Greig was the first woman to run two ultramarathons. In 1971 she ran the Isle of Man 40-mile race, finishing in 6:48:00. The race did not officially admit women until 1982. In 1972, she became the first woman to run the 55-mile London-to-Brighton race, finishing in 8:30:04. Women were not officially admitted to the race until 1980, where
Leslie Watson placed first. In 1971, Greig ran the
Ben Nevis fell race, again unofficially. She finished in 3:02:02. In 1974, at the age of 37, she won the first International Masters Marathon for women, at the World Veterans' Championships in Paris, with a time of 3:45:21. In 1976, she competed in the World Veterans' Marathon in Coventry finishing 10th woman in 3:39:44. Greig's competitive running career came to an end in 1982, following an accident in a swimming pool in which she injured both her feet. ==Athletics administration==