Stopping Exercise May Not Be Best for Painful Knees

Two studies reported at the Osteoarthritis Society International (OARSI) conference in Paris challenge standard concepts about exercise and knee osteoarthritis (OA): that painful knees should be rested rather than exercised, and that strengthening the quadriceps muscle will reduce loading on the knee joint.

If a knee OA exercise program is too painful to continue, one study found, a milder program will lead to decreased pain.

This study from Copenhagen is a further analysis of the exercise arm of a controlled study of OA interventions. Thirty-one patients with knee OA were assigned to an exercise arm, but five of them had so much pain (5 on a scale of 0 to 10) that they were instead given a rescue program, which excluded weight-bearing activities.

The standard exercise program consisted of core strength and control, hip stability, hip abductor strength, knee stability, quadriceps strengthening, and applying the basic exercises into functional tasks. The rescue program consisted of 15 minutes warm-up on an ergometer bike followed by core stability, hip stability, and hip strengthening only.

After three-quarters of the rescue sessions, the participants experienced a decrease in pain.

Quadriceps-strengthening exercise did not change quadriceps force or knee loadings during level walking in adults with knee OA. It did lower pain, improve strength, and improve function -- so there must be another mechanism.

In a two-center randomized controlled trial of quadriceps exercises, 30 adults with tibio-femoral OA were randomly allocated to 12 weeks of quadriceps strengthening or to a control group. Quadriceps strengthening consisted of leg extensions, leg press, and lunge exercises. The primary outcome was change from baseline in peak quadriceps force during walking.

The training group exhibited a significantly higher increase in isometric quadriceps strength, as well as lower pain scores and lower total WOMAC. However, quadriceps-strengthening exercise did not change quadriceps force or knee loading during level walking.

This study suggests that pain relief and improvements in function are not followed by changes in knee joint biomechanics such as quadriceps force and knee joint loadings. Moreover, increased muscle strength does not lead to lower knee joint compressive forces during walking.