An apparatus (1) for electrical stimulation of muscle tissue. The apparatus has an electrode system (10) with an electrode array (13). The array has a plurality of electrode pads (12) and can be placed in electrical contact with the muscle tissue. The electrode system further has a sensor (3031-36) for sensing a property of the muscle tissue. The property forms a measure for the activity of the muscle tissue. The apparatus (1) has an electrode selector (530) for selecting one or more stimulating electrode pads. A signal generator (531) is connected to the electrode array (13) for providing an electrical stimulation signal to the stimulation electrode pad, A signal processor (532) is connected to said sensor (3031-36), for determining from the sensor signal a value of the muscle activity and outputting the value in a for humans perceptible form. This reduces the accuracy required to position the electrode system (10) and increases the accuracy of measuring the muscle tissue activity. Figure 2
