 Cardiovascular CV Function Orthostatic Challenge Test. Prior to orthostatic assessments, subjects will lie supine in a temperature controlled room for 20 minutes rest. Beat-to-beat arterial blood pressure, heart rate, and respiratory rate will be determined in the supine position, and during a 20 minute passive orthostatic challenge sit up test. Indices of stroke volume, cardiac output and peripheral resistance will be calculated from the blood pressure wave-form. Mean systolic and diastolic arterial blood pressures and heart rate will be calculated at rest and during orthostatic stress. Catecholamine adrenaline and noradrenaline, nml levels will be measured during rest and orthostatic challenge test. A butterfly catheter 15mm will be inserted into an antecubital vein before data collection to draw the blood samples, this will allow the collection of blood without additional stress to the participant and activation of catecholamine release by venopuncture. The subject will rest for 20 minutes: a blood sample 10cc from the antecubital vein will then be taken. A second blood test 10cc will be obtained following the passive tilt sit up test. Serum level catecholamine levels will be measured. These data will be correlated with the other indices of CV autonomic function, and severity of injury to spinal autonomic pathways determined by SSR. Lower extremity EMG will be collected simultaneously to make sure that stimulation is not regenerating strong muscle contractions that might result in blood pressure control independent of improvements in CV function. 