Once you pick out your training program and determine what muscle group you want to train the app will show you where to apply the electrodes. From there you use the app to start your training session. Increase the power (+) until you feel the tingling sensation in your muscles. From there continue to increase the power until you experience a comfortable muscle contraction. EMS should not be painful. If you feel any discomfort from the muscle contraction just reduce the power (-) or stop the workout in just one click.