Data Sheet

biosignalsplux
User Manual
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period. In cases where the highest value for muscle activity estimation might exceed 50%
of the MVC, the normalization of EMG signals must be performed with a direct assessment
of 100% from the MVC. Otherwise, one might establish an underestimate of APDF.
The average level of contraction associated with a probability of P=0.5 indicates the
average value of the contraction developed during the work period. Usually, this average
level tends to the average contraction value when obtained from the EMG integration or
electromyographic signal’s RMS detection.
EMG amplitude distribution probability curve will feature how muscle behaves during
study period. Each type of work presents a characteristic profile concerning the amplitude
distribution probability curve.
When electromyographic records are used to obtain muscle activity levels’ evaluation,
criteria must be taken into account in order to define which obtained values for muscle
tension levels are acceptable and non-acceptable according to the performed
occupational tasks.
According to muscle fatigue studies, when performing static and dynamic tasks, a set of
limit values were suggested for the work performed over periods longer than one hour
(Jonsson, 1982):
• Static contraction level must not exceed 2% of the MVC and cannot overcome 5%
of the MVC;
• The average level must not exceed 10% of the MVC and cannot overcome 14% of
the MVC;
• Load’s highest values must not exceed 50% of the MVC and cannot overcome
70% of the MVC.
These limit values can be used as analysis criteria of the amplitude distribution
probability curves for the relative strength in occupational tasks. One must consider the
amplitude distribution probability level for an entire work day, and the limit should not
be exceeded for over an hour in continuous work. If limit is exceeded, it must be
exceptionally and for a 10 minutes maximum period.
These criteria can only be used for electromyographic records’ analysis of a group of
workers. The individual test results within workers can exceed these limits for several
reasons, such as unfavorable operational modes selection, although workers group’s
overall workload is not excessive.