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Clinic – How to stay hydrated!

With summer in full swing and the majority of the UK enjoying a heatwave over recent weeks, it’s about time the Clinic took a look at rehydration, dehydration and overhydration…

Up until the late 1960s, athletes were advised not to drink during exercise, as it was believed to impair performance. In fact, at this time, some viewed training without drinking as a way of physically toughening up the body. In 1969, a scientific publication on marathon runners shook things up and provided the incentive for more research on the issue of hydration, with many studies funded by a fledgling sports drink industry.

So what’s the answer? How much and what should you drink?

First, lets dispel some modern myths…

Keeping hydrated during sport does not mean drinking the maximum amount of fluid that you possibly can. One female recreational runner died during the 2002 Boston marathon from drinking too much water and her salt level dropping too low as a result.

Secondly, there’s no one-size fits all rule. The fluid requirements of all sportspeople are not always the same and in particular smaller individuals, that’s us women, need less than your average sized bloke.

Horses sweat, men perspire, women glow…

Of course the reason you have to drink during exercise is to replace the fluid you’re losing through sweat (rather than “glow”!). The heat and humidity of the environment you’re exercising in and your level of exertion will both increase the rates of sweating and, subsequently, dehydration. However, your individual level of fitness and heat acclimatisation also has an effect. The body’s ability to sweat more efficiently alters impressively with physical training, and although sweating increases by 12%, salt losses through sweat decrease by 60%, so as your body learns to regulate heat more efficiently you sweat a bit more but lose much less salt.

Sweat rates during competition have been studied mostly in runners. Endurance runners (distances lasting over 2 hrs) sweat an average of 1 litre/hr, while their fluid intake is around 600mls/hr. Top endurance runners expect to finish their event with less fluid on board than when they started. All of this is likely to be similar for endurance cyclists.

While you’re exercising, don’t set out trying to replace all the fluid you have sweated out. The first reason is because your guts can only absorb fluid at a certain rate so if you drink excessively you will end up with stomach cramps. The stomach cramps are a way of your body stopping you wanting to drink more while the fluid onboard is processed. Alternatively, you’ll be sick! Secondly, endurance events can be associated with a loss of up to 10 grams of salt just through sweat (even if you are sweating efficiently). To replace all of this salt in the amount of fluid your guts can handle you’d have to drink an incredibly salty drink, and even if you could cope with the taste, you’d probably be sick!

Salted or Sweet?

Drinking an isotonic sports drink (that has some salt or electrolytes in but not too much) will not fully replace the salt you lose through sweat but it will help get some back into your system. It’s important to have some salt in the fluid you drink otherwise as you replace sweat (relatively high salt content) with water (no salt content) the level of salt in your bloodstream can drop. It’s this drop in bloodstream salt (hyponatraemia) that can be dangerous and ultimately fatal. There are lots of isotonic sports drinks available in all sorts of flavours. Find one that you like the taste of (otherwise you’ll never drink it!) and use it. Aim for around 400mls per hour of exercise although, as I said earlier, everyone’s fluid requirements are different so play around in training and find out what works for you. Many isotonic drinks also contain carbohydrate, so what’s that all about?


Beyond 90 mins of exercise, your body has used up your store of liver glycogen (the stored form of glucose) and a drop in blood sugar can start limiting your performance. When your blood sugar drops significantly you will “hit the wall” or “bonk” and trying to continue any exercise, let alone maintain your race pace, will become incredibly difficult. To avoid this, taking a drink with carbohydrate in can keep you out of the red and allow you to maintain your effort. High concentrations of carbohydrate accumulating in the guts can impair fluid absorption and can lead to stomach cramps. Ideally, take a more dilute carbohydrate drink (3-5g/100mls for those that want to get technical) until you pass the 90 min time, after which take a more concentrated (10g/100mls) drink.

Just for the Taste of it!

A survey of riders at the 1997 US Professional Championship Road Race showed that many of all the cyclists drank Coca-Cola, usually during the last half of the race. Why is it so popular? Coca-cola has a good mixture of sugar and caffeine for that extra boost towards the end of the race. Caffeine is no longer a banned substance so there’s no concern there (that said under previous restrictions you would have had to drink over 6 cans within 2 hrs of the event to test positive). If you do try Coca-Cola do remember to de-fizz it!

Pre-Race Tips

Make sure you go into the race fully hydrated. Drink plenty of water the day before the event and you might want to try a carbohydrate drink in the 2hrs before the start.

Some people like using glycerol in their water before the event. The idea behind this is that you increase the amount of water your bowel can absorb, hence the coined title “glycerol hyperhydration”. However, a study by the Australian Institute for Sport found the use of glycerol did not improve performance and a significant number of athletes reported stomach cramps while using it. I don’t use it, but if it works for you then that’s fine and it’s certainly not a banned substance.

Race Tips

Drinking while racing is something I struggle with. I tend to get too caught up in the excitement of racing and forget about drinking! My tips are: firstly drink regularly in training, as you’d want to in racing. It then becomes second nature to drink while you’re on the bike and will feel less of a chore! Secondly, have a drinking strategy. With a lapped event like MTBing this is easy to plan. Go for a fresh bottle every lap. It doesn’t necessarily need to be full and gives you a fresh bottle to drink from every 30 mins or so.

Recovery Tips

Remember that although you won’t be able to completely replace the fluid you have lost during the event, you should carry on drinking afterwards to get back to the status quo. A recovery drink, which usually has a bit of protein as well as carbohydrate, is a good starter after hard sessions. A milkshake is a good alternative. My favourite’s chocolate! Alternatively, something sugary and, if it’s been cold, then something warm is perfect. If you haven’t rehydrated properly afterwards you’ll end up feeling grotty with a headache. If you have a headache you definitely need to drink more!

Clinic Top Tips

  • Training will allow your body to adapt and learn to sweat more efficiently.
  • Small women need less fluid than large men!
  • Find a drink that you like the taste of otherwise you’ll never drink it!
  • Aim for around 400mls fluid per hour of exercise, but remember everyone’s fluid requirement is different so play around in training to find out what you need!
  • For long endurance rides or races, drink isotonic drinks rather than just water. Especially in the heat when you will be sweating more.
  • For long endurance rides or races, having some carbohydrate in your drink will keep a drop in blood sugar at bay.
  • Teach yourself to drink regularly during training so it’s second nature for you during races.
  • Coca-Cola is popular with the pro’s!

    DISCLAIMER: Advice and information is provided via Clinic on a free of charge basis as a supportive service to women in sport. It should not replace the use of your General Practitioner for medical problems.

    Copyright 2006 Dr K Hurst

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