Muscle fiber conduction velocity: dip analysis versus cross correlation techniques.
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Among the various techniques in use for computing Muscle Fiber Conduction Velocities (MFCV) the Cross Correlation (CCT) and the Dip Analysis (DAT) Techniques are the most similar to each other. The CCT has been applied to intramuscular and surface EMG recordings, while the DAT has been applied to surface recording only. On theoretical grounds the CCT carries higher signal to noise ratio than the DAT and therefore should be preferred over the latter. This study was designated to test and proved the above for intramuscular recording at maximal contractions with real data. In this study 240 subjects had their biceps EMG Interference Pattern recorded intramuscularly at maximal isometric contraction with two concentric needle electrodes separated one cm from one another along and parallel to the muscle fibers. The recording period lasted for 5.84 seconds. One hundred and sixty nine subjects (70%) showed distinct peaks in their cross correlograms, while only in 20 subjects (8%) were dips discernible by DAT. While most peaks in the CCT were high, clear and distinct most dips were shallow and blurred; also, there were only three cases where dips were detected on the DAT but no peaks were detected on the CCT while there were 152 cases where the CCT was superior to the DAT. This study verifies the superiority of the CCT over the DAT in this specific paradigm. Discussed are suggestions on how to improve the DAT by recording and displaying each lead power spectra separately prior to the differential amplifications of the EMG sinal from the two channels.
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