Fluid and fuel intake during exercise

Abstract

The amounts of water, carbohydrate and salt that athletes are advised to ingest during exercise are based upon their effectiveness in attenuating both fatigue as well as illness due to hyperthermia, dehydration or hyperhydration. When possible, fluid should be ingested at rates that most closely match sweating rate. When that is not possible or practical or sufficiently ergogenic, some athletes might tolerate body water losses amounting to 2% of body weight without significant risk to physical well-being or performance when the environment is cold (e.g. 5-108C) or temperate (e.g. 21-228C). However, when exercising in a hot environment ( 4308C), dehydration by 2% of body weight impairs absolute power production and predisposes individuals to heat injury. Fluid should not be ingested at rates in excess of sweating rate and thus body water and weight should not increase during exercise. Fatigue can be reduced by adding carbohydrate to the fluids consumed so that 30-60 g of rapidly absorbed carbohydrate are ingested throughout each hour of an athletic event. Furthermore, sodium should be included in fluids consumed during exercise lasting longer than 2 h or by individuals during any event that stimulates heavy sodium loss (more than 3-4 g of sodium). Athletes do not benefit by ingesting glycerol, amino acids or alleged precursors of neurotransmitter. Ingestion of other substances during exercise, with the possible exception of caffeine, is discouraged. Athletes will benefit the most by tailoring their individual needs for water, carbohydrate and salt to the specific challenges of their sport, especially considering the environment's impact on sweating and heat stress.Keywords: carbohydrate, dehydration, fatigue, gastrointestinal function, hyperthermia, sodium. IntroductionWhen athletes exercise during training or while competing, it is clear that they sometimes benefit by ingesting various mixtures of water, carbohydrate and electrolytes (Convertino et al., 1996;Casa, 2000). The benefits can be expressed through improved performance and/or reduced physiological stress, on an athlete's cardiovascular, central nervous and muscular systems. Although ample scientific evidence exists to support the general theory for encouraging athletes to consume water, carbohydrate and electrolytes during exercise, the practical recommendations for optimally applying these general theories is not simple. This is due to the quite varied nature of the physical stresses encountered during training and competition for a wide range of sports, as well as the unique rules of each sport regarding the allowance for fluid and fuel intake during competition. Furthermore, variations in the physical intensity, duration and environment, as well as individual characteristics of a given athlete, might alter their optimal rate of water, carbohydrate and salt intake as well as the rate of gastrointestinal absorption and feelings of fullness. This task of developing consensus for general recommendations becomes less daunting when approached systematical...

Effects of aerobic fitness on hypohydration‐induced physiological strain and exercise impairment

“…In contrast to the seemingly well accepted notion that dehydration by 2% of body mass can impair endurance performance (Coyle 2004), athletes typically voluntarily dehydrate by 1–3% during prolonged training and by as much as 6% during competition (Cheuvront et al. 2003), almost independently of race distance or duration (Rehrer 2001).…”

Do energy drinks contain active components other than caffeine?

“…It is well documented that endurance exercise performance can be extended if carbohydrates are included in the fluid consumed at regular intervals . Optimal concentrations of 6–8% can provide an exogenous source of carbohydrate oxidation at rates approximating 60 g/h for each liter of fluid consumed . Sport drinks, such as Gatorade®, are designed to provide these optimal concentrations of carbohydrate, whereas the sugar content of most EDs are closer to 11–12% by volume (see Table ), which are levels at which gastric emptying would be slowed …”

“…The glucose content in EDs is not designed to optimize absorption of fluid and carbohydrates during exercise, as is the case for sport drinks, such as Gatorade® . As a result, if the ED is consumed as a source of fluid and carbohydrate during exercise, then better choices are available for this purpose.…”

Hydration in sport and exercise: water, sports drinks and other drinks

“… Sodium should be included in fluids consumed during exercise if the exercise lasts more than 2 hours. It should also be included in fluids consumed by individuals in any event who lose more than 3–4 g of sodium in their sweat (Coyle 2004). Normally, before commencing exercise, euhydration should be ensured.…”