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PURPOSE OF REVIEW: Climate change is predicted to increase the frequency and severity of exposure to hot environments. This can impair health, physical performance, and productivity for active individuals in occupational and athletic settings. This review summarizes current knowledge and recent advancements in nutritional strategies to minimize the impact of exertional-heat stress (EHS). RECENT FINDINGS: Hydration strategies limiting body mass loss to < 3% during EHS are performance-beneficial in weight-supported activities, although evidence regarding smaller fluid deficits (< 2% body mass loss) and weight-dependent activities is less clear due to a lack of well-designed studies with adequate blinding. Sodium replacement requirements during EHS depends on both sweat losses and the extent of fluid replacement, with quantified sodium replacement only necessary once fluid replacement > 60-80% of losses. Ice ingestion lowers core temperature and may improve thermal comfort and performance outcomes when consumed before, but less so during activity. Prevention and management of gastrointestinal disturbances during EHS should focus on high carbohydrate but low FODMAP availability before and during exercise, frequent provision of carbohydrate and/or protein during exercise, adequate hydration, and body temperature regulation. Evidence for these approaches is lacking in occupational settings. Acute kidney injury is a potential concern resulting from inadequate fluid replacement during and post-EHS, and emerging evidence suggests that repeated exposures may increase the risk of developing chronic kidney disease. Nutritional strategies can help regulate hydration, body temperature, and gastrointestinal status during EHS. Doing so minimizes the impact of EHS on health and safety and optimizes productivity and performance outcomes on a warming planet.
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Motor-racing drivers are often exposed to hot environments and may be susceptible to fluid loss and hydration issues, which could influence driving performance. This study assessed the effect of dehydration and heat stress on performance during a short, simulated motor-racing task. Nine healthy males (age: 26.6 ± 7.5 y, body mass: 78.8 ± 12.5 kg, mean ± SD) completed two passive dehydration (sauna) procedures (targeting -1% and -3% body mass loss (BML)) on separate occasions. Driving performance was assessed pre-dehydration (Baseline), immediately post-dehydration (Hot) and following a cooling period (Cool). Measures of driving performance included lap time and sector-time for one section of the track. Subjective ratings of mood, thermal stress and comfort were also collected during trials. Mean lap times were not different between Baseline, Hot, Cool conditions for both 1% (68.44 ± 1.43 s, 68.06 ± 1.17 s, 68.23 ± 1.25 s) and 3% (68.33 ± 1.68 s, 68.01 ± 1.15 s, 68.06 ± 1.26 s) trials respectively. In addition, mean sector times were not different between Baseline, Hot, Cool conditions for both 1% (11.61 ± 0.28 s, 11.55 ± 0.45 s, 11.59 ± 0.35 s) and 3% (11.49 ± 0.33 s, 11.56 ± 0.33 s, 11.63 ± 0.71 s) trials respectively. Changes in participants' subjective ratings (i.e. decreased alertness, concentration and comfort; increased tiredness and light-headedness) were observed at both levels of dehydration (1% and 3% BML), irrespective of heat stress. Thus, fluid loss and heat stress are unlikely to affect driver's motor-racing performance during short duration events. However, the impact of dehydration and heat stress on tasks of longer duration that accurately represent the demands associated with motor-racing requires further consideration.
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Motor racing is a physically and mentally demanding sport, associated with a high degree of risk for drivers. Hence, driving simulation provides a safe alternative to explore the impact acute physiological perturbations (e.g. heat stress or dehydration) on a driver's performance. This study aimed to determine sensitive and reliable simulated driving performance parameters that could be employed in future driving performance studies. Thirty-six healthy males (age: 26.5 ± 8.1 y, body mass: 75.6 ± 12.2 kg, mean ± SD) completed a single experimental trial involving four simulated motor-racing drives (2 initial drives and 2 repeat drives) separated by a 1 h period. Drives were conducted under two conditions, with one condition (wearing Fatal Vision Goggles (FVG)) designed to impair driving performance by distorting vision. Sensitivity was assessed by comparing Normal vs FVG outcomes and reliability was determined by comparing initial vs repeat drives for the same condition. Measures of driving performance included lap time (LT), sector-time (ST) for one section of the track, position displacement to a marker on the first track corner (PD), and vehicle Speed at PD. Results indicated that LT and ST were reliable and sensitive performance measures to a visual disturbance. However, PD was neither sensitive nor reliable and Speed at PD was not sensitive as driving performance measures to the study conditions. Overall, this study demonstrates two sensitive and reliable performance measures (LT and ST) that can be used to assess simulated motor-racing performance in future investigations.
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BACKGROUND: Fluid replacement during cycling exercise evolves on a spectrum from simply drinking to thirst to planned structured intake, with both being appropriate recommendations. However, with mixed findings suggesting fluid intake may or may not improve endurance cycling performance (ECP) in a diverse range of trained individuals, there is a clear need for summarised evidence regarding the effect of fluid consumption on ECP. OBJECTIVES: (1) Determine the magnitude of the effect of drinking fluid on performance during cycling exercise tasks of various durations, compared with no drinking; (2) examine the relationship between rates of fluid intake and ECP; and (3) establish fluid intake recommendations based on the observations between rates of fluid intake and ECP. STUDY DESIGN: Meta-analysis. METHODS: Studies were located via database searches and cross-referencing. Performance outcomes were converted to a similar metric to represent percentage change in power output. Fixed- and random-effects weighted mean effect summaries and meta-regression analyses were used to identify the impact of drinking fluid on ECP. RESULTS: A limited number of research manuscripts (n = 9) met the inclusion criteria, producing 15 effect estimates. Meta-regression analyses demonstrated that the impact of drinking on ECP under 20-33 °C ambient temperatures was duration-dependent. Fluid consumption of, on average, 0.29 mL/kg body mass/min impaired 1 h high-intensity (80% peak oxygen uptake [[Formula: see text]o2peak]) ECP by -2.5 ± 0.8% (95% confidence interval [CI] -4.1 to -0.9%) compared with no fluid ingestion. In contrast, during >1 to ≤2 h and >2 h moderate-intensity (60-70% [Formula: see text]o2peak) cycling exercise, ECP improved by 2.1 ± 1.5% (95% CI 1.2-2.9%) and 3.2 ± 1.2% (95% CI 0.8-5.6%), respectively, with fluid ingestion compared with no fluid intake. The associated performance benefits were observed when the rates of fluid intake were in the range of 0.15-0.20 mL/kg body mass/min for >1 to ≤2 h cycling exercise and ad libitum or 0.14-0.27 mL/kg body mass/min for cycling exercise >2 h. CONCLUSIONS: A rate of fluid consumption of between 0.15 and 0.34 mL/kg body mass/min during high-intensity 1 h cycling exercise is associated with reductions in ECP. When cycling at moderate intensity for >1 to ≤2 h, cyclists should expect a gain in performance of at least 2% if fluid is consumed at a rate of 0.15-0.20 mL/kg body mass/min. For cycling exercise >2 h conducted at moderate intensity, consuming fluid ad libitum or at a rate of 0.14-0.27 mL/kg body mass/min should improve performance by at least 3%. Until further research is conducted, these recommendations should be used as a guide to inform hydration practices.
