Brain Advance Access originally published online on August 2, 2004
Brain 2004 127(10):2232-2246; doi:10.1093/brain/awh252
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Brain Vol. 127 No. 10 © Guarantors of Brain 2004; all rights reserved
The human spinal cord interprets velocity-dependent afferent input during stepping
1 Department of Neurology and 2 Brain Research Institute, University of California, Los Angeles, CA, USA
Correspondence to: Susan J. Harkema, Department of Neurology, Brain Research Institute, David Geffen School of Medicine at UCLA, Human Locomotion Research Center, Rehabilitation Building, 1000 Veteran Avenue Suite A386, Los Angeles, CA 90095-7147 USA E-mail: sharkema{at}mednet.ucla.edu
We studied the motor response to modifying the rate of application of sensory input to the human spinal cord during stepping. We measured the electromyographic (EMG), kinematic and kinetic patterns of the legs during manually assisted or unassisted stepping using body weight support on a treadmill (BWST) in eight individuals with spinal cord injury (SCI). At various treadmill speeds (0.27–1.52 m/s), we measured the EMG activity of the soleus (SOL), medial gastrocnemius (MG), tibialis anterior (TA), medial hamstrings (MH), vastus lateralis (VL), rectus femoris (RF) and iliopsoas (ILIO); the hip, knee and ankle joint angles; the amount of body weight support (BWS); and lower limb loading. The EMG amplitude and burst duration of the SOL, MG, TA, MH, VL, RF and ILIO were related to the step cycle duration during stepping using BWST. EMG mean amplitudes increased at faster treadmill speeds, and EMG burst durations shortened with decreased step cycle durations. Muscle stretch of an individual muscle could not account for the EMG amplitude modulation in response to stepping speed. The effects on the EMG amplitude and burst duration were similar in subjects with partial and no detectable supraspinal input. We propose that the human spinal cord can interpret complex step-related, velocity-dependent afferent information to contribute to the neural control of stepping.
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