An adventurer with a rare brittle bone disease has suffered a “devastating head injury” while taking part in a half marathon yesterday.

Samuel Gibson, 39, is currently on life support, surrounded by family, a post on Facebook says.

Mr Gibson, who last week gave a TEDxAuckland talk, was born with a rare condition called osteogenesis imperfecta, a genetic disorder that makes for brittle bones that fracture easily. There is no cure, although some surgical treatments are used to strengthen bones and some medications are being tried.

But that hasn’t stopped Mr Gibson taking part in a number of adventures, including sailing solo across the Tasman in a 3.6m-long dinghy, with several other yachtsman, last year.

And yesterday he was taking part in the Sotheby’s 1.2 marathon in the Hawkes Bay, in his custom-made wheelchair which he helped design and build.

However, Mr Gibson was injured in an incident during the marathon.

“Dear family and friends, we are sorry to share with you that Samuel suffered a devastating head injury yesterday while competing in a half marathon,” a Facebook post by a family member said.

“Sam is currently on life support and his family are all with him. Thanks for your love and support.”

Messages of support have flooded into Mr Gibson’s Facebook page.

“Know that we are all praying for you Sam. Recover and come back stronger to tell us your story. Kia Kaha,” Bernadette Smith said.

Duncan McLean said: “Come on Sam, you can do this mate. Our thoughts and prayers are with you, Jenny and the girls.”

Jeanette Brownrigg posted: “Thinking of you Sam. One of the most inspirational people I've ever met. Send all our love and best wishes your way.”

While Judy Laws posted "Thinking of Sam and his family. An amazing man with a big heart.”

Deb Hurst said: “Sending love and light to you cuzzie! You're a tough guy so show us how it's done once again!”

Chris Mckenzie said: “Thinking of you and your family Sam. Your strength and determination will get you through this.”

It is understood Mr Gibson fell from his chair during the marathon.

In a post on its Facebook page, TVNZ’s Sunday programme said: “The SUNDAY team would like to send our love and support to Samuel Gibson and his lovely family.

“Sam was completing in a marathon yesterday when he fell from his chair. He was training for his big 300km ultra-trek which was to raise awareness of Brittle Bones and to help a little Christchurch boy who suffers from the same disease. Their story is the subject of a SUNDAY piece we're filming. Sam is still in hospital surrounded by his family.”

WATCH SAMUEL GET AROUND ON HIS SPECIAL POWER CHAIR AND INTERACT WITH HIS WIFE AND CHILDREN BELOW