Women with knee osteoarthritis increase knee muscle co-contraction to perform stand to sit

Background There is lack of sufficient research evidence when we examine how knee osteoarthritis (OA) affects performance of stand to sit, a very important task for daily function. Aim The aim of this study was to investigate if women with unilateral knee OA perform the stand to sit task in the same way as healthy adults of the same age. Methods Fifteen women with knee OA (age 64.05 +/- 4.23 years, height 161.52 +/- 5.03 cm, and mass 75.23 +/- 8.51 kg) and fifteen healthy subjects of the same age (age 62.13 +/- 4.15 years, height 160.73 +/- 5.10 cm, and mass 75.20 +/- 9.87 kg) volunteered to participate. The experimental task required sitting to a chair starting from a bipedal standing position. Electromyographic activity of the vastus lateralis and biceps femoris was examined for both legs. In addition, joint kinematics of the lower limb and vertical ground reaction forces were recorded bilaterally. Results Movement duration was not different between the groups. Women with knee OA showed significantly lower vastus lateralis activation and higher knee muscle co-contraction of the affected leg compared to the same leg of the control group. In addition, they had smaller knee range of motion for both legs compared to the control group participants. Conclusion Knee muscle co-contraction is employed by women with knee OA to perform the stand to sit movement at the same duration as their healthy counterparts. This compensatory mechanism may be important for the task execution, but at the same time, it can be harmful for the joint.