PHASE ONE HEALTHY SUBJECTS  Inclusion criteria:  Healthy volunteers, aged > 20 years without functional limitation. BMI of 18.5-25.9 kg/cm2. No scars on the heels.  Exclusion criteria:  Failure to meet all of the above criteria. Smokers. Consume high levels of alcohol (> 20g/week). Tattoos in the measurement areas.  PHASE TWO - PATIENTS  Inclusion criteria:  Patients aged > 20. Patients with risk of deterioration of skin integrity according to Braden score <16. no presence of Press Ulcer.  Exclusion criteria:  Presence of vasoactive drugs in infusion Subjects with a pacemaker and/or implanted defibrillator. Fever and anaemia with Hb <10 g/dl. Hypotension with systolic blood pressure <80 mmHg. Transfusion during the last four weeks.