Professor Collins said that "perceived physical competence" was vitally important up to the age of eight and shaped social status in both boys and girls. "Physicality is quite a big thing in terms of saying to someone whether you enjoy school and fit in with your mates and stay adjusted," he said.
By secondary school, interest falls. "All of a sudden girls say, 'I do not look good at this', 'I actually can't do this', 'I'm blowed if I'm going to play it'. But at 19 and 20, girls take up physical activity again. They will stand in the middle of a large group in an aerobics class.
At the ages of 23 or 24, women become more physically active than men because women are more conscious about their appearance.
Too many fell away and missed out on the lifelong activity that was vital for long-term health. Key factors that keep young people active are self-motivation, self-determination and perceived physical competence.
These are the same skills that make people successful in other spheres.
The Edinburgh University academic advised: "If you want people to be physically active, you have to teach them how to move." That begins in primary school.