Minimum EMG burst duration in healthy controls : implications for electrodiagnosis in movement disorders

Background EMG burst duration can provide additional diagnostic information when investigating hyperkinetic movement disorders, particularly when a functional movement disorder is suspected. It is generally accepted that EMG bursts <50ms are pathological. Objective To re‐assess minimum physiological EMG burst duration. Methods Surface EMG was recorded from face, trunk and limb muscles in controls (n=60; age 19‐85). Subjects were instructed to generate the briefest possible ballistic movements involving each muscle (40 repetitions) or, in muscles spanning joints, to generate rapid rhythmic alternating movements (20‐30s), or both. Results We found no effect of age on EMG burst duration. However, EMG burst duration varied significantly between body regions. Rhythmic EMG bursts were shorter than ballistic bursts but only significantly so for lower limbs (p<0.001). EMG bursts of duration <50ms were frequently observed, particularly in appendicular muscles. Conclusion We present normal reference data for minimum EMG burst duration, which may assist clinical interpretation when investigating hyperkinetic movement disorders