Heat Stress Test Research Articles

The repeatability of a cycling exercise-heat stress test in a male population

IntroductionThere is considerable inter-individual variability in the physiological responses to environmental stressors and so to accurately assess and monitor changes in an individual's ability to cope with exercise-heat stress, a reliable protocol is required. The aim of this study was to examine the repeatability of a 90-min steady-state heat exercise bout with physiological and subjective variables, and performance during an incremental test to exhaustion post 90-min steady-state exercise. MethodSixteen mixed ability males (Age: 39 ± 15yrs; Height: 176.5 ± 4.8 cm; BM: 79.7 ± 10.3 kg; V˙O2peak: 46.2 ± 8.6 ml/kg/min; PPO: 309 ± 39W) who trained at least three times a week undertook two 90-min steady-state – followed by an incremental protocol to exhaustion – cycling heat stress tests (HSTs) in a hot-humid environment (35 °C, 60%RH). Heart rate (HR), rectal (T‾re) and skin temperature (T‾sk), rating of perceived exertion (RPE), thermal sensation (TS), and thermal comfort (TC) were measured throughout. Data was analysed using Intraclass Correlation Coefficients (ICC), technical error of measurement (TEM), Bland-Altman plots, t-tests, and Cohen's d to indicate magnitude of change. ResultsPhysiological variables indicated good repeatability evident through moderate to strong ICC ratings, low magnitudes of change (d), lower mean biases compared to their respective calculated TEMs, and statistical non-significance, except HR90, ₸sk90, and ₸sk. Hydration status showed good repeatability except for urine osmolality (osmu90) and resting urine colour (colu). Perceptual variables showed encouraging repeatability apart from resting TS and mean TS. Performance data showed good repeatability overall, however 11 participants progressed to the incremental test to exhaustion in the second visit compared to 7 in the first. ConclusionCurrent data demonstrated favourable physiological, perceptual, and performance repeatability during repeated cycling HSTs in hot-humid conditions. However, given more participants progressed to the incremental trial to exhaustion protocol in the second visit, at least one familiarisation trial may improve the reliability of exercise capacity assessment.

Protective effects of butyric acid during heat stress on the survival, immune response, histopathology, and gene expression in the hepatopancreas of juvenile pacific shrimp (L. Vannamei)

This study looked at the effects of adding butyric acid (BA) to the diets of juvenile Pacific shrimp and how it affected their response to survival, immunity, histopathological, and gene expression profiles under heat stress. The shrimp were divided into groups: a control group with no BA supplementation and groups with BA inclusion levels of 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 %. Following the 8-week feeding trial period, the shrimp endured a heat stress test lasting 1 h at a temperature of 38 °C. The results showed that the control group had a lower survival rate than those given BA. Interestingly, no mortality was observed in the group receiving 1.5 % BA supplementation. Heat stress had a negative impact on the activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in the control group. Still, these activities were increased in shrimp fed the BA diet. Similar variations were observed in AST and ALT fluctuations among the different groups. The levels of triglycerides (TG) and cholesterol (CHO) increased with high temperatures but were reduced in shrimp-supplemented BA. The activity of an antioxidant enzyme superoxide dismutase (SOD) increased with higher BA levels (P < 0.05). Moreover, the groups supplemented with 1.5 % BA exhibited a significant reduction in malondialdehyde (MDA) content (P < 0.05), suggesting the potential antioxidant properties of BA. The histology of the shrimp's hepatopancreas showed improvements in the groups given BA. Conversely, the BA significantly down-regulated the HSPs and up-regulated MnSOD transcript level in response to heat stress. The measured parameters determine the essential dietary requirement of BA for shrimp. Based on the results, the optimal level of BA for survival, antioxidant function, and immunity for shrimp under heat stress is 1.5 %.

Responses of Healthy Young and Older Adults to Short-Term Passive Heat Acclimation

