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First published online June 15, 2007
Journal of Experimental Biology 210, 2333-2345 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004457

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Variations in motor unit recruitment patterns occur within and between muscles in the running rat (Rattus norvegicus)

E. F. Hodson-Tole^* and J. M. Wakeling

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

View larger version (22K): [in this window] [in a new window]   Fig. 1. (A) The three power spectra representing a clean signal (left panels), with examples of power spectra from subjects with a large low frequency component (right panels). (B) Example of a graph used to determine the transition between real signal and noise in the soleus muscle.

View larger version (13K): [in this window] [in a new window]   Fig. 2. The principal component weightings for the first four principal components (PCI–IV) from spectra from whole strides (solid lines, N=1178) and partitioned strides (broken lines, N=23 560).

View larger version (6K): [in this window] [in a new window]   Fig. 3. Reconstructed spectra [i(f)] calculated for as (solid thin line) and af (broken thin line) in Eqn 3, overlaid with optimised wavelets s (solid bold line) and f (broken bold line).

View larger version (8K): [in this window] [in a new window]   Fig. 4. Mean myoelectric intensity from whole strides for soleus (red, N=344), plantaris (green, N=364) and medial gastrocnemius (blue, N=477), normalised to unit area. Traces show means ± s.e.m.

View larger version (6K): [in this window] [in a new window]   Fig. 5. Principal component loading scores for PCI (diagonal hatch), PCII (speckled) and PCIII (dark hatch) for each muscle, calculated from data taken from whole strides. Values are means ± s.e.m.

View larger version (7K): [in this window] [in a new window]   Fig. 6. PCI and PCII loading scores for soleus (S, N=340), plantaris (P, N=364) and medial gastrocnemius (MG, N=477). Values are calculated from the data taken from whole strides. was calculated as the angle formed between PCI–PCII loading score vector and PCII loading score axis. Values are means ± s.e.m.

View larger version (27K): [in this window] [in a new window]   Fig. 7. (A) Mean myoelectric intensity (black, solid line) for soleus (N=340), plantaris (N=364) and medial gastrocnemius (N=477) muscles, showing interplay between Cs(t) (red dotted line) and Cf(t) (blue broken line). All values are means ± s.e.m. (B) Vector plot of PCI and PCII loading scores in the soleus (red, N=340), plantaris (green, N=364) and medial gastrocnemius (blue, N=477); each arrow represents a different time point during the stride. The vertical line in each diagram denotes the transition from stance to swing phase.

View larger version (12K): [in this window] [in a new window]   Fig. 8. PCI and PCII loading scores at partitioned time points during a stride for the soleus (S, N=6880), plantaris (N=7280) and medial gastrocnemius (MG, N=9540) muscles. Values are means ± s.e.m. Asterisks indicate foot on, 0% stride duration; hash marks indicate foot off. Note that in each muscle, activity begins during the swing phase, therefore the direction of each loop is indicated by the arrows; 1 indicates the beginning of myoelectric activity.