Repeatability of Ad Libitum Water Intake during Repeated 1 h Walking/Jogging Exercise Sessions Conducted under Hot Ambient Conditions.

A drinking strategy aiming to replace a given percentage of the sweat losses incurred during exercise should result in reproducible fluid intake volume and, hence, fluid balance from one exercise session to the other performed under similar scenarios. Whether this may also be the case with ad libitum drinking during exercise is unclear. We characterized the repeatability of ad libitum water intake during repeated 1 h exercise sessions and examined its effect over time on fluid balance and selected physiological functions and perceptual sensations. Twelve (3 women) healthy individuals participated in this study. At weekly intervals, they completed four 2 × 30 min walking/jogging exercise bouts (55% V˙O2max, 40 °C, 20-30% relative humidity) interspersed by a 3 min recovery period. During exercise, participants consumed water (20 °C) ad libitum. There were no significant differences among the four exercise sessions for absolute water intake volume (~1000 mL·h-1), percent body mass loss (~0.4%), sweat rate (~1300 mL·h-1) and percent of sweat loss replaced by water intake (~80%). Heart rate, rectal temperature, and perceived thirst and heat stress did not differ significantly between the first and fourth exercise sessions. Perceived exertion was significantly lower during the fourth vs. the first exercise session, but the difference was trivial (<1 arbitrary unit). In conclusion, ad libitum water intake during four successive identical 1 h walking/jogging sessions conducted in the heat will result in similar water intake volumes and perturbations in fluid balance, heart rate, rectal temperature, and perceived thirst, heat stress and exertion.

Effect of electric fan use in isolation or combined with ice slurry/cold water ingestion and lower-leg immersion in young men during intermittent physical activity in hot-humid conditions.

Using a randomized crossover protocol, 10 young men completed four 180 min exposures (38 °C, 60% relative humidity), alternating between 30 min of walking and 30 min of sitting where fluid or ice slurry were served. Participants underwent four trials: (i) 5 mL·kg body mass-1 of 20 °C water (CON); (ii) 5 mL·kg body mass-1 of 20 °C water + fan at 4 m·s-1 (FAN); (iii) fan + 3 mL·kg body mass-1 of ice slurry + 2 mL·kg body mass-1 of 4 °C water (FAN + ISCW); and (iv) FAN + ISCW + lower-leg immersion in 20 °C water (FAN + ISCW + LLI). Sweat and body mass losses were higher with FAN than CON, FAN + ISCW, and FAN + ISCW + LLI. Mean and peak changes in Δrectal temperature, heart rate, and perceived heat and thirst from baseline were not statistically and practically different between FAN and CON. FAN + ISCW + LLI decreased sweat loss compared with FAN + ISCW and mean and peak changes in Δrectal temperature, heart rate, and perceived thirst compared with CON. FAN + ISCW + LLI also attenuated the changes in Δrectal temperature (peak) and thirst (mean and peak) compared with FAN. In conclusion, FAN slightly exacerbates fluid loss but does not attenuate the changes in Δrectal temperature, heart rate, and perceived heat and thirst during intermittent physical activity in hot-humid conditions. However, coupling ISCW or ISCW + LLI with the use of a fan attenuates the increase in these outcomes compared with no intervention and to a greater extent for rectal temperature and thirst when fan is coupled with ISCW + LLI than when it is used in isolation.

CORE™ wearable sensor: Comparison against gastrointestinal temperature during cold water ingestion and a 5 km running time-trial.

Five km running time-trials (TT) are associated with rapid and significant increases in core body temperature (TC). For such races, real-time feedback from pre-exercise and exercise TC may be helpful in the design of an optimal pacing strategy aimed at limiting the possibility of developing heat-related illnesses. This study compared measurements of TC obtained with a wearable device, the CORE™, to those of a gastrointestinal pill (GI pill), during cold water ingestion and a 5 km running TT. Twelve participants (25 ± 4 yrs) ingested 7.5 mL/kg fat-free mass of 4 °C water over the first 5 min of a 120 min sitting period, after which they completed a 5 km running TT at 30 °C, 50% relative humidity. A TC difference > ± 0.25 °C between sensors was deemed clinically unacceptable. Prior to water ingestion, the CORE-derived TC was 0.49 ± 0.25 °C lower than the GI pill. The CORE was irresponsive to the 0.26 ± 0.22 °C peak decline in TC captured with the GI pill 40 min following water ingestion. Prior to the TT, TC was 0.30 ± 0.25 °C lower with the CORE than the GI pill. During the TT, the CORE underestimated the rate of increase in TC by 0.0125 ± 0.019 °C/min compared with the GI pill, and mean absolute difference in TC between sensors was of 0.47 ± 0.34 °C. In conclusion, the CORE does not capture the cooling effect of cold water ingestion and provides a clinically relevant underestimation of TC during a 5 km running TT in the heat.

