Every day we lose fluid by sweating, breathing and urinating. It’s the sweating that exercisers need to pay attention to because as soon as you start exercising you start to dehydrate. About 75 per cent of the energy you put into exercise is converted into heat, and is then lost. Extra heat has to be dissipated to keep your core body temperature within safe limits – around 37 to 38C. Your body keeps cool by sweating, which makes the replacement of fluids crucial.
If you fail to consume enough fluid your blood will thicken, reducing your heart’s efficiency, increasing your heart rate and raising your body temperature. Your body can lose a certain amount of sweat without your performance being affected but at some point that loss of fluid – and sodium – starts to take a toll. This usually occurs once you have lost around two per cent in body weight, and this can lead to anything up to a 20 per cent drop in performance. At this level, the exercise you’re doing starts to feel harder and fatigue sets in. If allowed to progress, dehydration can have more serious health consequences. A five per cent drop in body weight can result in headache, light-headedness, disorientation, muscle cramps and shortness of breath.
Overhydration can also have a negative impact on your health and on your workout. Too much fluid causes the sodium concentration in the body to become too diluted, a condition called hyponatraemia (or low blood sodium). Ironically, the symptoms are similar to those of dehydration: a drop in athletic performance, nausea, lethargy, dizziness and disorientation. If allowed to progress, there can be serious health consequences, such as blackouts and fits.
The hydration zone
The key to avoiding dehydration and overhydration is to stay in your hydration zone. This is the level of hydration that allows you to perform optimally. You can get a good idea as to whether you are within your zone by weighing yourself before and after exercise. You should never consume so much fluid that you actually end up gaining weight. Equally, you should try to avoid losing more than two per cent of your body weight. For example, if you weigh 68kg (150 lb), two per cent of your body weight is 1.4 kg (3 lb). So your hydration zone would be between 66.6 and 68 kg.
Developing your hydration plan/
All researchers agree on one thing: you need to start a workout or competition hydrated. This way you’ll have the best chance of putting in your best performance. By drinking 400 – 600 ml about two hours before working out you’ll have enough time for your body to excrete what you don’t need before you set off. It also ensures your body makes up for any previously incurred fluid deficit. Sip little and often during the warm up.
Check your hydration status before exercise
You can monitor you hydration status by checking the colour of your urine. University of Connecticut researchers found that urine colour correlates accurately with hydration status. A pale straw colour indicates good hydration. If it’s darker then that’s a sign that you need to drink more fluid before you start exercising.
Choose the right drink
For workouts lasting less than an hour, opt for water. It is absorbed rapidly and hydrates the body. For longer workouts, or perhaps for shorter intense workouts in hot or humid conditions, a sports drink that provides carbohydrates, fluid and sodium, is normally a better option. Such as drink provides a number of advantages. First, the extra carbohydrates will help maintain blood glucose levels and fuel the muscles during exercise. Second, the carbohydrate and sodium cause the fluid to get absorbed more quickly. Third, most people drink more freely when the drink is flavoured. Fourth, the sodium in a sports drink promotes helps retain the fluid you’ve drunk.
Drink the right amount
Expert organisations such as the American College of Sports Medicine (ACSM) no longer issue prescriptive guidance on how much to drink during exercise. Old advice to drink as much as possible as been withdrawn in light of the number of cases of hyponatraemia. Current advice is to drink when you are thirsty and listen to your body. For most workouts and climates, 400 – 800 ml per hour will prevent dehydration as well as overhydration. Aim to consume fluids at rate that keeps pace with your sweat rate. You’ll sweat more in hot and humid condition and when working out harder/ faster. It’s better to drink little and often say 100 – 150 ml every 15 minutes, as this results in greater retention and less urination.
Rehydrate after exercise
It takes on average 30 to 60 minutes for the body to rehydrate after exercise. The International Olympic committee (IOC) and ACSM both recommend drinking between 1.2 and 1.5 times the weight of fluid lost during exercise. This extra fluid compensates for the increased urine output that occurs after drinking a large volume. Weighing yourself before and after exercise will help you work out how much fluid you have lost. For each 1 kg of fluid lost you need to drink 1.2 – 1.5 litres. Drink this gradually, say, over an hour, rather than in one go. Consuming a little sodium in food or drink will promote recovery because it helps retain the fluid you have drunk. It also stimulates thirst and encourages you to drink more. If you find that you’ve gained weight during your workout, then cut back on the volume you drink during exercise.
How to make your own sports drink
- 500 ml fruit juice mixed with 500 ml water and 0.5–1 g (one eighth of a teaspoon) salt (optional)
- 200 ml squash mixed with 800 ml water and 0.5–1 g (one eighth of a teaspoon) salt (optional)
- 40 – 80g sugar and 0.5 – 1g (one eighth of a teaspoon) salt dissolved in 1 litre warm water. Add a little sugar-free squash for flavour, if preferred.