This study investigated the effect of exercise-induced dehydration on exogenous glucose oxidation during cycling in a temperate environment. Nine trained male cyclists/triathletes (22 ± 4 yr; 75.44 ± 5.03 kg; 59 ± 6 mL/kg/min) completed two trials of 160-min cycling at 50% peak power output (Wpeak) with low [dehydrated (DEH)] or high [euhydrated (EUH)] fluid intake. Participants ingested 60 g/h glucose (20 g every 20 min as a 27% mass:mass solution, followed by 15 mL water), enriched with 0.2% [U-13C6]glucose, in both trials. In EUH, additional water (2,260 ± 477 mL) was provided. Subjective measures, skin and gastrointestinal (GI) temperature, capillary blood, and expired breath samples were collected every 20 min, with venous blood collected pre- and postexercise. Peak (EUH: 0.79 ± 0.12 g/min; DEH: 0.70 ± 0.14 g/min; P = 0.041; dz = 0.81) and mean 40- to 160-min (EUH: 0.61 ± 0.09 g/min; DEH: 0.51 ± 0.11 g/min; P = 0.010; dz = 1.12) exogenous glucose oxidation were reduced in DEH. The largest between-trial difference occurred at 60 min (EUH: 0.49 ± 0.11 g/min; DEH: 0.33 ± 0.13 g/min; P = 0.015; dz = 1.52). DEH, but not EUH, produced significant body mass loss (DEH: -2.8 ± 0.4%; EUH: -0.2 ± 0.4%; P < 0.001; dz = 4.77), decreased plasma volume (P = 0.034), and increased plasma osmolality (EUH: 290 ± 3 mosmol/kg; DEH: 302 ± 5 mosmol/kg; P < 0.001; dz = 3.21) postexercise. Thermal sensation, skin/GI temperature, GI discomfort, intestinal fatty acid binding protein, and other measures were not different between trials (P ≥ 0.05). As exercise-induced dehydration decreases exogenous glucose oxidation, adequate fluid intake should be considered for athletes to optimize carbohydrate supplementation.NEW & NOTEWORTHY This study showed that dehydration/low fluid intake during exercise decreases exogenous glucose oxidation by ∼16% during endurance cycling in a temperate environment. These findings are important as endurance athlete vary substantially in their sweat rate and hydration responses to prolonged exercise, which could influence the efficacy of carbohydrate supplementation during exercise.

This study examined gastrointestinal temperature (TGI) during and body mass (BM) changes pre/post the Western States Endurance Run 100 (WSER), a 100-mile ultramarathon in hot conditions. Thirty-nine participants ingested a telemetric pill 30-90 min before the WSER start, and BM was measured pre- and post-race. Environmental conditions were recorded every 30 min at 15 locations along the course. In-race TGI data were obtained from 23 finishers (54%; 7 females; 42 ± 11 years), including 2 podium finishers and an additional top-10 finisher. Participants finished in 14-18 h (n = 4), 19-25 h (n = 6), and 26-30 h (n = 13). Peak TGI averaged 38.90°C ± 0.55°C (range 37.76°C-40.09°C) with 9 runners exceeding 39°C and 2 exceeding 40°C. Faster finish times were associated with higher peak TGI (r = -0.57, p = 0.004). Seven runners (30%) reached peak TGI in the final 2% of the race. Mean BM change was -1.8% ± 3.1% (range -7.4% to +6.4%), with no associations observed between BM change and peak TGI or finish time. Ambient temperature ranged 5°C-39.6°C and was associated with higher TGI (r = 0.80, p = 0.008). Despite ambient temperatures approaching 40°C, TGI >40°C were rare and transient. Faster runners experienced greater thermal strain, likely reflecting higher metabolic heat production and exposure to the hottest course segments. Hyperthermia risk may be highest near the race finish and during the most demanding segments.

