“Dehydration impairs performance!”
“You must drink during exercise!”
Before 1969 athletes were actually advised not to drink during exercise as it was assumed this would have a negative effect on performance.
In 1965 the first sports drinks were developed and from then on, the message to athletes was: “drink as much as you can” so as not to lose weight through sweating.
It appears that some athletes can perform successfully in a race having lost as much as 12% of their body weight through sweating.
It seems that the levels of dehydration that an athlete can tolerate are very individualised. The guidelines below are to help you develop a triathlon hydration strategy that minimizes dehydration. Bear in mind that you are probably better off being slightly dehydrated than you are over drinking and ending up with hyponaetremia (more on this below).
You should aim to start a race or training session fully hydrated. Thereafter, aim to minimize dehydration, but don’t worry about following these guidelines exactly if you don’t feel thirsty.
Do remember though that the best way to get energy on board during a triathlon is through a sports drink and so you need to make sure you take on board enough energy.
If you have any questions about your triathlon hydration strategy then please just ask us.
The most simple way to know if you are well hydrated is to look at the colour of your urine. When you are well hydrated your urine should be pale coloured. If it is dark then you probably need to drink more.
You can work this out by measuring your own sweat rate.
Drinking at a rate close to your sweat rate and aiming not to lose more than 2% body weight from sweat will help you to maintain hydration from training session to training session. Knowing your sweat rate will help you plan your triathlon hydration strategy.
Measure body weight (in kilograms) before and after at least one hour of training.
Do this wearing minimal clothing and with no shoes. Dry with a towel after exercise and obtain body weight as soon as possible (ideally within 10 minutes).
Sweat loss (litres) = body weight before exercise (kg) – body weight after exercise (kg) + fluid consumed during exercise.
To convert to a sweat rate per hour, divide by the exercise time in minutes and multiply by 60.
After a session you should aim to drink 1.2 - 1.5 times the amount lost, starting as soon as you finish the session. You need to drink more than you lost because you will still be producing urine. You also need to replace the electrolytes (salts) lost in your sweat.
Here’s an example to illustrate how to calculate how much you need to drink after a session:
60kg person during a 2h session:
Post session 59kg = 1kg loss,
Plus they drank 500ml (equivalent of 500g) during the session so,
Total loss = 1.5kg.
Minimum amount needed to be replaced in recovery = 1.2 x 1.5 = 1.8L
For a sweat rate per hour:
(1.5 litres/120) * 60 = 750ml. So sweat rate per hour = 750ml.
When a 60kg person loses 1.2L (2% body weight) or more, fatigue can occur. With a sweat rate of 750ml per hour, if the person had not drunk 500ml during the 2 hour session they would have exceeded 2% body weight loss and it is very likely that performance would have declined.
As a triathlete potentially doing more than one training session in a day, it is particularly important that you re-hydrate after a training session so that you don’t get progressively more and more dehydrated. Make sure you put your triathlon hydration strategy into action straight away!
It is difficult to work out how much sodium (salts) you are losing.
You would probably benefit from increasing your salt intake. Ideally this would be through a sports drink after training, allowing you to replace carbohydrates at the same time.
A moderate excess intake of salt is unlikely to be bad for your health if losses through sweat are high and your fluid intake is also high.
Your triathlon hydration strategy should include drinking 250 – 500ml before starting a session or race. Sip this up to 1 – 2 hours before the start. Get to know how well you can tolerate fluids. Some people can drink during the hour before a session or race and feel fine, for others this can cause gastrointestinal discomfort or a stitch.
You will usually not be affected by dehydration until you have lost around 2% of your bodyweight (although this can vary from person to person – some people can tolerate greater levels of dehydration than others). So it is unlikely that fatigue will be due to dehydration in a session lasting up to an hour, unless it’s very hot of course.
For longer sessions your triathlon hydration strategy should involve carrying a drinks bottle and trying to take 2 – 3 large mouthfuls every 30 – 40 minutes. Sports drinks (carbohydrate-electrolyte mix) are ideal – beware of water as it is not an ideal source of hydration during exercise. It is digested less well, and doesn’t replace the electrolytes (salts) lost in sweat.
You should plan and practice your triathlon hydration strategy for race day. The longer the duration of the event, and the hotter the weather, the more you will have to drink to prevent dehydration and compromised performance.
If you can calculate your sweat loss in training you will be able to work out roughly how much fluid you need to drink, allowing you to develop an effective triathlon hydration strategy. Just make sure you calculate sweat loss when exercising at a similar intensity to racing, and in similar weather conditions.
A recent research study found that the average volume of water lost during an Ironman was 1.1 litres every hour. That adds up to a lot over the course of the race – and potential disaster if you don’t replace the majority of it.
The bike section is the best opportunity to take on fluids. However you don’t want to overdo it. There is a limit to the rate at which your body can absorb fluids – drink too much and it will just slosh about inside you.
A study looking at fluid absorption when cycling found that the maximal rate of absorption when cycling at 85% of VO2max (around the intensity sustained in the bike section of an Olympic distance triathlon) was 0.5l/hour.
To find out more about the ideal content of your drink, refer to the nutrition for racing page.
Drink during the bike section, but no more than 500ml every hour – and try to sip regularly rather than knocking this back in a oner!
Commercial sports drinks are widely available and are a key element in your triathlon hydration strategy. However these can be quite expensive.
Follow the recipe below to make your own (from Professor M Gleeson, www.medicdirectsport.com):
The amounts shown are sufficient for 1 litre (1000 mL) of drink.
You might find the drink to be a bit too salty. If so, then instead of the table salt and baking soda, add 2.5 grams (about one level teaspoon) of sodium citrate (as trisodium citrate dihydrate). This will provide a similar amount of sodium, but without the salty taste.
Pour the drink into a bottle that can be kept airtight. Store it in the fridge if you are not going to use it on the same day. Use within 3 days.
Yes…. and this is also not good for you. If you drink too much water, this can result in your blood sodium concentration being too low. Combined with losing sodium in sweat, this can exacerbate the problem, known as hyponatraemia.
Symptoms of hyponatraemia include nausea, vomiting and headache, as well as confusion/agitation, shortness of breath and rapid breathing.
Risk factors for hyponatraemia include:
The incidence of hyponatraemia seems to be higher since the surge in availability of sports drinks, and the publicity promoting the importance of drinking enough during exercise.
There is now a school of thought that the guidelines for how much to drink during exercise are flawed. This is because they are based on the logic that body weight is the only variable that is homeostatically-regulated during exercise.
However, human fluid balance before, during and after exercise is regulated to maintain constant plasma osmolality (basically keeping the concentration of different ions, such as sodium, in the blood balanced). The controller is the thirst mechanism which insures that the plasma osmolality is maintained within the correct range.
Research has shown that when athletes follow this advice, and drink according to thirst, the risk that they will over-drink and so develop exercise-associated hyponatraemia is reduced.
There is also no evidence that their performance is affected by the mild to moderate level of “dehydration” that they develop as a result. So bear this in mind when planning your triathlon hydration strategy.
Got a question about your triathlon hydration strategy?
Then ask us!