Abstract
Objective: To determine the effect of occupant positioning on the response of the cervical muscles to whiplashβtype posterolateral impacts.
Methods: Twenty healthy volunteers underwent left posterolateral whiplashβtype impacts with the volunteers seated βoutβof positionβ. Electromyograms of the cervical muscles were recorded.
Results: Whether having the trunk flexed to the left or right at the time of impact, the muscle responses were low in magnitude, showing a trend to increasing EMG responses with increasing acceleration (P > 0.05). The time to onset and time to peak electromyogram for most muscles showed a trend to progressively decrease with increasing levels of acceleration. With the subject flexed to the left, all muscles generated 31% or less of the maximal voluntary contraction electromyogram. With the subject flexed to the right, all muscles generated 27% or less of their maximal electromyogram. In both positions, the trapezii were the most active (P < 0.05). Thus, having the trunk flexed out of neutral posture at the time of impact produces a very low magnitude cervical muscle response compared to impacts with the trunk in neutral posture.
Conclusions: In the absence of bodily impact, the flexed trunk posture appears to produce a biomechanical response that would probably decrease the likelihood of cervical muscle injury in low velocity posterolateral impacts. Β© 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.