More than 50 youngsters have dropped out of Ten Tors event on a stormy Dartmoor, according to the Army.
The event is being heavily monitored amid stormy conditions on the moor.
An Arnmy spokesman said the drop-out rate was normal.
In a tweet it said: "Ten Tors update - 53 fall outs, just the usual sprains & strains. Raining off and on and pretty windy. It's called a challenge for a reason."
The Army is out in force to ensure the huge hiking event runs smoothly.
Changes have been made to the course this year to avoid crossing rivers where water levels are deemed too high for safety reasons.
Hundreds of young people from schools and colleges across Devon are taking part in the event.
Among those taking part are Exeter School, Newton Abbot College, Coombeshead Academy, Teignmouth Community School and Teign Academy.
They set off on the epic trek from Okehampton Camp at 7am on Saturday.
The Ten Tors Challenge is also one of the biggest outdoors adventure events for young people in Britain today.
Some 2,400 youngsters aged between 14 and 19 will take part in Ten Tors, with a further 300 youngsters with physical or educational needs taking part in the Jubilee Challenge.
Immediately after the start of Ten Tors, up to 300 youngsters with special physical or educational needs - many in wheelchairs - will start the Jubilee Challenge, competing routes up to 15 miles.
More updates on the progress of the event will follow as we have them.
