Improved techniques for measuring muscle fiber conduction velocity
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Cross-correlation (CCT) and dip analysis (DAT) are accepted techniques for estimating muscle fiber conduction velocity (MFCV). In the DAT, the product of the power spectrum of the conducted EMG times a cosine function of the MFCV is added to and inseparable from the noise power spectrum. The inclusion of the noise power is the weakness of the DAT. We propose and evaluate 2 new techniques that directly estimate the cosine function and, hence, the MFCV, avoiding the noise power: (1) The power-modulating-component (PMC), which equals the real part of the cross-power-spectrum of the EMG signal divided by its magnitude; and (2) The power spectrum of the PMC (PMCP). We recorded intramuscular from 229 biceps in isometric maximum voluntary contraction. The EMG signals were analyzed by the 4 techniques, and the results were compared in pairwise design (sign-tests and t tests) for quality and bias. The PMC surpassed the DAT (P less than 0.00005); both the CCT and PMCP performed equally well and better than the DAT and the PMC (P less than 0.00005). Also, the new techniques were superior with simulated EMG. In many cases only the PMCP worked. We conclude that the new techniques are valuable in supplementing the others, and most likely will enhance clinical use of MFCV estimations.
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