Associations of quadriceps activation during step-up with pain during movement and physical function in people with...

Movement-evoked pain, and excessive muscle activation and co-activation during daily activities such as stair climbing are characteristic of knee osteoarthritis. Our objective was to examine the association between muscle activation and coactivation during step-up with pain during step-up and self-reported physical function in people with knee osteoarthritis.

We used data from participants with symptomatic knee OA (n = 43) who performed five 30-s step-up bouts. Maximum pain during step-up (range 0-10) was recorded as movement-evoked pain. We assessed mean vastus medialis and medial hamstrings activation during the ascent phase of step-up, normalized to activation during a maximum voluntary isometric contraction, using surface electromyography (EMG). We also derived muscle coactivation over the same period. Physical function was assessed using the McMaster Universities Osteoarthritis Index (WOMAC) Physical Function scale. We used hierarchical regression models to examine the additional contributions of EMG measures to movement-evoked pain and WOMAC scores in addition to age, sex, BMI, and quadriceps peak torque.

Greater vastus medialis activation during step-up was associated with lower movement-evoked pain (β = -0.47, p < 0.01, model R² = 0.28), explaining 18 % additional variance beyond age, sex, BMI, and isometric quadriceps torque. Similarly, greater vastus medialis activation was related to better WOMAC physical function (β = -0.35, p = 0.04, model R² = 0.36), explaining 8 % additional variance beyond age, sex, BMI, isometric quadriceps torque, and movement-evoked pain.

Greater vastus medialis activation may be a compensatory strategy to reduce pain during step-up and improve function in knee osteoarthritis.