4 August 2012 Last updated at 15:46

Olympic athletics: LaShawn Merritt crashes out of men's 400m

Defending Olympic Champion LaShawn Merritt of the United States fails to cross the finish line in his men's 400m heat after battling a recent injury.

Afterwards, the US athlete described the intensive treatment on his injury just to get him to the Games.

Watch the Saturday morning athletics session on BBC Sport's Interactive Video Player.

Available to UK users only.