1. A method for indicating a state of overstress in a nervous muscular system, the method comprising: steering an interference current into a part of the nervous muscular system, a frequency and a current strength of the interference current being adjustable; receiving feedback identifying at least one target response from a plurality of predetermined physical responses in an examined part of the nervous muscular system; storing a frequency value and a current strength value of the interference current which caused the at least one target response; calculating a measurement-specific average strength of the interference current for each identified target response from the plurality of predetermined physical responses in the examined part of the nervous muscular system, normalising the measurement-specific average strength of the interference current for each identified target response, and indicating a state of overstress in the nervous muscular system, if a measurement-specific normalised average strength of the interference current does not fulfil a set statistical criteria.