title: Nonlinear time-course of lumbar muscle fatigue using recurrence quantifications.
abstract: Isometric skeletal muscle fatigue is usually assumed to be a linear process based upon the monotonic decrease in spectral frequency of the EMG. Since spectral analysis by fast Fourier transform (FFT) constitutes a linear transformation of the data, the present study was designed to reevaluate the time-course of muscle fatigue with a nonlinear tool, recurrence quantification analysis (RQA). Surface EMG recordings were obtained from the multifidus muscle of 17 human subjects during isometric posture-holding of the upper torso. The process of muscle fatigue was found to be linear for 59% of the subjects by FFT criteria, but nonlinear for 76% by RQA criteria. As a demonstrative control, both slow and fast transients occurring within a nonlinear mathematical process could be accurately depicted by RQA, but not by FFT. It is concluded that assessment of EMG patterns by nonlinear techniques can give insight into the time-course of fatiguing muscles attributed to the summation of several nonlinear and competing processes.
authors.affiliation: Laboratory for Exercise Physiology, Tokyo Metropolitan College, Akishima, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ikegawa
authors.forename: M
authors.initials: M
authors.lastname: Shinohara
authors.forename: T
authors.initials: T
authors.lastname: Fukunaga
authors.forename: J P
authors.initials: JP
authors.lastname: Zbilut
authors.forename: C L
authors.initials: CL
authors.lastname: Webber
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008954:Models, Biological; D018763:Muscle Fatigue / Q000502:physiology*; D017711:Nonlinear Dynamics; D010807:Physical Endurance / Q000502:physiology; D012008:Recurrence