You're with Business Daily on the BBC World Service with Matthew Kenyon.

Today we're hearing from a former sportsman who's turned himself into a fundraising powerhouse

using astonishing physical challenges to bring in many millions of euros for cancer research.

And that's because it's personal.

I forgot how painful it was.

I forgot how scared I was.

But I do not forget the patients around me in the same hospital room

that did not have the luck to recover like I did.

Dutch swimmer Martin van der Weiden, who not only puts himself through extraordinary physical

and mental tests, but also set up and runs his own foundation to make sure the funds

raised go to the right causes.

So from the start, we were very clear that if you donate money

to our foundation, every single cent is going to cancer research. So what does it take to raise

nearly 18 million euros and counting? And once the money starts coming in, how do you manage it so it has the biggest impact?

That's Olympic champion swimmer Martin van der Viden's life.

And in the garden of the house he shares with his wife and two daughters,

there's a continuous flow pool, which was central to his most recent fundraising effort.

To call it a marathon would be seriously underselling it.

We'll come back to the extreme physical challenges Martin sets for himself later.

First, let's just get his simple story as told by the man himself.

I won Olympic Gordon 2008, 10 kilometers open water swimming.

After I was diagnosed leukemia 2001, and the last five, six years, I'm running my own

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