The impact of alterations in hydration status on human physiology and performance responses during exercise is one of the oldest research topics in sport and exercise nutrition. This body of work has ...mainly focussed on the impact of reduced body water stores (i.e. hypohydration) on these outcomes, on the whole demonstrating that hypohydration impairs endurance performance, likely via detrimental effects on a number of physiological functions. However, an important consideration, that has received little attention, is the methods that have traditionally been used to investigate how hypohydration affects exercise outcomes, as those used may confound the results of many studies. There are two main methodological limitations in much of the published literature that perhaps make the results of studies investigating performance outcomes difficult to interpret. First, subjects involved in studies are generally not blinded to the intervention taking place (i.e. they know what their hydration status is), which may introduce expectancy effects. Second, most of the methods used to induce hypohydration are both uncomfortable and unfamiliar to the subjects, meaning that alterations in performance may be caused by this discomfort, rather than hypohydration per se. This review discusses these methodological considerations and provides an overview of the small body of recent work that has attempted to correct some of these methodological issues. On balance, these recent blinded hydration studies suggest hypohydration equivalent to 2–3% body mass decreases endurance cycling performance in the heat, at least when no/little fluid is ingested.
Cycling time trial (TT) protocols have been shown to be reliable in trained cyclists, but their reproducibility in lesser-trained individuals is unknown. This study examined the reliability of a ...self-paced 15-minute cycling TT in recreationally active individuals. Twelve recreationally active males (age 27 ± 3 y; body mass 75.2 ± 8.9 kg;
$${\dot{\rm{V}}}$$
V
˙
O
2peak
= 51.10 ± 7.53 ml∙kg∙min
−1
) completed a
$${\dot{\rm{V}}}$$
V
˙
O
2peak
test and four experimental trials, separated by > 48 h. Experimental trials consisted of 10 min cycling at 60% W
max
, followed by a self-paced 15-min TT. Heart rate and work done were recorded every 5 min during the TT; and coefficient of variation (CV) was calculated. Work done was not different (P = 0.706) between trials (193.2 ± 45.3 kJ; 193.2 ± 43.5 kJ; 192.0 ± 42.3 kJ; 193.9 ± 42.8 kJ). Within participant CV ranged from 0.5-4.9% for the four TTs, with a mean CV of 2.1%. Mean CV decreased from 2.0% (range 0.1-5.0%) for the first two TTs to 1.7% (range 0.2-5.6%) for the second and third TTs, and further decreased to 1.0% (range 0.2-1.8%) for the third and fourth TTs. In conclusion, the use of a short-duration self-paced cycling TT in recreationally active individuals is a reliable performance measure.
Knowledge of hydration status may contribute to hypohydration-induced exercise performance decrements; therefore, this study compared blinded and unblinded hypohydration on cycling performance. ...Fourteen trained, nonheat-acclimated cyclists (age: 25 ± 5 yr; V̇o
: 63.3 ± 4.7 ml·kg
·min
; cycling experience: 6 ± 3 yr) were pair matched to blinded (B) or unblinded (UB) groups. After familiarization, subjects completed euhydrated (B-EUH; UB-EUH) and hypohydrated (B-HYP; UB-HYP) trials in the heat (31°C); 120-min cycling preload (50% W
) and a time trial (~15 min). During the preload of all trials, 0.2 ml water·kg body mass
was ingested every 10 min, with additional water provided during EUH trials to match sweat losses. To blind the B group, a nasogastric tube was inserted in both trials and used to provide water in B-EUH. The preload induced similar ( P = 0.895) changes in body mass between groups (B-EUH: -0.6 ± 0.5%; B-HYP: -3.0 ± 0.5%; UB-EUH: -0.5 ± 0.3%; UB-HYP -3.0 ± 0.3%). All variables responded similarly between B and UB groups ( P ≥ 0.558), except thirst ( P = 0.004). Changes typical of hypohydration (increased heart rate, rating of perceived exertion, gastrointestinal temperature, serum osmolality and thirst, and decreased plasma volume; P ≤ 0.017) were apparent in HYP by 120 min. Time trial performance was similar between groups ( P = 0.710) and slower ( P ≤ 0.013) with HYP for B (B-EUH: 903 ± 89 s; B-HYP: 1,008 ± 121 s; -11.4%) and UB (UB-EUH: 874 ± 108 s; UB-HYP: 967 ± 170 s; -10.1%). Hypohydration of ~3% body mass impairs time trial performance in the heat, regardless of knowledge of hydration status. NEW & NOTEWORTHY This study demonstrates, for the first time, that knowledge of hydration status does not exacerbate the negative performance consequences of hypohydration when hypohydration is equivalent to ~3% body mass. This is pivotal for the interpretation of the many previous studies that have not blinded subjects to their hydration status and suggests that these previous studies are not likely to be confounded by the overtness of the methods used to induce hypohydration.
