Extremity Manipulation Impact on Postural Sway Characteristics

The focus of this study is to explore the effect of upper and lower extremity chiropractic adjustments (manipulation) as well as surface condition (hard surface vs rocker board) on multisegmental postural control as represented by postural sway. Using a rocker (tilt) board, the participant cannot stand still, but has to adjust posture continuously to maintain balance. Body sways are considered to be self-induced because the design of the rocker board creates a natural instability without any external perturbation. This task provides a self-driven sensorimotor condition in addition to amplifying the sway dynamics. Because the rocker board has only one degree of freedom of motion, anteroposterior and lateral sways were considered separately on the device. The investigators had the following hypotheses. Hypothesis 1: Lower extremity adjustments will lead to reduced postural sway magnitude compared to upper extremity adjustments. Hypothesis 2: Lower extremity adjustments will reduce sway variability of the rocker board, trunk and head compared to upper extremity adjustments. Hypothesis 3: Lower extremity adjustments will facilitate the organization of sway behavior as assessed by the chaotic structure of sway.