The superficial hip adductor muscles are situated in close proximity to each other. Therefore, relative movement between the overlying skin and the muscle belly could lead to a shift in the position of surface electromyography (EMG) electrodes and contamination of EMG signals with activity from neighboring muscles. The aim of this study was to explore whether hip movements or isometric contraction could lead to relative movement between the overlying skin and 3 adductor muscles: adductor magnus, adductor longus, and adductor gracilis. The authors also sought to investigate isometric torque–EMG relationships for the 3 adductor muscles. Ultrasound measurement showed that EMG electrodes maintained a position which was at least 5 mm within the muscle boundary across a range of hip flexion–extension angles and across different contraction levels. The authors also observed a linear relationship between torque and EMG amplitude. This is the first study to use ultrasound to track the relative motion between skin and muscle and provides new insight into electrode positioning. The findings provide confidence that ultrasound-based positioning of EMG electrodes can be used to derive meaningful information on output from the adductor muscles and constitute a step toward recognized guidelines for surface EMG measurement of the adductors.
Walaa M. Elsais, Stephen J. Preece, Richard K. Jones, and Lee Herrington
Susana Meireles, Neil D. Reeves, Richard K. Jones, Colin R. Smith, Darryl G. Thelen, and Ilse Jonkers
Medial knee loading during stair negotiation in individuals with medial knee osteoarthritis has only been reported in terms of joint moments, which may underestimate the knee loading. This study assessed knee contact forces (KCF) and contact pressures during different stair negotiation strategies. Motion analysis was performed in 5 individuals with medial knee osteoarthritis (52.8 [11.0] y) and 8 healthy subjects (51.0 [13.4] y) while ascending and descending a staircase. KCF and contact pressures were calculated using a multibody knee model while performing step-over-step at controlled and self-selected speed, and step-by-step strategies. At controlled speed, individuals with osteoarthritis showed decreased peak KCF during stair ascent but not during stair descent. Osteoarthritis patients showed higher trunk rotations in frontal and sagittal planes than controls. At lower self-selected speed, patients also presented reduced medial KCF during stair descent. While performing step-by-step, medial contact pressures decreased in osteoarthritis patients during stair descent. Osteoarthritis patients reduced their speed and increased trunk flexion and lean angles to reduce KCF during stair ascent. These trunk changes were less safe during stair descent where a reduced speed was more effective. Individuals should be recommended to use step-over-step during stair ascent and step-by-step during stair descent to reduce medial KCF.