•Although there is a vast amount of research assessing short-term rehydration post-exercise (<6 h), little is known regarding prolonged rehydration (>6 h), particularly ad-libitum rehydration.•Given ...many athletes, including many team sports athletes, would typically train once per day, it is important to understand hydration responses over prolonged (24 h) time scales.•When team sports athletes were permitted to drink fluid ad-libitum during exercise and had access to food and fluid in a free-living environment, a small degree of hypohydration remained 20 h post-exercise.•Rehydration strategies may be required for team sports athletes to effectively rehydrate, even when exercise sessions are separated by a day.
This study documented 20 h rehydration from intermittent running while concealing the primary outcome of rehydration from subjects. Twenty-eight male team sports athletes (age 25 ± 3 y; predicted V̇O2max 54 ± 3 mL kg−1 min−1) were pair-matched to exercise (EX) or rest (REST) groups. To determine hydration status, body mass, urine and blood samples were collected at 08:00, pre-intervention (09:30), post-intervention (12:00), 3 h post-intervention and 08:00 the following morning (20 h). The intervention was 110 min intermittent running (EX) or seated rest (REST), with ad-libitum fluid provided in both. Subjects completed a weighed diet record and collected all urine for the 24 h. Changes typical of hypohydration were apparent in EX following the intervention period (body mass: EX -2.0 ± 0.5%; REST -0.2 ± 0.3%; serum osmolality: EX 293 ± 4 mOsm∙kgH2O−1; REST 287 ± 6 mOsm∙kgH2O−1; P ≤ 0.022). Fluid intake during the intervention period (EX 704 ± 286 mL, REST 343 ± 230 mL) and fluid intake within the first 3 h post-intervention (EX 1081 ± 460 mL, REST 662 ± 230 mL) were greater (P ≤ 0.004), and 24 h urine volume lower (EX 1697 ± 824 mL, REST 2370 ± 842 mL; P = 0.039) in EX. Compared to baseline, body mass remained lower (-0.6 ± 0.5%; P = 0.030) and urine osmolality elevated (20 h: 844 ± 197 mOsm∙kgH2O−1, 08:00: 698 ± 200 mOsm∙kgH2O−1; P = 0.004) at 20 h in EX. When games players drank fluid ad-libitum during exercise and post-exercise in free-living conditions, a small degree of hypohydration remained 20 h post-exercise.
This systematic review analyzed whether carbohydrate source (food vs. supplement) influenced performance and gastrointestinal (GI) symptoms during endurance exercise. Medline, SPORTDiscus, and ...citations were searched from inception to July 2021. Inclusion criteria were healthy, active males and females aged >18 years, investigating endurance performance, and GI symptoms after ingestion of carbohydrate from a food or supplement, <60 min before or during endurance exercise. The van Rosendale scale was used to determine risk of bias, with seven studies having low risk of bias. A total of 151 participants from 15 studies were included in the review. Three studies provided 0.6-1 g carbohydrate/kg body mass during 5-45 min precycling exercise (duration 60-70 min) while 12 studies provided 24-80 g/hr carbohydrate during exercise (60-330 min). Except one study that suggested a likely harmful effect (magnitude-based inferences) of a bar compared to a gel consumed during exercise on cycling performance, there were no differences in running (n = 1) or cycling (n = 13) performance/capacity between food and supplemental sources. Greater GI symptoms were reported with food compared with supplemental sources. Highly heterogenous study designs for carbohydrate dose and timing, as well as exercise protocol and duration, make it difficult to compare findings between studies. A further limitation results from only one study assessing running performance. Food choices of carbohydrate consumed immediately before and during endurance exercise result in similar exercise performance/capacity responses to supplemental carbohydrate sources, but may slightly increase GI symptoms in some athletes, particularly with exercise >2 hr.
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/m
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.
As a global industry, sport makes potentially significant contributions to climate change through both carbon emissions and influence over sustainability practices. Yet, evidence regarding impacts is ...uneven and spread across many disciplines. This paper investigates the impacts of sport emissions on climate and identifies knowledge gaps. We undertook a systematic and iterative meta‐analysis of relevant literature (1992–2022) on organized and individual sports. Using a defined search protocol, 116 sources were identified that map to four sport‐related themes: (1) carbon emissions and their measurement; (2) emissions control and decarbonization; (3) carbon sinks and offsets; and (4) behavior change. We find that mega sport events, elite sport, soccer, skiing, and golf have received most attention, whereas grass‐roots and women's sport, activity in Africa and South America, cricket, tennis, and volleyball are understudied. Other knowledge gaps include carbon accounting tools and indicators for smaller sports clubs and active participants; cobenefits and tradeoffs between mitigation‐adaptation efforts in sport, such as around logistics, venues, sports equipment, and facilities; geopolitical influence; and scope for climate change litigation against hosts and/or sponsors of carbon‐intensive events. Among these, researchers should target cobenefits given their scope to deliver wins for both climate mitigation and risk management of sport.
