Regular exercise tends to steeply decline among youth as they move to university or college, according to a study by researchers at McMaster University. Researchers found a 24 per cent decrease in physical activity over the 12 years from adolescence to early adulthood. The steepest declines were among young men entering university or college.

The research recently appeared in the American Journal of Preventive Medicine. The study, based on Statistics Canada's National Population Health Survey, followed 683 Canadian adolescents 12 to 15 years old, who were interviewed twice a year until they were 24 to 27 years of age.

While the children were most active, the research suggests that this advantage quickly disappears.

"This is a critical period, as the changes in physical activity during the transition from late adolescence to early adulthood represents the most dramatic declines in physical activity across a person's life," said Matthew Kwan, the principal investigator for the study and a postdoctoral fellow of the Department of Family Medicine of the Michael G. DeGroote School of Medicine.

"In particular, the transition into post-secondary is a one-time period when individuals become much less active."

Risk estimates suggest 20 per cent of premature deaths could be prevented with regular physical activity. Yet, recent data show 85 per cent of Canadian adults are not active enough to meet the recommended 150 minutes of moderate-to-vigorous physical activity a week.

Public health campaigns encourage Canadians to be more active but the McMaster researchers say little work has been done to prevent the decline in physical activity and they suggest this issue should be made a priority.

For the study, physical activity was measured by estimating the amount of total energy used during leisure activities over a three-month period during the transition from adolescence into early adulthood, including the move to college or university.

The researchers found the rate of decline in physical activity was greater for men than for women, who showed only a modest 1.7 per cent decrease in their overall activity levels; however, the women were less active in high school.

"It may be that girls experience the greatest declines in physical activity earlier in their adolescence," said Kwan.

For comparative purposes, the researchers also examined other health-risk behaviours of smoking and binge drinking（酗酒，豪饮） . While both increased through adolescence, the researchers found the behaviours began to plateau（达到平衡） or decrease in early adulthood; suggesting that individuals may be maturing out of these health-risk behaviours.

Conversely, Kwan added, physical activity decline does not appear to revert itself, but continues on a downward trajectory（轨道） into adulthood.