Dr David Crombie is a very unassuming athlete. If you saw him at 
the start of a race you’d think: “I could easily take him”. And over a short distance you probably would. But in extreme endurance ultras your burst of youthful exuberance and arrogance would peter out, and you’d be forced to watch the rear view of a meticulously paced figure disappearing ahead of you.

That’s because your face-value judgments of his athletic ability 
didn’t realise that his body has been battle-hardened from the 
ravages of cancer and most recently a bone marrow transplant.
 Or that his fiercely uncompromising psyche has driven his legs 
across thousands of kilometres.

Last year, Crombie, a sports scientist at the Sports Science Institute of South Africa, returned from running 62 marathons’ worth of jungle along the banks of the Mekong River, which snakes through Laos, Cambodia and Vietnam into the South China Sea.

The enormity of the distance is as impressive as the stand Crombie is making – defiance against doubt, cancer and the notion that men can “retire” their bodies from middle age.