When keen runner John Reynolds completes the London Marathon on Sunday, he won't be putting his feet up like the rest of the athletes.
Instead the 51-year-old fundraiser will keep on running for another 170 miles.
The engineering worker from Radstock won't stop until he reaches the National Osteoporosis Society in Camerton.
It will be a more gruelling version of a run he did before last month's Bath Half Marathon.
Mr Reynolds said: "I'm running for the society because we all need to stop taking our bones for granted. We think about our muscles, but we forget about our bones and it is so important to look after them, whatever age we are.
"I'm asking people to support me so that we can build stronger bones for everyone and I'm running because it's one of the best ways of keeping my bones strong and healthy."
Nine years ago, after battling a thyroid condition, his dream was to be able to walk a mile again.
He said: "Now, through my running and the incredible inspiration from others, I hope to show sometimes impossible dreams can become a reality if you truly believe in them."
In 2004, the after-effects of radiotherapy left Mr Reynolds struggling to walk even the shortest of distances, but within a few months, he had completed his first half marathon.
In the nine years since, he has run more than 20 half-marathons, four marathons, 24 ultra-marathons and six extreme marathons.
In March Mr Reynolds ran 57 miles, the equivalent of two marathons, through the night in sub-zero temperatures and arrived in Bath just in time to join thousands of other runners at the start line for the Bath Half.
Jess Price, community fundraising manager for the society, said: "By taking on this amazing challenge, John not only inspires other runners, but is also improving awareness that we all need to look after our bones at all stages of life."
People can track his progress on Twitter via @marathonmanjohn and anyone wanting to sponsor him on his epic run should visit his webpage, www.virginmoneygiving.com/Johnreynolds.
