2009-08-26 23:42:09 -

Pop superstar and fitness fanatic MADONNA is preparing for a gruelling ultra marathon - dubbed the toughest race on earth, according to U.S. reports.
The 51-year-old singer, who keeps in shape with regular yoga sessions and daily trips to the gym,

has reportedly cleared her schedule next April (10) so she can jet to Morocco for the Marathon des Sables.
The epic trek is 156 miles long, takes six days to complete, and is the equivalent of six marathons.
A source tells America's Star magazine, "She's always been in great shape, but she is now taking things to a whole other level."