The test-retest reliability of the onset of core and vasti electromyographic activity while ascending and descending stairs in healthy controls and patellofemoral pain patients

Background: Patellofemoral pain (PFP) is a common affliction and complex clinical entity. It is hypothesized to result from abnormal patellar tracking caused by altered motor control. Deficit in neuromotor control of the core may be a remote contributing factor to the development of PFP. Application of reliable EMG measures would be helpful to handle this theory. Therefore, the purpose of this study was to determine the test-retest reliability of the core and vasti EMG onsets, while ascending/descending stairs. Methods: Ten males with PFP and ten healthy controls participated in this study. Vasti and Core EMG onsets during stair stepping were assessed two times a day. Intraclass correlation coefficients (ICCs) and standard errors of measurement (SEMs) were calculated. Results: During both ascending/descending, high reliability was found for all EMG onsets of control cases (ICC 3,1 ≥ 0.70) except Quadratus Lumborum (QL) which showed a moderate reliability (ICC for ascending=0.59 and for descending = 0.61). In controls, Vasti in both tasks showed the highest absolute reliability. During ascending, high reliability (ICC ≥ 0.70) in PFP group was demonstrated for all EMG onsets except Gluteus maximus (GMAX) and QL which showed a moderate reliability (ICC = 0.69 and 0.63 respectively). In this group while descending stairs, all EMG onsets showed high relative reliability (ICC ≥ 0.70). Moderate to high absolute reliability was obtained for onset times while ascending/descending stairs in PFP group. Conclusion: Most EMG onsets during stair ascending/descending had moderate to high reliability.