Effect of Glycerol-Induced Hyperhydration on a 5-kilometer Running Time-Trial Performance in the Heat in Recreationally Active Individuals.

Maximal oxygen consumption (V˙O2max) is a major determinant of 5-km running time-trial (TT) performance. Glycerol-induced hyperhydration (GIH) could improve V˙O2max in recreationally active persons through an optimal increase in plasma volume. Moreover, ingestion of a large bolus of cold fluid before exercise could decrease thermal stress during exercise, potentially contributing to improved performance. We determined the effect of GIH on 5-km running TT performance in 10 recreationally active individuals (age: 24 ± 4 years; V˙O2max: 48 ± 3 mL/kg/min). Using a randomized and counterbalanced protocol, participants underwent two, 120-min hydration protocols where they ingested a 1) 30 mL/kg fat-free mass (FFM) of cold water (~4 °C) with an artificial sweetener + 1.4 g glycerol/kg FFM over the first 60 min (GIH) or 2) 7.5 mL/kg FFM of cold water with an artificial sweetener over the first 20 min (EUH). Following GIH and EUH, participants underwent a 5-km running TT at 30 °C and 50% relative humidity. After 120 min, GIH was associated with significantly greater fluid retention (846 ± 415 mL) and plasma volume changes (10.1 ± 8.4%) than EUH, but gastrointestinal (GI) temperature did not differ. During exercise, 5-km running TT performance (GIH: 22.95 ± 2.62; EUH: 22.52 ± 2.74 min), as well as heart rate, GI temperature and perceived exertion did not significantly differ between conditions. This study demonstrates that the additional body water and plasma volume gains provided by GIH do not improve 5-km running TT performance in the heat in recreationally active individuals.

Change in heart rate variability during two firefighting work cycles.

This study aimed to determine whether the change in heart rate variability from pre to post firefighting is modulated by different work cycles. Thirteen male firefighters underwent two firefighting simulations that comprised two identical 25-min work bouts intercalated by a passive recovery period of either 20 min (T20) or 5 min (T5). The square root of the mean squared differences of successive R-R intervals (RMSSD) and aural temperature were measured at rest before (PRE) and after (POST) firefighting simulations. The decrease in RMSSD was different between firefighting simulations (T20: -10 ± 21.2 ms, T5: -19.9 ± 20.9 ms, interaction, p = 0.02). Post-firefighting aural temperature was greater (p = 0.05) in T5 (37.18 ± 0.53 °C) than in T20 (36.88 ± 0.49 °C). In conclusion, a shorter recovery period of 5 min between firefighting work bouts decreases post-firefighting heart rate variability, possibly attributed to a lower parasympathetic reactivation and a higher absolute value of body temperature.

Impact of dehydration on perceived exertion during endurance exercise: A systematic review with meta-analysis.

Background: Understanding the impact of stressors on the rating of perceived exertion (RPE) is relevant from a performance and exercise adherence/participation standpoint. Athletes and recreationally active individuals dehydrate during exercise. No attempt has been made to systematically determine the impact of exercise-induced dehydration (EID) on RPE. Objective: The present meta-analysis aimed to determine the effect of EID on RPE during endurance exercise and examine the moderating effect of potential confounders. Data analyses: Performed on raw RPE values using random-effects models weighted mean effect summaries and meta-regressions with robust standard errors, and with a practical meaningful effect set at 1 point difference between euhydration (EUH) and EID. Only controlled crossover studies measuring RPE with a Borg scale in healthy adults performing ≥30 min of continuous endurance exercise while dehydrating or drinking to maintain EUH were included. Results: Sixteen studies were included, representing 147 individuals. Mean body mass loss with EUH was 0.5 ± 0.4%, compared to 2.3 ± 0.5% with EID (range 1.7-3.1%). Within an EID of 0.5-3% body mass, a maximum difference in RPE of 0.81 points (95% CI: 0.36-1.27) was observed between conditions. A meta-regression revealed that RPE increases by 0.21 points for each 1% increase in EID (95% CI: 0.12-0.31). Humidity, ambient temperature and aerobic capacity did not alter the relationship between EID and RPE. Conclusion: Therefore, the effect of EID on RPE is unlikely to be practically meaningful until a body mass loss of at least 3%.