Sport makes potentially significant contributions to climate change through both carbon emissions and influence over sustainability practices. Evidence regarding impacts is uneven and spread across many disciplines. This systematic review and meta‐analysis investigates the impacts of sport emissions on climate and identifies knowledge gaps. Researchers should target co‐benefits given their scope to deliver wins for both climate mitigation and risk management of sport.
Research assessing exercise-induced hypohydration on running performance in a temperate environment is scarce. Given the weight-bearing nature of running, the negative effects of hypohydration might ...be offset by the weight-loss associated with a negative fluid balance. Therefore, this study investigated the effect of exercise-induced hypohydration on running performance in temperate conditions. Seventeen intermittent games players (age 22 ± 1 y; VO
2peak
52.5 ± 4.1 mL∙kg
−1
∙min
−1
) completed preliminary and familiarisation trials, and two experimental trials consisting of 12 blocks of 6 min of running (65% VO
2peak
; preload) with 1 min passive rest in-between, followed by a 3 km time trial (TT). During the preload, subjects consumed minimal fluid (60 mL) to induce hypohydration (HYP) or water to replace 95% sweat losses (1622 ± 343 mL; EUH). Body mass loss (EUH −0.5 ± 0.3%; HYP −2.2 ± 0.4%; P < 0.001), and other changes indicative of hypohydration, including increased serum osmolality, heart rate, thirst sensation, and decreased plasma volume (P ≤ 0.022), were apparent in HYP by the end of the preload. TT performance was ~6% slower in HYP (EUH 900 ± 87 s; HYP 955 ± 110 s; P < 0.001). Exercise-induced hypohydration of ~2% body mass impaired 3 km running TT performance in a temperate environment.
Abstract The aim of the present study was to examine the effect of mild hypohydration on performance during a prolonged, monotonous driving task. Methods Eleven healthy males (age 22 ± 4 y) were ...instructed to consume a volume of fluid in line with published guidelines (HYD trial) or 25% of this intake (FR trial) in a crossover manner. Participants came to the laboratory the following morning after an overnight fast. One hour following a standard breakfast, a 120 min driving simulation task began. Driver errors, including instances of lane drifting or late breaking, EEG and heart rate were recorded throughout the driving task Results Pre-trial body mass ( P = 0.692), urine osmolality ( P = 0.838) and serum osmolality ( P = 0.574) were the same on both trials. FR resulted in a 1.1 ± 0.7% reduction in body mass, compared to − 0.1 ± 0.6% in the HYD trial ( P = 0.002). Urine and serum osmolality were both increased following FR ( P < 0.05). There was a progressive increase in the total number of driver errors observed during both the HYD and FR trials, but significantly more incidents were recorded throughout the FR trial (HYD 47 ± 44, FR 101 ± 84; ES = 0.81; P = 0.006) Conclusions The results of the present study suggest that mild hypohydration, produced a significant increase in minor driving errors during a prolonged, monotonous drive, compared to that observed while performing the same task in a hydrated condition. The magnitude of decrement reported, was similar to that observed following the ingestion of an alcoholic beverage resulting in a blood alcohol content of approximately 0.08% (the current UK legal driving limit), or while sleep deprived.
Ingested ketogenic agents offer the potential to enhance endurance performance via the provision of an alternative exogenous, metabolically efficient, glycogen-sparing fuel (i.e. ketone bodies). This ...study aimed to assess the impact of combined carbohydrate and 1,3-butanediol (CHO-BD) supplementation on endurance performance, blood beta-hydroxybutyrate (βHB) concentration and glycolytic activity, in comparison to carbohydrate supplementation alone (CHO).
Eleven male runners (age 38±12years, mass 67.3±6.5kg, height 174.5±5.0cm, V˙O2peak 64.2±5.0ml⋅kg−1⋅min−1) performed two experimental trials in a randomised crossover design.
Each trial consisted of 60min of submaximal running, followed by a 5km running time-trial (TT), and was performed following the ingestion of an energy matched ∼650ml drink (CHO-BD or CHO).
There was no difference in TT completion time between the trials (CHO: 1265±93, CHO-BD: 1261±96s; p=0.723). However, blood βHB concentration in the CHO-BD trial was at least double that of the CHO trial at all time points following supplementation (p<0.05). While blood lactate concentration was lower in the CHO-BD versus CHO trial after 30min submaximal exercise (CHO-BD: 1.46±0.67mmol⋅L−1, CHO: 1.77±0.46mmol⋅L−1, p=0.040), it was similar at other time points. Blood glucose concentrations were higher post-TT in the CHO-BD trial (CHO-BD: 5.83±1.02mmol⋅L−1, CHO: 5.26±0.95mmol⋅L−1, p=0.015).
An energy matched CHO-BD supplementation drink raised βHB concentration and acutely lowered blood lactate concentration, without enhancing 5km TT running performance.
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