Context: Aging is accompanied by a reduced capacity to dissipate heat. Heat acclimation has been shown to improve heat loss capacity in young healthy adults, yet few studies have investigated the capacity of older adults to adapt to repeated bouts of heat exposure, particularly when using a passive heat acclimation protocol. Furthermore, it remains unclear whether the magnitude of adaptations is affected by age. Objective and hypothesis: To compare physiological adaptations following 7 consecutive days of passive heat exposure between healthy young and older adults. We hypothesized that heat acclimation would enhance heat loss capacity in both groups but to a higher extent in young than in older adults. Methods: Fourteen healthy young (5F/9M, 27 ± 5 years) and 9 older adults (6F/3M, 66 ± 5 years) were exposed to passive heat stress with a water-perfused suit before (pre) and after (post) 7 consecutive days of immersion in 40°C water (~30 min to reach a rectal temperature of 38.5°C, followed by 60 min ≥38.5°C). During the pre/post heat stress test, mean body temperature was computed as 0.8 × esophageal temperature + 0.2 × mean skin temperature. Local sweat rate (LSR) and cutaneous vascular conductance (CVC) were measured at the forearm level. The mean body temperature onset thresholds of LSR and CVC were determined by segmented linear regression. During acclimation visits, rectal temperature and change in body mass were measured. Data are presented as means ± standard deviation or mean differences [95% confidence interval]. Results: Immersion duration (young: 90 ± 10, older: 92 ± 9 min, p=0.53), water temperature (young: 40.3 ± 0.3, older: 40.0 ± 0.5°C, p=0.09) and mean rectal temperature (young: 38.9 ± 0.1, older: 38.8 ± 0.1°C, p=0.07) during heat acclimation did not differ significantly between groups. In response to heat acclimation, rectal temperature decreased similarly ( p=0.36) in young (-0.33°C [-0.50, -0.16]) and older adults (-0.46°C [-0.68, -0.25]) from day 1 to day 7 whereas sweat rate increased to a higher extent ( p=0.05) in young (+511 mL/h [285, 738]) compared with older adults (+232 mL/h [112, 352]). Heat acclimation similarly reduced the mean body temperature onset threshold for CVC in young (-0.18°C [-0.32, -0.05]) and older adults (-0.19°C [-0.36, -0.02]) ( p=0.91), as well as, the mean body temperature onset threshold for LSR (young: -0.13°C [-0.25, -0.01], older: -0.15°C [-0.30, 0.00], p=0.84) during the pre/post heat stress test. Conclusion: These results suggest that passive heat acclimation improves heat loss capacity in young and older adults. However, age may blunt the increase in whole-body sweat rate that accompanies passive heat acclimation, but not other classical markers of human heat acclimation. Natural Sciences and Engineering Research Council of Canada. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mixed-Method Heat Acclimation Induces Heat Adaptations in International Triathletes Without Training Modification

PurposeHeat acclimation (HA) kinetics often necessitates that the intervention is conducted in the weeks immediately preceding athletic competitions, potentially interfering with a training taper. Therefore, we investigated the efficacy of a mixed-method HA protocol, superimposed over planned external training loads, during the 3-weeks prior to the 2022 U23 World Triathlon Championships.MethodsSix international triathletes completed 8 pre-competition HA sessions (5 active: running/cycling, 3 passive: hot water immersion [HWI]), across 2-weeks. Outdoor high-intensity training sessions were followed by 30–60 min HWI, whilst low-intensity cycling/running sessions were completed in a hot, humid environmental chamber. To assess heat adaptations, participants completed three 25 min heat stress tests (HST) involving iso-speed treadmill running (session 1 = HST1, session 5 = HST2, and session 8 = HST3). Physiological, haematological and wellbeing monitoring were conducted throughout HA.ResultsReduced heart rate (~ − 6 beats/min) was observed within HST3 (P = 0.01, ηp2 = 0.64), versus HST1 and HST2. No changes in core temperature were observed across HSTs (P = 0.055,ηp2 = 0.44). Sweat sodium concentration was lower by HST2 at the arm (− 23 ± 16 mmol/L, P = 0.02) and back (− 27 ± 17 mmol/L, P = 0.01). White blood cell count reduced from baseline to the end of HA (P = 0.02, ηp2 = 0.27), but no changes were found in any other haematological markers (all P > 0.05). Perceptual wellbeing measures did not change across HA (all P > 0.05).ConclusionBy HST3, seven prior mixed-method HA sessions improved markers of heat adaptation (exercising HR and sweat concentration) within international triathletes. Mixed-method HA may be implemented without modifying training load, with no apparent detrimental effects on athlete health or training stress markers.

Zexie decoction reduce glucose-dependent lipid accumulation and oxidative stress in Caenorhabditis elegans

BackgroundObesity has become a global public health problem. Zexie decoction (ZXT) is a classic formula from Synopsis of the Golden Chamber. However, the long-term effect of ZXT in lipid accumulation remain unclear. PurposeThis study aims to investigate the effect of ZXT on aging, lipid metabolism and oxidative stress. MethodsDifferent concentration of ZXT was administered to Caenorhabditis elegans (C. elegans) cultured in NGM or the high glucose nematode growth media (GNGM). The lifespan, heat stress resistance, lipid accumulation and related mRNA expression of the worms were examined. Oil Red staining and triglyceride were used to evaluated the lipid accumulation. Nhr-49, fat-5/fat-7, fat-5/fat-6 or skn-1 knockout mutants were used to clarify the effect on lipid metabolism of ZXT. GFP-binding mutants were used to observe the changes in protein expression. ResultsZXT improved the survival rate of C. elegans in lifespan test and heat stress test. ZXT also reduced lipid accumulation in C. elegans and significantly changed the expression of fatty acid synthesis related genes and lipid metabolism related genes. In addition, ZXT-treated C. elegans showed a higher expression of anti-oxidative protein, and reduced the expression of oxidative stress and mitochondrial dysfunction marker. However, when skn-1 was knockdown, ZXT no longer had the effect of maintaining the mitochondria membrane potential and lipid lowering but still effectively decreased the O2·− induced by high glucose. ConclusionsZXT reduced fat accumulation by regulating lipid metabolism via multiple targets and enhanced stress resistance by its antioxidant effect in C. elegans.

