Hydration and exercise

Hydration during exercise

What you drink on the day of your event matters. But it’s also important to stay hydrated in the days coming up to the event.

If you have been monitoring and keeping on top of your day-to-day hydration, there should be no need to drink excessively the night before or in the hours leading up to your event. You should be having 6-8 glasses of fluid a day whether you are training or not. This should be mostly water, low-fat milk, soy milk, no added sugar squash, or herbal teas.

Pre-event guidelines: Start the race well hydrated. Aim to have 400-600ml of water 2-3 hours before and then 200-250ml in the lead up to the start. It can be a challenge to drink this much, so start practising around 2 weeks before your event.


How to monitor your hydration

• Choose the right fluids and right amount for the length of time you exercise
• Listen to your body – if you're thirsty or sweating a lot then drink more
• You may not have to drink at every drink station at an event
• If it’s hot, choose drinks with electrolytes to avoid dehydration
• Resist drinking too much if you’ve got a slow pace on a long event
• Practice drinking during exercise whilst training
• Urine frequency and colour is also a good guide.

Can I drink too much water?

It is possible to drink too much water. If you’re not also taking on enough electrolytes, you’ll dilute and affect the balance of your body’s fluids (hyponatraemia). This can make you feel bloated and nauseous; in extreme cases it can be fatal. Cases of this have been seen in recent years at big marathons where runners have drunk too much plain water.

Remember, as well as replacing lost fluid, you also must replace lost electrolytes too. Use sports drinks that contain electrolytes or add electrolyte tablets to your water bottle.


Do I need to avoid alcohol?

You don’t need to avoid alcohol while you are training, but it might make your training easier. Drinking alcohol the night before an event or long training session can negatively affect your performance. Alcohol can affect your sleep quality, make you dehydrated, sluggish and affect your ability to recover. Having put in months of hard training it would be a shame to not perform at your best for a few missed drinks!

If you do decide to drink, stick to just one drink and ensure you have it with food. Drinking after exercise is not advisable if you haven’t consumed enough water to replace the fluids you lost. Try to stick to low risk drinking guidelines – no more than 14 units a week and avoid drinking the day before an event.

Will drinking coffee improve my performance?

A moderate intake of coffee, tea (3-5 cups) or other caffeinated beverages does count towards fluid and caffeine has been shown to also improve athletic performance especially for endurance exercise. It seems to work on the central nervous system resulting in you thinking you feel less tired. This allows you to keep going longer, so caffeine is especially useful for endurance sports.

The guidance around caffeine and exercise is:

Drink between 1-2 large cups of standard filter coffee for an average man or woman, at least an hour before exercise. This is about 3mg per kg of body weight. Do not overdo it – coffee is useful before the start, before a hill climb (bike or running) or a sprint finish.

Everyone responds differently to caffeine, so you might not perform better with a caffeine-boost. You could end up feeling sick or jittery at a time when you're already nervous.

And be warned: while a morning cup of coffee can help with a desirable bowel movement, a pre-competition cup might lead to stomach issues. Experiment during training to determine if a caffeinated beverage or plain water is your best bet.

What's the difference between hypotonic, isotonic and hypertonic drinks?

Hypotonic drinks replace lost fluids very quickly, but don’t provide energy or electrolytes. Some examples include plain water or squash. They can also reduce your desire to drink more before you’ve replaced adequate fluids and leave you feeling bloated. They are fine for rehydrating less than an hour after an exercise session.

Isotonic drinks are the same concentration as your body fluids so are absorbed as fast as or faster than water. They contain carbohydrates and electrolytes so can help with both rehydration and refuelling. Some examples include Isostar, Lucozade Sport or fruit juice diluted half and half with water. These are most suitable for endurance sports.

Hypertonic drinks, such as cola, lemonade or neat fruit juice, are more concentrated than body fluids, and will be absorbed more slowly than plain water. Hypertonic drinks slow down the rate at which the stomach empties and therefore reduce the speed of fluid replacement. These are most suitable as post-run drinks that offer a higher dose of energy with the fluid.

Event specific hydration tips

Swimming

It's a common myth that swimmers don't sweat. Even though a lot of excess heat is taken away from your body through the water, a rise in body temperature triggers your sweat glands to release sweat. You just don’t notice because you're in water.

The need for energy and electrolyte supplements depends on the duration of the event. For events under 90 minutes (e.g. a triathlon and Bournemouth Pier to Pier) rehydration and refueling is not needed during the swim, but pre-event hydrations guidelines do apply.

Trekking

While trekking, you are constantly sweating - even though you may not physically see sweat dripping off your forehead. The amount of water you should drink depends on the temperature outside and your level of activity.

Hydration tips for hiking:

• Take a water bottle with you on the walk
• Find out where the water-points are on the trail
• You can also incorporate water in the form of warm beverages like tea, soup and hot chocolate.
• Don’t wait to feel thirsty before you drink water, especially if walking in cooler temperatures. Try to have a few sips every 15 to 20 minutes while trekking.