Neck Muscle and Head/Neck Kinematic Responses While Bracing Against the Steering Wheel During Front and Rear Impacts

Area of Science:

• Biomechanics
• Human Factors Engineering
• Automotive Safety

Background:

• Drivers often brace against the steering wheel in anticipation of a collision.
• The physiological effects of this bracing behavior on neck musculature and kinematics during impacts are not fully understood.

Purpose of the Study:

• To quantify the impact of pre-collision steering wheel bracing on neck muscle activity and head/torso kinematics.
• To compare muscle and kinematic responses in relaxed versus braced conditions during simulated low-speed front and rear impacts.

Main Methods:

• Eleven subjects underwent sled-induced impacts simulating low-speed front and rear collisions.
• Neck muscle electromyographic (EMG) activity and head/torso kinematics were recorded in both relaxed and braced conditions.
• Data were analyzed using linear mixed models to compare responses between conditions.

Main Results:

• Pre-impact bracing showed minimal increase (<5% maximum voluntary contraction) in baseline neck muscle activity.
• Bracing did not elevate peak neck muscle responses during impacts; it reduced peak activity in the trapezius and multifidus muscles during front impacts.
• Significant alterations in torso and head kinematics were observed, suggesting torso-seat coupling rather than head-neck-torso stiffening.

Conclusions:

• Pre-impact bracing does not enhance neck muscle resistance during low-speed impacts.
• Bracing behavior modifies torso kinematics by increasing coupling to the seat, without necessarily rigidifying the head-neck system.
• Findings suggest bracing may alter injury biomechanics in ways not predicted by simple stiffening models.