Cutaneous reflexes during rhythmic arm cycling are insensitive to asymmetrical changes in crank length

Journal of Neurophysiology

Loadman

Hundza

2012

Self Cite

Disordered reflex activity and alterations in the neural control of walking have been observed after stroke. In addition to impairments in leg movement that affect locomotor ability after stroke, significant impairments are also seen in the arms. Altered neural control in the upper limb can often lead to altered tone and spasticity resulting in impaired coordination and flexion contractures. We sought to address the extent to which the neural control of movement is disordered after stroke by examining the modulation pattern of cutaneous reflexes in arm muscles during arm cycling. Twenty-five stroke participants who were at least 6 mo postinfarction and clinically stable, performed rhythmic arm cycling while cutaneous reflexes were evoked with trains (5 × 1.0-ms pulses at 300 Hz) of constant-current electrical stimulation to the superficial radial (SR) nerve at the wrist. Both the more (MA) and less affected (LA) arms were stimulated in separate trials. Bilateral electromyography (EMG) activity was recorded from muscles acting at the shoulder, elbow, and wrist. Analysis was conducted on averaged reflexes in 12 equidistant phases of the movement cycle. Phase-modulated cutaneous reflexes were present, but altered, in both MA and LA arms after stroke. Notably, the pattern was "blunted" in the MA arm in stroke compared with control participants. Differences between stroke and control were progressively more evident moving from shoulder to wrist. The results suggest that a reduced pattern of cutaneous reflex modulation persists during rhythmic arm movement after stroke. The overall implication of this result is that the putative spinal contributions to rhythmic human arm movement remain accessible after stroke, which has translational implications for rehabilitation.

Section: Methodologic Considerationscontrasting

confidence: 49%

Section: Protocolmentioning

confidence: 70%

Section: Independence Of Reflex and Background Emg Amplitudes After Smentioning

confidence: 95%

Section: Methodologic Considerationsmentioning

confidence: 99%

Section: Protocolmentioning

confidence: 99%

See 3 more Smart Citations

Neural control of rhythmic arm cycling after stroke

Journal of Neurophysiology

Loadman

Hundza

2012

Self Cite

Task-specific modulation of cutaneous reflexes expressed at functionally relevant gait cycle phases during level and incline walking and stair climbing

Lamont

2006

Exp Brain Res

Reflexes are exquisitely sensitive to the motor task that is being performed at the time they are evoked; in other words, they are "task-dependent". The purpose of this study was to investigate the extent to which the pattern of reflex modulation is conserved across three locomotor tasks that differ in muscle activity, joint kinematics, and stability demands. Subjects performed continuous level and incline walking on a treadmill and stair climbing on a stepping mill. Cutaneous reflexes were evoked by delivering trains of electrical stimulation to the sural nerve at the ankle at an intensity of two times the radiating threshold. Electromyographic (EMG) recordings were collected continuously from muscles in the arms, legs and trunk. Results showed that middle-latency reflex modulation patterns were generally conserved across the three locomotor tasks with a few notable exceptions related to specific functional requirements. For example, a reflex reversal was observed for tibialis anterior during stair climbing, which may be indicative of a specific adaptation to the task constraints. Overall our data suggest that the underlying neural mechanisms involved in coordinating level walking can be modified to also coordinate other locomotor tasks such as incline walking and stair climbing. Therefore, there may be considerable overlap in the neural control of different forms of locomotion.

Muscle activation and cutaneous reflex modulation during rhythmic and discrete arm tasks in orthopaedic shoulder instability

Hundza

2006

Exp Brain Res

In orthopaedic shoulder instability, muscle activity (EMG) is altered during unconstrained discrete arm movement tasks (e.g. elevation against a load). These findings have been ascribed to deficits in afferent feedback and neural control with glenohumeral instabilities resulting from orthopaedic injury. However, the integrity of neural control during shoulder movements in those with unstable shoulders is unclear. It is not known if there are altered EMG patterns during rhythmic arm movement or during discrete tasks involving no load, as would be experienced in many arm motions performed in daily living. The primary objective of this study was to evaluate neural control of arm movements between those with unstable shoulders and control participants, within a constrained arm movement paradigm involving both rhythmic arm cycling and discrete reaching. To achieve this objective, we determined if the amplitude and timing of EMG related to the movement pattern (background EMG) was significantly different between groups. Cutaneous reflexes were used to simulate a perturbation to the upper limb that would typically evoke a coordinated response. In the elevation phase of the movement path for anterior and posterior deltoid, upper trapezius, infraspinatus and serratus anterior, background EMG during rhythmic arm cycling was significantly (24%, p < 0.05) larger in unstable shoulders than in controls. No differences were found in background EMG between the groups during the discrete task. Significant differences (p < 0.05) were also noted in cutaneous reflexes between groups for both the rhythmic and discrete tasks with the reflex amplitudes being either increased or reduced in unstable shoulders as compared to controls. The differences in the background EMG and the cutaneous reflexes patterns in those with shoulder instabilities suggest that neural control is altered during rhythmic movement.