telegraph.co.uk Wrote:Mr Buss broke the previous record of 468 miles in seven days on Friday - his sixth day of running.
By the deadline of noon on Saturay he had reached 517.25 miles, smashing the record set last summer by fellow ex-soldier Lee Chamberlain.
Mr Buss, 35, from Highworth, in Swindon, has been running three marathons a day on the treadmill at the Brunel Shopping Centre in the town.
He has had only two hours sleep a day with brief breaks for food and a massage.
The former Army physical training instructor has been burning around 11,000 calories a day and as he only takes in around 3,500 calories he has lost eight and a half pounds in weight.
Mr Buss has been running between 3.7 miles an hour and six miles an hour and has lost two toenails during the challenge.
He is raising money for the charity Help For Heroes, which assists injured British servicemen and their families, and hopes to raise £100,000 by Christmas and £1m by 2014.
He has been supported by soldiers from 29 Regiment Royal Logistics Corps, based at South Cerney, Gloucestershire, who have served in Iraq and Afghanistan.
Also supporting Mr Buss was Lance Corporal Matthew Croucher who was awarded the George Cross after throwing himself on a grenade to save the lives of his comrades in Afghanistan in February 2008.
Mr Buss, who has held countless other fitness world records, said he planned to take it easy for the rest of the day before getting back into his fitness regime.
''I was always looking at hitting the 500 mark so to go 17 miles further is brilliant,'' he said.
''I've lost two toenails, my legs are aching and the arches of my feet are painful after hitting the treadmill for more than 20 hours a day but I feel good.
''What kept me going was the guys from 29 Regiment who really motivated me and kept my mind off the pain.
''I wanted to use my abilities as an endurance athlete to raise as much money as possible.
''I'm going home to have a bath, then have beef stew for dinner and chill out for the rest of the day.
''But I'll do a light run on Monday and Tuesday and do six miles on Wednesday before getting back into the pool on Thursday.'
