Sports active: GOOD GEAR ENERGY DRINKS Solutions for success ; Dehydration can be dangerous, but so can drinking too much on the move. Whether it's for racing or recreation, Robin Barton picks the liquid to give your system a boost - The Independent on Sunday (London, England)

How do you finish running a marathon weighing more than you didwhen you started it? Easy: drink too much. A study published inApril's New England Journal of Medicine made headlines with therevelation that some runners in the 2002 Boston Marathon wereoverhydrating to hazardous levels.

The study found that out of 488 runners surveyed, 13 per cent hadhypo- natremia, the technical term for dangerously low levels ofsodium in the bloodstream. Sports scientists have noticed a rise inthe number of cases as the message about avoiding dehydrationreaches more and more people.

'Hydrate or die,' after all, is the slogan of Camelbak, thehydration- system manufacturers. Drinking is essential when doingexercise that causes sweating; dehydration can lead from dizzinessand lethargy to heatstroke. But the researchers found that therunners most likely to suffer from hyponatremia were the slowercompetitors, who perhaps were not sweating as much as the seriousathletes. Some were drinking at every mile marker, and retainingenough fluid to dilute the essential salts in their bloodstream.

Cool conditions at the springtime Boston event may compound theproblem, although organisers note that the vast majority of peoplewho need medical attention are suffering from dehydration.

So how do you avoid the twin perils of dehydration andhyponatremia? 'Use an energy drink with electrolytes,' says PeteSlater of Science in Sport. Electrolytes, as found in products suchas Science in Sport's Go energy drink, are the salts and mineralsthat are essential for the body to absorb water. Endurance athleteswho train hard, such as runners and cyclists, know how much salt islost by sweating simply by looking at their salt-encrusted kit.

But there is more to an energy drink than just replacing salts;they are a useful source of energy, in the form of carbohydrates,and after exercise a protein-based drink can speed recovery. Sciencein Sport's PSP22 is probably the most popular drink on the market,because it can be consumed in higher concentrations than ordinarysugar-based drinks, thanks to a more complex carbohydrate in theingredients which the body can easily absorb.

There are several competing products on the market, includingHigh Five and Maxim. The trick is to find one that works for you.Don't expect a taste sensation on the palate. Connoisseurs come toappreciate the cloudy, slightly grainy body, the metallic bouquet ofwhatever fruit flavouring is being used and the flat taste at theback of the mouth. And remember that energy drinks are typicallyserved lukewarm.

The energy payload of these carbohydrate-based drinks is similar' High Five's Energy Source drink provides about 388 calories per100g, while Science in Sport's PSP22 offers about 371 ' but checkthe advised concentrations. Maxim's Energy Drink can be prepared ina slightly higher concentration than High Five's Energy Source.

After exercise, a recovery drink will help replenish the energy-giving stores of glycogen in your muscles, as long as it is takenduring the golden hour immediately after finishing ' ideally, within20 minutes. Science in Sport's Rego contains protein high inglutamine to repair damaged muscles and carbohydrate to restockenergy stores. Maxim's Protein Recovery Drink contains a similar mixof protein and carbohydrate.

Professional athletes, however, make up their own rules; many apro cyclist has a drink of diluted Coke for an energy burst in thelast hour of a race. And one endurance athlete's tipple of choice iscold, weak tea with sugar.

Maxim Energy Drink

Contains sodium to replace lost salts as well as energy-providing carbohydrates. Stockists: www.1000mile.co.uk

Price: pounds 18.99 (2kg)

Science in Sport Rego

Protein and carbs help muscles recover for the next trainingsession. Stockists: 01254 246 060, www. scienceinsport.com

Price: pounds 7.50 (500g)

Science in Sport PSP22

Complex carbohydrates mean it can be taken in higherconcentrations. Stockists: 01254 246 060, www.scienceinsport.com

Price: pounds 7 (500g)

Maxim Protein Recovery Drink

For best results, drink this mix of protein and carbs within anhour of exercise. Stockists: www.1000mile.co.uk

Price: pounds 7.99 (450g)

Science in Sport Go

Energy drink with extra salts, minerals and electrolytes forexertion in hot weather. Stockists: 01254 246 060,www.scienceinsport.com

Price: pounds 7 (500g)

High Five Energy Source

Carbohydrate drink sweetened with fructose and containingelectrolytes. Stockists: www.highfive.co.uk

Price: pounds 8 (600g)