Effect of Pre-Exercise Caffeine Intake on Endurance Performance and Core Temperature Regulation During Exercise in the Heat: A Systematic Review with Meta-Analysis.

BACKGROUND: Heat is associated with physiological strain and endurance performance (EP) impairments. Studies have investigated the impact of caffeine intake upon EP and core temperature (CT) in the heat, but results are conflicting. There is a need to systematically determine the impact of pre-exercise caffeine intake in the heat. OBJECTIVE: To use a meta-analytical approach to determine the effect of pre-exercise caffeine intake on EP and CT in the heat. DESIGN: Systematic review with meta-analysis. DATA SOURCES: Four databases and cross-referencing. DATA ANALYSIS: Weighted mean effect summaries using robust variance random-effects models for EP and CT, as well as robust variance meta-regressions to explore confounders. STUDY SELECTION: Placebo-controlled, randomized studies in adults (≥ 18 years old) with caffeine intake at least 30 min before endurance exercise ≥ 30 min, performed in ambient conditions ≥ 27 °C. RESULTS: Respectively six and 12 studies examined caffeine's impact on EP and CT, representing 52 and 205 endurance-trained individuals. On average, 6 mg/kg body mass of caffeine were taken 1 h before exercises of ~ 70 min conducted at 34 °C and 47% relative humidity. Caffeine supplementation non-significantly improved EP by 2.1 ± 0.8% (95% CI - 0.7 to 4.8) and significantly increased the rate of change in CT by 0.10 ± 0.03 °C/h (95% CI 0.02 to 0.19), compared with the ingestion of a placebo. CONCLUSION: Caffeine ingestion of 6 mg/kg body mass ~ 1 h before exercise in the heat may provide a worthwhile improvement in EP, is unlikely to be deleterious to EP, and trivially increases the rate of change in CT.

Cognitive Performance Before and Following Habituation to Exercise-Induced Hypohydration of 2 and 4% Body Mass in Physically Active Individuals.

We investigated the effect of repeated exposures to hypohydration upon cognitive performance. In a randomized crossover design, ten physically active adults completed two 4-week training blocks, one where they maintained euhydration (EUH) and the other where they were water-restricted (DEH) during walking/running at 55% V.O2max, 40 °C. Three sessions per week were performed: (1) 1 h of exercise, (2) exercise until 2% or (3) 4% of body mass has been lost or replaced. Limited to the first and fourth training week, a 12 min walking/running time-trial was completed following the 2 and 4% exercise bouts. Trail making, the Wisconsin card sort, the Stop signal task, Simple visual reaction time and Corsi block-tapping tests were performed immediately following the time-trials. Body mass loss was maintained < 1% with EUH and reached 2.7 and 4.7% with DEH following the time-trials. Except for a lower percentage of correct responses (% accuracy) during the Wisconsin card sort test (p < 0.05) with DEH compared to EUH, no statistically significant decline in cognitive performance was induced by low and moderate levels of hypohydration. Compared to week 1, no statistical differences in cognitive responses were observed after repeated exposures to hypohydration (all p > 0.05). From a practical perspective, the gains in cognitive performance following training to DEH were mostly unclear, but under certain circumstances, were greater than when EUH was maintained. Based on the battery of cognitive tests used in the current study, we conclude that whether physically active individuals are habituated or not to its effect, exercise-induced hypohydration of 2 and 4% has, in general, no or unclear impact on cognitive performance immediately following exercise. These results encourage further research in this area.

Impact of Repeated Acute Exposures to Low and Moderate Exercise-Induced Hypohydration on Physiological and Subjective Responses and Endurance Performance.

