Computation and study of the low-frequency oscillation of surface electromyogram recorded in biceps during isometric upper limb contraction.

This study has experimentally studied the low frequency oscillation in surface electromyogram (sEMG) during isometric muscle contraction for Biceps brachii muscle. The time constant corresponding to this low frequency oscillation was computed for sEMG. Experiments were repeated for 25 subjects, and for isometric muscle contraction, ranging between 25% and 100 % maximum voluntary contraction (MVC), while the subjects were given real-time visual feedback of the force of contraction, recorded at 1000 samples/ second. The time constant (Tc) corresponding to the variability of sEMG was computed using the Hilbert transform and envelope detection. The results show that the time constant, Tc of sEMG recorded from the biceps during isometric contraction was the same for all the subjects, and for different levels of force of muscle contraction, and was 78 ms (± 1.1). This suggests that the low frequency oscillation of sEMG of the biceps brachii muscles is a fundamental property of that muscle, and corresponds to a fundamental phenomenon, which has never been observed earlier. By comparison from delays reported in literature, this delay is similar to M2 stretch reflex latency, and may be attributed to the neural pathway delay.