Reliability of electromyographic methods used for assessing hip and knee neuromuscular activity in females diagnosed with patellofemoral pain syndrome.

Patellofemoral pain syndrome (PFPS) is one of the most common, yet misunderstood, knee pathologies. PFPS is thought to result from abnormal patella tracking caused from altered neuromuscular control. Researchers have investigated neuromuscular influences from the gluteus medius (GM), vastus medialis (VM), and vastus lateralis (VL) but with inconsistent findings. A reason for these discrepancies may be from varying methodology. The purpose of this study was to determine the reliability of electromyographic (EMG) methods used to assess amplitudes and timing differences of the GM, VM, and VL in subjects with PFPS. Seven females with PFPS participated. GM, VM, and VL activity was assessed during the stance phase of a stair descent task on two separate occasions. Amplitudes during the different intervals of stance were recorded and expressed as a percent of each muscle's maximum voluntary isometric contraction. Muscle onsets at the beginning of stair descent were also determined. VM-GM, VL-GM, and VL-VM onset timing differences were quantified. Intraclass correlation coefficients (ICCs) and standard errors of measurement (SEMs) were calculated to assess between-day reliability. Most EMG measures had acceptable reliability (ICC(3,5)>or=0.70). Although some measures had moderate reliability (ICC<0.70), they had low SEMs, which suggested high measurement precision. These findings support using these methods for examining neuromuscular activity in subjects with PFPS.