 Spinal mobilization and spinal manipulation are common techniques utilized in the field of physical therapy. Despite their common utility, little is known about the physiological mechanisms underlying the changes experienced following the interventions. Recent research suggests that neurological mechanisms may be involved in the post interventional changes, but research supporting this view is still evolving. Therefore, this study will explore whether there is a neurophysiological difference between spinal manipulation and spinal mobilization techniques. The neurophysiological difference will be measured by monitoring heart rate variability, a cardiovagal indicator of autonomic nervous system activity. The primary hypotheses of this study are three-fold, first that spinal manipulation will result in a change in heart rate variability that is different then sham intervention. Second, spinal mobilization will result in a change in heart rate variability that is different then sham intervention. Finally, the investigators hypothesize that spinal mobilization and spinal manipulation will produce different changes in heart rate variability. 