Upper-Body versus Lower-Body Cooling in Individuals with Paraplegia during Arm-Crank Exercise in the Heat.

For wheelchair users with a spinal cord injury, the lower body may be a more convenient cooling site than the upper body. However, it remains unknown if leg cooling reduces thermal strain in these individuals. We compared the impact of upper-body versus lower-body cooling on physiological and perceptual outcomes during submaximal arm-crank exercise under heat stress in individuals with paraplegia. Twelve male participants with paraplegia (T4-L2, 50% complete lesion) performed a maximal exercise test in temperate conditions, and three heat stress tests (32°C, 40% relative humidity) in which they received upper-body cooling (COOL-UB), lower-body cooling (COOL-LB), or no cooling (CON) in a randomized counterbalanced order. Each heat stress test consisted of four exercise blocks of 15 min at 50% of peak power output, with 3 min of rest in between. Cooling was applied using water-perfused pads, with 14.8-m tubing in both COOL-UB and COOL-LB. Gastrointestinal temperature was 0.2°C (95% confidence interval (CI), 0.1°C to 0.3°C) lower during exercise in COOL-UB versus CON (37.5°C ± 0.4°C vs 37.7°C ± 0.3°C, P = 0.009), with no difference between COOL-LB and CON ( P = 1.0). Heart rate was lower in both COOL-UB (-7 bpm; 95% CI, -11 to -3 bpm; P = 0.01) and COOL-LB (-5 bpm; 95% CI, -9 to -1 bpm; P = 0.049) compared with CON. The skin temperature reduction at the cooled skin sites was larger in COOL-LB (-10.8°C ± 1.1°C) than in COOL-UB (-6.7°C ± 1.4°C, P < 0.001), which limited the cooling capacity in COOL-LB. Thermal sensation of the cooled skin sites was improved and overall thermal discomfort was lower in COOL-UB ( P = 0.01 and P = 0.04) but not in COOL-LB ( P = 0.17 and P = 0.59) compared with CON. Upper-body cooling more effectively reduced thermal strain than lower-body cooling in individuals with paraplegia, as it induced greater thermophysiological and perceptual benefits.

Dietary arachidonic acid affects the growth performance, fatty acid profile, immunity and resistance to heat stress in juvenile abalone Haliotis discus hannai Ino

A 93-day feeding trial was performed to evaluate the effects of dietary arachidonic acid (ARA) on the growth performance, antioxidative capacity, immunity and anti-stress capacity of juvenile abalone Haliotis discus hannai Ino with an initial mean body weight of 4.26 ± 0.11 g. Six practical diets with 0.04% (the control), 0.31%, 0.44%, 0.68%, 0.94% and 1.34% of ARA were designed. After the feeding trial, abalones were subjected to a heat stress test. The findings showed that the survival of abalone (91.7–96.7%) after the feeding trial was not significantly influenced by dietary ARA. The 0.31–0.44% of dietary ARA significantly increased the weight gain rate (WGR). The feed conversion ratio (FCR) was decreased by 0.31–0.68% of dietary ARA. The 0.44% of dietary ARA significantly enhanced the activity of trypsin, lipase and α-amylase in the intestine. Besides, dietary ARA supplementation significantly elevated the total antioxidative capacity and activity of superoxide dismutase, catalase and lysozyme in the cell-free hemolymph. Higher levels of dietary ARA (≥0.94%) significantly up-regulated the mRNA levels of nuclear factor κB, inhibitor of κBα and transcription factor AP-1 in the digestive gland. The 0.68% of dietary ARA significantly decreased the falling rate of abalone after heat stress. In conclusion, appropriate dietary ARA levels improved the growth performance and feed utilization of abalone. The optimal dietary ARA content for juvenile abalone was 0.52% based on the quadratic regression analysis of WGR. The 0.44–0.68% of dietary ARA improved the antioxidative capacity, immunity and anti-heat stress of abalone.

