Does the fast Fourier transformation window length affect the slope of an electromyogram's median frequency plot during a fatiguing isometric contraction?

Abstract

Reduced median frequencies (MDFs) are the hallmark of muscle fatigue in an electromyogram (EMG), the magnitude of which may be influenced by window lengths in fast Fourier transformation (FFT) algorithms used to compute power spectra. This study examined whether MDF reductions in fatigued muscles differed across varying FFT windows. EMG data were acquired from the gluteus maximus and semitendinosus muscles during a modified Biering–Sørensen test. Data were processed through varying FFT windows (0.1-, 0.5-, 1.0-, 2.0- and 5.0-s) and MDF slopes were compared with repeated measures analyses of variance. While FFT windows influenced variability in MDFs, the slopes did not differ across window lengths in either muscle group. When muscle fatigue is assessed via MDF slopes during submaximal isometric contractions, the FFT windows through which spectral characteristics are processed may have little bearing on results.