The investigators are developing two new medical instruments: 1. the Intelligent Sensor Belt (ISB), and 2. the Body Composition and Hydration Status Analyzer (BC-HS-A). ISB serves the purpose of measuring calorie/ energy consumption of the human body during physical activity. The BC-HS-A measures the body composition, i.e. the fat and lean body mass and the hydration status i.e the amount of water inside and outside of the body cells.