Dietary L-carnitine supplementation for heat stressed juvenile pearl gentian grouper(Epinephelusllanolatus (Epinephelus♂×Epinephelusfuscoguttatus♀): Effects on the antioxidant enzyme, survival, and gene expression

The effects of increasing dietary inclusion levels of L-carnitine at 0 (control group) 200, 400, 600, 1200, 1400, and 1600 mg/kg were evaluated in juvenile hybrid groupers exposed to heat shock stress. The feeding trial was conducted for eight weeks. After the feeding trial, hybrid groupers were subjected to a heat stress test for an hour at a temperature of 36 °C to determine the influence of the treatments on survival, biochemical parameters, and gene expression. The results of the current study showed that the survival rate of hybrid grouper was low in fish fed the control diet. A large number of survivors were observed in the treatment group with 400 mg/kg L-carnitine supplementation (LC 400), obtaining the highest survival rate. Heat stress decreased (P < 0.05) the activities of alkaline phosphatase and acid phosphatase in the control group but was increased in fish fed the LC 400 diet. Additionally, in the LC 400 treatment, malondialdehyde content decreased considerably (P < 0.05) compared to LC0. Hybrid grouper exposed to a high temperature of 36 °C for 1 h without L-carnitine (LC0, control group) supplementation showed the most increased Aspartate Aminotransferase activity (2.04 U L−1). Additionally, the LC 400 group reached the maximal value for the expressions of genes in the PPARs (peroxisome proliferator-activated receptors) signaling pathway, which showed a tendency of downregulation and, subsequently, up-regulation. The gene expression of FAS (fatty acid synthase) was discovered upstream and downstream (P < 0.05). The lowest mRNA level was found in the lowest L-carnitine supplementation treatment (200 mg/kg). A CPT-1 (carnitine palmitoyltransferase) that controls fatty acid oxidation showed upstream and downstream activity in response to increasing doses of L-carnitine supplementation. Our findings showed that dietary supplementation with L-carnitine 400 mg/kg reduced heat stress-related mortality and oxidative damage by enhancing the survival and oxidative enzymes of grouper, which provides a nutritional method of minimizing the consequences of heat exposure.

Heating Up to Keep Cool: Benefits and Persistence of a Practical Heat Acclimation Protocol in Elite Female Olympic Team-Sport Athletes

Although recommendations for effective heat acclimation (HA) strategies for many circumstances exist, best-practice HA protocols specific to elite female team-sport athletes are yet to be established. Therefore, the authors aimed to investigate the effectiveness and retention of a passive HA protocol integrated in a female Olympic rugby sevens team training program. Twelve elite female rugby sevens athletes undertook 10 days of passive HA across 2 training weeks. Tympanic temperature (TTymp), sweat loss, heart rate, and repeated 6-second cycling sprint performance were assessed using a sport-specific heat stress test Pre-HA, after 3days (Mid-HA), after 10days (Post-HA), and 15 days post-HA (Decay). Compared with Pre-HA, submaximal TTymp was lower Mid-HA and Post-HA (both by -0.2 [0.7] °C; d ≥ 0.71), while resting TTymp was lower Post-HA (by -0.3 [0.2] °C; d = 0.81). There were no differences in TTymp at Decay compared with Pre-HA, nor were there any differences in heart rate or sweat loss at any time points. Mean peak 6-second power output improved Mid-HA and Post-HA (76 [36]W; 75 [34]W, respectively; d ≥ 0.45) compared with Pre-HA. The observed performance improvement persisted at Decay by 65 (45) W (d = 0.41). Ten days of passive HA can elicit some thermoregulatory and performance benefits when integrated into a training program in elite female team-sport athletes. However, such a protocol does not provide a sufficient thermal impulse for thermoregulatory adaptations to be retained after 15 days with no further heat stimulus.

Reliability of biomarkers of physiological stress at rest and post-exertional heat stress.

The purpose of this study was to assess the reliability of blood biomarkers that can signify exercise-induced heat stress in hot conditions. Fourteen males completed two heat stress tests separated by 5-7 days. Venous blood was drawn pre- and post- heat stress for the concentration of normetanephrine, metanephrine, serum osmolality, copeptin, kidney-injury molecule 1 and neutrophil gelatinase-associated lipocalin. No biomarker, except copeptin, displayed systematic trial order bias (p ≥ 0.05). Normetanephrine, copeptin and neutrophil gelatinase-associated lipocalin presented acceptable reliability (CV range: 0.9-14.3%), while greater variability was present in metanephrine, osmolality and kidney-injury molecule 1 (CV range: 28.6-43.2%). Normetanephrine exhibited the largest increase (p <0.001) in response to heat stress (trial 1 = 1048 ± 461 pmol. L-1; trial 2 = 1067 ± 408 pmol. L-1), whilst kidney-injury molecule 1 presented trivial changes (trial 1 = -4 ± 20 ng. L-1; trial 2 = 2 ± 16 ng. L-1, p >0.05). Normetanephrine, copeptin and neutrophil gelatinase-associated lipocalin demonstrated good reliability and sensitivity to an acute bout of heat stress. These biomarkers may be suitable for application in laboratory and field research to understand the efficacy of interventions that can attenuate the risk of thermal injury whilst exercising in the heat.

Effectiveness of short-term isothermic-heat acclimation (4 days) on physical performance in moderately trained males.

