Loud preimpact tones reduce the cervical multifidus muscle response during rear-end collisions: a potential method for reducing whiplash injuries.

ABSTRACT

BACKGROUND CONTEXT Neck muscle responses after unexpected rear-end collisions consist of a stereotypical combination of postural and startle responses. Prior work using surface electromyography (EMG) has shown that the superficial neck muscle responses can be attenuated when a loud tone (105 dB) is presented 250 milliseconds before impact, but the accompanying response of the deeper multifidus muscles remains unknown. Quantifying this response in multifidus is important because this muscle attaches directly to the cervical facet capsule and can potentially increase the strain in the capsule during an impact and contribute to whiplash injury. PURPOSE: To investigate if a loud preimpact tone decreases the cervical multifidus muscle response during rear-end perturbations. STUDY DESIGN: After approval by the University Clinical Ethics Review Board, human volunteers experienced a series of three whiplash-like perturbations. PATIENT SAMPLE Twelve subjects with no history of neurologic disorders or whiplash injury were recruited to participate in this experiment. OUTCOME MEASURES: Bilateral indwelling EMG of multifidus at the C4 and C6 levels, surface EMG of sternocleidomastoid (SCM) and C4 paraspinals (PARAs), and kinematics of the head/neck were measured. METHODS: Subjects experienced three whiplash-like perturbations (peak acceleration of 19.5 m/s(2)) preceded by either no tone or a loud tone (105 dB) presented 250 milliseconds before sled acceleration onset. RESULTS: The loud tone decreased the muscle activity of C6 multifidus (42%) and C4 PARAs (30%), but did not affect the C4 multifidus or SCM activity. Peak head kinematic responses (extension angle 6%, retraction 9%, linear forward acceleration 9%, and angular acceleration in extension 13%) were also decreased by the loud preimpact tone. CONCLUSIONS: The attenuation of peak C6 multifidus activity and head kinematic responses suggests that a loud preimpact tone may reduce the strain in the cervical facet capsule, which may reduce the risk of whiplash injury during rear-end collisions.