Many older women do not take enough exercise
Females are less physically active at both ends of life than their male counterparts, two studies suggest.
Researchers studied activity levels in school children and the over 70s - and in both cases found males tended to be more active.
The studies are being presented at the UK Society for Behavioural Medicine annual conference.
Liverpool John Moores University found girls take part in 6% less vigorous playtime activity than boys.
The researchers, who focused on 10 and 11 year-old children in the school playground, found that boys and girls tend to play differently.
Girls tended to spend time in smaller groups and engage in verbal games, conversation and socialising.
Most boys, however, played in larger groups, which lend themselves more to physically active games, such as football.
Researcher Dr Nicky Ridgers said: "It is a concern that girls' activity levels are lower than boys and, although it is just one piece in a complex picture, this could be contributing to girls being overweight and obese.
"Schools should be aware of the differences between the way girls and boys behave in the playground and the fact that girls tend to favour small group activities.
"They could then consider the availability of equipment and provision of playtime activities that would encourage girls to take part in more vigorously active play."
The gender difference was mirrored in a second study, led by the University of Bristol, which looked at activity levels among the over-70s.
In general, levels of physical activity were very low among most people of both sexes aged over 70.
More than 70% of the people who took part in the study walked for fewer than 5,000 steps a day.
However, women were more likely to be less active than men.
Researcher Professor Ken Fox said: "Men accomplish more higher intensity physical activity than women and this seems to be explained by trips out of the house.
"However, there is evidence that they also sit down for longer periods in the day.
"Women do more lower intensity activity which probably represents daily tasks around the house.
"This would suggest that traditional family roles are still identifiable in this generation."
Professor Adrian Taylor, of the University of Exeter, which is organising the conference, said development of ways to promote greater physical activity across all age groups was vital.
He said: "Society and our environment are leading us to do increasingly less physical activity with adverse health consequences such as heart disease, diabetes and mental health problems for people of all ages."
Professor Alan Maryon-Davis, president of the UK Faculty of Public Health, said both findings had important public health implications.
He said: "Vigorous activity helps build strong bones and joints. I'm worried that girls who are less active at playtime could be more vulnerable to osteoporosis (brittle bone disease) in later life.
"All the more reason to ensure that girls have plenty of organised sports and active games.
"For people in their 70s the key needs are mobility and flexibility, so a mix of activities is important for men and women alike to keep up their suppleness, strength and stamina - all the more reason to take up dancing!"