AB Gait Estim Neurophysiology

OTHER

Gait Training

Gait training: One or multiple short bouts of stepping practice on a treadmill at self-selected or fast speeds will be delivered without FES.

DEVICE

Functional electrical stimulation (FES)

Electrical stimulation involving the parameters and settings proposed here is commonly used in clinical practice and research for pain relief and other applications also referred to as neuromuscular or transcutaneous electrical nerve stimulation. The FES will be delivered using the UDel Stimulator, a custom-designed FES system from the University of Delaware FES lab. Researchers will use a customized, real-time system to control the stimulator and deliver stimulation during appropriate phases of the gait cycle. Stimulation will be delivered to the ankle dorsiflexors when the subject's foot is in the air (swing phase). Stimulation will be delivered to the ankle plantarflexors during the terminal stance phase of gait. 30-Hz variable frequency stimulation trains will be delivered during gait.

DEVICE

Peripheral electrical stimulation paired with cortical magnetic stimulation pulses

The paired associative stimulation (PAS) will be conducted in a static posture (seated or standing), to evaluate effects on somatosensory, spinal-reflex, and/or corticospinal neurophysiology delivered with different stimulation parameters. One or multiple short bouts of stepping practice on a treadmill at self-selected or fast speeds may be completed before and/or after PAS to evaluate gait performance

Gait Performance

Time frame: Pretest (up to 60 seconds), during test (up to 36 minutes), post-test (up to 60 seconds)

Marker data will be collected using a 7-camera motion analysis system at 120 Hz (Vicon, Oxford, UK). During treadmill walking, ground reaction forces during the treadmill walking will be collected using a treadmill instrumented with two 6-component force platforms under each belt (Bertec, USA). Ground reaction forces will be evaluated using a force plate embedded within the lab floor (AMTI, USA).

Corticospinal excitability

Time frame: Pretest (up to 60 seconds), during test (up to 36 minutes), post-test (up to 60 seconds)

Corticospinal excitability will be assessed using a non-invasive technique called transcranial magnetic stimulation (TMS). TMS will be delivered using MagStim Stimulators with a double circular coil, custom-built double-cone, or batwing coil (Magstim Ltd, Wales, UK). Electrical activity from muscles in response to the TMS will be collected using surface EMG electrodes attached to muscles that play critical roles during walking (e.g., quadriceps femoris, tibialis anterior, soleus, gastrocnemius, hamstrings, etc.). In addition, EMG signals may be recorded from a couple of upper extremity muscles (e.g., first dorsal interosseus, flexor digitorum indicis) to be used as a control.

Spinal circuit excitability

Time frame: Pretest (up to 60 seconds), during test (up to 36 minutes), post-test (up to 60 seconds)

Spinal excitability may be assessed using peripheral electrical stimulation delivered to the nerves innervating the ankle muscles. The methods for electrical stimulation are similar to those used for delivering functional electrical stimulation except that the subjects are seated and the stimulation is used to obtain outcome measures assessing spinal excitability. Muscles of interest are the soleus and medial gastrocnemius (calf muscles), and tibialis anterior (front of lower leg). EMG activity will be recorded while 50-60 electrical stimuli (short 1 ms square pulses, ranging in intensity from 1mA - 80 mA), 7-10 seconds apart, are delivered to the muscle. Researchers may also deliver 5-20 electrical stimulus pulses at intensities that elicit a percentage of the maximum reflex response.

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