A GYM owner says he will face a "horrendous" task when he tackles a marathon next month.

Gary Nicholas, who runs Calso Health and Fitness Centre in Bromley, will run the 26.2-mile London Marathon with a 10kg dumbbell weight in each hand.

He will not be allowed to put them down at any point, and, just to make the task a little harder, after every mile he will complete 100 step-ups on a 14in step being carried round the course by his training partner John Currell.

Mr Nicholas, 43, said: "It is horrendous, but I am confident I can do it.

"If you can imagine being smashed on both shins with a sledgehammer, or being repeatedly kicked in the back of the legs, that is how it feels after about three miles.

"The only way I am not going to do it is if I suffer a heart attack or really severe cramps."

He added: "I decided to do it because I needed a kick up the backside.

"I wanted a challenge, as I like them in my life, and straight after Christmas I said I would love to do this."

He expects to complete the course in around nine hours.

Trucker Mr Currell, 42, from Farnborough, will be with Mr Nicholas for the whole course, carrying his step and feeding and watering him.

Mr Nicholas, who lives in Treebourne Road, Biggin Hill, said: "John is a real fitness fanatic, and a real star."

Previously, he did 3,000 step-ups in two hours but says he has not done anything on this scale before.

Mr Nicholas has built up his fitness by doing 15, 17, and 19-mile training runs around Hayesford Park, Bromley.

He limits his training to the weekend, leaving him the rest of the week to recuperate.

The two runners are hoping to raise £3,000 for charity Whizz-Kidz, which helps children with disabilities, ahead of the marathon on April 13.

So far, they have collected more than £2,000.

To sponsor Mr Nicholas and Mr Currell's efforts, make cheques payable to Whizz-Kidz and send them to Garry Nicholas, Calso Health and Fitness Centre, 28-30 Letchworth Drive, Bromley, BR2 9BE.