Unstable sitting postures affect head and neck muscle activity during mastication.

Area of Science:

• Biomechanics
• Human Physiology
• Ergonomics

Background:

• Mastication involves complex muscle coordination.
• Sitting posture can influence motor control and muscle activity.
• The interplay between postural stability and masticatory function requires further investigation.

Purpose of the Study:

• To determine if masticatory muscle activity (masseter, suprahyoid, trapezius) varies with different sitting postures.
• To investigate the impact of sole-ground contact and postural instability on muscle activation during chewing.

Main Methods:

• Electromyography (EMG) was used to measure muscle activity in the masseter, suprahyoid, and trapezius muscles.
• Participants (n=13 healthy young adults) chewed gummy candies under three conditions: stable sitting with sole-ground contact, sitting without sole-ground contact, and sitting on an unstable balance board.
• Mastication time, chewing cycles, and muscle activity integrals were analyzed.

Main Results:

• Significantly higher integrated electromyography (iEMG) values were observed for the masseter and suprahyoid muscles in the no sole-ground contact and balance-board conditions compared to the sole-ground contact condition.
• The right trapezius muscle also showed significantly greater iEMG values in the unstable sitting conditions (no sole-ground contact, balance board) versus the stable condition.
• No significant differences were found in mastication time or chewing cycle count across conditions.

Conclusions:

• Unstable sitting postures, characterized by lack of sole-ground contact or use of a balance board, lead to increased activity in masseter and suprahyoid muscles during mastication.
• The enhanced activity of the right trapezius muscle in unstable postures suggests a compensatory mechanism for maintaining postural stability.
• These findings underscore the importance of a stable sitting posture for efficient mastication and highlight the interconnectedness of postural and masticatory muscle functions.