Upper extremity kinematics and muscle activation patterns in subjects with facioscapulohumeral dystrophy

OBJECTIVE: To compare the kinematics and muscle activity of facioscapulohumeral dystrophy (FSHD) subjects with healthy controls during the performance of standardized upper extremity tasks. . DESIGN: Exploratory case-control study. SETTING: The study was performed in the movement laboratory of the University of Maastricht, The Netherlands. PARTICIPANTS: 11 subjects with FSHD and 8 healthy controls were measured. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Kinematic data were recorded using a VICON MX system. Muscle activities, recorded using electromyography (EMG) were obtained from six superficial muscles around the glenohumeral joint. Shoulder elevation and elbow flexion angles, and maximum EMG activity during the movements, as a percentage of maximum voluntary contraction (%MVC), were calculated. RESULTS: Kinematic differences between the FSHD group and the healthy control group were found in the shoulder elevation angle during single shoulder movements and both reaching tasks. In general, FSHD subjects presented higher percentages of muscle activation. The median activity of the trapezius was close to the MVC activity during the single shoulder movements. Moreover, deltoid and pectoralis muscles were also highly active. CONCLUSIONS: Higher activation of the trapezius in FSHD subjects indicates a mechanism that could help relieve impaired shoulder muscles during arm elevation around 90 degrees . Compared to healthy subjects, persons with FSHD activated their shoulder muscles to a greater extent during movements that required arm elevation.