Data Sheet

biosignalsplux
User Manual
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5.3 Scientific Background – Muscle Load
The scientific background for the Muscle Load add-on is based on B. Jonsson’s paper from
1982 “Measurement and Evaluation of Local Muscular Strain in the Shoulder During
Constrained Work”.
Please find below detailed information about this work and the Amplitude Probability
Distribution Function for deeper understanding of how the functionality of the Muscle
Load add-on.
5.3.1 Amplitude Probability Distribution
Proper electromyography signal processing can provide a reference for the analysis of the
relationship between work and required muscular load. Jonsson (1982) described a
technique in which the frequency of occurrence of a particular level of EMG is calculated,
generating a curve of the probability distribution function of amplitude (APDF). The APDF
is the distribution of the muscle contraction levels during a certain observation period.
The APDF concept was originally developed to extract information from EMG records of
muscular activity and has been used to analyze EMG in many Ergonomics studies.
5.3.2 Computation
The determination of APDF allows to obtain the profile of muscle tension that workers
are subject during a work period. The determination process involves the following
sequence:
• Calculation of the envelope of the EMG signal obtained by rectifying and
smoothing using a low pass filter.
• Determination of the histogram of the EMG signal amplitude for each muscle
during the execution of the task to be studied relative to the maximum voluntary
contraction (MVC) of the same muscle;
• Calculation of the cumulative histogram of EMG amplitude distribution and
mapping of the probability values regarding the distribution of the muscle for
MVC. This way, the amplitude of EMG, as well as the probability distribution is
related to the MVC, which allows comparing between several muscles or between
several tasks as well as the estimation of the average APDF function groups of
workers and/or tasks.