At this distance you need to focus on maintaining energy levels as well as staying hydrated. Sarah Coope gives practical advice on how to get it right for the big day.

The week before:

I recommend carrying a water bottle with you and drinking a daily minimum of three litres (just over five pints) of water. Monitor the colour of your urine - if it is almost clear you are well hydrated. Avoid fizzy drinks, caffeinated beverages and alcohol due to their dehydrating effects.

You may be increasing your food intake as part of a carbohydrate-loading programme. If you feel uncomfortable with increasing your volume of food then you could try a carbohydrate replacement drink as an alternative, following the manufacturer's guidelines about the level of dilution. I Increase the volume of carbohydrates in my diet to up to 70% of my total intake e.g. someone who ingests 3000 calories daily would increase the carbohydrate content to about 2100 calories or 525 grams.

Eat little and often such as breakfast, snack, lunch, snack, dinner, snack, so distributing the calories throughout the day. Your choice of foods should be familiar ones, avoid experimenting the week before the race with new foods or drinks. Avoid heavily spiced foods, foods which can cause gas and bloating, and deep fried foods.

The day before the race you should not need to eat excessively. The purpose of carbo-loading all week is so that by then your energy stores should be at their optimum, with only the need to top up reserves. Ensure you have a low fibre, high carbohydrate meal at about 5 p.m. the evening before the race.

Race day:

Get up at least 2 hours before the race. Have a snack of between 50 to 75g of carbohydrate (200 to 300 calories) at least an hour before racing. Fat takes longer to digest so if you want to have a high fat snack allow more time for this.

If you choose to drink coffee to get you going then ensure you counter the dehydrating effects of this by drinking a glass of water too. Have a water bottle handy and aim to drink at least one bottle (750ml) before you start the race - your urine should be clear on your last toilet stop!

If you are still hungry try a sports gel or drink rather than filling your stomach up too much, solid food takes longer to digest and can cause digestive upsets during your race.

Warm up with a jog and allow time to use the toilet after this, as the running action can stimulate the bowel.

During the race:

Drink at each water stop even if it is only a few sips. Do not run past the first one or wait until you feel thirsty.
Each sip amounts to approximately 25 ml of fluid. As your aim should be to take about 200 ml of fluid, try to have at least 8 sips at each water stop. Water is lost from the beginning, even on cold days, so stick to the plan and start to take fluid on board as early as possible. You should have practised drinking on the go in training, remember not to gulp it down.

Energy intake can be either liquid or solid food, although if you are running hard, it may be difficult to chew without drastically slowing down and the solid food will not digest very well. Therefore if you are looking for a best time and are working hard it is best to take a gel or sports drink. Take gel before a water station so that you can drink a cup of water to aid digestion.

If you plan to run for less than 1.5 hours then one energy gel (or equivalent) after 45 minutes should be sufficient.
If you are going to be out there longer it would be best to take one every 40 minutes.

If you choose to take solid food, space it out, again having some every 40 minutes. Aim for about 40 grams of carbohydrate each time. Suggestions of good solid food to take are soft fruit, cookies, a small amount of dried fruit or an energy bar.

Remember not to try anything new, you should have tried everything out during hard training sessions.

Post race:

Drink plenty of water to replace fluid lost - 1 litre of liquid (nearly 2 pints) per 1 kg (2.2 lb) of body weight lost. You will probably be estimating your weight loss after a race but you can bet that it will be 1 to 2 kg, so err on the side of caution and drink more rather than less.

Begin replacing glycogen stores within 15 minutes of finishing. Look for a carbohydrate snack with approximately 280 calories and 70 calories from protein - ideal snacks are chicken sandwiches, jacket potato with tuna, cereal with low fat milk or a rehydration drink or energy bar which has carbohydrates and protein in it.

Avoid too much alcohol and drink a glass of water for each alcoholic drink drunk. Snack regularly for the next 48 hours, keeping to healthy (high carbohydrate) options that will replenish your glycogen stores.

Avoid a hard workout for the next few days to allow the muscles to repair and the glycogen stores to refuel.