Abstract: A portable biofeedback device for monitoring electric signals produced by muscle activity is disclosed. Electrodes attached to the skin of the person being monitored couple muscle signals to a preamplifier which amplifies the signal and does preliminary filtering of unwanted frequency components in this signal. Further high and low pass filtering and amplification is then performed such that only signals in a certain frequency range are amplified. Sensitivity control is added to enable the level of detected muscle activity to be selectively set. Both visual and audio feedback is generated from the filtered and amplified signal for use by the person being monitored. The visual feedback includes easy to read visual indicators, including an overrange indicator and underrange indicator, for displaying the varying levels of muscle activity.