An eclectic mix of celebrities will take their place on the London Marathon start line today, with newsreaders and actors lining up alongside models and reality TV stars.
BBC presenter Sophie Raworth will hope to avoid a repeat of her performance last year, when she crashed into a barrier on the side of the road and blacked out after hitting the 23-mile mark.
The 43-year-old was given oxygen and cared for by a St John Ambulance crew for two hours.
"I thought I was at a pop concert at Leeds when I woke up. It was black and there was a lot of screaming.
"It honestly took me about 10 minutes to realise why I was there," she said.
The newsreader blamed the unusually high temperature of 19C (66.2F) for her collapse.
The cast of The Only Way Is Essex is strongly represented with James "Arg" Argent, Cara Kilbey and Billi Mucklow all competing.
Kilbey and Mucklow are running together and declared there was "no chance" they would finish behind Arg.
"We've got to beat him," Mucklow said.
She revealed that her experience of teaching yoga has helped with her breathing while pounding the streets, but admitted that "nothing prepares you for this run".
Other famous faces competing include celebrity chef Gordon Ramsay, who failed to complete the 2010 marathon owing to cramp, and ex-model Nell McAndrew, running her sixth marathon.
The former Playboy cover-girl is looking to break the three-hour mark for the first time today.
McAndrew's past times have been so quick that she has qualified to compete with the elite athletes.
"I am in the best shape, the fittest, I have ever been in my life," said the 2005 Rear of the Year winner.
Former Holby City actress Amanda Mealing will celebrate her 45th birthday at the race.
Mealing is running for the charity Breast Cancer Care after making a full recovery from the disease.
"I would get up on stage in front of thousands of people absolutely fine (but) I'm terrified of this.
"I think it's because it's so personal," she said.
Famous figures from the world of sport include England cricket coach Andy Flower, raising money for the Lord's Taverners, who took time out from the team's recent tour of Sri Lanka to train with a 15-mile run through rush-hour traffic in Galle.
James Cracknell, a double Olympic gold medal winner with the British rowing team, is aiming to continue his remarkable record of physical feats by running a third sub-three hour marathon.
The athlete, running for the Children's Trust, has also rowed the Atlantic, walked to the South Pole and recovered from a life-threatening head injury suffered while attempting to cycle, row, run and swim from Los Angeles to New York in under 16 days.
Clayton Blackmore, the former Manchester United full-back, is running for the Rhys Daniels Trust, whilst fellow ex-Wales international Matt Jones is running to raise money for the Spinal Injuries Association, the Bobby Robson Foundation, and the John Hartson Foundation.
Television stars include former I'm a Celebrity... contestant Linda Barker, presenter Isobel Lang, Coronation Street's Paula Lane, Bruno Langley, Conor Ryan and Nikki Sanderson, and Irish broadcaster Craig Doyle.
Alex Reid was forced to withdraw from the race after suffering an injury. A statement on the cage fighter's website revealed he had fallen down a flight of stairs and sprained his ankle.