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

Objective To compare the kinematics and muscle activity of subjects with facioscapulohumeral dystrophy (FSHD) and healthy control subjects during the performance of standardized upper extremity tasks. Design Exploratory case-control study. Setting A movement laboratory. Participants Subjects (N=19) with FSHD (n=11) and healthy control subjects (n=8) were measured. Interventions Not applicable. Main Outcome Measures Kinematic data were recorded using a 3-dimensional motion capturing system. Muscle activities, recorded using electromyography, were obtained from 6 superficial muscles around the glenohumeral joint. Shoulder elevation and elbow flexion angles, and maximum electromyographic 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, subjects with FSHD had 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 subjects with FSHD indicates a mechanism that could help relieve impaired shoulder muscles during arm elevation around shoulder height. Compared with healthy subjects, persons with FSHD activated their shoulder muscles to a greater extent during movements that required arm elevation.