Dehydration is bad for you and your work out! you’re just about to start off on
a long training session. But if you want to make it to the end in the best possible condition and with the maximum training benefit, you need to be thinking of drinking long before you feel thirsty.
What is dehydration?
During high intensity exercise, the watery part of your blood – the plasma volume – decreases as you sweat and the concentration of substances such as sodium, chloride and glucose in your blood
increases. In an effort to keep the right balance, known as homeostasis, your body triggers a cascade of physiological processes to try and maintain cardiovascular function for the exercise you’re
doing. For instance, your heart beats faster, blood flow increases and your breathing quickens. Then, as your body temperature rises, you sweat more to cool down.
Dehydration is a downward spiral, which is made faster by a hot day, hard training or insufficient fluid intake, and since you also need water to absorb carbohydrates and electrolytes from your digestive tract, exhaustion is the natural consequence.
A much more subtle cause of dehydration – but with the same result – involves our adrenal glands, known as the stress glands, which sit on top of our kidneys. These produce various hormones including cortisol, adrenalin and aldosterone. Aldosterone helps control sodium, potassium and fluid levels. The problem is that under the stress of ongoing, intense training sessions or long run’s without sufficient recovery, levels of aldosterone can fall, and as they do, sodium levels in the blood drop too. The knock-on effect is that the body pulls sodium and water from surrounding body tissue into the blood to maintain balance, leaving the cells dehydrated and sodium deficient.
The result? Apart from craving for salt and vinegar crisps or other salty snacks, again it’s fatigue, poor performance and potential burnout.
Fluid needs for Exercising
In general, we need to drink about two litres of fluid a day to be properly hydrated. However, it’s quite likely that exercise will increase our fluid needs. The more you sweat, the more you need to drink to replace the lost fluid. Some people naturally sweat heavily, but even small losses can cause fatigue. Plus, the fitter you are, the more effectively you keep your body cool – so the more you sweat! Training harder, running longer or exercising in hot and humid surroundings will also make you sweat more.
How much is enough?
Since we all have different sweat rates, different exertion levels and training lengths in varied conditions, there’s no set rule for hydration volume. So the answer is a frustrating ‘it depends’.
Even slight dehydration, such as a 1-2% loss in body weight (or 640-1600ml in an 80kg fighter) can have up to a 20% negative effect on performance, according to research. A loss of just 2% in your body weight may affect your ability to exercise; a 4% loss can cause exhaustion. If you’re competing, for every 1% drop in body weight there’s about a 5% drop in performance
Crucially, don’t wait until you’re thirsty to start drinking. You need to drink regularly enough during the day to prevent the subtle signs of dehydration, becoming evident (thirst, headache, growing
fatigue, irritability, inability to concentrate and so on).
Current fluid replacement guidelines advise that the goal should be to replace 100% sweat loss during exercise. If you’re performing high intensity exercise, a sweating rate may be between 1-2.5 litres per hour when it’s hot. While it’s not really realistic to consume more than a litre per hour, it’s best to minimize dehydration as much as possible.
Drinking too much has risks of its own and can lead to hyponatremia, which is a dilution of sodium levels, and something you might want to watch out for.
The only accurate way to determine exactly how much to drink is to record your nude body weight before and after exercise or training session, taking into account whatever you drink during your workout. So if you lose a pound (453ml) during a exercise session, you should drink at least that much extra in future sessions of the same intensity and in similar conditions.
A good way to monitor your hydration state is during, or before any training session, is to look at urine colour and smell – ideally it should be light yellow and clear in appearance, with no distinctive
smell! In practical terms, always take in fluid at regular intervals during and after your workout ends.
Water on its own is a poor rehydrator because it dilutes the concentration of sodium too much in the blood, reducing thirst before you are truly hydrated and affecting cell function. Conversely, a
sports drink containing sodium will stimulate thirst and help maintain the desire for drinking.
Your drink is not just about hydration though, it’s one of the best sources of riding fuel too. If you’re exercising for over an hour you need carbohydrates to restock glycogen levels in your blood to feed
your muscles and brain.
Where you need to sustain fluid levels and maintain performance, opt for a drink where the carbohydrate composition is low (below 7%). Some research also suggests that protein, which could be in the form of L-glutamine or branch chain amino acids (BCAAs) in sports drink may
assist endurance training and reduce breakdown of muscle mass.
Avoid carbonated and high carbohydrate drinks as these will be emptied more slowly from the stomach and slow down rehydration.
Which fluid you opt for depends on how hard you exercise, and for how long. However, choose a flavour you like to encourage you to drink more. If you’re exercising at a low-to-moderate intensity for less than an hour, then water is great. If you find it difficult to drink large quantities of plain water, try adding some juice or squash, which will also provide you with some carbohydrates to help restock glycogen stores and add a pinch of salt.
An hour or two before your exercise, drink 500ml of water or sports drink.
Plan to take in between 150-300ml every 15-20 minutes if your session lasts more than 1 hour.
If your exercise session lasts 1-3 hours, you need to consume 30-60g carbohydrate every hour. This equates to at least 500ml sports drink with 7% carbohydrate solution.
Aim to replace fluid losses as completely as possible after exercise.
For events of more than three hours or in hot weather, including sodium is essential – so checks labels and look for between 20-40mmol/litre NaCI.
If you like energy gels, check the labels – you can get isotonic ones, avoiding the need for additional water, but you’ll still want to check your overall fluid levels for long Run’s or training sessions.
How much fluid you need depends on how much you lost, but you’ll probably need at least 500ml. Try to drink 1.5 litres of fluid for every kg of weight lost during exercise, or keep drinking until you pass light-coloured urine.
Alcohol and Exercise
Although alcohol in moderation is fine, it’s not a good idea to drink it just before exercise as it has a detrimental effect on co-ordination skills and exercise performance and also
increases injury risk. You also need to rehydrate properly before drinking alcohol after running – alcohol can cause dehydration and slow down recovery from injury.
Isotonic Useful if exercising for more than 1 hour. Contains fluid, electrolytes and 6-8% carbohydrate. Some products will have additional vitamins and minerals too, for example Lucozade Sport, SIS GO or Powerade. Some are too low in sodium for very intense training or rides, or during hot weather. Often people find that drinks based on maltodextrin and fructose are more easily tolerated on the stomach than those based on sucrose. Many sports drinks come as powders, so
you can make them up to your own concentration. Look for sachets that you can pack with you and then mix with water when needed.
Alternatively you can easily make up your own isotonic drink by diluting 200ml orange squash with 1 litre of water and adding a pinch (1g) salt.
Hypotonic More dilute and may contain electrolytes but with lower levels of carbs.
Hypertonic High levels of carbohydrates and some will also contain protein – popular in endurance training to prevent carbohydrate depletion. Those based on glucose polymers provide more fuel and are less sweet, but should be used with isotonic drinks to ensure adequate
As always you should get doctors advice before under taking any new exercise resumé and seek professional advice for your training needs. This is intended as a help full guide to point you in the right direction with your training. It is for educational and resource purposes only. It is there to help you make informed decisions about fitness training. It is NOT a substitute for any advice given to you
by your physician.
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