Fluid Replacement: Regular topping-up is far more than a matter of just quenching thirst.
The importance of fluids in sports nutrition is, thankfully, beginning to be recognised. This year, for instance, the exercise physiologist Ron Maughan was invited to give what was an excellent paper on the subject at the Sports Nutrition Foundation Symposium on the Young and Veteran Athlete. Comprehensive research is being carried out in such areas as the amount of fluid lost during various types of exercise, and the optimal composition of sports drinks for use before, during and after exercise.
And fluids are a vital part of proper nutrition.Whether you're an elite marathon runner, rower or cyclist, or simply work out a couple of times a week in the gym or local health club, it is a virtual certainty that some sort of fluid replacement will improve your performance. Here are two important points to bear in mind. First, get rid of the idea that you only need to think about sports drinks on match or race day. Correct fluid replacement is essential for training just as much as competition, although more attention tends to be given to the latter. If you are going to use sports drinks in competition, it is imperative that you have tried them out in training first because some drinks cause stomach upsets in the uninitiated.
Second, it is wrong to think that you only need to drink on extremely hot days when you have become a little thirsty - you need to drink whatever the temperature. Indeed, on a hot day if you wait until you are thirsty the chances are you are already on the way to becoming dehydrated, with potentially disastrous consequences for your workout or competition.
Why you need to take in fluid
When you exercise, many metabolic reactions take place in order to produce the energy needed for muscular contractions. One of the by-products of these reactions is a large amount of heat. This means that if you are exercising for a long time at moderate to heavy intensity your heat production is going to be considerable. You may not think this is a problem until you remember that the body temperature has to be kept within a very narrow range. When you are exercising the extra heat has to be lost somehow and this is done by a variety of mechanisms, the most effective of which is, of course, sweating.
The problem with sweating is that after a while you are in danger of losing of losing a considerable plasma volume from your circulatory system and this will certainly impair your performance. It is well-documented that a loss of fluids equating to just 2% of your body mass will have a very detrimental effect on performance. Identifying how much fluid you actually lose is not always easy, but the best method is to weigh yourself before and after exercise. I need hardly remind you that excessive fluid losses in very hot environments can even lead to death.
Such risk of fluid loss is not confined to marathon runners and cyclists but can occur in most sports, especially those involving high-intensity intermittent exercise such as invasion games, or during gym workouts. The point I'm making is that, although you must pay special attention to fluid replacement in a warm environment, it is also possible to lose fluid in a cool one if you are working hard or long enough.
To limit the drop in plasma volume while exercising, it obviously makes sense not to be at all dehydrated before you start. This means making sure that you have replaced any fluid losses from previous workouts. In addition, it also means avoiding diuretic drinks such as tea, coffee and alcohol, which stimulate the body to pass more urine than the amount of fluid taken in, thus dehydrating you. So always ensure you have taken enough of the right fluids before you start your exercise.
If you are exercising for a reasonable amount of time, it make sense to take drinks en route. This doesn't just apply to marathon runners but to games players on pitches as well as to racket sports. It is customary to take on fluid during official breaks in the game such as half-time in soccer or change-overs in tennis but this should be the minimum, especially in a warm environment. It is no coincidence that while an Italian soccer player is allegedly writhing in agony after a foul, his team-mates make a beeline for the drinks bottles that the physio just happens to bring on with him. You must aim to drink whenever you can. If you're a rower, get in the habit of taking a couple of drinks bottles in the boat with you, rather than leaving them on the river bank for an occasional sip. Little and often is the key, instead of waiting until you are driven to the bottle by thirst. Once your workout has ended it is still important to keep drinking. Although the great rush to maintain plasma volume is over, it is important that you are fully rehydrated before your next workout. If your exercise ends in the traditional visit to the bar, make sure you are well rehydrated first and be prepared to drink more water after you' ve staggered home.
Which is the right drink for you?
With so many sports drinks on the market, it is often difficult to decide which is the most appropriate. It is fair to say that drinking plain water is better than drinking nothing at all. There are, however, a number of drinks that can speed up the rate that ingested fluid leaves the stomach and is actually absorbed. These are the ones with a small sodium or electrolyte concentration. These will not only speed up the rate at which fluid leaves the gut but will also increase the the percentage of fluid that is absorbed. For this reason, such sports drinks are particularly useful during exercise.
It has also been shown that a small concentration of carbohydrate can speed up the rate of gastric emptying and thus improve performance. In one particular piece of research, which studied cyclists using different drinks in a warm environment, it was shown that a greater volume of fluid ingested during exercise produced superior performance (see PEAK PERFORMANCE, issue 34, July 1993).
These drinks should not be confused with the large number of high-carbohydrate drinks that are also on the market. If you are exercising in a particularly hot environment, it's probably wise to avoid such drinks because the high-carbo content actually slows down the rate at which you can absorb the fluid. In a hot environment the dangers of dehydration are greater than the loss of muscle glycogen.
However, if your exercise is of moderate to high intensity, the need for carbohydrate replacement increases. A very well-trained marathon runner may cover most of the race metabolising fats and not dip too far into his carbohydrate stores. A soccer player, however, competes for 90 minutes (longer with extra time) and performs some of the work at extremely high intensity (which eats up carbohydrate much more quickly). It then comes down to a balance of which need is greater, fluid replacement or carbohydrate feeding.
High-carbohydrate drinks can be especially useful in the immediate post-exercise period. That's the time when muscle glycogen stores are usually low and most receptive to replenishment. It is most effective to load on carbohydrate during this period but you may not fancy a huge bowl of pasta so soon after training. A high-carbo drink makes it easier to take the required amount. It also won't make you feel quite so bloated as the pasta, a big plus if you are training two or three times a day To summarise, then:
1 Fluids are important for both training and competition
2 A fluid loss of 2% body mass can be detrimental to performance
3 Most types of exercise risk considerable fluid loss
4 Fluid loss is not confined to hot environments, though heat can exacerbate the situation
5 Make sure you are hydrated before you start and don't wait to get thirsty before you begin drinking
6 The more you drink comfortably while exercising, the less chance of under-performance
7 Electrolyte drinks or a small amount of sugar will increase the speed of absorption
8 High-concentration carbohydrate drinks slow the rate of absorption
9 High-carbo drinks can be useful right after exercise, especially if you train two or three times a day.
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