Phelps' latest plunge fraught with risk

Michael Phelps has been swimming against the tide all his life. Time and time again he has proved the doubters wrong, setting the standard for Olympic achievement with his 18 gold medals.

But now, almost two years after retiring from swimming and two months shy of his 29th birthday, the American is plunging into uncharted waters by attempting a comeback where the risk-reward ratio is heavily stacked against him.

If all goes well, Phelps could be back on the podium at Rio, although he insists he is still undecided about whether he wants to go to the 2016 Olympics.