New research suggests that a lack of exercise is killing as many people globally as smoking or obesity.
The study, published in The Lancet medical journal, says urgent action is needed to tackle what it calls "the pandemic of inactivity".
The study estimates that about a third of adults are not doing enough physical activity.
The lack of activity is causing nearly a tenth of premature deaths worldwide or 5.3 million deaths a year.
Researchers said tackling the problem required a new way of thinking.
It is suggested that the public needed to be warned about the dangers of inactivity rather than just reminded of the benefits of exercise.
The Lancet study found people in higher income countries were the least active.
The team of 33 researchers drawn from centres across the world also said governments needed to look at ways to make physical activity more convenient, affordable and safer.
It is recommended that adults do 150 minutes of moderate exercise, such as brisk walking, cycling or gardening, each week.