Cervical Muscle Responses to Multi-Directional Perturbations

Conference poster, 2014

Numerical human models are widely used in the design process and evaluation of passive and active vehicle safety systems in pre-crash and crash situations. Development and validation of human models that simulate neuromuscular control requires information on muscle activation patterns and contraction levels for different loading directions. Due to the lack of experimental data on cervical muscle recruitment strategies, the aim of this study was to provide activation patterns for superficial and deep cervical muscles during multidirectional perturbations. Eight volunteers received three perturbations (apeak=1.5g, ∆v=0.5m/s) in each of eight different directions while seated unrestrained on a sled-mounted car seat without a head restraint. Volunteers received no warning of perturbation onset. Electromyographic (EMG) activity was measured with wire electrodes inserted into the left sternocleidomastoid (SCM), trapezius (Trap), levator scapulae (LS), splenius capitis (SPL), semispinalis capitis (SCap), semispinalis cervicis (SCerv), and multifidus (Multi) muscles, and with surface electrodes over the sternohyoid (STH) muscle. All EMG signals were normalized with maximum voluntary isometric contraction activity. All median muscle activities were below 5%MVC before perturbation onset. During perturbation, most muscles showed distinctive activation patterns consistent with their anatomical location and function. Anterior muscles (SCM, STH) activated to counteract head extension and posterior muscles, except SPL, activated to counteract flexion (Figure). Although with different levels of contraction, SCap, SCerv, and Multi activated synergistically with the highest activity (89%, 50%, and 36%MVC respectively, 110ms after perturbation onset) during rearward and ipsilateral rearward oblique perturbations. Activation levels were generally five times lower in other directions. Despite its posterior location, SPL had activities between 19%MVC and 27%MVC during forward, forward oblique and lateral perturbations, but <15%MVC during rearward and rearward oblique perturbations. SCM had approximately 60%MVC activation during forward and ipsilateral forward oblique perturbations and <4%MVC for the opposite directions. LS and Trap activities remained below 8%MVC and 17%MVC, respectively. The different activation patterns indicate that applying uniform contraction levels to all posterior cervical muscles, a common assumption in numerical models, is an oversimplification. The provided activation patterns can be utilized to improve, tune or validate future numerical models with active musculature.