How much is too much when it comes to teenagers' weekly exercise? New research shows that too much weekly sport seems to be as bad as too little for teen well-being.
Research published online in the Archives of Disease in Childhood found that the maximum benefit seems to be obtained from 14 hours of sport a week, which is double the official recommendation of seven hours.
The researchers quizzed more than 1,200 16-to-20-year-olds in the French-speaking part of Switzerland between February 2009 and January 2010 about how much sport they did.
Their mental and physical well-being was assessed using validated scoring criteria from the World Health Organisation, on a scale of 0 to 25.
Just under one-in-10 (9pc) was overweight or obese. The average well-being score for the entire sample was 17.
Weekly sports participation was categorised as low (0-3.5 hours, 35pc of respondents); average (3.6-10.5 hours, 41.5pc); high (10.6-17.5 hours, 18.5pc); and very high (more than 17.5 hours, 5pc).
Compared with the teens in the average group, teens in the low and very high groups were more than twice as likely to score below 13. Those in the high group, on the other hand, were around 50pc less likely to score below 13.
The peak scores of well-being obtained were for around 14 hours a week of sports practice a week, with this protective effect reversed beyond 17.5 hours a week.
Regular exercise is known to have a positive impact on mental and physical well-being, reducing stress and anxiety, and boosting self-esteem and brain power, say the authors.
But while doubling the time spent playing sports to 14 hours seems to be good at this age, going beyond this seems to be detrimental, they conclude.