Endurance performance is predicted by maximal oxygen uptake, its fractional utilisation at lactate threshold (FULT) and exercise economy. These variables are used to estimate speed or power at lactate threshold (LT) and lactate turnpoint (LTP), which serve as performance proxies. This study examined the relationships between these variables in a large cohort of runners and cyclists and quantified their relative contributions to performance prediction. 495 runners (105 females) and 393 cyclists (42 females) completed incremental exercise tests to determine maximal oxygen uptake (running [R]: 56 mL/kg/min, 3.94 L/min; cycling [C]: 52 mL/kg/min, 3.99 L/min), economy (R: 220 mL/kg/km; C: 14.7 mL/min/W), FULT (R: 78

OBJECTIVES:This study examined heat preparation, nutritional strategies, and gastrointestinal symptoms of runners competing in the 2025 Western States Endurance Run, a 100-mile ultra-marathon with extreme heat exposure. DESIGN:1. Cross-sectional and 2. prospective observational study. METHODS:Pre- and post-race surveys (n = 106 pre-race; n = 66 post-race) collected data on demographics, heat experience, heat acclimat(isat)ion, nutrition and hydration strategies, and race-related symptoms. Finishers were grouped by race time (<18 h, 18-24 h, 24-30 h). Chi-square tests with Cramer's V evaluated associations between variables and performance categories. RESULTS:Most runners (90%) completed heat preparation, including acclimatisation (67%) and acclimation (70%), with >70% reporting >10 days or exposures. Mid-race cooling strategies were planned by 92%, mainly neck collars (89%) and cold towels (52%). Most (96%) runners tested their strategies during training. Faster finishers were more likely to have structured carbohydrate plans (<18 h: 100% vs 24-30 h: 69%; χ2 = 8.43; P = 0.015) and higher sodium intake (χ2 = 17.64; P = 0.007). Gastrointestinal symptoms occurred in 63% of finishers and 38% of those who dropped out. Symptoms were most frequent in slower runners (χ2 = 17.2; P = 0.045). No differences in heat-related symptoms were observed between groups. CONCLUSIONS:Runners were highly heat-prepared and widely adopted cooling strategies, likely facilitated by pre-race communication, logistics, and prior experience. This, in addition to tested nutritional strategies may have contributed to fewer severe gastrointestinal issues compared with previous studies.

Exercise-induced hypohydration exacerbates biomarkers of renal injury, but studies isolating the effects of hypohydration without exercise have produced mixed findings. This study investigated the effects of 24-h severe fluid restriction on biomarkers of renal injury and glucose tolerance. Fifteen males (age: 27 ± 5 y; BMI: 24.1 ± 3.8 kg/m2) completed two randomised trials, involving consuming either 40 mL/kg body mass water to maintain euhydration (EU) or severe fluid restriction via limiting water consumption to 100 mL (HYP). A standardised dry food diet was consumed in both trials ( 300 g water). At baseline and 24 h post-baseline, nude body mass, and blood and urine samples (additional urine sample at 12 h) were collected. An oral glucose tolerance test was conducted after 24-h post-baseline measurements (n = 12). At 24 h, body mass loss (HYP: − 1.52 ± 0.34

Postural changes elicit well-described haemodynamic effects on plasma volume, affecting blood-based hydration variables. While the time required for plasma volume stabilisation is well-established for supine rest, less is known for blood samples collected in a seated position, as is commonplace in physiology and nutrition experiments. Seventeen healthy participants (9 males; 8 females) stood stationary for 20 min in an upright position before walking on a treadmill at 4 km/h for 20 min (to simulate active travel to blood sampling locations). After walking, participants sat upright (within 7 ± 1 s), and venous blood samples were drawn from a cannula at 0, 5, 10, 20, 30 and 40 min after sitting. Time points were compared to 40 min. At 0 and 5 min, blood (0 min: -3.3

ABSTRACT:Macrae, HZ, Reynolds, KM, Cable, TG, Barutcu, A, Hansell, EJ, Mears, SA, Midwood, KL, Mould, C, Funnell, MP, Goosey-Tolfrey, VL, and James, LJ. Twice a day lacrosse training in temperate conditions results in a negative 24-hour sodium balance in male and female university lacrosse players. J Strength Cond Res 39(9): e1091-e1098, 2025-This study measured 24-hour fluid and sodium balance in 27 university lacrosse players (13 males, 14 females; 21 ± 1 years). For 24 hours, participants maintained their usual fluid and food intake, completed a weighed food diary, and collected all urine produced. Participants completed 2 bouts of 1.5 hours (males) or 2 hours (females) lacrosse training (16.0 ± 3.9°C, 62.3 ± 11.7% relative humidity) separated by 2-2.5 hours rest. Nude body mass was measured at baseline (0 hour), 24 hours later, before and after training, and corrected for food/fluid consumed and urine/feces produced during training to determine sweat losses. A sweat patch was applied (scapula) and analyzed for sweat sodium concentration. Data are mean ± standard deviation or median (Q1-Q3), p < 0.05. Sodium balance at 24 hours was negative for both male (-0.76 ± 1.31 g) and female (-0.47 ± 0.70 g) players but was not different between sexes ( p = 0.350). Body mass at 0 hour and 24 hours was not different for male (79.99 ± 10.02 kg vs 79.69 ± 10.15 kg) or female (65.68 ± 10.17 kg vs 65.82 ± 10.21 kg; both p > 0.05) players. Sweat rates were relatively low and not different between male (0.39 ± 0.23 L/h) and female (0.33 ± 0.18 L/h; p = 0.286) players. There was no difference in sweat sodium concentration (male players: 27 (23-28) mmol/L; female players: 27 (23-31) mmol/L; p = 0.786). Ad libitum drinking, combined with low sweat rates, generally prevented dehydration accruing to a level that might impair performance. Sodium balance deficit was small (∼0.61 g) but may require investigation to understand whether daily deficits accumulate.

