As if running 26 miles isn't punishment enough on a Sunday morning, you might also have the misfortune of picking up an injury.
Worry not, though, because Paul Martin, a physiotherapist at the English Institute of Sport, is here to talk you through those minor niggles.
Cramp can happen in a number of ways - fatigue, high-level exercise, dehydration and high-level loading can all bring it on.
In runners it generally affects the calf muscles, which will tighten up, become incredibly sore and feel rock solid to touch.
Staying hydrated can help prevent cramp
The best way to prevent it is to make sure you've been stretching well during your preparations - and putting in the training to make sure your muscles are ready. On the big day, make sure you stay hydrated throughout the race.
If the worst happens and you get cramp on the way round, the best thing is to try and stretch the calf out immediately.
If there's someone from a first aid area around who can give you a massage that would help, and you'll need to keep your fluids up as well.
But it shouldn't mean the end of your race. You'll have to slow things down while you see it through and you may even need to stop for a minute to give it a rub, but as long as you can keep stretching it you should be okay.
A stitch is a build up of lactic acid in the muscle, which needs to be flushed away. It's caused by eating or drinking a bit too much and a bit too quickly.
If you want to avoid it during the race, avoid taking on too much fluid all at once. Take sips from your drink, rather than gulping down a litre in the first mile.
If you do get a stitch the important thing is to get lots of oxygen into the body - perhaps try and stretch the area a bit. Concentrate on getting lots of air into the system.
As with cramp, if your training has been good there isn't too much danger of getting a stitch.
Blisters are caused by a build up of friction and sweat in the trainers. If you've got well-fitted shoes they shouldn't be a problem.
Wearing socks made from a neutral material like cotton will help prevent them. Nowadays you can buy socks that draw moisture away from the skin to another part of the trainer.
Painful blisters can be avoided
If you've had a problem with blisters in the past, a good tip is to put some electrical tape over the area. Some of the runners I work with say it works for them.
Runner's nipple: This tends to happen if you're wearing a synthetic shirt and there's a lot of sweat. The friction builds and breaks down the skin, causing it to bleed. It's easily prevented - a couple of plasters over the nipples and you'll be fine.
Falls: There are first aid people stationed throughout the course, so if you do take a tumble they'll check you out and advise you whether or not to carry on.