Mixed-method heat acclimation induces heat adaptations in international triathletes without training modification

Data Availability Statement: Data may be made available upon request to the corresponding author...

Defining the determinants of endurance running performance in the heat

In cool conditions, physiological 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) or 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; V̇O2max r=-0.7, RE r=0.36, LT r=-0.77, LTP r=-0.78 and in GXTCOOL; V̇O2max r=-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.

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

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.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.Funding sources: None. Acknowledgments: The authors would like to thank Para-Monte, the Adam Savory Altitude Awareness Charity, Eastbourne, East Sussex (https://www.para-monte.org/) for their charitable support that has underpinned our hypoxic research

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

Hyperthermia and exertional heat illness increase gastrointestinal (GI) permeability, although whether the latter is only via hyperthermia is unclear. The aim of this pilot study was to determine whether different changes in GI permeability, characterized by an increased plasma lactulose:rhamnose concentration ratio ([L:R]), occurred in exercise hyperthermia in comparison to equivalent passive hyperthermia. Six healthy adult male participants (age 25 ± 5 years, mass 77.0 ± 6.7 kg, height 181 ± 6 cm, peak oxygen uptake [urn:x-wiley:2051817X:media:phy214945:phy214945-math-0001] 48 ± 8 ml.kg−1.min−1) underwent exercise under hot conditions (Ex-Heat) and passive heating during hot water immersion (HWI). Heart rate (HR), rectal temperature (TCORE), rating of perceived exertion (RPE), and whole-body sweat loss (WBSL) were recorded throughout the trials. The L:R ratio, peak HR, change in HR, and change in RPE were higher in Ex-Heat than HWI, despite no differences in trial duration, peak core temperature or WBSL. L:R was strongly correlated (p < 0.05) with HR peak (r = 0.626) and change in HR (r = 0.615) but no other variable. The greater L:R in Ex-Heat, despite equal TCORE responses to HWI, indicates that increased cardiovascular strain occurred during exercise, and exacerbates hyperthermia-induced GI permeability at the same absolute temperature

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

Multistage, ultra-endurance events in hot, humid conditions necessitate thermal adaptation, often achieved through short term heat acclimation (STHA), to improve performance by reducing thermoregulatory strain and perceptions of heat stress. This study investigated the physiological, perceptual and immunological responses to STHA prior to the Marathon des Sables. Eight athletes (age 42 ± 4 years and body mass 81.9 ± 15.0 kg) completed 4 days of controlled hyperthermia STHA (60 min·day‒1, 45°C and 30% relative humidity). Pre, during and post sessions, physiological and perceptual measures were recorded. Immunological measures were recorded pre-post sessions 1 and 4. STHA improved thermal comfort (P = 0.02), sensation (P = 0.03) and perceived exertion (P = 0.04). A dissociated relationship between perceptual fatigue and Tre was evident after STHA, with reductions in perceived Physical (P = 0.04) and General (P = 0.04) fatigue. Exercising Tre and HR did not change (P > 0.05) however, sweat rate increased 14% (P = 0.02). No changes were found in white blood cell counts or content (P > 0.05). Four days of STHA facilitates effective perceptual adaptations, without compromising immune status prior to an ultra-endurance race in heat stress. A greater physiological strain is required to confer optimal physiological adaptations

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

To prepare for extremes of heat, cold or low partial pressures of O2, humans can undertake a period of acclimation or acclimatization to induce environment specific adaptations e.g. heat acclimation (HA), cold acclimation (CA), or altitude training. Whilst these strategies are effective, they are not always feasible, due to logistical impracticalities. Cross adaptation is a term used to describe the phenomenon whereby alternative environmental interventions e.g. HA, or CA, may be a beneficial alternative to altitude interventions, providing physiological stress and inducing adaptations observable at altitude. HA can attenuate physiological strain at rest and during moderate intensity exercise at altitude via adaptations allied to improved oxygen delivery to metabolically active tissue, likely following increases in plasma volume and reductions in body temperature. CA appears to improve physiological responses to altitude by attenuating the autonomic response to altitude. While no cross acclimation-derived exercise performance/capacity data have been measured following CA, post-HA improvements in performance underpinned by aerobic metabolism, and therefore dependent on oxygen delivery at altitude, are likely. At a cellular level, heat shock protein responses to altitude are attenuated by prior HA suggesting that an attenuation of the cellular stress response and therefore a reduced disruption to homeostasis at altitude has occurred. This process is known as cross tolerance. The effects of CA on markers of cross tolerance is an area requiring further investigation. Because much of the evidence relating to cross adaptation to altitude has examined the benefits at moderate to high altitudes, future research examining responses at lower altitudes should be conducted given that these environments are more frequently visited by athletes and workers. Mechanistic work to identify the specific physiological and cellular pathways responsible for cross adaptation between heat and altitude, and between cold and altitude, is warranted, as is exploration of benefits across different populations and physical activity profiles