This study aimed to examine whether repeated exposures to low (2%) and moderate (4%) exercise-induced hypohydration may reverse the potentially deleterious effect of hypohydration on endurance performance. Using a randomized crossover protocol, ten volunteers (23 years, V˙O2max: 54 mL∙kg-1∙min-1) completed two 4-week training blocks interspersed by a 5-week washout period. During one block, participants replaced all fluid losses (EUH) while in the other they were fluid restricted (DEH). Participants completed three exercise sessions per week (walking/running, 55% V˙O2max, 40 °C): (1) 1 h while fluid restricted or drinking ad libitum, (2) until 2 and (3) 4% of body mass has been lost or replaced. During the first and the fourth week of each training block, participants completed a 12 min time-trial immediately after 2% and 4% body mass loss has been reached. Exercise duration and distance completed (14.1 ± 2.7 vs. 6.9 ± 1.5 km) during the fixed-intensity exercise bouts were greater in the 4 compared to the 2% condition (p < 0.01) with no difference between DEH and EUH. During the first week, heart rate, rectal temperature and perceived exertion were higher (p < 0.05) with DEH than EUH, and training did not change these outcomes. Exercise-induced hypohydration of 2% and 4% body mass impaired time-trial performance in a practical manner both at the start and end of the training block. In conclusion, exercise-induced hypohydration of 2% and 4% body mass impairs 12 min walking/running time-trial, and repeated exposures to these hypohydration levels cannot reverse the impairment in performance.

Validity and Reliability of the Computrainer Lab™ During Simulated 40 and 100 km Time-Trials.

The validity and reliability of the Computrainer Lab™ (CT) was assessed, for the first time, using a high-precision motor-driven calibration rig during simulated variable intensity 40 and 100 km time-trials (TTs). The load patterns imposed by the CT were designed from previously published studies in trained cyclists and included multiple 1 or 4 km bursts in power output. For the 40 and 100 km TTs, cluster-based analyses revealed a mean measurement error from the true workload of respectively 0.7 and 0.9%. However, measurement errors were dependent upon the workload variations, fluctuating from 0.2 to 5.1%. Average biases between repeated trials were contained within ± 1.1% for both TTs. In conclusion, using 40 and 100 km TTs containing 1 or 4 km bursts in power output, the present results indicate that (1) the CT can reliably be used by scientists to determine differences between research interventions; (2) the CT provides valid results of power output when data are being analyzed as a whole to derive one mean value of power output and; (3) variations in workload make it difficult to determine at any one time the veracity of the true power output produced by the athlete.

Provision of instructions to drink ad libitum or according to thirst sensation: impact during 120 km of cycling in the heat in men.

The terms drinking to thirst and ad libitum drinking are used interchangeably, but should they? We investigated the differences in how athletes consumed fluids during exercise when instructed to drink according to thirst or ad libitum. Using a randomized, crossover, and counterbalanced design, 10 males (27 ± 4 y) cycled 120 km (48 ± 4% of peak power, 33 °C, 40% relative humidity) on 2 occasions, while drinking water according to thirst or ad libitum. Participants covered the cycling trials in 222 ± 11 min (p = 0.29). Although the body mass loss at the end of exercise and total volume of water consumed were similar between trials, thirst perception before each sip and the volume consumed per sip were significantly higher with thirst than ad libitum drinking, whereas the total number of sips was significantly lower with thirst than ad libitum drinking. Perceived exertion, rectal temperature, and heart rate were all significantly higher with thirst than ad libitum drinking, but the difference was trivial. In conclusion, thirst and ad libitum drinking are associated with different drinking patterns, but equally maintain fluid balance during prolonged exercise. The terms drinking to thirst and ad libitum drinking can be used interchangeably to guide fluid intake during prolonged exercise. Novelty: Both strategies are associated with different patterns of fluid ingestion during prolonged exercise, but are equally effective in maintaining fluid balance. Perceived exertion, rectal temperature, and heart rate are regulated dissimilarly by thirst and ad libitum drinking, but the difference is trivial.

Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment.

We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% V˙O2peak followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.

Validity and Reliability of the CorTempTM Telemetric Pill during 50 h of Reuse in a Circulating Water Bath.

It has been shown that CorTempTM telemetric pills (CTTPs) provide valid measures of rectal temperature when used as suppositories. While encapsulated into a condom linked to a thread, CTTPs can be inserted in and extracted from the rectum and be reused. The validity and reliability of the CTTP throughout repeated use remains to be demonstrated. Three CTTPs were compared to a YSI 401 wired rectal probe inside a circulating water bath (temperatures varying from 36.5 to 39.4 °C) during 50 h of intermittent use. Each CTTP underwent 20 trials comprising 6 protocols of varying duration: 6 · 1 h, 5 · 2 h, 4 · 3 h, 3 · 4 h and 2 · 5 h. All CTTPs were washed, switched off and disinfected after each trial to reproduce real-life use. Acceptable agreement between sensors was taken as a mean bias within ±0.27 °C. None of the pills showed signs of deterioration following 50 h of reuse. As for relative validity, where all CTTPs showed robust coefficients of determination ranging from 0.98 to 0.99, absolute validity was excellent with each CTTP showing mean biases and typical errors of the estimate (TEE) within ±0.27 °C. Comparisons between the first and last trial each CTTP underwent resulted in means biases and TEEs within ±0.27 °C and coefficients of determination ranging from 0.97 to 0.99, which indicates strong absolute and relative reliability. The present results show that CTTPs can provide valid and reliable measurements of temperature when reused up to 50 h.

