AP protocol: The subject will first lie on his/her side quietly for 10 minutes to collect the baseline skin blood flow, followed by lying supine on the Dabir AP overlay for 40 minutes, and then side lying for 30 minutes to collect the first reactive hyperemic response. To test the effect of preconditioning, the subject will then lie supine on the OR overlay for 40 minutes followed by side lying for 30 minutes for the second reactive hyperemic response.