You've got the gear, trained in the plummeting temperatures of winter - now don't forget one last crucial part of your training plan: nutrition.
A good diet filled with the right nutrients is an essential part of any exercise routine, but it's especially important for endurance events like marathons or triathlons. Follow our tips to make sure you bound over that finish line...
The C factor - carbohydrate
'Hitting the wall' or 'bonking' is every distance runner's fear. It might sound like an old wives' tale, but it's a phenomenon that can happen to anyone, no matter how much training you've done. It occurs when the body's carbohydrate fuel tank - the body's preferred energy source during high intensity activity that is stored in the muscles and liver as glycogen - gets low and the brain and muscles show signs of fatigue. If you hit the wall during a marathon you'll know about it, every step feels like wading through treacle. You can avoid the dreaded wall by 'carb loading' before and during a run to maximise your energy stores, which means stocking up on lots of carbohydrate-rich pasta, potatoes, and certain fruits and vegetables.
The power of protein
Protein helps to rebuild muscle, so is particularly important after a long run to repair damaged tissue and stimulate the development of new tissue. Good protein foods to eat after a run include milk, cheese and yoghurt, white meats and eggs.
You need a different balance of nutrients at each stage of your training plan. With a few weeks to go, now's the time to try out foods and recipes to make sure they work for you.
Your nutrition plan needs to kick in at least a few weeks before the big day. Experimenting with foods before and after a run and finding recipes you like is important - the last thing you need during the race is an unhappy stomach. Low GI carbohydrates such as wholegrain rice and pasta are good to introduce into your general diet at this stage as they release energy slowly and will build up your carbohydrate tank. The final week is the time for real carb-loading, so make pasta and porridge your friend. Be wary of gas-inducing carbs, however, such as broccoli, cabbage, beans or too much fruit, or it could make for an uncomfortable run!
Before long runs
A few hours before any long run, eat a meal high in low GI carbohydrates, moderate in protein and low in fat to give your body all the nutrients it needs for the next few hours. Porridge with fruits, a chicken sandwich and fruit or a bagel and peanut butter are good options.
During long runs
It's important to replenish your carbohydrate stores during runs of 90 minutes or more. The body can only store around 2,000 kcals of glycogen and after a few hours of running, your fuel tank warning light will flicker on unless you frequently top up your carb stores. High GI carbohydrate foods are best during a run as they release energy quickly. Choose specially designed sport gels and isotonic drinks, or try bananas, oranges, honey, dried fruit or gummy sweets such as jelly beans. Fuel every 45-60 minutes during a long run, with around 30-60 grams of carbohydrate (120-140 calories) per hour (e.g. a large banana, white bread honey sandwich or energy gels), and don't forget to stay hydrated with plenty of fluids and electrolytes.
You have a window of around 30 mins when the body is primed to replenish its carbohydrate stores and soak upmuscle-repairing protein after a run. Chocolate milk is a good mix of protein and carbs, or whizz up a smoothie with lots of fruit. Drink plenty of fluids too to replace water and electrolytes lost through sweat.
Looking for some inspiration? Get recipes and training tips from our marathon meal plans.
Will you be racing in a marathon this year? Tell us your top tips for training and how you're getting on below.
Katie Hiscock is a fitness writer with diplomas in personal training and sports massage therapy. With an interest in sports nutrition, antenatal exercise and injury prevention, she works as a therapist for Brighton & Hove Albion.