::Results
click thumbnails for actual size
Results for 2 ND and 3 SCI subjects are shown graphically in figure 3, which demonstrates the differences among subjects in the coordination of each lower limb muscle pair across increasing speed and load stepping conditions.
Figure 4 shows the differences in coordination among the 3 muscle pairs across speed and load conditions for ND-1. The changes in coordination shown in the summary line graphs on the left are expanded in selected linear envelope and scatter plots on the right. While there is a difference between unloaded and loaded states, changing limb loading does not affect SOL/MG coordination. SOL/TA and MG/TA coordination increases as load increases, as the TA becomes active during stance. There is an earlier onset of MG activity as speed increases, resulting in an increase in SOL/MG coordination. TA activation during stance decreases as speed increases, resulting in a decrease in SOL/TA and MG/TA coordination.
Figure 5 shows the differences in coordination among the 3 muscle pairs across speed and load conditions for SCI-C2. The changes in coordination shown in the summary line graphs on the left are expanded in selected linear envelope and scatter plots on the right. Antagonistic muscle pairs generally increase in coordination with increasing load and speed, as the TA becomes active during stance. There also appears to be some co-modulation of the MG and TA, as the coordination pattern does not change with speed.
Figure 6 shows the differences in coordination among the 3 muscle pairs across speed and load conditions for SCI-A1. The changes in coordination shown in the summary line graphs on the left are expanded in selected linear envelope and scatter plots on the right. This subject did not display TA activity during any stepping condition. Therefore, changes in SOL/TA and MG/TA coordination occur as a result of changes in SOL or MG activation pattern. The decrease in SOL/TA and MG/TA coordination occurs because both the SOL and MG increase in activity as load and speed increases. From 0% to 45% BWL SOL and MG increase in a similar fashion, whereas at 55% BWL, the MG is active throughout a greater portion of the step-cycle than the SOL. As speed increases, SOL/MG coordinaiton decreases as the MG is activated earlier.
Figure 7 shows the differences in coordination among the 3 muscle pairs across speed and load conditions for SCI-C1. The changes in coordination shown in the summary line graphs on the left are expanded in selected linear envelope and scatter plots on the right. At 0% BWL there is no activity present in any of the muscles studied. With loading, the SOL/MG coordination increases, as SOL and MG activity increases. The SOL/TA and MG/TA coordination decreases with increased loading as the TA remains inactive while the SOL and MG increase in activity. The high SOL/MG coordination at low speeds is due to high clonicity at those speeds, which decreases as speed increases. Any activity in the TA is clonic activity, but it is most clonic at the low speed. Thus SOL/TA and MG/TA coordination decreases as speed increases.
::Conclusion
1. Lower limb loading and stepping velocity can affect muscle coordination patterns in both ND and SCI subjects during stepping.
2. Agonist muscle pairs (SOL/MG) are less coordinated following SCI, as evidenced by a lower coordination value in SCI subjects compared with ND subjects across load and speed conditions.
3. Antagonist muscle pairs (SOL/TA and MG/TA) are more coordinated following SCI, as evidenced by a higher coordination value in SCI subjects compared with ND subjects across load and speed conditions.
4. Stepping in the absence of load is interpreted differently than weight bearing stepping, as evidenced by the large difference in coordination value among all three muscle pairs in both ND and SCI subjects.
5. The abnormal activation patterns seen in following SCI may not only be reflective of deficits following injury, but also of the abnormally low stepping velocities, as evidenced by figure 3.
::References
1. Harkema SJ, Hurley SL, Patel UK, Requejo PS, Dobkin BH, & Edgerton VR. (1997). Human lumbosacral spinal cord interprets loading during stepping.
2. Johnson TD, Elashoff RM, & Harkema SJ. (2000). Bayesian change-point analysis of muscular coordination from electromyographic data. (under review). [See also Davis BC, et al. (2000). Quantification of muscle coordination and clonic-like motor firing patterns in spinal-cord injured subjects during stepping. SFN 2000 Poster.]
3. Maynord FM, et al. International standards for neurological and functional classification of spinal cord injury (1997). American Spinal Injury Association. Spinal Cord: 35, 266-274.
:: Acknowledgements
We would like to thank Roscelle Joaquin, Morteza Tavakol, Rita Lukacs, Ani Balmanoukian and Sue Ono for their contributions to this poster.
This work was supported by NIH NS36854, NS16333, and RR00865.
Quantitative Assessment of
