Fluid replacement - What and when should I drink?

Here are a few things culled from the scientific literature recently that are interesting to athletes and coaches:

  • Fluid replacement is best spaced out over the available time - even though the natural impulse is to take as much fluid on board as possible right away. Because of the way the kidneys handle the excess fluid you will get more complete rehydration if the fluid is taken in over time.

  • As athletes prefer to take on fluid right after exercise, and as carbohydrate replacement is most effective right after exercise - a sports drink suits both needs right after exercise. Moreover, the small amount of sodium in sports drinks improves fluid replacement.

  • When competitions are spaced less than 24 hr apart - as often happens in rowing - fluid replacement must be well structured. For example, 2L of fluids are best replaced in four 500 mL increments every 20-30 minutes than one large consumption.

  • Rehydration within 6 hours of exercise requires consuming 125%-150% of the body weight lost due to fluid loss. Sodium needs to be a part of this replenishment. Only sports drinks, or sodium that is part of a normal healthy diet, would be adequate sources.

  • Drinking sports drinks compared with water during exercise 40-50 minutes or longer (i.e. in training for rowing) enhances performance.

  • For athletes prone to cramping there is no evidence that supplementing with minerals such as potassium have any beneficial effect, although sodium chloride as in food or a sports drink can help.

And now for the items supported in the literature, but perhaps somewhat controversial:

  • There is also a growing belief that caffeine is not the enemy is was once perceived to be. While high levels of caffeine can act as a diuretic, at normal levels, especially in habitual caffeine drinkers it is not a problem. Caffeinated beverages can be considered part of the normal daily fluid intake - but not if rapid fluid replacement is needed i.e. when dehydrated already.

  • While alcohol shouldn't be used to rehydrate the concentration in drinks such as beer will not adversely affect rehydration status.

  • The traditional recommendation of 8-10 glasses of water per day SHOULD include things like coffee and tea normally consumed or else you will be taking on too much water.

  • Use of a sports drink, especially when training is a good idea as it will enhance performance and time to exhaustion.

  • In multi-day competitions on hot days use a scale and plan your rehydration. Replace 125% or more of the weight lost and do it in a number of doses spaced out over the available time rather than in one large drink.

  • Heathly, but salted, foods OR a sports drink should be part of this fluid replacement strategy.