Neck muscle biomechanics and neural control

Area of Science:

• Biomechanics
• Neuroscience
• Human Motor Control

Background:

• Human neural control relies on intrinsic biomechanical properties of joints, segments, and muscles.
• Understanding the relationship between muscle biomechanics and neural control is crucial for motor control research.

Purpose of the Study:

• To investigate if the biomechanical actions of individual neck muscles predict their neural control.
• To compare the moment direction and variability from electrical stimulation (biomechanics) with preferred activation direction and variability (neural control).

Main Methods:

• Subjects performed isometric neck moments at varying intensities (7.5% and 15% MVC).
• Electromyogram (EMG) data and 6-axis load cell measurements were used to determine preferred activation and moment directions.
• Electrical stimulation of sternocleidomastoid (SCM), splenius capitis (SPL), and semispinalis capitis (SSC) muscles quantified biomechanical moment direction.

Main Results:

• Preferred activation directions differed significantly from electrically stimulated directions for SCM (23°), SPL (39°), and SSC (21°).
• Intrasubject variability was lower for electrically stimulated moments compared to voluntary activations.
• Variability in neural control decreased with increasing activation levels.

Conclusions:

• Neural control of neck muscles is not solely based on optimizing individual muscle biomechanics.
• Biomechanical constraints partially dictate synergistic muscle activation as intensity increases.
• Computational models of neck muscles cannot solely rely on isolated muscle biomechanics for activation schemes.