Electromyography (EMG) is a technique for the evaluation and recording of electrical activity of skeletal muscles. Surface EMG (sEMG) can be detected by surface electrodes on the skin and represents the sum or mixture of the electrical contributions generated by the motor units of the muscles. Studies have been reported in which trapezius muscle sEMG is used to estimate stress levels. This article presents a review of different research papers on the relationship between stress and electrical activity of the trapezius muscle, under two approaches: multimodal and unimodal, considering muscular electrical activity as the only physiological indicator to estimate stress.