A typical heat acclimation (HA) protocol takes 5-7 d of 60-90 minutes of heat exposure. Identifying the minimum dose of HA required to elicit a heat adapted phenotype could reduce financial constraints on participants and aid in the tapering phase for competition in hot countries. Therefore, the aim of this study was to investigate a 4 d HA regimen on physical performance. Twelve moderately trained males were heat acclimated using controlled hyperthermia (Tre&gt;38.5°C), with no fluid intake for 90 min on 4 consecutive days, with a heat stress test (HST) being completed one week prior to (HST2), and within one-week post (HST3) HA. Eleven completed the control study of HST1 versus HST2, one week apart with no intervention. Heat stress tests comprised of cycling for 90 min @ 40% Peak Power Output (PPO); 35°C; 60%RH followed by 10 minutes of passive recovery before an incremental test to exhaustion. Physical performance outcomes time to exhaustion (TTE), PPO, end rectal temperature (Tre END), and heart rate (HREND) was measured during the incremental test to exhaustion. Physiological markers indicated no significant changes in the heat; however descriptive statistics indicated mean resting Tre lowered 0.24°C (-0.54 to 0.07°C; d = 2.35: very large) and end-exercise lowered by 0.32°C (-0.81 to 0.16; d = 2.39: very large). There were significant improvements across multiple timepoints following HA in perceptual measures; Rate of perceived exertion (RPE), Thermal Sensation (TS), and Thermal Comfort (TC) (P&lt;0.05). Mean TTE in the HST increased by 142 s (323±333 to 465±235s; P = 0.04) and mean PPO by 76W (137±128 to 213±77 W; P = 0.03). Short-term isothermic HA (4 d) was effective in enhancing performance capacity in hot and humid conditions. Regardless of the level of physiological adaptations, behavioural adaptations were sufficient to elicit improved performance and thermotolerance in hot conditions. Additional exposures may be requisite to ensure physiological adaptation.

Effects of dietary methionine on growth and body composition, indicators of digestion, protein metabolism and immunity, and resistance to heat stress of abalone Haliotis discus hannai

The present study was conducted to investigate the effects of dietary methionine on growth performance, protein metabolism, immunity and resistance to heat stress of abalone Haliotis discus hannai. Seven isonitrogenous (about 32% of crude protein) and isolipidic (about 3% of crude lipid) diets were designed with graded levels of methionine (0.46%, 0.77%, 0.97%, 1.19%, 1.41%, 1.71% and 2.07%, respectively). The experimental diets were named as M1 (control), M2, M3, M4, M5, M6 and M7, respectively. An 84-day feeding trial was conducted in sea cages (40 cm × 35 cm × 70 cm) for abalones (initial body weight: 4.10 ± 0.01 g), which were fed once every two days. The results showed that the biomass gain (BG) of abalone significantly increased (from 560.20 g to 643.83 g) with the increasing dietary methionine levels from 0.46% to 1.19%, and then decreased (from 643.83 g to 484.29 g) (P < 0.05). Based on the broken-line regression analysis of BG, the requirement of dietary methionine for abalone was determined to be 0.99% (dry matter of diet). The highest trypsin activity (862.10 U/mg prot.) and α-Amylase activity (0.28 U/mg prot.) in the intestine of abalone were observed in the M4 and M5 group, respectively. In the digestive gland, the gene expression of mtor, s6k and eif4e showed a significant quadratic trend with the increasing dietary methionine levels, and all of them reached their highest values in the M4 group. The highest mRNA level of gcn2 was observed in the M1 group. The glutathione content and total anti-oxidative capacity in cell-free hemolymph (CFH) were significantly increased as dietary methionine levels increasing from 0.46% to 1.19%, and then decreased (P < 0.05). The lowest gene expression level of keap1, nf-κb and tnf-α, and the highest gene expression level of nrf2 and iκbα in the digestive gland were found in the M4 group. After the heat stress test at the end of feeding trial, the minimum falling rate (19.44%) and the highest gene expression level of hsp70 and hsp90 in the digestive gland of abalone were found in the group with 1.19% of dietary methionine. In conclusion, appropriate dietary methionine (0.97%–1.19%) could improve the growth, protein synthesis, immunity and resistance to heat stress of abalone.

Reliability of pulse photoplethysmography sensors: Coverage using different setups and body locations