This study investigated the effect of running in a hot environment compared with a temperate environment on exogenous carbohydrate oxidation, while maintaining a state of euhydration. Ten trained runners (24 ± 6 yr; 72.7 ± 8.3 kg; V̇o2peak: 63 ± 6 mL/kg/min) completed two trials [100 min of steady state running at ∼65% V̇o2peak in either a temperate (19°C; TEMP) or a hot environment (34°C; HOT)]. Water was provided every 20 min to replace ∼90% of body mass losses (TEMP: 0.8 ± 0.2 L; HOT: 1.7 ± 0.4 L). In each trial, participants consumed 60 g/h (bolus every 20 min) of a 35% dextrose solution enriched with [U-13C] glucose (145 ± 2 δ‰ vs. PDB). Expired breath (analyzed for 13C:12C) and blood samples were collected every 20 min during exercise. Average (40-100 min) and peak exogenous carbohydrate oxidation rates were 20% (HOT: 0.43 ± 0.09 vs. TEMP: 0.54 ± 0.12 g/min; P = 0.006) and 18% (HOT: 0.67 ± 0.10 vs. TEMP: 0.81 ± 0.11 g/min; P = 0.002) lower in HOT than in TEMP, respectively. Total carbohydrate oxidation (P = 0.111) was not significantly different between trials, resulting in a greater contribution from endogenous sources in HOT versus TEMP (2.10 ± 0.35 vs. 1.86 ± 0.30 g/min; P = 0.020). Gastrointestinal temperature and heart rate (P < 0.001) were greater in HOT. Even with adequate hydration, running in a hot environment reduced exogenous carbohydrate.NEW & NOTEWORTHY This study showed that exogenous carbohydrate oxidation is reduced by ∼20% during running in the heat, even while controlling fluid intake to maintain euhydration, highlighting that heat stress alone impairs exogenous carbohydrate use. These findings suggest a lower exogenous carbohydrate oxidation and a greater reliance on endogenous stores when exercising in the heat, independently of the effects of dehydration.

This case study provides the first comprehensive, in-race assessment of physiological, nutritional, and thermoregulatory responses in a world-class ultra-endurance athlete during the 2025 Western States Endurance Run. Using doubly labeled water, ingestible telemetry, and renal biomarkers, this study quantifies the upper limits of energy expenditure (18.8 kcal·min −1 ), carbohydrate intake (86 g·h −1 ), and fatigue resistance achievable in competitive ultra-endurance performance under extreme environmental conditions.

