(Medical Xpress)—How children spend their after-school hours has a big impact on their levels of physical activity, new research has discovered, highlighting the need for children to be given more opportunities to play outdoors with friends.

Researchers at the University of Bristol have shown that hours spent outdoors with friends have the greatest positive affect on a child's level of . However, researchers found children spend most of their after-school time indoors, either alone or with parents.

For every hour spent outdoors with friends, the study found children doing an extra 17 minutes of physical activity. The government recommends children are physically active for at least one hour a day.

Dr Angela Page, from Bristol University's Centre for Exercise, Nutrition and Health Sciences, said: "We found that children spend most of their after-school time indoors and little time outdoors playing with other children, which makes the biggest contribution to the amount of physical activity they get.

"Building stronger neighbourhood community links between parents and children could restore the social norm of children playing outdoors and relieve some concerns parents may have about safety."

The research was part of the Personal and Environmental Associations with Children's Health (PEACH) project and published in the International Journal of Behavioral Nutrition and Physical Activity. It studied a sample of 427 children aged 10 to 11 from the Bristol area. The intensity of their physical activity was measured with accelerometers while GPS determined whether they were indoors or outdoors. The children used diaries to recorded who they spent their time with.

For both boys and girls, being outdoors showed a stronger link with physical activity than being indoors. Time spent indoors with friends was also positively linked with physical activity but not as strongly as when outdoors (six minutes of physical activity per hour spent with friends inside).

The study was funded by the the National Prevention Research Initiative and World Cancer Research Fund.

Dr Rachel Thompson, Head of Research Interpretation at World Cancer Research Fund, added: "There is evidence that physical activity protects against cancer, particularly bowel cancer, one of the most common forms of the disease in the UK. Getting into healthy habits during childhood is a big advantage when it comes to reducing the risk of getting cancer in later life as active children are more likely to become active adults.

"Being active is also beneficial in other areas of physical and mental well-being. This research demonstrates how are most active when they're playing outside with , so we should be looking at ways we can encourage this in a safe environment."

Today marks the start of Cancer Prevention Week, during which World Cancer Research Fund has launched the Move More Challenge to encourage families to take part in physical activities and games in an informal setting.

More information: "Who children spend time with after school: associations with objectively recorded indoor and outdoor physical activity." Matthew Pearce, et al. International Journal of Behavioral Nutrition and Physical Activity 2014, 11:45  DOI: 10.1186/1479-5868-11-45

Journal information: International Journal of Behavioral Nutrition and Physical Activity