2.3. Interventions

The chiropractic spinal manipulation and control interventions were similar to those used in previous studies [27,28,37,39,41] that have investigated the neurophysiological effects of chiropractic spinal adjustments. The same chiropractor performed the actual and control adjustments. At the end of the second session, the subjects were asked if they felt that they had undergone active treatment in each session (‘yes’ or ‘no’).

The standard adjustment techniques used by the chiropractors, also known as spinal manipulation, were used in the chiropractic spinal adjustment session. The chiropractor performed manual high-velocity low-amplitude adjustments or instrument-assisted adjustments to the spine or pelvic joints [44]. The chiropractor used standard clinical indicators of spinal and pelvic dysfunction to decide where to adjust. [45] These indicators included tenderness to palpation, restricted intersegmental motion, muscle asymmetry, and blocked jopint play or end-feel. Chiropractic adjustments were applied to multiple spinal segments if required.

The control intervention was performed by the same chiropractor who provided the chiropractic intervention. In the control session, the chiropractor interacted with the patient in a similar way to the active session, including assessing the spine and pelvis for dysfunction and then moving and setting up the patient as if they were going to apply an adjustive thrust. However, during the adjustment set up, the chiropractor took care not to provide an adjustive thrust or to take a vertebral segment that was deemed to be subluxated to tension. The control session was designed to control for the interaction and time taken during the chiropractic intervention and to control for the mechanoreceptive input associated with the chiropractor assessing the patient’s spine, while ensuring the afferent input associated with the adjustive thrust was minimized.