Mar 2, 2009, 9:20 GMT
Gary Barlow "collapsed in a heap" on the first day of his trek up Mount Kilimanjaro.
Chris Martin and Gary Barlow. The Take That singer - who injured his back last month while training for the 19,000ft climb for British charity Comic Relief - broke down in agony after a gruelling four-hour walk. EPA/DANIEL DEME
The Take That singer - who injured his back last month while training for the 19,000ft climb for British charity Comic Relief - broke down in agony after a gruelling four-hour walk.
Girls Aloud stars Cheryl Cole and Kimberley Walsh, singer Alesha Dixon, presenter Fearne Cotton and actress Denise Van Outen took turns carrying Gary's backpack on the first leg of their eight-day climb.
A source said: "He was in a great deal of pain but everyone rallied around to get him through it. It was a hellish experience."
In his trek diary, Gary said: "It's very steep and I'm having to use two poles for my back - but I'm told it will loosen up after the first day's climb.
"We only walked for four hours today because of the intense heat and steep incline."
However, Boyzone singer Ronan Keating thought the first day was easy.
He said: "Today wasn't too tough a day. I don't mind sleeping in a tent - I go camping with the kids once or twice a year and you get used to it.
"I've got my gear, it's all here, we've got a little mattress. It's cosy and cool."
The climb will raise money for Comic Relief's charity projects in the UK and Africa.
Organisers hope to raise £1 million, some of which will be used to fight malaria in Tanzania, where Mount Kilimanjaro is located.
The mountain is Africa's highest summit.
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