YOPI is the first digital personal health and fitness instructor that combines an intelligent personal training applications using machine-learning algorithms with cutting-edge proprietary biosensors. During exercise the body needs more Oxygen to feed the muscles in order to keep it working. Oxygen consumption is a key factor for optimal training. Oxygen consumption is individual and depends on physiology and fitness level. Today the only way to measure changes in Oxygen consumption is in a special “Metabolic Fitness Testing Laboratory”. YOPI measures Oxygen consumption on-line from the user’s body, using breakthrough wearable biosensors and sophisticated algorithms. YOPI biosensors measure bio-markers in the skin and the sweat that are correlated to the Oxygen intake. YOPI instructs, in real time, the trainee according to his momentary physiology and goals. YOPI is a 24/7 personal instructor companion for health, wellness and fitness.