HEALTH:SWINGING A golf club, considered a low-impact activity, places as much stress on artificial knee joints as does jogging or tennis, according to findings from the first study to measure forces inside the knees of humans.

By contrast, exercising on a stationary bicycle generated relatively little force on the knee, even lower than walking on a treadmill. This information could help doctors decide which recreational activities are suitable for knee replacement patients.

So why is golf so stressful on the knees, particularly the leading knee - the left knee of a right-handed golfer?

"We believe this to be due to inertial forces transferred from the upper body and the twisting that takes place at the knee during the swing," according to study chief Dr Darryl D D'Lima, director of an orthopedic research laboratory at the Scripps Clinic in La Jolla, California.

The findings, presented last week at the annual meeting of the American Academy of Orthopedic Surgeons in San Francisco, are based on a study of four patients who had total knee arthroplasty using artificial joints capable of measuring knee forces.

Jogging, tennis and golf produced the greatest force on the knees.

Walking on level ground produced less force than these activities and walking on a treadmill generated even lower force.

Cycling produced the lowest force.

"Biking has been recommended as a safer exercise than jogging for patients with knee pathology (disease) or prosthetic replacements.

"Our data supports this recommendation," D'Lima said.

Knee replacement patients should not necessarily stop playing golf, tennis or jogging, D'Lima advised, but they should consider modifying the activities so they cause less strain on the knees.

As for future research, he said his team is "collecting tremendous amounts of (knee force) data over several activities and conditions, such as skiing, rehabilitation, exercise, and recreational equipment.

"We are also investigating the effect of orthotics and braces on knee joint forces."