Carbohydrate metabolism during prolonged endurance exercise can be influenced by heat stress and dehydration. While heat exposure and dehydration have been shown to independently affect glycogen use and carbohydrate oxidation, their combined impact remains unclear. No previous review has systematically evaluated the effects of these factors on carbohydrate metabolism during prolonged endurance exercise or undertaken a meta-analysis. The aim was to systematically review the literature and meta-analyse the effects of heat stress (hot compared to temperate conditions) and dehydration (dehydrated compared to hydrated status) on (1) respiratory exchange ratio, (2) carbohydrate oxidation and (3) glycogen use. A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA)-compliant systematic review with meta-analysis was completed ( https://osf.io/uq8n5 ). PubMed/MEDLINE and SportDiscus databases were searched for original articles (published up to November 2024) that assessed changes in (main outcomes) (1) respiratory exchange ratio, (2) carbohydrate oxidation or (3) glycogen use. The population included healthy, active, trained adults (> 18 years). Interventions involved exercise in hot conditions compared to temperate conditions and/or dehydration compared to a hydrated state. The exercise duration was required to be ≥ 15 min. Meta-analysis was performed using a random-effects model to calculate standardised mean differences (SMDs) between experimental conditions (hot compared to temperate conditions and/or dehydrated compared to hydrated statuses). Heterogeneity was assessed using χ2 and I2 statistics, with significance set at P ≤ 0.05. Fifty-one studies (502 participants; 31 females) were included. Carbohydrate oxidation (SMD 0.29, P = 0.006) and glycogen use (SMD 0.78, P = 0.006) were greater in hot conditions compared to temperate conditions. In a dehydrated state, carbohydrate oxidation (SMD 0.31, P = 0.002) and glycogen use (SMD 0.62, P = 0.003) were greater compared to in a hydrated state. Greater carbohydrate oxidation in a dehydrated compared to a hydrated state was observed in hot (SMD 0.37, P = 0.001) but not in temperate conditions (SMD 0.27, P = 0.199). Carbohydrate utilisation increases during prolonged endurance exercise in hot conditions. Dehydration appears to increase carbohydrate use, especially when combined with heat stress; however, these effects are not consistently observed under temperate conditions. Consequently, dehydration does not appear to be the primary driver of elevated carbohydrate utilisation but may play a significant role by affecting thermoregulatory responses.

Step incremental exercise tests are widely used to assess endurance performance determinants; however, to what extent step duration influences oxygen uptake (V̇O2) and carbon dioxide production (V̇CO2) is unclear. This study assessed the influence of sampling duration on V̇O2, V̇CO2, and fat oxidation (Fatox) across different exercise intensities and modalities, and participant age and biological sex during graded exercise tests. A total of 169 participants (41 females; peak V̇O2 [V̇O2peak]: 54.7 ± 8.6 mL/kg/min) completed a running (n = 96) or cycling (n = 73) submaximal step test with V̇O2 and V̇CO2 measured continuously. Each stage was 6 min, and three 30 s averaging windows (2.5-3, 3.5-4, and 4.5-5 min) were compared to the 5.5-6 min reference. Linear mixed models assessed the effects of averaging window, exercise intensity domain, biological sex, age, fitness status, and exercise modality. The analysis included 1031 valid stages (588 running; 443 cycling). In running, V̇O2 differences from the 6-min averaging window were observed at 3 (-28 mL/min), 4 (-15 mL/min), and 5-min averaging windows (-8 mL/min) (all p < 0.001), with similar results for V̇CO2. No differences in V̇O2 or Fatox between averaging windows were observed in cycling. These findings were consistent across exercise intensity, fitness status, biological sex, and age. Averaging window differences were < 2% for all conditions. Despite subtle differences, 3-, 4-, and 5-min averaging windows do not meaningfully impact V̇O2, V̇CO2, or Fatox compared to a 6-min stage duration. In conclusion, stage durations of ≥ 3 min may be sufficient to estimate these variables in running and cycling in participants with a wide range of characteristics.

This study compared oxygen consumption and substrate oxidation while exercising in hot and temperate conditions in individuals with different physical activity statuses (i.e., inactive individuals vs. trained runners). Ten inactive individuals (IA: 26 ± 6 yr; 79.1 ± 14.1 kg; 40.7 ± 5.1 mL·kg-1·min-1) and 10 trained runners (TR: 25 ± 6 yr; 69.5 ± 9.1 kg; 63.1 ± 5.1 mL·kg-1·min-1) completed two incremental exercise tests (4-min stages) until exhaustion in temperate (TEMP: 18.7 ± 0.1°C; 43.2 ± 4.1% relative humidity) and hot (HOT: 34.4 ± 0.2°C and 42.6 ± 1.6% relative humidity) conditions. Expired gas and blood lactate concentrations were measured at the end of each stage. Peak oxygen consumption similarly decreased in HOT compared with TEMP for IA and TR [-13.2 ± 4.5% vs. -15.2 ± 7%; P = 0.571; effect size (ES) = 0.25]. In HOT compared with TEMP, lipid oxidation, from 30% to 70% of peak oxygen consumption (V̇o2peak), was reduced for both groups (IA: P = 0.023, ES = 0.43; TR: P < 0.001, ES = 0.72), whereas carbohydrate oxidation was increased for TR (P = 0.011; ES = 0.45) but not for IA (P = 0.268; ES = 0.21). Core temperature was different between conditions for TR (higher in HOT, P = 0.017; ES = 0.66) but not for IA (P = 0.901; ES = 0.25). Despite reduced physiological capacities in IA, both populations demonstrated reductions in lipid utilization and peak oxygen consumption in hot compared with temperate conditions. However, the increased carbohydrate oxidation in HOT for TR was not observed in IA, potentially explained by lower thermal strain. NEW & NOTEWORTHY This study shows that lipid oxidation and oxygen consumption are similarly affected by heat exposure in trained runners and inactive individuals. Carbohydrate oxidation and core temperature are greater in hot conditions in trained runners but not in inactive individuals. A lower metabolic heat production in inactive individuals for a similar relative intensity compared with trained runners could explain these differences in core temperature.

