Muscle activation during unilateral stepping occurs in the nonstepping limb of humans with clinically complete spinal cord injury

Abstract

Study design:Comparison of different kinematic and loading conditions on muscle activation in clinically complete spinal cord-injured subjects stepping unilaterally with manual assistance. Objective: To determine if rhythmic lower limb loading or movement could produce rhythmic muscle activation in the nonstepping limb of subjects with clinically complete spinal cord injury (SCI). Setting: Human Locomotion Research Center, Department of Neurology, University of California, Los Angeles, USA. Methods: We recorded electromyography, joint kinematics, and vertical ground reaction forces as four subjects with clinically complete SCI stepped with manual assistance and partial bodyweight support. For all trials, one limb continuously stepped while the other limb underwent different conditions, including rhythmic lower limb loading in an extended position without limb movement, rhythmic lower limb movement similar to stepping without limb loading, and no lower limb loading or movement with the leg in an extended or flexed position. Results: Three subjects displayed rhythmic muscle activity in the nonstepping limb for trials with rhythmic limb loading, but no limb movement. One subject displayed rhythmic muscle activity in the nonstepping limb for trials without ipsilateral limb loading or movement. The rhythmic muscle activity in the nonstepping limb was similar to the rhythmic muscle activity during bilateral stepping. Conclusions: The human spinal cord can use sensory information about ipsilateral limb loading to increase muscle activation even when there is no limb movement. The results also indicate that movement and loading in one limb can produce rhythmic muscle activity in the other limb even when it is stationary and unloaded. These findings emphasize the importance of optimizing load-related and contralateral sensory input during gait rehabilitation after SCI.

Tools for understanding and optimizing robotic gait training

“…Our results with the rat stepper highlight the importance of maintaining appropriate somatosensory input to elicit stepping following SCI. These results are consistent with recent clinical results in patients with SCI [13,[21][22]. Initial work with computational models of motor training following SCI suggests that assisting in movement only as needed will be more effective than providing a fixed amount of assistance, because assistance-as-needed can limit stepping errors, while still allowing learning of a novel sensorimotor transformation.…”

“…Similar principles likely apply to humans with SCI [13,[21][22]. The implication is that robotic gait trainers should be designed to maintain appropriate patterns of loading on the feet and legs and phasing between the legs to increase the quantity and quality of stepping activity.…”

Detection of the neuronal activity occurring caudal to the site of spinal cord injury that is elicited during lower limb movement tasks

“…The activity detected is in agreement with known physiology and together with previous findings of increased contralateral activation in response to stimulation of the injured spinal cord suggest that spinal fMRI is providing reliable results. 2,[16][17][18][19] This occurrence and the implications for recovery of function in injured persons have recently come under closer investigation. 19 Investigation of neuronal circuitry caudal to a spinal cord injury site is required.…”

Two chronic motor training paradigms differentially influence acute instrumental learning in spinally transected rats

“…In addition, the physiological states of the limbs and spinal cord continue to influence each other even when supraspinal connectivity is removed. Ferris et al [21] reported that unilateral stepping in chronic SCI humans induces alternating and rhythmic EMG activity in the non-stepping limb, in a loadingdependent manner. Similar results have been observed in decerebrate cats stepping unilaterally on a treadmill [16].…”