Abstract
The primary objective of the study was to explore the nonlinear characteristics of surface myoelectrical activity of the biceps muscle during four static postures observed on the assembly line. The results showed significant differences in the largest Lyapunov exponents between four postures. The surface EMG of the biceps brachii was more chaotic under the maximum loading in MVC posture with elbow fully extended (180 degrees) and static posture with 180 degrees shoulder flexion compared to two other static postures. Based on the Kaplan-Yorke dimension, it was found that dimensional complexity was higher for MVC posture than for posture with 135 degrees shoulder flexion, posture with 180 degrees shoulder flexion, and posture with 90 degrees shoulder flexion and abduction. Interaction effects of posture and trial with respect to the largest Lyapunov exponents and Kaplan-Yorke dimension characteristics of the EMG signals showed higher levels of chaos and complexity patterns in MVC postures compared to other static postures.
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