Pulse photoplethysmography (PPG) is a simple and economical technique for obtaining cardiovascular information. In fact, PPG has become a very popular technology among wearable devices. However, the PPG signal is well-known to be very vulnerable to artifacts, and a good quality signal cannot be expected for most of the time in daily life. The percentage of time that a given measurement can be estimated (e.g., pulse rate) is denoted coverage (C), and it is highly dependent on the subject activity and on the configuration of the sensor, location, and stability of contact. This work aims to quantify the coverage of PPG sensors, using the simultaneously recorded electrocardiogram as a reference, with the PPG recorded at different places in the body and under different stress conditions. While many previous works analyzed the feasibility of PPG as a surrogate for heart rate variability analysis, there exists no previous work studying coverage to derive other cardiovascular indices. We report the coverage not only for estimating pulse rate (PR) but also for estimating pulse arrival time (PAT) and pulse amplitude variability (PAV). Three different datasets are analyzed for this purpose, consisting of a tilt-table test, an acute emotional stress test, and a heat stress test. The datasets include 19, 120, and 51 subjects, respectively, with PPG at the finger and at the forehead for the first two datasets and at the earlobe, in addition, for the latter. C ranges from 70% to 90% for estimating PR. Regarding the estimation of PAT, C ranges from 50% to 90%, and this is very dependent on the PPG sensor location, PPG quality, and the fiducial point (FP) chosen for the delineation of PPG. In fact, the delineation of the FP is critical in time for estimating derived series such as PAT due to the small dynamic range of these series. For the estimation of PAV, the C rates are between 70% and 90%. In general, lower C rates have been obtained for the PPG at the forehead. No difference in C has been observed between using PPG at the finger or at the earlobe. Then, the benefits of using either will depend on the application. However, different C rates are obtained using the same PPG signal, depending on the FP chosen for delineation. Lower C is reported when using the apex point of the PPG instead of the maximum flow velocity or the basal point, with a difference from 1% to even 10%. For further studies, each setup should first be analyzed and validated, taking the results and guidelines presented in this work into account, to study the feasibility of its recording devices with respect to each specific application.

Heat acclimation does not negatively affect salivary immunoglobulin-A and self-reported illness symptoms and wellness in recreational athletes

ABSTRACT Heat acclimation (HA) protocols repeatedly expose individuals to heat stress. As HA is typically performed close to the pinnacle event, it is essential that the protocol does not compromise immune status, health, or wellbeing. The purpose of this study was to examine the effect of HA on resting salivary immunoglobulin-A (s-IgA) and salivary cortisol (s-cortisol), self-reported upper-respiratory tract symptoms, and self-reported wellness parameters. Seventeen participants (peak oxygen uptake 53.2 ± 9.0 mL·kg−1·min−1) completed a 10-day controlled-hyperthermia HA protocol, and a heat stress test both before (HST1) and after (HST2) HA (33°C, 65% relative humidity). Resting saliva samples were collected at HST1, day 3 and 7 of the HA protocol, HST2, and at 5 ± 1 days post-HA. Upper-respiratory tract symptom data were collected weekly from one week prior to HA until three weeks post HA, and wellness ratings were reported daily throughout HA. HA successfully induced physiological adaptations, with a lower end-exercise rectal temperature and heart rate and higher whole-body sweat rate at HST2 compared to HST1. In contrast, resting saliva flow rate, s-IgA concentration, s-cortisol concentration, and s-cortisol secretion rate remained unchanged (n = 11–14, P = 0.10–0.48). Resting s-IgA secretion rate increased by 39% from HST1 to HST2 (n = 14, P = 0.03). No changes were observed in self-reported upper respiratory tract symptoms and wellness ratings. In conclusion, controlled-hyperthermia HA did not negatively affect resting s-IgA and s-cortisol, self-reported upper-respiratory tract symptoms, and self-reported wellness parameters in recreational athletes.

Efficacy of Isothermic Conditioning over Military-Based Heat Acclimatization and Interval Training in Tropical Native Males.

We compared the effectiveness of three field-based training programs, namely military-based heat acclimatization (MHA), isothermic conditioning (IC) and interval training (IT), in inducing physiological adaptations in tropical natives. Fifty-one untrained tropical native males (mean ± standard deviation: age, 25 ± 2 yr; body mass index, 23.6 ± 3.2 kg·m -2 ; body fat, 19% ± 5%; 2.4-km run time, 13.2 ± 0.9 min) donned the Full Battle Order attire (22 kg) and performed a treadmill route march heat stress test in an environmental chamber (dry bulb temperature, 29.9°C ± 0.5°C; relative humidity, 70% ± 3%). Heat stress tests were conducted before (PRE) and after (POST) a 2-wk training intervention consisting of either a MHA ( n = 17, 10 sessions of military-based heat acclimatization), IC ( n = 17, 10 sessions with target gastrointestinal temperature ( Tgi ) ≥ 38.5°C) or IT ( n = 17, six sessions of high-intensity interval training) program. Tgi , HR, mean weighted skin temperature ( Tsk ), physiological strain index (PSI) and thigh-predicted sweat sodium concentration ([Na + ]) were measured and analyzed by one-factor and two-factor mixed design ANOVA with a 0.05 level of significance. Field-based IC induced a greater thermal stimulus than MHA ( P = 0.029) and IT ( P < 0.001) during training. Reductions in mean exercise Tgi (-0.2°C [-0.3°C, 0.0°C]; P = 0.009) , PSI (-0.4 [-0.7, -0.1]; P = 0.015) and thigh-predicted sweat [Na + ] (-9 [-13, -5 mmol·L -1 ]; P < 0.001) were observed in IC but not MHA and IT (all P > 0.05). Resting HR (MHA, -4 bpm [-7, 0 bpm]; P = 0.025; IC, -7 bpm [-10, -4 bpm]; P < 0.001; IT, -4 bpm [-8, -1 bpm]; P = 0.008) and mean exercise HR (MHA, -4 [-8, 0 bpm]; P = 0.034; IC, -11 bpm [-15, -8 bpm]; P < 0.001, IT = -5 bpm [-9, -1 bpm]; P = 0.012) were lowered in all groups after training. Isothermic conditioning elicited a greater attenuation in mean exercise HR and thigh-predicted sweat [Na + ] relative to MHA (both P < 0.05). No between-group differences were observed when comparing MHA and IT (all P > 0.05). Isothermic conditioning induced a more complete heat-adapted phenotype relative to MHA and IT. Interval training may serve as a time efficient alternative to MHA.

