (10.9±6.2%), but not CONT (0.7±14.3%). TTE post SIT was significantly improved from pre SIT in NORM and HYP but not CONT (CONT=1±6, NORM=56±25, HYP=34±25%, P<0.05). Peak and recovery heart rate was lower in NORM (P<0.05) than HYP as SIT sessions progressed. SpO2 (%) was lower in HYP (86.1±4.3%) compared to NORM (97.1±0.7%), decreasing within all HYP sessions, and increasing with SIT. CONCLUSION: Hypoxic and normoxic SIT caused improvement in V̇O2peak and TTE compared to a control. Hypoxic SIT did not cause further improvements, indicating hypoxia based SIT offers no additional benefit for improvement of endurance performance.

Simulated moderate hypoxia reduces intermittent sprint performance in games players.

BACKGROUND: Exercise at altitude places additional physiological stress on the individual in comparison with sea-level performance. This study examines the effect of a moderate hypoxic environment (FiO2=~17%) on intermittent sprint exercise performance. METHODS: Nine male games players completed two consecutive sets of a 40 minute cycling intermittent sprint protocol (CISP×2) in a hypoxic (HYP; FiO2=~17%) and normoxic (NORM; FiO2=~21%) environment. During each sprint peak power output (PPO; the highest power during each 5 s sprint), mean power output (MPO; the average power during the 3 s sprint) were measured and total work done (WD; force applied from the highest 3 s period of power output) was calculated. Physiological responses were recorded throughout the testing procedure. RESULTS: Reductions were found in PPO (944±155 vs. 983±167 W), MPO (900±176 vs. 853±177 W) and WD (102±20 vs. 108±20 kJ) during the CISP×2 (P<0.05) at HYP compared to NORM. Reductions in PPO, MPO and WD were also found between the 1st half and 2nd half CISP (P<0.05) and there was a greater decline from the 1st half CISP to the 2nd half CISP in PPO, MPO and WD at HYP. Heart rate was higher and peripheral arterial oxygen saturation lower during HYP compared to NORM (P<0.05). CONCLUSION: Moderate hypoxia significantly reduced PPO (~4%), MPO (~5%) and WD (~5%) compared to normoxia. The results suggest athletes will be at a disadvantage when performing intermittent sprinting at moderate altitude.