Purpose : This study aimed to evaluate the effect of telemetric-pill ingestion timing on gastrointestinal temperature measurements during exercise with tepid fluid intake. Methods : Twelve participants swallowed temperature pills 12, 3, or 0.5 hours before completing 60 minutes of treadmill running, consuming 200 mL of room-temperature water every 15 minutes. Results : Pills ingested 0.5 or 3 hours before exercise resulted in significantly lower gastrointestinal temperature compared with those ingested 12 hours prior. Conclusions : These results indicate that ingesting pills closer to exercise with fluid ingestion may confound gastrointestinal temperature measurements, underlining the need for sufficient ingestion time before exercise to avoid interference with fluid intake.

Purpose Rapid gastric emptying and intestinal absorption of beverages is essential for rapid rehydration, and certain amino acids (AA) may augment fluid delivery. Three sugar-free beverages, containing differing AA concentrations (AA + PZ), were assessed for fluid absorption kinetics against commercial sugar-free (PZ, GZ) and carbohydrate-containing (GTQ) beverages. Methods Healthy individuals ( n = 15–17 per study) completed three randomised trials. Three beverages (550–600 mL) were ingested in each study (Study 1: AA + PZ [17.51 g/L AA], PZ, GZ; Study 2: AA + PZ [6.96 g/L AA], PZ, GZ; Study 3: AA + PZ [3.48 g/L AA], PZ, GTQ), containing 3.000 g deuterium oxide (D 2 O). Blood samples were collected pre-, 2-min, 5-min, and every 5-min until 60-min post-ingestion to quantify maximal D 2 O enrichment (Cmax), time Cmax occurred (Tmax) and area under the curve (AUC). Results Study 1: AUC (AA + PZ: 15,184 ± 3532 δ‰ vs. VSMOW; PZ: 17,328 ± 3153 δ‰ vs. VSMOW; GZ: 17,749 ± 4204 δ‰ vs. VSMOW; P ≤ 0.006) and Tmax ( P ≤ 0.005) were lower for AA + PZ vs. PZ/GZ. Study 2: D 2 O enrichment characteristics were not different amongst beverages ( P ≥ 0.338). Study 3: Cmax (AA + PZ: 440 ± 94 δ‰ vs. VSMOW; PZ: 429 ± 83 δ‰ vs. VSMOW; GTQ: 398 ± 81 δ‰ vs. VSMOW) was greater ( P = 0.046) for AA + PZ than GTQ, with no other differences ( P ≥ 0.106). Conclusion The addition of small amounts of AA (3.48 g/L) to a sugar-free beverage increased fluid delivery to the circulation compared to a carbohydrate-based beverage, but greater amounts (17.51 g/L) delayed delivery.

The upcoming Paris 2024 Olympic and Paralympic Games could face environmental challenges related to heat, air quality and water quality. These challenges will pose potential threats to athletes and impact thousands of stakeholders and millions of spectators. Recognising the multifaceted nature of these challenges, a range of strategies will be essential for mitigating adverse effects on participants, stakeholders and spectators alike. From personalised interventions for athletes and attendees to comprehensive measures implemented by organisers, a holistic approach is crucial to address these challenges and the possible interplay of heat, air and water quality factors during the event. This evidence-based review highlights various environmental challenges anticipated at Paris 2024, offering strategies applicable to athletes, stakeholders and spectators. Additionally, it provides recommendations for Local Organising Committees and the International Olympic Committee that may be applicable to future Games. In summary, the review offers solutions for consideration by the stakeholders responsible for and affected by the anticipated environmental challenges at Paris 2024.

