Trapezius muscle EMG as predictor of mental stress

Stress is a growing problem in society and can cause musculoskeletal complaints. It would be useful to measure stress for prevention of stress-related health problems. An experiment is described in which EMG signals of the upper trapezius muscle were measured with a wireless system during three different stressful conditions: a calculation task (the Norinder test), a logical puzzle task and a memory task. The latter two tests were newly designed and aimed at creating circumstances that are similar to work stress. Amplitudes of the EMG signals were significantly higher during stress compared to rest (+2.6% of reference contraction level) and relative time with EMG gaps was lower during stress (−14.3% of time). Also, mean and median frequencies were significantly lower during stress than during rest (−8.6 and −8.8 Hz, respectively). EMG amplitude increased not only from rest to stress conditions, but also during stressful conditions and decreased during relaxation periods. EMG features correlated with subjectively indicated stress levels (correlations of 0.32 with RMS and −0.32 with relative gaptime). The results indicate that EMG is a useful parameter to detect stress. Together with other physiological sensors, EMG sensors can be included in a wireless system for ambulatory monitoring of stress levels.