Estimation of instantaneous median frequency in surface electromyography signals using quadratic time frequency...

Surface electromyography (sEMG) technique gives a non-stationary and multi component signal which can be used for neuromuscular analysis, ergonomics, rehabilitation and sports biomechanics. It records the electrical activity of skeletal muscles. The sEMG signals are often analyzed in the time domain, frequency domain and time-frequency domain. Although several methods of signal analyses are reported in the literature, the extraction of useful information still remains a challenging task. In this work, an attempt has been made to analyze sEMG signals in fatigue and non-fatigue conditions by using the quadratic time frequency distribution (QTFD). Signals are recorded for 25 normal control adult subjects during dynamic contractions in biceps brachii muscle. The acquired signals are subjected to QTFD by using a modified B distribution. The median frequency is extracted from the processed signal. The result shows that median frequency is distinct for fatigue and non fatigue conditions. Further it shows variation with flexion and extension. Thus the study seems to be clinically useful for the dynamic analysis of neuromuscular conditions.