The double peak-to-peak analysis for determining EMG onset of muscle contraction.
OBJECTIVE
Identification of the onset of muscle contraction with EMG signal amplitude double of the baseline value (DP-P) has been recently reported for determining the temporal parameters of muscular activity. Due to its convenience, it is suitable for clinical application. However, there is a lack of report on the reliability and comparability of this method to other established methods. Therefore, this study examined the test-retest reliability of the DP-P method and compared it with an established method that used the mean + 3 standard deviations (mean + 3 s.d.) over the baseline value for muscles of the knee.


METHODS
The onset of contraction of vastus medialis obliquus (VMO) and vastus lateralis (VL) of eleven able-bodied volunteers performing isometric knee extension at 50%, 75% and 100% of MVC in 30-minute and 7-day intervals were analyzed with both the DP-P and mean + 3 s.d. methods.


RESULTS
The ICC for within-day measurements of DP-P method ranged from 0.64 to 0.86 and that for between-day measurements ranged from 0.63-0.81. The ICC values were higher with submaximal than maximal contractions. There was a consistent delay of about 3 ms in EMG onset detection with the DP-P as compared to the mean + 3 s.d method.


CONCLUSIONS
The DP-P method is a reliable method for muscle onset determination but the absolute onset time of muscle contraction obtained from this method should not be directly compared with other methods such as the mean + 3 s.d.
Wong
Y M
YM
Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
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G Y F
GY
D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D019415:Torque