Cervical Muscle Response to Head Rotation in Whiplash-Type Right Lateral Impacts
Received 22 June 2004
Objective
To determine the electromyogram (EMG) response of the cervical muscles to a right lateral impact whiplash-type perturbation when the head is rotated.
Methods
Twenty healthy volunteers were subjected to right lateral impacts of 4.2, 8.1, 10.3, and 12.5 m/s2 and were looking either left or right. Bilateral EMGs of the sternocleidomastoid, trapezius, and splenius capitis muscles were recorded. Triaxial accelerometers recorded the acceleration of the chair, torso at the shoulder level, and head of the participant.
Results
In a right lateral impact, muscle responses were of low magnitude with the head rotated to either the left or the right. At the highest acceleration of 12.5 m/s2, all generated less than 39% of their maximal voluntary contraction EMG. The sternocleidomastoid muscle showed a greater EMG response than its counterpart and the muscles contralateral to the direction of impact had higher EMG responses. The time to onset of the EMG for the splenii capitis and trapezii generally decreased with increasing levels of acceleration. As anticipated, an increase in applied acceleration resulted in an increase in accompanying head accelerations (P < .05), and when the head acceleration increased, so too did the force equivalent exertions by the various muscles.
Conclusions
Overall, a right lateral impact with head rotation to either right or left appears to reduce the activity and thus the risk of muscle injury, perhaps because of “bracing” by muscles actively producing rotation or because of greater spinal stability from other structures when the head is in the rotated position.
aProfessor, Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4
bClinical Associate Professor, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4
cResearch Engineer, Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4
Submit requests for reprints to: Shrawan Kumar, PhD, DSc, FErgS, Department of Physical Therapy, Faculty of Rehabilitation Medicine, 3-75 Corbett Hall, University of Alberta, Edmonton, Alberta, Canada T6G 2G4.
Sources of support: No external funding was received for this study.
ABSTRACT