Impact of Mild Hypohydration on 100 m Front Crawl Performance and Starting Block Peak Force Production in Competitive University-Level Swimmers.

Unstructured, ad libitum drinking may predispose some athletes to start exercise already slightly hypohydrated (decreased body water). The impact of pre-exercise mild hypohydration on subsequent swimming performance is still unknown. Hence, the goal of this study was to examine its effect on peak force production on the starting block and 100 m front crawl swimming performance in competitive university-level swimmers. At least one hour after having been passively exposed to heat where a body mass loss of 1.5% was induced or euhydration (normal body water) maintained, nine participants (age: 22 ± 2 years) underwent an assessment of their peak force production on the starting block and 100 m front crawl performance. One hour following hypohydration, rectal temperature had returned to baseline in each condition. Urine osmolality and specific gravity were higher (p < 0.05) with hypohydration than euhydration (995 ± 65 vs. 428 ± 345 mOsmol/kg; 1.027 ± 0.003 vs. 1.016 ± 0.007 g/mL) prior to exercise testing, as was perceived thirst. Swimming performance (p = 0.86) and peak force production (p = 0.72) on the starting block did not differ between the hypohydration and euhydrated condition (63.00 ± 4.26 vs. 63.09 ± 4.52 s; 1322 ± 236 vs. 1315 ± 230 N). The current results indicate that mild hypohydration, which may occur with ad libitum drinking, does not impede peak force production on the starting block and 100 m front crawl performance in university-level competitive swimmers. Planned drinking is not required prior to such an event.

Permanent tattooing has no impact on local sweat rate, sweat sodium concentration and skin temperature or prediction of whole-body sweat sodium concentration during moderate-intensity cycling in a warm environment.

PURPOSES: This study investigated the impact of permanently tattooed skin on local sweat rate, sweat sodium concentration and skin temperature and determined whether tattoos alter the relationship between local and whole-body sweat sodium concentration. METHODS: Thirteen tattooed men (27 ± 6 years) completed a 1 h (66 ± 4% of [Formula: see text]) cycling trial at 32 °C, 35% relative humidity. Sweat rate and sweat sodium concentration were measured using the whole-body washdown and local absorbent patch techniques. Patches and skin-temperature probes were applied over the right/left thighs and tattooed/non-tattooed (contralateral) regions. RESULTS: Local sweat rates did not differ (p > 0.05) between the right (1.11 ± 0.38) and left (1.21 ± 0.37) thighs and the permanently tattooed (1.93 ± 0.82) and non-tattooed (1.72 ± 0.81 mg cm-2 min-1) regions. There were no differences in local sweat sodium concentration between the right (58.2 ± 19.4) and left (55.4 ± 20.3) thighs and the permanently tattooed (73.0 ± 22.9) and non-tattooed (70.2 ± 18.9 mmol L-1) regions. Difference in local skin temperature between the right and left thighs (- 0.043) was similar to that between the permanently tattooed and non-tattooed (- 0.023 °C) regions. Prediction of whole-body sweat sodium concentration for the permanently tattooed (41.0 ± 6.7) and the non-tattooed (40.2 ± 5.3 mmol L-1) regions did not differ. CONCLUSION: Permanent tattoos do not alter local sweat rate, sweat sodium concentration or local skin temperature during moderate-intensity cycling exercise in a warm environment. Results from a patch placed over a tattooed surface correctly predicts whole-body sweat sodium concentration from an equation developed from a non-tattooed region.

Comment on: "The Utility of Thirst as a Measure of Hydration Status Following Exercise-Induced Dehydration".

In their study, Adams et al. [1] attempted to determine whether thirst perception could serve as a reliable marker of hydration status during 3 h of exercise where participants either dehydrated by 3% of their body mass or maintained euhydration through water intake, and following exercise where they either could not drink or were allowed to consume water ad libitum during the first 10 min of a 60 min long recovery period [...].

The ability of exercise to meaningfully improve glucose tolerance in people living with prediabetes: A meta-analysis.

