We compared EMG activity during attempted voluntary movements and during stepping using BWST and manual assistance that facilitated the kinetics and kinematics of walking in individuals with SCI. We compared EMG activity from muscles during voluntarily attempted non-weight bearing single-joint movements, multi-joint movements approximating stepping in a supine position, and weight bearing stepping using BWST. Clinically complete SCI individuals could activate motor pools with reciprocal activation patterns between agonists and antagonists during weight bearing stepping when they were unable to generate movement or EMG activity in the lower limbs during voluntarily attempted movements.

Fig. 1

Fig. 1 Single- and multijoint movements and stepping from a clinically complete SCI subject. Electromyographic (EMG) activity (µV) from the soleus (SOL) medial gastrocnemius (MG), tibialis anterior (TA), medial hamstrings (MH), vastus lateralis (VL), and rectus femoris (RF); knee and ankle angles (°); and limb load in Newtons (N) during an attempted single-joint movement (A-D), multijoint movements (E), and during weight-bearing stepping at 0.22 m/sec with 56% body weight support (BWS) (F). None of the muscles studied were recruited during attempted single- and multijoint movements with limbs unloaded (A-E). During stepping (F) discrete flexor bursts occurred at terminal stance/initial swing and extensors were active during stance. Similar to clinically incomplete SCI subjects, MH activity occurred during terminal swing and early stance. The TA was coactivated with plantarflexors during stance.

None of the muscles studied were recruited during attempted single- and multi-joint movements with limbs unloaded in resting positions. However, during stepping, discrete flexor bursts occurred at terminal stance/initial swing and extensors were active during stance. The tibialis anterior (TA) was co-activated with plantarflexors during stance.

Clinically incomplete SCI subjects who were able to generate some voluntary movement in the lower limbs also had significantly higher EMG mean amplitudes during stepping in all muscles studied than during voluntary attempted single- and/or multi-joint movements.

Fig. 2

Fig. 2 Single- and multijoing movements, and stepping from a clinically incomplete SCI subject. Electromyographic (EMG) activity (µV) from the soleus (SOL) medial gastrocnemius (MG), vastus lateralis (VL), and rectus femoris (RF); knee and ankle angles (°); and limb load in Newtons (N) during and attempted single-joing movement (A and B), multijoint movements (C), and during weight-bearing stepping at 0.33 m/sec with 35% body weight support (BWS) (D). The nonspecificity in the activation of the muscles was present during attempts to dorsiflex the ankle and flex the knew. Slight activation of the VL and RF occurred with attempted ankle dorsiflexion (A). When the same subject attempted to flex the knee the MH was activated, but so was the TA and RF (B). Note that the TA awas not activated during attmpts to dorsiflex the ankle (A). Each muscle was activated during multijoint efforts (C), although at a lower amplitude than during stepping (D). MH EMG bursts were reciprocal to the VL and RF and the TA EMG was largely synchronized with the SOL and MG during stepping with some activation during swing.

Summary results from both clinically complete and incomplete SCI subjects demonstrate that during weight bearing stepping using BWST individuals with SCI could achieve greater activation of motor pools and more reciprocal patterns of activity between agonists and antagonists than during voluntarily initiated movements.

Fig. 3

Fig. 3 The SOL, MG, MH and VL had a higher group average EMG mean amplitude during weight-bearing stepping compared to conditions when the subject performed voluntary taks without weight bearing (p < 0.05). The mean TA and RF EMG amplitudes did not differ statistically among the motor tasks. The group mean EMG amplitudes during the multijoing and single-joing tasks were similar in all muscles studied.

These results are significant because they demonstrate that stepping with alternating lower limb loading provides proprioceptive inputs to the spinal cord that increase motor recruitment compared to voluntary efforts in SCI subjects. These results demonstrate that sensory cues mediated by the human spinal cord play a significant role in the generation of locomotor patterns.

Levels of voluntary control of the legs does not solely predict the ability to walk.

Click here for related studies.

Related Publications:

Maegele M, Mueller S, Wernig A, Edgerton VR, Harkema SJ. Recruitment of spinal motor pools during voluntary movements versus stepping after human spinal cord injury. J Neurotrauma 2002;19(10):1217-29.