The aim of the study was to investigate differences in frontal plane knee kinetics, onset timing and duration of the gluteus medius (GMed), adductor longus (AL), and vastus medialis oblique (VMO) during stair ambulation between those with and without patellofemoral pain syndrome (PFPS). Twenty PFPS patients and twenty healthy participants completed stair ambulation while surface electromyography (EMG), video, and ground reaction forces were collected. PFPS patients had a higher peak internal knee abduction moment during stair ascent, and a higher internal knee abduction impulse for both ascent and descent. During stair ascent, PFPS patients displayed earlier onset of the AL and later onset of GMed, compared to the healthy individuals. Also, PFPS patients had longer activation duration of the AL and shorter activation durations of the VMO and GMed during stair ascent. During stair descent, PFPS patients displayed delayed GMed onset and shorter activation duration of GMed and VMO. The results of the study suggest that altered neuromuscular control of the medial thigh musculature may be an important contributor to PFPS.
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