Each participant will be administered 2 injections of saline - the first in the right gluteal area and the second in the left gluteal area. Both injections will be administered intra-muscularly by the same clinician. One injection will be given with vacuum (Pneumatic Skin Flattening or PSF Machine) and the other without vacuum. The order of the injections will be randomly assigned. Each subject will serve as a control for himself. Between injections a 30 min pause will be given to minimize pain sensation bias of the previous injection. Immediately after each injection the pain level will be assessed by the VAS scale. The researcher assessing the pain will be blinded for the type of injection given. The evaluation of the pain reduction will be made by comparison of the pain level with and without the application of the PSF.