Muscle activity, as a possible fundamental cause of functional limitation, has been extensively investigated in knee osteoarthritis (KOA). Many trials investigated muscle activity during dynamic movements and functional tasks in KOA. In addition, gender-related differences has been also investigated during functional movements in KOA. However, no trial investigated gender-related differences in muscle activation during static movement in KOA.

Muscle activity, as a possible fundamental cause of functional limitation, has been extensively investigated in knee osteoarthritis (KOA). Interestingly, studies concentrated mainly on investigation of muscle activity during dynamic movements and different functional tests. Moznuzzaman et al displayed greater muscle activation during sitting to standing test (STS) and standing to sitting test in KOA patients compared to healthy participants. Interestingly, some studies investigated muscle activation standing up from a knee-height seat during STS and illustrated a greater muscle activation amongst KOA patients compared to healthy controls. Moreover, Amer et al found greater muscle activation while performing STS from a lower height seat compared to a knee-height seat amongst women and men patients with uni/bilateral KOA. These findings might be of interest due to compensatory mechanisms observed by female patients during STS transition increases loading on the joint surfaces and consequently leading to progression of KOA. Furthermore, different studies also presented gender-differences of muscle activation during different weight-bearing tasks (gait, STS, stair ascend/descend, and squat) amongst patients with KOA and healthy control. Interestingly, both studies showed women with KOA representing higher muscle activation compared to men. Therefore, an analytical comparative study might be useful for identification of gender-differences in muscle activation amongst patients with KOA.

Investigation of static muscle activity during functional movements is very rare in KOA. Zhang et al investigated muscle activation after single whole body vibration trial in standing position at 0°, 30° and 60° static knee flexion angles amongst women with KOA. Authors found that muscle activation in 60° was greater compared to 30°, and it was also greater in 30° compared to 0°. Based on our literature search, no further study examined muscle activity in static knee flexion in KOA. However, investigating static knee flexion might be useful as it could be related to different knee moments in KOA.

Inclusion Criteria:

• radiologically diagnosed KOA based on the Kellgren-Lawrence grading system 1-3,
• age above 60 years
• at least 60° active knee flexion
• sufficient mental status

Exclusion Criteria:

• acute inflammation of the knee
• intraarticular injections within the last 3 months
• total knee replacement in the opposite side
• class II obesity (body mass index, BMI>35kg/m2)
• severe degenerative lumbar spine disease (e.g., spondylolisthesis)
• systemic inflammatory arthritic or neurological condition
• conservative intervention attendance within 6 months
• contraindication to conservative therapy and manual therapy
• unstable heart condition
• complex regional pain syndrome

Patients with radiologically diagnosed KOA