But at the age of 28, he slowly found himself struggling to walk up stairs and get out of low furniture.
He was diagnosed with a degenerative neuromuscular condition called inclusion body myositis.
The disease causes Mr Grant's muscles to waste away to the point that he may one day struggle to breathe and swallow.
"To a degree there was a loss of identity," he said.
"I used to love riding motorbikes, sailing and working on cars and bushwalking and doing active things.