A theoretical basis for the action of OMT and its effect in the body has been advanced based on autonomic activation causing concomitant vasodilatation, smooth muscle relaxation, and increased blood flow, resulting in improved range of motion, decrease in pain perception, or change in tissue. Until recently this association remained largely a theoretical consideration due to the inability to accurately measure autonomic activity directly. Over the past two decades indirect methods have been developed and refined to provide noninvasive markers of autonomic balance,5,6 with heart rate variability (HRV) being commonly used. HRV is based on the inherent variation of the R-to-R intervals of a standard electrocardiogram (ECG), with these variations largely due to changes in autonomic balance at the sinus node.6-8