The concentration of lactate in the blood is one of the leading indicators of the athlete's individual training activity. Constant monitoring of this parameter is necessary for more effective training and ensuring that the training does not harm the health of the athlete. This application was designed, and the device created in conjunction with specialists from the Faculty of Chemistry at Moscow State University, Lomonosov, who determined the relationship between the concentration of lactate in sweat and in human blood. The Lactate Sensor helps to non-invasively determine the concentration of lactic acid in the blood. The small device is attached to the skin using a replaceable cartridge electrode and records the readings in real-time.