Running a marathon - what are the risks?
Running a marathon puts immense strain on the body. But just how dangerous for your health can it be?
What are the main health risks?
Thankfully, most of the casualties that occur during a race concern minor injuries, like sprains and strains.
Dehydration is the biggest problem that marathon runners have to overcome. In a hard race on a hot and humid day, up to four litres of fluid can be lost through sweating and exhalation. It is important for runners to keep well hydrated.
And there are other things you can do to prepare for the race. Following a training plan in the months leading up to the race to get yourself in shape is advisable.
A great many injuries can be avoided by warming up and doing stretches immediately before the race.
During the 2012 London Marathon, 4,923 runners and members of the public needed assistance, but the bulk of these consultations were for minor concerns. In 2011, 6,000 needed help - many for heat exhaustion linked to the hot weather on the race day.
What about fatalities?
Fatalities are very rare. The 30-year-old woman who collapsed close to the finish line of the 2012 London Marathon is the 11th participant to die since the event began in 1981 - and the first woman.
Professor Sanjay Sharma, medical director for The Virgin London Marathon, said seven of these deaths had since been linked to heart conditions like blocked heart blood vessels or a structural congenital problem with the heart.
He said: "Until now, these deaths have occurred solely in males. All were aged over 40 and out of those seven whose deaths were linked to heart problems, five had furred arteries - a sign of coronary artery disease.
"Two had something called hypertrophic cardiomyopathy - a problem that affects the structure of the heart."
Another man died due to drinking too much water - a condition doctors call exercise-associated hyponatremia - and two died from brain haemorrhage.
Prof Sharma said: "We are still waiting for the postmortem on the young woman, but her death is likely to be due to a heart problem I should think.
"I was there at the arrest and was deeply shaken. To see a 30-year-old who is amazingly athletic die is so counterintuitive.
"These deaths are rare."
Similarly, US research has looked at nearly 11 million runners who participated in marathons or half-marathons between 2000 and 2010.
Over the decade, 59 of the runners had a cardiac arrest - where the heart stops working - and 42 of these people died. This means one death in every 259,000 runners.
Most had underlying heart conditions or heart disease.
How do I know if I am fit enough to run?
If you have any medical issues which you think may put you at risk, you should see your GP before you begin training for a race.
People with existing conditions like heart disease or diabetes should also seek medical advice.
Once you start training, increase running distances gradually to avoid exhaustion and separate your days of heavy mileage with one or two days of lighter training or rest, so that your body can recover.
By following a training plan you will be able to build stamina. However, if you become ill or injured during this training period, take a break. Do not start training again until you have fully recovered. And, again, seek medical help if you need to.
As a rule of thumb, experts advise that, a month before the race, you should be able to "comfortably" run a continuous 15 miles. By comfortably, they mean that you should feel as though you could still run more at the end of the distance.
You should also notify the event organisers of any medical conditions that you have and should not compete if you do not feel fit on the day of the race.
Judy O'Sullivan, Senior Cardiac Nurse at the British Heart Foundation, said: "Events such as the marathon are a big physical undertaking so it is important that you train in advance, ensuring that you build up to the event steadily and safely. On the day of your event, remember to warm up, pace yourself and to rest if you feel pain or discomfort.
"Sadly, in very rare circumstances some people will experience unforeseen complications, usually connected to a pre-existing condition. But for the overwhelming majority of people the health benefits of exercising outweigh the risks.
"We would always advise anyone who has any concerns to visit their GP before taking part."