Rehydration solutions necessary for athelets

Rehydration solutions for athelets are generally designed to replace fluid and minerals lost by sweating and also limited amounts of energy in the form of carbohydrates. All three substances are either lost or used during endurance exercise. Higher exercise intensities require a higher degree of energy production for which CHO as energy source is most suitable.
Accordingly, with higher exercise intensities , more metabolic heat will be produced.
Consequently sweat rate will be increased , as well the excretion of electrolytes.
The longer the exercise lasts, the larger the amount of fluid, electrolytes and CHO needed to replace the losses.
There are large differences between individuals in sweat rate,sweat electrolyte content, degree of CHO utilization, etc.
These differences can be further influenced by climatological circumstances.
As a result, it is impossible to recommend a general rehydration solution that will exactly compensate for the losses of any individual in any situation. Commercial rehydration solutions are generally designed to cover the needs of a large exercising population under different circumstances.

1. Rehydration solutions

2. Rehydration solutions for athletes are generally designed to replace fluid and minerals lost by sweating and also limited amounts of energy in the form of CHO . All three substances are either lost or used during endurance exercise. Higher exercise intensities require a higher degree of energy production for which CHO as energy source is most suitable.

3. Accordingly, with higher exercise intensities, more metabolic heat will be produced. Consequently sweat rate will be increased, as will the excretion of electrolytes. The longer the exercise lasts, the larger the amount of fluid, electrolytes and CHO needed to replace the losses.

4. There are large differences between individuals in sweat rate, sweat electrolyte content, degree of CHO utilization, etc. These differences can be further influenced by climatological circumstances. As a result, it is impossible to recommend a general rehydration solution that will exactly compensate for the losses of any individual in any situation. Commercial rehydration solutions are generally designed to cover the needs of a large exercising population under different circumstances.

5. General guidelines for the composition of rehydration solutions have been obtained from a large number of studies in the field of gastric emptying, intestinal absorption, fluid balance, regulatory factors and fatigue/performance

6. The general outcome from these studies is that addition of small to moderate amounts of CHO to a drink does not delay gastric emptying and improves absorption, compared to plain water. The scientific rationale behind these findings is the fact that coupled glucose sodium transport across the gut membrane is very fast and stimulates water absorption due to the osmotic action of these solutes when being absorbed.

7. The addition of electrolytes, in small quantities as lost by the whole body sweat, will influence neither gastric emptying nor absorption. The CHO fraction will contribute to the maintenance of a normal blood glucose level and will lead to a sparing of the endogenous CHO reserves The latter may influence protein breakdown, delay fatigue and thus influence performance.

8. A large body of scientific evidence shows that different types of CHO in amounts of 30 - 80 g/l and sodium in amounts of 400 - 1100 mg/l induce a high rate of gastric emptying and fluid absorption. A maximal fluid absorption rate seems to be a prerequisite only in the event that the quantity of fluid ingested balances or exceeds the quantity that can be absorbed at the same time.

9. However, fluid intake during exercise generally does not exceed 600 ml/h in runners or 800 ml/h in cyclists. This seems less than the amount that could be absorbed maximally. Thus, slightly more concentrated CHO electrolyte solutions (up to 100 g CHO per litre ) are known to reduce the rate of net fluid absorption, but enhance CHO availability.

10. Flavoured drinks are preferred by athletes compared to plain water. Consequently such drinks are ingested in larger volumes. A general guideline should be that rehydration solutions should not be strongly hypertonic (i.e. < 500 mosmol and preferably < 300 mosmol ) . Drinks in the low hypertonic range (414 mOsm ) do not differ significantly in rate of fluid absorption, urine production and plasma volume, from isotonic (297 mOsm ) or hypotonic drinks (197 mOsm )

11. Hypertonic solutions have been shown to reduce the rate of net fluid absorption by inducing fluid secretion into the gastrointestinal tract. Additionally, they may also reduce the rate of gastric emptying. The latter may lead to feelings of fullness and influence/limit quantitative fluid consumption.

12. The source of CHO will influence fluid osmolality. Therefore, so as not to result in very high osmolalities , the quantity of monosaccharides dissolved is recommended to be smaller than that of disaccharides or polysaccharides. Based on current knowledge and evidence, a general recommendation for the composition of oral rehydration beverages for sport is given in Table 4.