A Critical Review and Proposed Improvement in the Assessment of Muscle Interactions Using Surface EMG

Abstract

The purpose of this chapter is to propose a mathematical relationship between EMG excitation recorded from muscles in opposition to, or in coordination with each other. The concept of correlating co-activation between muscles with EMG parameters is not new. Cowan et al. (1998) investigated the use of the Pearson Product-Moment correlation coefficient to quantify muscle co-activation using electromyography. They concluded that this method shows promise for describing side differences in diplegics and for assessing the effects of physical therapy and other interventions. Careful reading of this work shows that only "select" intervals of the EMG data were compared. These intervals were selected on the basis of "burst activity" of one muscle. This selection is done by hand and for large quantities of data, typical of a gait laboratory, would be labor intensive. In our laboratory the authors have found the Pearson Product-Moment unable to distinguish between two noisy signals from inactive muscles and two that are fully active. Using insights from the literature review, presented below, this chapter will propose an alternative, continuous function for describing muscle interaction over any and all portions of a gait cycle.