Determining patterns of motor recruitment during locomotion
James M. Wakeling1,*,
Motoshi Kaya1,
Genevieve K. Temple2,
Ian A. Johnston2 and
Walter Herzog1
1 Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada T2N 1N4 and
2 Gatty Marine Laboratory, School of Environmental and Evolutionary Biology, University of St Andrews, Fife KY16 8LB, UK
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Fig. 1. Fifth, fiftieth and ninety-fifth percentiles of the muscle fibre diameters in the rainbow trout. Percentiles were calculated from the µprobability density functions of the muscle fibre diameter distribution for each fish. The columns show the mean diameter + S.E.M. for the fifth, fiftieth and ninety-fifth percentiles for each size class of fish. Red and blue columns show the percentiles for the red and white fibres, respectively. The size classes were: L=0.13±0.02 m, N=6; L=0.22±0.03 m, N=5; L=0.32±0.06 m, N=5, where L is total fish length.
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Fig. 2. Myoelectric signals and intensity spectra from fast- and slow-twitch muscle fibres. Data are taken from one fish. EMGs were recorded from red muscle (mean fibre diameter 36 µm) during slow swimming (A) and from white muscle (mean fibre diameter 74 µm) during a fast-start (B). The boxes indicate the time regions for the red fibres (red box) and white fibres (blue box) analysed for frequency content. The intensity spectra for these regions (C) show a threefold increase in mean frequency, MF, between the red (red triangles) and white (blue circles) muscle fibre types. Spectra are normalized so that total intensity equals 1.
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Fig. 3. Mean myoelectric frequencies for red and white muscle fibres. Each point denotes the mean ± S.E.M. (N=5–6) from one fish. White muscle fibres (blue circles) showed a significantly greater mean frequency than red muscle fibres (red triangles). There was no significant linear regression between mean frequency and mean fibre diameter for either fibre type. Solid lines indicate the average mean frequency across all fish for each muscle fibre type.
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Fig. 4. Myoelectric intensity spectra for different movements in the cat. Each point shows the mean ± S.E.M. myoelectric intensity for paw-shaking (blue circles, N=24) and treadmill-walking (red triangles, N=31) at 0.4 m s–1 calculated from all four cats. The mean intensities for each activity were normalized to a maximum value of 1.
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Fig. 5. EMG, intensity and tendon force for the medial gastrocnemius in the cat. Intensities are summed from wavelet domains 3 and 4 (red line, band-width 50–110 Hz) and from wavelet domains 7 and 8 (blue line, band-width 190–300 Hz). Recordings were made during treadmill-walking at 0.4 m s–1 (A), during walking up a 45° incline (B), during galloping (C) and during paw-shaking (D).
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Fig. 6. Recruitment between fast and slow motor units in the medial gastrocnemius of the cat. Intensities were summed from wavelet domains 3 and 4 to represent slow motor unit activity (red columns, band-width 50–110 Hz) and from wavelet domains 7 and 8 to represent fast motor unit activity (blue columns, band-width 190–300 Hz). The maximum intensity was measured for separate strides and paw-shakes for the cat shown in Fig. 5. Values are means + S.E.M. (N=10) of these maximum intensities. Values are shown for each of the four movements.
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Fig. 7. Wavelets for k=2 (red) and k=7 (blue) shown in the time domain. k, wavelet number.
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Fig. 9. Wavelets for k=3, 4 and 5 shown in the frequency domain. The vertical line at a frequency of 100 Hz (red) illustrates how one frequency within a signal can be partitioned into a3, a4 and a5 amplitude components in three adjacent wavelet domains. k, wavelet number.
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Fig. 10. Calculation of the myoelectric intensity at wavelet domain 2. The raw EMG signal (A) is convoluted with wavelet 2 (B) and squared (C). The intensity (red line) is calculated from the slope and magnitude of the square of the convolution (C) and then filtered (D).
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© The Company of Biologists Ltd 2002
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