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JOURNAL
OF
SPORTS SCIENCE &
MEDICINE
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Research
article
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MYOELECTRIC ALTERATIONS AFTER VOLUNTARY INDUCED HIGH - AND LOW - FREQUENCY FATIGUE |
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Katja Tomazin  ,
Nejc Sarabon and Vojko Strojnik |
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University of Ljubljana, Faculty of Sport, Slovenia |
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© Journal of Sports Science and Medicine (2008) 7, 242 - 248 |
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| ABSTRACT | |||
| The aim of the study was to find whether voluntary induced high-
and low-frequency peripheral fatigue exhibit specific alteration in surface
EMG signal (SEMG) during evoked and maximum voluntary contractions. Ten
male students of physical education performed 60 s long stretch-shortening
cycle (SSC) exercise with maximal intensity and 30 s long concentric (CON)
exercise with maximal intensity. To verify voluntary induced peripheral
fatigue, knee torques during low- (T20) and high-frequency electrical stimulation
(T100) of relaxed vastus lateralis muscle (VL) were obtained. Contractile
properties of the VL were measured with passive twitch and maximal voluntary
knee extension test (MVC). Changes in M-waves and SEMG during MVC test were
used to evaluate the differences in myoelectrical signals. T100/T20 ratio
decreased by 10.9 ± 8.4 % (p < 0.01) after the SSC exercise and increased
by 35.9 ± 17.5 % (p < 0.001) after the CON exercise. Significant SEMG
changes were observed only after the CON exercise where peak to peak time
of the M-waves increased by 9.2 ± 13.3 % (p < 0.06), SEMG amplitude during
MVC increased by 32.9 ± 21.6 % (p < 0.001) and SEMG power spectrum median
frequency decreased by 11.0 ± 10.5 % (p < 0.05). It is concluded that
high frequency fatigue wasn't reflected in SEMG, however the SEMG changes
after the CON seemed to reflect metabolic changes due to acidosis.
Key words: M-wave, stretch-shortening cycle, electrical stimulation, median frequency. |
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