 Subjects will be instrumented with the abdominal belt and controller box containing the waist accelerometer sensor. The external accelerometer sensor will be fixed with a Velcro around the thigh. In addition, subjects will wear two commercially available accelerometer sensors: 1 the ActivPal on the thigh of the other leg, and 2 an external accelerometer attached to the back of the belt at the level of the waist. The ActivPal can detect the upright posture but cannot distinguish between supine and sitting. The sensor placed on the back will be less affected by belly size in case of obese subjects. Both sensors will be used as a reference and for comparison. We will record all accelerometer signals during different body positions and activities. The activities will include lying down, sitting, getting up and standing still, walking, and climbing up and down steps for about one minute each for a total of 15-20 minutes per group of activities. Participants will perform 3 groups of activities. The order of activities within each group will be randomized. We might also ask you to perform 3 small jumps to synchronize the sensors at the beginning, middle and the end of each set of activities. 