Effectiveness of Short-Term Heat Acclimation on Intermittent Sprint Performance in the Heat with Moderately Trained Males

Purpose: Effectiveness of short-term heat acclimation (STHA), over 5-days (permissive dehydration), on intermittent heat stress test (HST) with males. Methods: Ten, moderately-trained, males (mean [SD]; age 25.6 [8.9] y; stature 180.7 [5.6] cm; body mass 83.2 [10.8] kg; and 45.3 [6.5] mL.kg-1.min-1) participated. The HST was 9 x 5min (45-min) of intermittent exercise based on professional soccer players. One week apart, HST1 vs HST (11.0°C; 50%RH), as a reliability trial and HST3 in 31.0°C; 50%RH were completed. Then 90 min dehydration, STHA (no fluid intake), for 5 consecutive days (39.5oC; 60%RH), using controlled-hyperthermia (~rectal temperature [Tre] 38.5oC). The HST4 within one week after STHA. Blood plasma constituents: percent plasma volume (%PV), aldosterone, total protein, albumin, electrolytes, cortisol and HSP70. Data analysis reported as mean differences with 95% confidence intervals (95%CI) and Cohen’s d effect size. Results: Post STHA, there was a decrease of -0.20 Tre at 45-min in the HST (95%CI -0.40 to -0.05°C; P=0.03; d =-0.56); mean skin temperature (-0.80; -1.30 to -0.30°C; P=0.007; d =-1.46) and mean body temperature (-0.30; -0.50 to -0.10°C, P=0.01; d =-0.75). Cardiac frequency reduced (-3: -5 to -1 b.min-1; P=0.01; d =-0.20) and %PV increased (7.3: 0.9 to 13.7%; P=0.03; d=0.59). Mean Peak Power (MPO) increased (Pd =0.63). Conclusions: Short-term heat acclimation (5-days) with dehydration, using controlled-hyperthermia technique, is effective for physiological adaptations during intermittent exercise in the heat, with moderately trained males.

Errors of Measurement for Blood Parameters and Physiological and Performance Measures After the Decay of Short-Term Heat Acclimation

Introduction: It is important to determine the accuracy of measurements relative to potential treatment effects, with time intervals between tests. Purpose: The aim of this study was to assess the error of measurement for blood parameters, physiological, and performance measures after the decay of short-term heat acclimation. Methods: Ten trained males (Mean±SD: age 28±7 y; body mass 74.6±4.4 kg; 4.26±0.37 L.min-1; peak power output (PPO) 329±42 W) completed an exercising heat stress test (HST) at baseline, 2nd day after acclimation and then during decay at 1, 2, 3 and 5-6 wks. CoV (95% CI), SE (95% CI) and Pearsons (r) were used for analysis of blood volume (blood, plasma, red cell volume, mean hemoglogin mass); plasma (aldosterone, arginine vasopressin [AVP], total protein, albumin, sodium); physiological (rectal temperature, cardiac frequency) and performance (exercise performance capacity, PPO). Results: The CoV (95% CI), SE (95% CI) and r with a 1-wk interval for blood volume was 2.3% (1.6 to 4.3; 1.9 [1.3 to 3.4 mL.Kg-1]; r=0.93; n=10). After 2-wk and 5-6 wks this had increased to 4.9% (3.4 to 9.3; 3.8 [2.6 to 7.0 mL.Kg-1]; r=0.76; n=9) and 5.5% (3.6 to 12.8; 4.5 [2.9 to 10.0 mL.Kg-1]; r=0.65; n=7) respectively. Conclusions: Blood volume and physiological measures demonstrated the least error one week apart but increased thereafter. Plasma concentrations and performance markers had the greatest error with repeat measures after one week. Therefore, for greater reliability and low measurement error measures should be taken no more than one week a part in repeated experimentation.

