Characterization of the Multidirectional Strength of the Neck and of the Neuromuscular Coordination of the Superficial Neck Muscles
The goal of this dissertation is to enhance our knowledge of the three-dimensional impulsive strength capacity available at the upper cervical spine and its anticipatory neuromuscular control of the superficial neck muscles by characterizing relevant strength- and muscle activity outcome variables. A scoping review was conducted to critically appraise the level and quality of evidence relating neck strength and neck muscle resistance training to the incidence of concussion in contact sports. Our analysis did not support the position that peak isometric strength lowers the impact severity of hits to the head. We identified the need to investigate short-latency, impulsive strength capacity and feedforward muscle activity as a potential strategy to decrease risk of head injury. The first study characterized the effects of head posture on the multidirectional modulation of neck strength. Results demonstrated that the upper cervical spine has a significantly decreased strength capacity compared to the lower portion, due to smaller mechanical moment arm. Impulsive static strength capacity was also significantly decreased when exerting efforts along diagonal planes and positioned in 20˚ head flexion posture. The second study characterized the anticipatory neuromuscular activity of the superficial neck muscles during multidirectional, ballistic-intent static contractions. The central nervous system utilizes simplifying intermuscular coordination synergies during the anticipatory phase of a ballistic-intent muscle contraction. The feedforward activities of posterior muscles frequently predict high magnitudes of static impulse generation at the upper cervical spine and are most influenced by peripheral sensory inputs induced by head flexion posture. The third study evaluated the effects of a simple repetitive ballistic-intent training stimulus to facilitate an acute increase in early-phase neck strength capacity and muscle activation. The single-bout of ten ballistic-intent static maximal efforts produced significant and clinically meaningful acute increases in early-phase neck strength capacity and feedforward muscle activity that persisted for at least two days post-training. Through our biomechanical platform, we have enhanced our understanding of how neck muscle strength capacity and activation contribute to the stability of the upper cervical spine, which serves to increase our ability to diagnose, rehabilitate, and ultimately develop strategies to prevent head and upper cervical spine injuries.