The primary goal of this thesis was to systematically describe biomechanical and electromyographic (EMG) responses of the human musculoskeletal system associated with cervical and upper thoracic spinal manipulation (SM). The overarching hypotheses were that:​ i) greater three-dimensional (3D) movements of the head and neck would be associated with larger vertebral artery (VA) strains;​ and ii) SM applied with greater force and more quickly would result in larger EMG responses.

In the first project, a basic science methodology was used to measure:​ i) 3D movements of the head and neck and associated VA strains during cervical SM applied to human cadaveric donors;​ and ii) the elongation required for mechanical failure of the VA. Pre-positioning of the head and neck resulted in the largest changes in angular kinematics and arterial strain, while small changes occurred during the thrust. There were correlations between angular displacements and VA strains during cervical SM, however these were variable in direction (positive vs. negative) and strength (negligible to high). Arterial strains during cervical SM did not exceed those required to produce tensile stretch;​ therefore, it is unlikely the procedures delivered in this study could result in mechanical disruption of a healthy vessel wall.

In the second project, an applied methodology was used to investigate:​ i) reflexogenic effects of cervical and upper thoracic SM in asymptomatic and neck pain participants;​ and ii) the relationship between SM kinetics and EMG responses. In asymptomatic participants, cervical and upper thoracic SM was often associated with EMG responses. However, responses occurred less frequently in symptomatic participants, suggesting that the reduction in EMG responses may be associated with pain-induced reflex inhibitions. Further, when two thrusts were delivered to the same spinal segment, following one another in quick succession, the second thrust was delivered more forcefully and more quickly, resulting in greater peak EMG responses and shorter neuromuscular delays.

Collectively, the data in this thesis demonstrate that high-velocity, low-amplitude (HVLA) cervical and upper thoracic SM causes biomechanical and EMG responses within the musculoskeletal system. Further, these studies provide important safety and mechanistic data on cervical and upper thoracic SM.