Physical activity among adults in China fell sharply over the two decades ending in 2011, according to a study published on Wednesday in the International Journal of Behavioral Nutrition and Physical Activity.

While activity appears to have increased over the last five years, the study points to patterns that researchers say should be heeded if the country is to avoid major health trouble in the future.

"Lack of physical activity contributes to major noncommunicable diseases, such as coronary heart disease, stroke, hypertension, Type II diabetes, and certain forms of cancer," said Zang Jiajie, the lead author. "These trends are highly relevant for health policy and preventive health measures in China and other countries that are now facing similar challenges."

For 20 years, between 1991 and 2011, Chinese adults became more sedentary. The decline was more pronounced among women than among men, the study found. Each new generation had lower activity levels than the previous one.

The study was jointly conducted by researchers at the University of North Carolina at Chapel Hill in the United States and the Shanghai Municipal Center for Disease Control and Prevention. It was based on the China National Health and Nutrition Survey - research conducted periodically since 1989, with 2011 providing the most recent data.

Some encouraging news was delivered by two unrelated surveys in December. The China Institute of Sport Science found that sports participation has been on the rise in recent years as part of people's pursuit of a healthy modern lifestyle; and the General Administration of Sport of China, showed that overall fitness among Chinese people had improved slightly over the past five years.

But the study published on Wednesday pointed to trends that should help inform public policy decisions going forward, the study's authors said.

For example, physical activity among all women between 25 and 48 years of age was similar in 1991, but by 2011 had declined across all age groups - and more sharply than among men.

The difference might be explained by the changing role of women in society. For instance, they now spend less time in domestic pursuits as a result of smaller families and the helping hand of electric appliances in household chores, the study said.

Living in urban areas and owning a car, a TV or a computer were associated with lower levels of physical activity, as were higher education levels and being overweight, the authors said.

Professionals, such as doctors, lawyers and architects, had less physical activity than people in other occupations. Owning a bicycle, being married or having a larger household were associated with more exercise.

The survey looked at more than 13,000 adults who were between 20 and 59 years of age in 1991.