Methods and apparatus for surface electromyography (sEMG) index calculation and applications. The sEMG data points are quantified by accessing sEMG data points describing activity of a muscle. A single value is calculating from the sEMG data points. The single value is calculated using the sEMG data points as an input to a mathematical algorithm. The mathematical algorithm can include an integral. The mathematical algorithm can also include consideration of high points, low points, averages within the sEMG data points, first-order derivatives, second-order derivatives, and other direct or indirect data based at least in part upon sEMG data. The E-index calculated can be used in many applications and in combination with EKG and EEG.