Neck and shoulder muscle activity during standardized work-related postural tasks

Area of Science:

• Biomechanics
• Human Physiology
• Ergonomics

Background:

• Understanding muscle activity in static postures is crucial for ergonomic assessments and preventing musculoskeletal disorders.
• The sternocleidomastoid and upper trapezius muscles are commonly involved in head and neck postures, making them key areas of interest.
• Previous research has explored muscle activity, but standardized data across sexes for specific static postures is limited.

Purpose of the Study:

• To quantify the electromyographic (EMG) activity levels of the sternocleidomastoid and upper trapezius muscles during standardized static postural tasks.
• To investigate potential sex-based differences in muscle activation patterns for these muscles.
• To establish normative EMG values for specific static postures to aid future research.

Main Methods:

• Electromyographic (EMG) activity was recorded from the sternocleidomastoid and upper trapezius muscles in 17 participants.
• Participants performed various static postural tasks under controlled conditions.
• EMG amplitude was normalized to % maximum voluntary contraction (%MVC) and categorized into light, moderate, and substantial activity levels.

Main Results:

• During most static tasks, both the sternocleidomastoid and upper trapezius muscles exhibited light to moderate EMG activity (<8%MVC).
• Substantial muscle activity (>8%MVC) was observed in both muscles during head leaning and shoulder shrugging postures.
• No statistically significant differences in muscle activity were found between male and female participants (p=0.078).

Conclusions:

• Static postures generally elicit low to moderate activity in the sternocleidomastoid and upper trapezius muscles, with exceptions for demanding tasks like head leaning and shoulder shrugging.
• The findings suggest that sex is not a significant factor influencing the muscle activity levels of the sternocleidomastoid and upper trapezius during these static postures.
• This study provides essential normative EMG data that can serve as a benchmark for future ergonomic and biomechanical research in occupational and daily living contexts.