Effects of dietary chromium yeast levels on growth performance, anti-oxidative capacity, immune response and flesh quality of abalone Haliotis discus hannai

A 110-day feeding trial was conducted to investigate the effects of dietary chromium (Cr) on the growth performance, immune response, anti-oxidative capacity, stress resistance, flesh quality of abalone Haliotis discus hannai. Seven isonitrogenous and isolipidic experimental diets were formulated with graded levels of Cr (0.04, 0.67, 1.21, 1.58, 2.21, 2.72 and 3.33 mg/kg) from Cr yeast. The results showed that weight gain rate (WGR) was highest in the group with 1.21 mg/kg of dietary Cr. Based on the broken-line regression analysis for WGR, the dietary Cr requirement of abalone was estimated to be 1.32 mg/kg. With the increase of dietary Cr level from 0.04 to 1.21 mg/kg, the total anti-oxidative capacity and lysozyme activity in the cell-free hemolymph were increased and then decreased when the dietary Cr level exceeded 1.21 mg/kg. After the challenge of Vibrio parahaemolyticus, the cumulative mortality of abalone was significantly decreased in the group with 1.21 mg/kg of dietary Cr compared with that in the control group. Meanwhile, after the heat stress test, the cumulative mortality of abalone was significantly reduced in the groups with 1.58, 2.21 and 2.72 mg/kg of dietary Cr compared with that in the control group. The liquid and water loss of foot muscle were significantly increased in the groups with 2.72 and 3.33 mg/kg of dietary Cr. With the increase of dietary Cr levels, the hardness of foot muscle was significantly elevated. The chewiness of foot muscle was significantly increased with the increase of dietary Cr level from 0.04 to 1.21 mg/kg, and thereafter showed no significant difference when dietary Cr exceeded 1.21 mg/kg. In conclusion, based on the WGR, dietary Cr requirement of abalone (initial weight: 22.31 ± 0.31 g) was estimated to be 1.32 mg/kg. Appropriate dietary Cr levels (1.21–1.58 mg/kg) had positive effects on growth performance, immune response, anti-oxidation, anti-stress and flesh quality of abalone. Overhigh dietary Cr level (2.72–3.33 mg/kg) decreased the flesh quality. Excessive dietary Cr level (3.33 mg/kg) had a negative effect on the health of abalone.

Post-exercise, passive heat acclimation with sauna or hot-water immersion provide comparable adaptations to performance in the heat in a military context

To mitigate the effects of heat during operations in hot environments, military personnel will likely benefit from heat acclimation (HA) conducted prior to deployment. Using post-exercise, passive heating, 25 participants completed a 5 d HA regime in sauna (70 °C, 18% RH) or hot-water immersion (HWI) (40 °C) for ≤40 min, preceded and followed by a heat stress test (1-h walking at 5 km.h−1 in 33 °C, 77% RH in military uniform (20 kg) before an incremental ramp to exhaustion). Fifteen completed both regimes in a randomised, cross-over manner. While performance did not significantly improve (+14%, [-1, 29], p = .079), beneficial adaptations were observed for mean exercising core temperature (-0.2 °C, [-0.2, −0.2], p <.001), skin temperature (-0.2 °C, [-0.2, −0.2], p = 035) and heart rate (-8 bpm, [-6, −10], p<.001) in both conditions. Post-exercise, passive HA of either modality may benefit military units operating in the heat. Practitioner summary: Strategies are required to prevent health and performance impairments during military operations upon arrival in hot environments. Using a randomised, cross-over design, participants completed five-day passive, post-exercise heat acclimation using sauna or hot-water immersion. Both regimes elicited beneficial albeit modest heat adaptations. Abbreviations: HA: heat acclimation; HST: heat stress test; HWI: hot-water immersion; RH: relative humidity

No protective benefits of low dose acute L-glutamine supplementation on small intestinal permeability, epithelial injury and bacterial translocation biomarkers in response to subclinical exertional-heat stress: A randomized cross-over trial

ABSTRACT Exertional heat stress disrupts gastrointestinal permeability and, through subsequent bacterial translocation, can result in potentially fatal exertional heat stroke. Glutamine supplementation is a potential countermeasure although previously validated doses are not universally well tolerated. Ten males completed two 80-minute subclinical exertional heat stress tests (EHSTs) following either glutamine (0.3 g kg FFM−1) or placebo supplementation. Small intestinal permeability was assessed using the lactulose/rhamnose dual sugar absorption test and small intestinal epithelial injury using Intestinal Fatty-Acid Binding Protein (I-FABP). Bacterial translocation was assessed using the total 16S bacterial DNA and Bacteroides/total 16S DNA ratio. The glutamine bolus was well tolerated, with no participants reporting symptoms of gastrointestinal intolerance. Small intestinal permeability was not influenced by glutamine supplementation (p = 0.06) although a medium effect size favoring the placebo trial was observed (d = 0.73). Both small intestinal epithelial injury (p < 0.01) and Bacteroides/total 16S DNA (p = 0.04) increased following exertional heat stress, but were uninfluenced by glutamine supplementation. Low-dose acute oral glutamine supplementation does not protect gastrointestinal injury, permeability, or bacterial translocation in response to subclinical exertional heat stress.