Michael O'Brien's world changed when he took on the challenge of 75 Hard. The gruelling fitness challenge that requires a real mental and physical commitment from people.

From there, after never being a particular sporty individual he got the running bug, which saw him run nine marathons, before joining the Bravehearts 777 Challenge, where people run seven marathons in seven states/territories in seven days.

Now he's recently completed a 100 kilometre race here in Canberra which has him once again in pursuit of his limits.