Cow’s milk is one of the most hydrating beverages, but many individuals choose not to consume dairy in their diet due to intolerance, allergy, or dietary preference. Milk is commonly replaced with plant-based beverages, including soya which has the most comparable protein content, but little is known about their hydration potential. This study compared fluid and electrolyte balance responses between a soya beverage and skimmed cow’s milk. Ten healthy males [age 27 (6) y; body mass index 24.6 (2.3) kg/m2] completed two randomised counterbalanced trials, involving consuming 1000 mL water from approximately isocaloric amounts of skimmed cow’s milk (MILK) or a sweetened soya beverage (SOYA), in four aliquots over 30 min in a euhydrated fasted state. Volume, specific gravity, and electrolyte (sodium, potassium, chloride) concentrations were determined in total-void urine samples collected pre-/post-beverage ingestion, and hourly for 180 min thereafter. Hunger, thirst, nausea and stomach fullness were rated proximal to urine samples. Total urine mass (MILK, 986 ± 254 g; SOYA, 950 ± 248 g; P = 0.435) and urine specific gravity (P = 0.156) did not differ between trials. Potassium balance was greater in SOYA 0–180 min post-beverage (P ≤ 0.013), whilst chloride balance was greater in MILK 0–120 min post-beverage (P ≤ 0.036). Sodium balance (P = 0.258), total electrolyte balance (P = 0.258), and subjective measures (P ≥ 0.139) were not different between trials. Replacing cow’s milk with a soya beverage did not negatively impact fluid balance in healthy young males, making it a viable option for those who choose not to consume dairy in their diet.

7 days L-citrulline supplementation has been reported to improve blood pressure, V^. O2 kinetics, gastrointestinal (GI) perfusion and endurance cycling performance through increasing arterial blood flow. In situations where blood volume is compromised (e.g., hyperthermia/hypohydration), L-citrulline may improve thermoregulation and exercise performance by redistributing blood flow to aid heat loss and/or muscle function. This study assessed 7 days L-citrulline supplementation on running performance in the heat, whilst mildly hypohydrated. 13 endurance runners (2 female, 31 ± 8 y, V^. O2peak 60 ± 6 mL/kg/min) participated in a randomised crossover study with 7 days L-citrulline (CIT; 6 g/d) or placebo (maltodextrin powder; PLA) supplementation. Participants completed a 50 min running ‘preload’ at 65 V^. O2peak (32 °C, 50

Dehydration of >3 % body mass impairs endurance performance irrespective of the individual's knowledge of their hydration status, but whether knowledge of hydration status influences performance at lower levels of dehydration is unknown. This study examined whether perception of hydration status influenced endurance performance. After familiarisation, nine active males (age 25 ± 2 y, V̇O2peak 52.5 ± 9.1 mL kg min-1) completed two randomised trials at 34 °C. Trials involved an intermittent exercise preload (8 × 10 min cycling/5 min rest), followed by a 15 min all-out cycling performance test. During the preload in both trials, water was ingested orally every 10 min (0.3 mL kg body mass-1), with additional water infused into the stomach via gastric feeding tube to produce dehydration of ∼1.5 % body mass pre-performance test. Participants were told intra-gastric infusion was manipulated to produce euhydration (0 % dehydration; Perceived-EUH) or dehydration (2 % dehydration; Perceived-DEH) pre-performance test, which was told to them pre-preload and confirmed after body mass measurement pre-performance test. Body mass loss during the preload (Perceived-EUH 1.6 ± 0.2 %, Perceived-DEH 1.7 ± 0.2 %; P = 0.459), heart rate, gastrointestinal temperature and RPE (P ≥ 0.110) were not different between trials. Thirst was greater at the end of the preload and performance test in Perceived-DEH (P ≤ 0.040). Work completed during the performance test was 5.6 ± 6.1 % lower in Perceived-DEH (187.4 ± 37.0 kJ vs. 176.9 ± 36.0 kJ; P = 0.038). These results suggest that at lower levels of dehydration (<2 % body mass), an individual's perception of their hydration status could impair their performance, as well as their thirst perception.

Recent studies have shown that hypohydration can increase renal injury. However, the contribution of hypohydration to the extent of renal injury is often confounded by exercise induced muscle damage. Therefore, the aim of the present study was to investigate the effect of manipulating hydration status during moderate-intensity cycling in the heat on biomarkers of renal injury. Following familiarisation, fourteen active males (age: 21 [20–22] y; BMI: 22.1 ± 1.9 kg/m2; V̇ O2peak: 55 ± 9 mL/kg/min) completed two experimental trials, in a randomised cross-over design. Experimental trials consisted of up to 120 min of intermittent cycling ( 50