Time-frequency analysis of motor unit recordings to characterize rhythmic behavior in activity pattern of trapezius muscle

This study demonstrates that Cohen Class time-frequency and cross-time-frequency transformations may reveal nonstationary rhythmic behaviors in motor unit firing patterns. Recordings were performed from the upper trapezius muscle in nine subjects with no known neuromuscular or motor control related disorders during static contractions. The proposed procedures demonstrated that rhythmic firing patterns may be detected during sustained muscle contractions. Two components were typically identified around 0.3 and 0.1 Hz respectively. Coherent rhythmic behaviors were shown across motor units. To our knowledge this is the first time that time-frequency and cross-time-frequency techniques are applied to motor unit recordings. We see the observations reported in this study as of paramount importance because they provide new elements toward a full understanding of CNS mechanisms underlying upper trapezius muscle contraction.