On 19 April 1967, Kathrine Switzer ran her way into international fame. A 20-year-old English literature and journalism student at Syracuse University in New York, she was competing in the Boston Marathon when a man suddenly appeared by her side, furiously attempting to tear off her race bib.

Startled, Switzer ran faster, away from the man’s outstretched hands. Her boyfriend at the time, who was running with her, shoved the stranger aside. As they sped on, she realised the man was a race official, and he’d been trying to physically remove her from the marathon.

The official was a Scottish-American runner called Jock Semple, and his fury was prompted by the fact that the Boston Marathon in 1967 was a strictly male-only event. It was also the only major marathon in the United States, one that Switzer – a keen runner since she was 12 – had trained ferociously for. She’d managed to get around the no-women rule by signing up using her initials, and her obvious femaleness somehow went unnoticed until she was a mile and a half into the race.

Photos of Switzer’s altercation with Semple were splashed across newspaper front pages around the world. They are extraordinary images, ones that capture the mood of a time when young women were beginning to push back against patriarchal norms. Switzer – trim, youthful, big-eyed – wears an expression of horrified disgust as she darts away from the livid, middle-aged Semple. It was the 1967 equivalent of a viral sensation.

More than half a century on from that famous race, Switzer, now 71, is still running. In 2017, she took part in the Boston Marathon for the third time, 50 years after her first race (incredibly, it took her just 20 minutes longer to run it at 70 than it had taken her at 20). This year, she’s got her sights set on the Virgin Money London Marathon on 22 April. It will be the 42nd marathon she’s run in her lifetime.

She was the first woman ever to run a marathon. Now, she’s taking on London