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First published online October 7, 2004
Journal of Experimental Biology 207, 3883-3890 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01223

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Motor units are recruited in a task-dependent fashion during locomotion

James M. Wakeling

Structure and Motion Laboratory, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire, AL9 7TA, UK

View larger version (33K): [in a new window]   Fig. 1. (A) Myoelectric signal from the biceps femoris for one stride of running at 4.5 m s–1. Heel-strikes occurred at times of 0 and 750 ms. (B) The mean myoelectric intensity for 20 consecutive strides is shown as a function of time and frequency, with high intensities denoted by dark shading. The 20 time-windows that divide the stride are indicated by the vertical grey lines. (C) The myoelectric intensity spectra for each of the 20 time-windows shown in B.

View larger version (16K): [in a new window]   Fig. 2. Weightings for (A) the first principal component (PC I) and (B) the second principal component (PC II) shown with the proportion of the signal that this component describes. (C) Intensity spectra reconstructed from the vector product of the PC loading scores and the PC weightings. The mean frequencies (MF) for the reconstructed spectra are shown. The angle is a measure of the relative PC I and PC II loading scores and of the myoelectric frequency.

View larger version (23K): [in a new window]   Fig. 3. Principal component loading scores for PC I and PC II during walking and running for the leg flexors. Each point shows the mean ± S.E.M. loading scores pooled from the six subjects (N>348). The 20 points on each graph show the PC loading scores at the 20 successive time-windows during each stride, graded from black immediately after heel-strike to light grey immediately before the next heel-strike. Data are shown for the biceps femoris (A), the semitendinosus (B) and the tibialis anterior (C).

View larger version (23K): [in a new window]   Fig. 4. Principal component loading scores for PC I and PC II during walking and running for muscles in the quadriceps group. Each point shows the mean ± S.E.M. loading scores pooled from the six subjects (N>342). The 20 points on each graph show the PC loading scores at the 20 successive time-windows during each stride, graded from black immediately after heel-strike to light grey immediately before the next heel-strike. Data are shown for the vastus lateralis (A), the rectus femoris (B) and the vastus medialis (C).

View larger version (22K): [in a new window]   Fig. 5. Principal component loading scores for PC I and PC II during walking and running for muscles in the triceps surae group. Each point shows the mean ± S.E.M. loading scores pooled from the six subjects (N>348). The 20 points on each graph show the PC loading scores at the 20 successive time-windows during each stride, graded from black immediately after heel-strike to light grey immediately before the next heel-strike. Data are shown for the lateral gastrocnemius (A), the medial gastrocnemius (B) and the soleus (C).