Sexual marathons lasting all night are boring but 10 minutes is just about perfect for most people, researchers have concluded.

A survey of 50 members of the Washington-based Society for Sex Therapy and Research suggested the time range for adequate, too short and too long copulation.

They said that sex lasting between seven and 13 minutes was "desirable".

The researchers noted that popular culture had tended to reinforce unrealistic ideas about how long sex should last.