An analogue instantaneous median frequency tracker for EMG fatigue monitoring

Electromyography analysis can provide information about a muscle´s fatigue state. The Power Spectral Density (PSD) function of the EMG signal undergoes a progressive compression towards lower frequencies and change of shape during fatigue. These changes are best represented by the instantaneous median frequency (iMDF) of the myoelectric signal. This paper presents an analogue based system developed in CMOS that extracts muscle fatigue through iMDF estimation of the EMG signal. The complete circuit design was simulated and evaluated using real retrospective muscle fatigue data. Results show that the average error in iMDF estimation, assuming a maximum iMDF of 150 Hz, would be less than 6 Hz. The system has been implemented in a commercially available 0.35 μm CMOS technology requiring a total power consumption of 250 μW from a 3.3 V supply.