Investigators will collect the EMG activity of VMO, VL, GM, multifidus, and TrA using bipolar Ag-AgCl disposable surface electrodes (Better signal solution medical supply Co., limited, Zhongshan, China) and eight channels highresolution wireless bio amplifier (WBA) system (Biomation, Almonte, Canada). Electromyographic data will be sampled at 1000 Hz and bandpass filtered at 50-200 Hz. For each muscle, three electrodes will be used; two electrodes will be placed ~30 mm apart in the direction of the muscle fibers and a ground electrode will be placed over the closest bony prominence. Before placement of the electrodes, the subject's skin will be cleaned with alcohol to reduce impedance and excess hair will be removed to eliminate shifting of the electrodes if needed. The stair-stepping task consists of descending 2 steps. Patients should start descending the steps immediately in response to a command, at their normal speed with their affected limb. Healthy subjects should start descending stairs with their dominant limb . Before data acquisition, participants should perform one practice trial of stair descent to get familiarized with the task. Then the participants should perform three test trials with thirty seconds of rest after each trial to prevent fatigue. The raw data will be stored on a personal computer for analysis with a custom program in Matlab (Math Works, Natick, Massachusetts, USA). Investigators should use a mean of data in three trials for analysis.
Objective: to investigate whether females with PF OA descend stairs with different muscular recruitment strategies contrasted with similar aged healthy females.~Methods: An observational comparative study will be conducted with thirty females with PF OA and 10 healthy ones. The onset times and electromyography (EMG) duration of multifidus, transversus abdominus (TrA), gluteus medius (GM), and vasti muscles will be measured by quantitative EMG during stair descent task. hypothesis: Investigators hypothesize that there won't be a significant difference between females with PF OA and their matched healthy group regarding the onset times and duration of vastus medialis obliqus (VMO), vastus lateralis (VL), gluteus medius (GM), multifidus, and transversus abdominus (TrA), during stair descent task.