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Neuromechanics of neck muscles : implications for whiplash injury

University of British Columbia

Occupants involved in automobile collisions can adopt various postures preceding impact. Epidemiologic data have shown increased rates of whiplash associated disorders for drivers who have a rotated head posture or braced themselves before impact. In this dissertation we investigated how neck muscle activity and head/neck kinematics of volunteers are influenced by rotated non-neutral head postures and by bracing against the steering-wheel. We also provided important biomechanical and neuromuscular data to improve computational human body models of the neck (HBMs). In experiment one, 9 males performed neck maximum voluntary isometric contractions (MVIC) in 17 three-dimensional directions. We discovered how neck MVICs scale in directions not aligned with the principal axes and discuss how this scaling relationship can be used to validate an HBM’s off-axis strength, an important step before simulating rotated head postures. In experiment two, the biomechanical lines of action of three key neck muscles, as determined via electrical stimulation, were compared to their preferred activation directions, as determined via muscle activity during 15% MVICs in 26 3D directions (8M volunteers). We showed that neck muscles’ biomechanical lines of action are not an accurate predictor of their function, a finding which will help guide the development of realistic neck muscle controllers in HBMs. In experiment three, we quantified the non-neutral head postures that 20(14M, 6F) drivers adopted while driving on public roads. These data were then used in experiment four, where 12(5F, 7M) volunteers were exposed to low-speed rear impacts on a perturbation sled while in a neutral posture or four common non-neutral postures. In the final experiment, 11(3F, 8M) volunteers were exposed to low-speed frontal and rear impacts with their hands on the steering-wheel while either relaxed or braced by pushing with their arms. We found that non-neutral postures and bracing increased pre-impact muscle activity, but generally did not alter peak muscle activity during impact. Further, sagittal plane kinematic changes suggest a stiffer neck in both non-neutral postures and bracing, but non-neutral postures resulted in motions beyond the sagittal plane. The results of these experiments will help inform injury prevention methods, improve HBMs, and ultimately lead to safer automobiles.

Text

2019-05-01

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/70026

Kinesiology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/