Sensitivity of trapezius electromyography to differences between work tasks - influence of gap definition and...

Area of Science:

• Occupational Health
• Biomechanics
• Ergonomics

Background:

• Surface electromyography (EMG) is vital for assessing muscular load in work-related musculoskeletal disorders, particularly for the trapezius muscle.
• Commonly used measures include EMG silence (gaps), muscular rest, and amplitude probability distribution functions (APDF).
• The impact of calculation criteria on these measures' sensitivity to differentiate workloads remains unclear.

Purpose of the Study:

• To investigate how different criteria for calculating EMG-derived measures affect their sensitivity in differentiating between various work tasks.
• To determine optimal parameters for gap duration, threshold levels, and normalization methods for trapezius EMG analysis.

Main Methods:

• Bilateral trapezius EMG data were collected over a full workday from 58 subjects.
• Maximal Voluntary Effort (MVE) and submaximal Reference Voluntary Effort (RVE) contractions were used for normalization.
• Gap frequency, muscular rest, and APDF percentiles were calculated using varied criteria for eight fundamental work tasks.

Main Results:

• Optimized sensitivity to task differences was achieved with a gap duration < 0.5s and threshold levels of ~0.3% MVE for gap frequency, and ~0.5% MVE for muscular rest.
• Normalizing to RVE improved task differentiation sensitivity and reduced variability compared to MVE.
• Muscular rest demonstrated greater sensitivity to task variations than APDF percentiles.

Conclusions:

• Specific, optimized criteria for gap duration and threshold levels are crucial for enhancing the sensitivity of EMG measures in distinguishing work tasks.
• RVE normalization is recommended over MVE for improved task differentiation and reduced inter-individual variability in trapezius EMG analysis.
• Muscular rest is a more sensitive indicator of task differences than APDF percentiles in this context.