More than 1.4 billion adults are putting themselves at heightened risk of deadly diseases by not getting enough exercise, according to the World Health Organization.
It says a third of women and a quarter of men worldwide are in the firing line for killer conditions such as heart disease, diabetes and cancer unless they up their physical activity.
Researchers found there had been no improvement in physical activity levels since 2001, despite numerous public health initiatives extolling the benefits of exercise.
The WHO says a lack of regular physical activity increases the risk of poor health, including cardiovascular disease, several types of cancer and diabetes, as well as mental health conditions.
"Insufficient physical activity is a leading risk factor for non-communicable diseases, and has a negative effect on mental health and quality of life," said the study of world exercise levels published by The Lancet Global Health Journal.
The WHO recommends each adult do at least 150 minutes "moderate-intensity" exercise - such as brisk walking, swimming or gentle cycling - each week, or 75 minutes "vigorous-intensity" activity - such as running or team sports.
The study tracked activity levels of 1.9 million people in 168 countries across the world, including Ireland, during 2016.
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The study authors highlighted several worrying trends, including a stark divide in exercise rates between poor and rich nations, and between men and women.
Levels of insufficient activity to guard off non-communicable killers, including dementia and cardiovascular diseases, are more than twice as high in high-income countries compared to developing nations.
One of the study authors, Dr Regina Guthold, said the link between the lifestyle in wealthier nations - more time indoors, longer office hours, more easily accessible high-calorie foods - and lower exercise levels, was part of a "clear pattern" of poorer health coming with urbanisation.
"As countries urbanise, people who used to be, say, farmers, and got a lot of physical activity through their work all of a sudden live in an urban environment where they might be without work or move to a sedentary job, so societies need to compensate."
In four countries - Kuwait, American Samoa, Saudi Arabia and Iraq - more than half of adults were classified as insufficiently active.
In Kuwait, an oil-flush Gulf state where temperatures regularly top 45 degrees, two-thirds (67%) of adults were not exercising enough.
Melody Ding of the University of Sydney, who also worked on the paper, said there were a variety of reasons why some countries were more active than others, including "biological, psychosocial, institutional, cultural and environmental barriers".
"I consider one of the biggest barriers being our environment - physical activity has been engineered out of life, with desk-based jobs replacing labour jobs, lifts replacing stairs, cars replacing active travel.
"Technological advancement has made our life more convenient but also less active."
Women still lag behind men in nearly every region of the world, with the gender exercise gap highest in Bangladesh, Eritrea, India, Iraq and the Philippines, the study found.