Can ten days of heat acclimation training improve temperate-condition rowing performance in national-level rowers?

Long-term heat acclimation training in mice: Similar metabolic and running performance adaptations despite a lower absolute intensity than training at temperate conditions

This study investigated the impact of long-term heat acclimation (HA) training on mouse thermoregulation, metabolism, and running performance in temperate (T) and hot (H) environments. Male Swiss mice were divided into 1) Sedentary (SED) mice kept in T (22 °C; SED/T), 2) Endurance Trained mice (ET, 1 h/day, 5 days/week, 8 weeks, 60 % of maximum speed) in T (ET/T), 3) SED kept in H (32 °C; SED/H), and 4) ET in H (ET/H). All groups performed incremental load tests (ILT) in both environments before (pre-ET) and after four and eight weeks of ET. In the pre-ET period, H impaired (∼30 %) performance variables (maximum speed and external work) and increased (1.3 °C) maximum abdominal body temperature compared with T. In T, after four weeks, although ET/H exercised at a lower (∼30 %) absolute intensity than ET/T, performance variables and aerobic power (peak oxygen uptake, VO2peak) were similarly increased in both ET groups compared with SED/T. After eight weeks, the external work was higher in both ET groups compared with SED/T. Only ET/T significantly increased VO2peak (∼11 %) relative to its pre-ET period. In H, only after eight weeks, both ET groups improved (∼19 %) maximum speed and reduced (∼46 %) post-ILT blood lactate concentrations compared with their respective pre-ET values. Liver glycogen content increased (34 %) in both ET groups and SED/H compared with SED/T. Thus, ET/H was performed at a lower absolute intensity but promoted similar effects to ET/T on metabolism, aerobic power, and running performance. Our findings open perspectives for applying HA training as part of a training program or orthopedic and metabolic rehabilitation programs in injured or even obese animals, reducing mechanical load with equivalent or higher physiological demand.

Reduced running performance and greater perceived exertion, but similar post-exercise neuromuscular fatigue in tropical natives subjected to a 10 km self-paced run in a hot compared to a temperate environment

Environmental heat stress impairs endurance performance by enhancing exercise-induced physiological and perceptual responses. However, the time course of these responses during self-paced running, particularly when comparing hot and temperate conditions, still needs further clarification. Moreover, monitoring fatigue induced by exercise is paramount to prescribing training and recovery adequately, but investigations on the effects of a hot environment on post-exercise neuromuscular fatigue are scarce. This study compared the time course of physiological and perceptual responses during a 10 km self-paced treadmill run (as fast as possible) between temperate (25°C) and hot (35°C) conditions. We also investigated the changes in countermovement jump (CMJ) performance following exercise in these two ambient temperatures. Thirteen recreational long-distance runners (11 men and 2 women), inhabitants of a tropical region, completed the two experimental trials in a randomized order. Compared to 25°C, participants had transiently higher body core temperature (TCORE) and consistently greater perceived exertion while running at 35°C (p < 0.05). These changes were associated with a slower pace, evidenced by an additional 14 ± 5 min (mean ± SD) to complete the 10 km at 35°C than at 25°C (p < 0.05). Before, immediately after, and 1 h after the self-paced run, the participants performed CMJs to evaluate lower limb neuromuscular fatigue. CMJ height was reduced by 7.0% (2.3 ± 2.4 cm) at 1 h after the race (p < 0.05) compared to pre-exercise values; environmental conditions did not influence this reduction. In conclusion, despite the reduced endurance performance, higher perceived exertion, and transiently augmented TCORE caused by environmental heat stress, post-exercise neuromuscular fatigue is similar between temperate and hot conditions. This finding suggests that the higher external load (faster speed) at 25°C compensates for the effects of more significant perceptual responses at 35°C in inducing neuromuscular fatigue.

Heat Adaptation for Females: A Systematic Review and Meta-Analysis of Physiological Adaptations and Exercise Performance in the Heat

BACKGROUND

Heat adaptation regimes are used to prepare athletes for exercise in hot conditions to limit a decrement in exercise performance. However, the heat adaptation literature mostly focuses on males, and consequently, current heat adaptation guidelines may not be optimal for females when accounting for the biological and phenotypical differences between sexes.

OBJECTIVES

We aimed to examine: (1) the effects of heat adaptation on physiological adaptations in females; (2) the impact of heat adaptation on performance test outcomes in the heat; and (3) the impact of various moderators, including duration (minutes and/or days), total heat dose (°C.min), exercise intensity (kcal.min-1), total energy expended (kcal), frequency of heat exposures and training status on the physiological adaptations in the heat.

METHODS

SPORTDiscus, MEDLINE Complete and Embase databases were searched to December 2022. Random-effects meta-analyses for resting and exercise core temperature, skin temperature, heart rate, sweat rate, plasma volume and performance tests in the heat were completed using Stata Statistical Software: Release 17. Sub-group meta-analyses were performed to explore the effect of duration, total heat dose, exercise intensity, total energy expended, frequency of heat exposure and training status on resting and exercise core temperature, skin temperature, heart rate and sweat rate. An explorative meta-regression was conducted to determine the effects of physiological adaptations on performance test outcomes in the heat following heat adaptation.

RESULTS

Thirty studies were included in the systematic review; 22 studies were meta-analysed. After heat adaptation, a reduction in resting core temperature (effect size [ES] =  - 0.45; 95% confidence interval [CI] - 0.69, - 0.22; p < 0.001), exercise core temperature (ES =  - 0.81; 95% CI - 1.01, - 0.60; p < 0.001), skin temperature (ES =  - 0.64; 95% CI - 0.79, - 0.48; p < 0.001), heart rate (ES =  - 0.60; 95% CI - 0.74, - 0.45; p < 0.001) and an increase in sweat rate (ES = 0.53; 95% CI 0.21, 0.85; p = 0.001) were identified in females. There was no change in plasma volume (ES = - 0.03; 95% CI - 0.31, 0.25; p = 0.835), whilst performance test outcomes were improved following heat adaptation (ES = 1.00; 95% CI 0.56, 1.45; p < 0.001). Across all moderators, physiological adaptations were more consistently observed following durations of 451-900 min and/or 8-14 days, exercise intensity ≥ 3.5 kcal.min-1, total energy expended ≥ 3038 kcal, consecutive (daily) frequency and total heat dose ≥ 23,000 °C.min. The magnitude of change in performance test outcomes in the heat was associated with a reduction in heart rate following heat adaptation (standardised mean difference =  - 10 beats.min-1; 95% CI - 19, - 1; p = 0.031).

CONCLUSIONS

Heat adaptation regimes induce physiological adaptations beneficial to thermoregulation and performance test outcomes in the heat in females. Sport coaches and applied sport practitioners can utilise the framework developed in this review to design and implement heat adaptation strategies for females.