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KMID : 1101220000320030292
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2000 Volume.32 No. 3 p.292 ~ p.299
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Surface EMG Spectral Parameters as a Fatigue Indicator After Electrically Induced Contraction of Vastus Medialis
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Jin Bok-Hee
Lee Jae-Hyoung
Hideaki Onishi
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Abstract
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The estimation of electrically induced muscle contraction forces is important for the reduce of muscle fatigue during neuromuscular electrical stimulation. The electromyographic signal has potential as an indicator of muscle fatigue. The purpose of this study was to assess muscle fatigue using electromyographic spectral analysis with median power frequency and mean frequency during muscle contraction. Twelve healthy male subjects were divided into the neuromuscular electrical stimulation and control group. Fatigue was induced by having neuromuscular electrical stimulation subjects perform 50 second isometric contractions followed by 10 second rests for 10 minutes using Russian current electrical stimulation with 80 Hz. All subjects lies comfortably on a table to perform sustained contraction in the vastus medialis muscle for 30 seconds with maximal voluntary isometric contraction. The electromyogram was recorded using MP 100 System from vastus medialis muscle in both neuromuscular electrical stimulation and control group. The time serial data of the electromyographic signals were transformed into frequency serial data by Fast Fourier Transformation. The frequency changes ratio of median frequency was significantly lower in neuromuscular electrical stimulation group compared with control group (p<0.001) and the frequency changes ratio of mean frequency was significantly lesser in neuromuscular electrical stimulation group compared with control group (p?0.05). These results showed that the median frequency and mean frequency were declined by muscle fatigue. These results suggest that in neuromuscular electrical stimulation there is a trend for more fatigue to occur than in control group. This would seem to suggest that the analysis of median frequency and mean frequency of surface electromyographic spectra can use for indicator of muscle fatigue. Also, in treatment programs for muscle strengthen using neuromuscular electrical stimulation, some parameters such as on-off ratio, frequency should be considered.
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KEYWORD
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EMG, Fatigue, NMES
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