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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°Cand 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. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the efficacy of heat acclimation (HA) in the young (Y EX ) and elderly (E EX ) following exercise-HA, and the elderly utilising post-exercise hot water immersion HA (E HWI )., Design: Cross-sectional study., Method: Twenty-six participants (Y EX : n = 11 aged 22 ± 2 years, E EX: n = 8 aged 68 ± 3 years, E HWI : n = 7 aged 73 ± 3 years) completed two pre-/post-tests, separated by five intervention days. Y EX and E EX exercised in hot conditions to raise rectal temperature (T rec ) ≥38.5 °C within 60 min, with this increase maintained for a further 60 min. E HWI completed 30 min of cycling in temperate conditions, then 30 min of HWI (40 °C), followed by 30 min seated blanket wrap. Pre- and post-testing comprised 30 min rest, followed by 30 min of cycling exercise (3.5 W·kg -1 Ḣ prod), and a six-minute walk test (6MWT), all in 35 °C, 50% RH., Results: The HA protocols did not elicit different mean heart rate (HR), T rec , and duration T rec  ≥ 38.5 °C (p > 0.05) between Y EX , E EX , and E HWI groups. Resting T rec , peak skin temperature, systolic and mean arterial pressure, perceived exertion and thermal sensation decreased, and 6MWT distance increased pre- to post-HA (p < 0.05), with no difference between groups. Y EX also demonstrated a reduction in resting HR (p < 0.05). No change was observed in peak T rec or HR, vascular conductance, sweat rate, or thermal comfort in any group (p > 0.05)., Conclusions: Irrespective of age or intervention, HA induced thermoregulatory, perceptual and exercise performance improvements. Both exercise-HA (E EX ), and post-exercise HWI (E HWI ) are considered viable interventions to prepare the elderly for heat stress., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Objectives: We aimed to determine the agreement between actual and predicted core body temperature, using the Heat Strain Decision Aid (HSDA), in non-Ground Close Combat (GCC) personnel wearing multi terrain pattern clothing during two stages of load carriage in temperate conditions., Design: Cross-sectional., Methods: Sixty participants (men = 49, women = 11, age 31 ± 8 years; height 171.1 ± 9.0 cm; body mass 78.1 ± 11.5 kg) completed two stages of load carriage, of increasing metabolic rate, as part of the development of new British Army physical employment standards (PES). An ingestible gastrointestinal sensor was used to measure core temperature. Testing was completed in wet bulb globe temperature conditions; 1.2-12.6 °C. Predictive accuracy and precision were analysed using individual and group mean inputs. Assessments were evaluated by bias, limits of agreement (LoA), mean absolute error (MAE), and root mean square error (RMSE). Accuracy was evaluated using a prediction bias of ±0.27 °C and by comparing predictions to the standard deviation of the actual core temperature., Results: Modelling individual predictions provided an acceptable level of accuracy based on bias criterion; where the total of all trials bias ± LoA was 0.08 ± 0.82 °C. Predicted values were in close agreement with the actual data: MAE 0.37 °C and RMSE 0.46 °C for the collective data. Modelling using group mean inputs were less accurate than using individual inputs, but within the mean observed., Conclusion: The HSDA acceptably predicts core temperature during load carriage to the new British Army non-GCC PES, in temperate conditions., (Copyright © 2021. Published by Elsevier Ltd.)