LIZ McColgan, Scotland most successful female athlete, has been forced into retirement. She confirmed her decision yesterday, after having suffered her fifth stress fracture inside a year.

The 37-year-old former world and commonwealth champion at 10,000 metres had been fighting injuries to her back and feet for several years and had already defied medical advice to make a successful return.

She had been in training to race the New York marathon in November. ''I hoped to get the qualifying time for next year's Commonwealth Games,'' she said, speaking between physiotherapy treatment at the sports injury clinic which she and her husband, Peter, operate on the outskirts of Carnoustie.

''I had hoped to bow out by winning a championship marathon for Scotland in Manchester, but that's just one wee bit of unfinished business.''

The final blow came when she broke a bone in her left foot, when training last week on the road near her home.

''Everything was going fine until then and I still felt my best marathon was in front of me. I know I said many times that if had one more injury, I would stop, but then came back again.

''This time it is for certain. There is no going back. I've had five stress fractures and one full fracture in the last year.

''I have to think 10 years into the future. I am happy with what I have achieved but I have been warned that I could be crippled by the time I'm 50 if I try to continue. I have to think of the quality of life afterwards.

''Every time I step up above 70 miles, or intensify training, something goes.''

Her competitive record was unmatched by any British long-distance runner. She was narrowly denied Olympic gold in 1988 and won world medals on every surface: road, indoor and outdoor track, and cross-country.

She set five world records, four on roads, and one indoors. She was the only Scot successfully to defend a Commonwealth title, the latter after a near nervous breakdown and on minimal training.

She had been feuding with her coach - a recurring theme - and almost retired, yet after having her first child, returned to take what remains Britain's only global endurance gold by a woman. That was in Tokyo, 10 years ago this month.

Though she also recorded the fastest debut marathon that year, the track success was her finest hour, saluted as the finest achievement by any UK endurance athlete by Brendan Foster, former European champion and Olympic medallist, who commentated on the race.

The marathon, in particular, was good to McColgan. She raced the distance 10 times, winning three times, and was reputed to have pocketed upwards of (pounds) 500,000 from London alone. She won the event once and also finished second and third.

She enjoyed a keen rivalry with Yvonne Murray, who was also highly successful internationally, and had McColgan's measure over shorter distances without winning an outdoor global title or setting world bests. Her career also ended prematurely, through injury.

''I never enjoyed competition for the sake of it,'' McColgan, a mother-of-three, said. ''I always wanted to be the best.''

She was brought up in a council house in the Whitfield area of Dundee but now lives in almost baronial splendour, with her parents occupying a second house within the grounds.

Blunt spoken, wilful, but unfailingly honest about her own frailties, she was never far from controversy. Yesterday, she was scathing about doping cheats and was right behind Paula Radcliffe, the English athlete who staged an amazing personal protest at the world championships in Edmonton, Canada.

the record

Olympic games

1996: 16th marathon; 1992: 5th 10,000m; 1988: 2nd 10,000m

World championships

1987: 5th; 1991: 1st; 1995: 6th, all at 10,000m

Commonwealth games

1986: 1st at 10,000m; 1990: 1st at 10,000m, 3rd at 3000m

European championships

1986: 7th at 10,000m, 12th at 3000m

World indoor 5000m record

1992: 15:03.17, Birmingham.

Set four UK and Commonwealth 10,000m records; and won three marathons from 10 starts, in New York, 1991; Tokyo, 1992; and London, 1996