Nonlinear time-course of lumbar muscle fatigue using recurrence quantifications |
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| Authors: | Shigeki Ikegawa Minoru Shinohara Tetsuo Fukunaga Joseph P. Zbilut Charles L. Webber Jr. |
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| Affiliation: | (1) Laboratory for Exercise Physiology, Tokyo Metropolitan College, Azumacho 3-6-33, Akishima 196, Tokyo, Japan, JP;(2) Department of Life Sciences, The University of Tokyo, Komaba 3-8-1, Meguro, Tokyo 153, Japan, JP;(3) Department of Molecular Biophysics and Physiology, Rush Medical College, Chicago, IL 60612, USA, US;(4) Department of Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, IL 60153, USA, US |
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| 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. Received: 12 November 1998 / Accepted in revised form: 29 November 1999 |
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