BACKGROUND: Individuals with prediabetes are likely to progress to Type 2 diabetes. Although exercise training is an established method to improve glycemic control, the degree to which this translates into meaningful improvements, particularly in individuals with prediabetes, is unclear. The purpose of this meta-analysis was to investigate the ability of exercise training to improve 2-hour glucose tolerance beyond the smallest worthwhile difference in individuals with prediabetes. It was hypothesized that the majority of implemented exercise programs designed for individuals with prediabetes would not result in meaningful improvements in glucose tolerance. METHODS: Searches were performed in MEDLINE, The Cumulative Index to Nursing and Allied Health Literature, SPORTDiscus, and the Cochrane Library. Included studies reported glucose tolerance using a 2-hour oral glucose tolerance test at baseline and post-intervention; implemented an exercise program lasting at least 12 weeks; and included adults living with prediabetes. Mean effect summaries were determined using random-effects models. Magnitude-based inference statistic was used to estimate the likelihood that observed changes in glucose tolerance were meaningful to patients. RESULTS: Nine articles were included in the meta-analysis, producing 12 independent exercise interventions. The interventions led to an average improvement in glucose tolerance of 5.9% (95% confidence interval: 3.7%-8.0%). Seven (58%) exercise interventions were deemed likely to benefit patients, whereas five (42%) had trivial or unclear findings. CONCLUSION: While exercise intervention led to statistically significant improvements in 2-hour glucose tolerance, the benefit for individuals living with prediabetes remains unclear. Further research is needed to delineate optimal prescription parameters for generating meaningful benefits in glucose tolerance.

Impact of Pre-exercise Hypohydration on Aerobic Exercise Performance, Peak Oxygen Consumption and Oxygen Consumption at Lactate Threshold: A Systematic Review with Meta-analysis.

BACKGROUND: Progressive exercise-induced dehydration may impair aerobic exercise performance (AEP). However, no systematic approach has yet been used to determine how pre-exercise hypohydration, which imposes physiological challenges differing from those of a well-hydrated pre-exercise state, affects AEP and related components such as peak oxygen consumption [Formula: see text] and [Formula: see text] at lactate threshold [Formula: see text]. OBJECTIVE: To determine, using a systematic approach with meta-analysis, the magnitude of the effect of pre-exercise hypohydration on AEP, [Formula: see text] and [Formula: see text]. DESIGN: This was a systematic review with meta-analysis of well-controlled studies. DATA SOURCES: MEDLINE, SPORTDiscus and CINAHL databases and cross-referencing. INCLUSION CRITERIA FOR SELECTING STUDIES: (1) well-controlled human (≥ 18 years) studies; (2) pre-exercise hypohydration induced at least 1 h prior to exercise onset; (3) pre-exercise body mass loss in the hypohydrated, experimental condition was ≥ 1% and ≥ 0.5% than the well-hydrated, control condition; (4) following the dehydrating protocol body mass change in the control condition was within - 1% to + 0.5% of the well-hydrated body mass. RESULTS: A total of 15 manuscripts were included, among which 14, 6 and 6 met the inclusion criteria for AEP, [Formula: see text] and [Formula: see text], respectively, providing 21, 10 and 9 effect estimates, representing 186 subjects. Mean body mass decrease was 3.6 ± 1.0% (range 1.7-5.6%). Mean AEP test time among studies was 22.3 ± 13.5 min (range 4.5-54.4 min). Pre-exercise hypohydration impaired AEP by 2.4 ± 0.8% (95% CI 0.8-4.0%), relative to the control condition. Peak oxygen consumption and [Formula: see text], respectively, decreased by 2.4 ± 0.8% (95% CI 0.7-4.0%) and 4.4 ± 1.4% (95% CI 1.7-7.1%), relative to the control condition. Compared with starting an exercise hypohydrated, it is respectively likely, possible and likely that AEP, [Formula: see text] and [Formula: see text] benefit from a euhydrated state prior to exercise. Meta-regression analyses did not establish any significant relationship between differences in body mass loss and differences in the percent change in AEP or [Formula: see text]. However, [Formula: see text] was found to decrease by 2.6 ± 0.8 % (95% CI 0.7-4.5%) for each percent loss in body mass above a body mass loss threshold of 2.8%. CONCLUSION: Pre-exercise hypohydration likely impairs AEP and likely reduces [Formula: see text] (i.e., the aerobic contribution to exercise was lower) during running and cycling exercises ≤ 1 h across different environmental conditions (i.e., from 19 to 40 °C). Moreover, pre-exercise hypohydration possibly impedes [Formula: see text] during such exercises.