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±0.52L.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

Predicting change in core temperature during exercise-heat stress

Controlling internal temperature is crucial when prescribing exercise-heat stress, particularly during interventions designed to induce thermoregulatory adaptations. This study aimed to determine the relationship between the rate of rectal temperature (Trec) increase, and various methods for prescribing exercise-heat stress, to identify the most efficient method of prescribing isothermic heat acclimation (HA) training. Thirty-five males cycled in hot conditions (40[degrees]C, 39%R.H.) for 29+/-2 min. Subjects exercised at 60+/-9%V[Combining Dot Above]O2peak, with methods for prescribing exercise retrospectively observed for each participant. Pearson product moment correlations were calculated for each prescriptive variable against the rate of change in Trec ([degrees]C.hr-1), with stepwise multiple regressions performed on statistically significant variables (p<0.05). Linear regression identified the predicted intensity required to increase Trec by 1.0-2.0[degrees]C between 20-45 min periods, and the duration taken to increase Trec by 1.5[degrees]C in response to incremental intensities to guide prescription. Significant (p<0.05) relationships with the rate of change in Trec were observed for prescriptions based upon relative power (W.kg-1; r=0.764), power (%Powermax; r=0.679), RPE (r=0.577), V[Combining Dot Above]O2 (%V[Combining Dot Above]O2peak; r=0.562), HR (%HRmax; r=0.534), and TS (r=0.311). Stepwise multiple regressions observed relative power and RPE as variables to improve the model (r=0.791), with no improvement following inclusion of any anthropometric variable. Prescription of exercise under heat stress utilizing power (W.kg-1 or %Powermax), has the strongest relationship with the rate of change in Trec with no additional requirement to correct for body composition within a normal range. Practitioners should therefore prescribe exercise intensity using relative power during isothermic HA training to increase Trec efficiently and maximize adaptation

Relationships between opponent ranking and locomotor activity in international field hockey

No research has investigated the effect of opponent world ranking (WR) on locomotor activity within modern (post-2015) international men's hockey. A retrospective analysis of 71 matches (vs. 24 opponents, WR# 12 ± 11, WR# 1–86) investigated the relationships between opponent ranking at team and positional levels, on locomotor activity. Data were analysed using linear mixed modelling to; (1) explore relationships between opponent ranking and locomotor activity and (2) to compare between predefined ranking groups (WR# 1–8 ‘HIGHER’ [n = 8], WR# 9–17 ‘SIMILAR’ [n = 8] and WR >#18 ‘LOWER’ [n = 8]), relative to the reference team (WR# 11). Significant relationships were found between opponent world ranking and total distance (β = −6.11; p = 0.003), high-speed running ([HSR], β = −4.87, p < 0.001), sprint distance ([SD], β = −2.41, p < 0.001), sprint efforts ([SE], β = −0.10, p < 0.001) and average speed (β = −0.19, p < 0.001), but not low-speed running (β = −0.94, p = 0.57). When analysed by ranking groups, HSR, SD and SE increased against HIGHER (+12%–14% vs. grand mean, p < 0.05) and reduced against LOWER teams (−15%–18% vs. grand mean, p < 0.05). The largest differences in SD were observed in forwards (HIGHER +14% and LOWER −19%) and defenders (HIGHER +20% and LOWER −18%). In international hockey, average speed is greatest when facing higher-ranked rather than similarly ranked opponents. Furthermore, high-speed but not low-speed activity, is modulated by opponent ranking