People aged between 45 and 55 years old who exercise heavily could be at risk from developing knee arthritis, according to new research from the University of California, San Francisco (UCSF), US.

The study - presented to the annual meeting of the Radiological Society of North America (RSNA) - found that excess physical activity in middle aged people can cause damage to the knee and increase the chances of osteoarthritis.

A total of 236 participants who had not previously reported knee injuries took part in the study, all within a "healthy" weight range. Responses to a Physical Activity Scale for the Elderly (PASE) questionnaire helped determine what is a high level of exercise.

A group of researchers, including Dr Christoph Stehling, research fellow at the UCSF's department of radiology and biomedical imaging, helped to conduct the new study.

Stehling said: "Our data suggest that people with higher physical activity levels may be at greater risk for developing knee abnormalities and, thus, at higher risk for developing osteoarthritis.

"This study and previous studies by our group suggest that high-impact, weight-bearing physical activity, such as running and jumping, may be worse for cartilage health.

"Conversely, low-impact activities, such as swimming and cycling, may protect diseased cartilage and prevent healthy cartilage from developing disease."