Running a whopping 26.2 miles is an incredible achievement which doesn’t come without major risk to the human body. Despite some people making it look incredibly easy, with some running it in around 2 hours, their bodies will face a myriad of aches and pains afterwards. Kicking off at Greenwich Park on April 27, the London Marathon saw 56,000 people at the start line before embarking on the long run.

According to Professor Alister Hart, many of these brave runners will be barely able to walk after they cross the finish line. The orthopaedic surgeon at the Royal National Orthopaedic Hospital in London, explains the consequences using firsthand experiences when he took part in his first marathon 13 years ago. "I couldn’t walk [properly] for two weeks afterwards," Professor Hart told iNews.

Following his own experience prompted him to conduct research into the impact of running so many miles on the body. The scientist discovered, after many in-depth looks at MRI scans of runners before and after the race, that damage in the knees, hips and spines were present before the subjects even began training.

However, none of them complained of any symptoms and ran the marathon anyway. Interestingly, some of the runners' joints actually improved after the 26.2 mile race. Professor Hart has pinpointed this to the improved blood supply to the joints.

Another explanation may be that the participants had strengthened their bones through training.

The study also looked into the effects on the lumbar spine of runners, finding that eight of the 28 participants had fluid in the bone marrow of the spinal vertebrae.

After running the marathon, there had been a major improvement in this in a few of the runners.

"We know that bone health reduces as you get older, and one way to counteract that is by increasing loading,” Professor Hart says.

He added that people are advised to train for about four to five months ahead of a marathon, which is the length of time it takes for your body to adapt to running long distances.