Shrawan Kumar1, Robert Ferrari, Yogesh Narayan. 1. Department of Physical Therapy, Faculty of Rehabilitation Medicine, 3-75 Corbett Hall, University of Alberta, Edmonton, Alberta, Canada T6G 2G4. shrawan.kumar@ualberta.ca
Abstract
OBJECTIVE: To test the hypothesis that the head kinematic and the cervical muscle EMG responses to unexpected impacts of increasing low-velocity in the posterolateral direction will be greater than to expected impacts. DESIGN:Ten healthy volunteers were subjected to right posterolateral of 5.0, 8.6, 12.2, and 15.4 m/s2 acceleration in expected and unexpected conditions. BACKGROUND: The effect of a posterolateral impact on the cervical muscle responses is unknown. METHODS:Bilateral EMG of the sternocleidomastoids, trapezii, and splenii capitis were recorded and compared. The acceleration of the chair, torso, and head was recorded and compared. RESULTS: At an acceleration of 15.4 m/s2, the sternocleidomastoids generated the highest EMG in the unexpected impact conditions with lower percentages for the expected impact (50% of their maximal voluntary contraction). The splenii exhibited between 30% and 40% EMG, the trapezii generated approximately 25%. The EMG was significantly affected by the levels of acceleration (P < 0.01) for the sternocleidomastoids and splenii. The time to onset and peak EMG for all muscles progressively decreased with increasing levels of acceleration and regressed significantly on it (P < 0.01). Head accelerations were greater in the unexpected impacts (P < 0.5). CONCLUSIONS: The cervical muscles play a primary role in posture control. They may be a at risk of injury in whiplash especially in unexpected impacts. In the case of the right posterolateral impacts the sternocleidomastoids and splenii show a differentially higher response compared to the trapezii (P < 0.5). This may suggest an increased risk of injury to these muscles. RELEVANCE: The results presented contribute to an understanding of head and neck responses in posterolateral impacts. Copyright2004 Elsevier Ltd.
RCT Entities:
OBJECTIVE: To test the hypothesis that the head kinematic and the cervical muscle EMG responses to unexpected impacts of increasing low-velocity in the posterolateral direction will be greater than to expected impacts. DESIGN: Ten healthy volunteers were subjected to right posterolateral of 5.0, 8.6, 12.2, and 15.4 m/s2 acceleration in expected and unexpected conditions. BACKGROUND: The effect of a posterolateral impact on the cervical muscle responses is unknown. METHODS: Bilateral EMG of the sternocleidomastoids, trapezii, and splenii capitis were recorded and compared. The acceleration of the chair, torso, and head was recorded and compared. RESULTS: At an acceleration of 15.4 m/s2, the sternocleidomastoids generated the highest EMG in the unexpected impact conditions with lower percentages for the expected impact (50% of their maximal voluntary contraction). The splenii exhibited between 30% and 40% EMG, the trapezii generated approximately 25%. The EMG was significantly affected by the levels of acceleration (P < 0.01) for the sternocleidomastoids and splenii. The time to onset and peak EMG for all muscles progressively decreased with increasing levels of acceleration and regressed significantly on it (P < 0.01). Head accelerations were greater in the unexpected impacts (P < 0.5). CONCLUSIONS: The cervical muscles play a primary role in posture control. They may be a at risk of injury in whiplash especially in unexpected impacts. In the case of the right posterolateral impacts the sternocleidomastoids and splenii show a differentially higher response compared to the trapezii (P < 0.5). This may suggest an increased risk of injury to these muscles. RELEVANCE: The results presented contribute to an understanding of head and neck responses in posterolateral impacts. Copyright 2004 Elsevier Ltd.