FORRESTER, S.E. and PAIN, M.T.G., 2010. A combined muscle model and wavelet approach to interpreting the surface EMG signals from maximal dynamic knee extensions. Journal of Applied Biomechanics, 26 (1), pp. 62-72.
This study aimed to identify areas of reduced surface EMG amplitude and changed frequency across the phase space of a maximal dynamic knee extension task. The hypotheses were: (1) amplitude would be lower for eccentric contractions compared to concentric contractions and unaffected by fibre length; and (2) mean frequency would also be lower for eccentric contractions and unaffected by fibre length.
Joint torque and EMG signals from the vastii and rectus femoris were recorded for eight athletic subjects performing maximum knee extensions at thirteen joint velocities spanning ±250° s–1. The instantaneous amplitude and mean frequency were calculated using the continuous wavelet transform time – frequency method, and the fibre dynamics were determined using a muscle model of the knee extensions.
The results indicated: (1) only for the rectus femoris were amplitudes significantly lower for eccentric contractions (p = 0.019), for the vastii amplitudes during eccentric contractions were less than maximal, but this was also the case for concentric contractions due to a significant reduction in amplitude towards knee extension (p = 0.023); and (2) mean frequency increased significantly with decreasing fibre length for all knee extensors and contraction velocities (p = 0.029). Using time – frequency processing of the EMG signals and a muscle model allowed the simultaneous assessment of fibre length, velocity and EMG.