Quadriceps EMG frequency content following isometric lumbar extension exercise

A relationship exists between muscles of the lumbar spine and those of the lower extremity where the quadriceps become more inhibited after lumbar paraspinal. The purpose of this experiment was to compare surface electromyography (sEMG) total frequency content after lumbar paraspinal fatiguing exercise. Scope: 50 subjects performed fatiguing lumbar extension exercise indexed by downward shifts in median frequency calculated from lumbar paraspinal sEMG signal. Before and after each exercise set we recorded maximal, isometric knee extension torque and quadriceps central activation ratio (QI) using the superimposed burst technique while recording vastus lateralis sEMG. We calculated total frequency content of the sEMG signal (fEMGTOTAL) as the area of the quadriceps sEMG frequency spectrum. Quadriceps fEMGTOTAL decreased from baseline following the first and second exercise sets. There was no significant change in quadriceps sEMG median frequency among baseline and post-exercise measures. The change in fEMGTOTAL was correlated with the change in QI following the first (r = −0.41, P = 0.003) and second (r = −0.32, P = 0.02) exercise sets. Conclusion: Quadriceps fEMGTOTAL decreased following fatiguing lumbar extension exercise, in the absence of a significant change in quadriceps median frequency.