On the face of it life has been good to the American television and movie star Martin Lawrence. He was paid $8.5m (£5.3m) to appear opposite Eddie Murphy in his latest film, Life, which opens in Britain today.

His network series Martin was a hit in the US for five years, but still 34-year-old Lawrence felt the pressures of fame so strongly that to keep his weight down for his next role the former stand-up comedian went running in heat of up to 38°C (100#176;F), collapsed and spent three days in a coma.

He was said last night to be in a critical but stable condition in Los Robles regional medical centre at Thousand Oaks, California, responding to voices but unable to speak.

He is hardly the first actor to take extreme measures for a role - Robert De Niro has put on weight for the screen and Jim Carrey and Kate Winslet have shed the pounds. But Lawrence pushed himself to the point of risking his life by running in several layers of clothing and raising his body temperature to more than 42#176;C (107#176;F).

"When you come in with a temperature of 107, that's not very compatible with life," said Susie Faz, a critical care nurse. "He's a very lucky man."

Lawrence's girlfriend opened the door after the actor had gone for a run to find him keeled over on the doorstep, moaning and having trouble breathing, according to the hospital.

The actor was suffering from heat exhaustion and hyperpyrexia - raised body temperature - for which he was treated by emergency staff with ice and fans. Extreme overheating can cause permanent kidney, brain and heart damage, and doctors would not speculate on Lawrence's chances of a full recovery.

"He has improved some but he still remains very critical, although his vital signs are stable," a hospital spokes woman said. "He's not able to respond to you if you ask him a question. He's basically sleeping.

"He was doing what he saw fighters do. He put on several layers of heavy clothing and was jogging in the intense heat and collapsed in front of his home."

The actor, who appeared in the movies Bad Boys and Nothing to Lose, is said to have been preparing for his next role, as a postal worker who adopts a dog in See Spot Run. Sony Pictures Entertainment, for whom he recently finished the police comedy Blue Streak, said the picture's release would go ahead as planned.

Lawrence, who played a number of different parts in his TV show and came to prominence when he won a stand-up comedy award 12 years ago, has had several run-ins with the law.

He ran into traffic in Los Angeles in 1996 screaming "fight the establishment" at oncoming cars. Police found a gun in his pocket. Later the same year he was sued by an actress for sexual harassment and the case was settled out of court.

Going to extremes: stars who suffered for their art

Demi Moore

In preparations for her role in GI Jane (1997), Moore put herself through a gruelling two-week training session at the Navy Seal base in Coronado, California. She was reported to have got such bad blisters from running that her socks filled with blood

Robert De Niro

To prepare for the film Raging Bull (1980), in which he played the ageing boxer Jake La Motta, De Niro gained three and a half stone (22kg) in the name of authenticity.

Laird Cregar

An American character actor in the 40s - noted for his performances in The Lodger and Hangover Square - Cregar was seriously overweight. His crash diets contributed to heart strain and he died in his late 20s.

Daniel Day-Lewis

For his role as the disabled Christy Brown in My Left Foot (1989), Day-Lewis stayed in his wheelchair both in front of and behind the cameras. He also taught himself to paint with his foot. As Gerry Conlon in In the Name of the Father (1993), Day-Lewis prepared for an interrogation scene by depriving himself of sleep for three days.

Ralph Fiennes

For his role as the Nazi officer Amon Goeth in Schindler's List (1993), Fiennes put on two stone by eating three big meals a day and washing down dinner with Guinness.

Tom Hanks

While playing Andrew Beckett, a gay lawyer who contracts Aids in Philadelphia (1993), Hanks lost just under two stone to play the last few scenes in which Beckett is in the final stages of the disease. For one scene he was required to drop 5lbs (2.3kg) in a weekend.