People who are unfit and feeble stand to gain the most from physical exercise, research has shown.
Scientists looked at the benefits of physical activity such as increased life span and reduced heart disease risk in a group of almost 500,000 study participants.
High or low levels of activity made little difference to people at the top end of the fitness scale.
Exercise was much more likely to benefit individuals with low levels of fitness and grip strength, the study found.
Dr Jason Gill, from the Institute of Cardiovascular and Medical Sciences in Glasgow, said: "We wanted to determine whether somebody's level of fitness or grip strength influenced the effect of physical activity on risk of mortality and cardiovascular disease.
"Our data showed that the benefits of being physically active were far greater in those with low levels of fitness or grip strength. Those with high fitness or strength were at low risk whether or not they had a high level of physical activity."
The findings are published in the European Heart Journal.
Current UK guidelines suggest that all adults should engage in 150 minutes of moderate or 75 minutes of vigorous physical activity per week.
The researchers said a more targeted campaign directed at those who are unfit could be more effective.
