Phys-ed classes aim to establish healthy habits in students. (CBC)

Focus on fun not health to get inactive teens to exercise, a new study suggests.

The study looked at 128 students aged 16 to 19 in England. Participants received daily text messages for two weeks encouraging exercise.

The researchers studied whether highlighting the emotional benefits of sport and exercise to young people increased their levels of physical activity more than highlighting the physical health benefits, said Reema Sirriyeh of the University of Leeds.

Texts on the emotional benefits included: "Physical activity can make you feel cheerful. What activity will you do today?" A second group received texts that highlighted the physical benefits, such as, "Physical activity can keep your heart healthy. What activity will you do today?" A third group received text messages that were a combination of the two.

The physical activity levels of all participants increased by an average of 31.5 minutes of moderate level activity per week after receiving the messages for two weeks, the researchers reported in this week's online issue of the British Journal of Health Psychology.

But inactive teens who received messages stressing the emotional benefits of exercise boosted their levels of activity by two hours per week. That suggests that people who believe that physical activity is enjoyable and fun are more likely to get moving.

Since statistics from the British Heart Foundation show that girls' physical activity levels begin to decrease at age 16, it's important that teens get into healthy patterns like exercising regularly, Sirriyeh said.

Among Canadians aged 15 to 19, the percentage whose waist circumference put them at an increased or high risk of health problems more than tripled between 1981 to 2009, from less than three per cent to 15 per cent among boys, and from nine per cent to 28 per cent among girls, according to Statistics Canada.