Stability of the EMG Signal Level Within a Six-Day Measuring Cycle

This paper presents the results of research on the identification of changes in the electromyographic (EMG) signal recorded with the surface method (sEMG) over the course of six consecutive days. The signal was recorded for two people. The electrodes were fixed on the upper limb in two places of the forearm (over the brachioradialis and the bully of the superficial flexor (flexor digitorum superficialis). Muscles were activated by the hand clamp on the handle in the range of 25 \(\div \) 100 N. 21 measurement series were analysed, which consisted of 966 individual clamps. Estimates like root mean square, average value, energy and turn per second were used for the research. Due to the lack of a normal distribution of the estimators, non-parametric tests were performed in most cases. The tests carried out did not allow us to infer about the lack of changes in the signal over the period of six days under investigation. Moreover, by shortening the period of the tested series even to several successive series of measurements, it was also impossible to determine consistent conclusions for all the tested forces. Registered signals were characterized by very high variability between particular series. What’s more, the correlation studies between changes of individual forces per day also do not support the hypothesis that there is a constant, time-independent measurement of the relationship between the recorded EMG signal and the force.