1. A method for indicating a state of overstress in a nervous muscular system, the method comprising: feeding an interference current, the frequency and current strength of which can be adjusted, into a part of the nervous muscular system storing those adjustment values of the interference current, which cause certain predetermined physical responses in the examined part of the nervous muscular system, giving feedback in the measuring, when the target response is observed, calculating a measurement-specific average strength of the interference current for each predetermined physical response in the examined part of the examined nervous muscular system, normalising the measurement-specific average of the interference current for each physical response, and indicating a state of overstress in the nervous muscular system, if some measurement-specific normalised average of the interference current does not fulfil a set statistical criteria.