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Volume 28, Issue 6, Pages 393-401 (July 2005)


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Cervical Muscle Response to Head Rotation in Whiplash-Type Right Lateral Impacts

Shrawan Kumar, PhD, DSc, FErgSaCorresponding Author Informationemail address, Robert Ferrari, MDb, Yogesh Narayan, BSc(EE), PEngc

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.

a Professor, Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4

b Clinical Associate Professor, Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4

c Research Engineer, Department of Physical Therapy, Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2G4

Corresponding Author InformationSubmit 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.

PII: S0161-4754(05)00175-2

doi:10.1016/j.jmpt.2005.06.014


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