BACKGROUND:Patellofemoral OA is characterized by PF pain during activities that load a flexed knee. Stair stepping ability is frequently impaired, yet little is known of the muscular recruitment strategies utilized during this task. Altered recruitment strategies may provide targets for clinical interventions. We aimed to determine if people with PFOA ascend and descend stairs with different muscular recruitment strategies compared to similar aged healthy individuals. METHODS:Twenty-two people with PFOA and 20 controls were recruited. Electromyographic recordings from gluteus maximus and medius, medial and lateral hamstrings, vastus medialis and lateralis, medial and lateral gastrocnemius and soleus were acquired during stair ascent and descent. Force plate data was acquired to determine timing of foot placements and characterize dynamic stability. RESULTS:Seventeen people with PFOA (59 ± 10 years, 73 ± 13 kg, 167 ± 9 cm) and 15 controls (57 ± 10 years, 73 ± 16 kg, 171 ± 11 cm) had complete data. People with PFOA demonstrated: longer vastii activation duration during descent (lateralis: p = 0.01; medialis: p = 0.02); earlier onset of vastus lateralis for ascent (p < 0.01) and descent (p = 0.04); earlier onset of soleus in descent (p = 0.04); and shorter duration of GMax during ascent (p = 0.05). Peak Fz timing (time between the start of the anticipatory postural adjustment and the end of the stepping task) was ∼70ms later during stair descent in PFOA compared to controls (p = 0.01). SIGNIFICANCE:People with PFOA utilize muscular activation strategies consistent with minimizing knee pain during stair ambulation. Clinical interventions aimed at gluteal and quadriceps activation may be warranted in PFOA.