Variability in commercial electromyographic biofeedback devices

The purpose of this study was to evaluate the functional characteristics of a sample of commercial electromyographic feedback devices for the purpose of determining variability between instruments. Seventeen physical and functional characteristics (such as input impedance, filter bandwidth, and sensitivity) were evaluated on a sample of 11 instruments. Wide variability was found in several important functional characteristics. Input impedance, for example, was found to vary from 13K to more than 1 megohm and filter bandwidths ranged from 55 Hz to 2,600 Hz. Such variability makes the comparison of data from studies using different instruments quite difficult; it also suggests the need to develop equipment standards and common calibration procedures.