Neuromechanical considerations for the incorporation of rhythmic arm movement in the rehabilitation of walking
Date
2010-09-17T20:45:00Z
Authors
Klimstra, Marc D.
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Abstract
Evidence suggests that the basic neural elements controlling and coupling the arms and the legs in humans during coordinated rhythmic movements are similar to that observed in quadrupedal animals. Further, it is possible that these interlimb connections may be exploited to assist in locomotor rehabilitation after neurotrauma. Specifically, the effect of arm activity on leg neural circuitry has great implications for walking retraining. However, our understanding of the neuromechanics of rhythmic arm movement as well as the neuronal connections between arms and legs active during rhythmic movement is
lacking. Greater knowledge on details of interlimb coupling and combined neural and
mechanical measurement of rhythmic arm movement are necessary to optimize
parameters of interlimb coupling for use in walking rehabilitation. The primary goals of
this thesis were to further our understanding of neural interlimb connections during combined arm and leg rhythmic movement and conduct neuromechanical investigations of rhythmic arm movement.
First, this thesis developed a method for multiple parameter analysis of the Hoffmanreflex recruitment curve. A sigmoid function was found to be a reliable analysis
technique that mimics the physiologically based prediction of the input/output relation of the ascending limb of the recruitment curve. This technique provided a baseline for evaluation of neural interactions between the arms and the legs during rhythmic movement and was utilized during following experiments. Second, the effect of rhythmic leg cycling on reflexes within, and corticospinal projections to, stationary arm muscles was examined. Rhythmic leg cycling significantly
suppressed H-reflexes in forearm muscles. Additionally, sub-threshold transcranial
magnetic stimulation (TMS) facilitation of H-reflexes was similar during leg cycling as
during static contraction suggesting a considerable sub-cortical component. These results supports the hypothesis of a loose, but significant, neural coupling between the arms and the legs during rhythmic movement.
Third, we used a reduced walking model of combined arm and leg cycling to examine the
separate and combined effects of rhythmic arm and leg movement on the modulation of
lower limb H-reflexes with and without stimulating a nerve innervating the hand. The
suppressive effect of arm movement was less than that for leg movement and combined
arm and leg rhythmic movement, which were generally equivalent. For H-reflexes
conditioned by cutaneous input to the hand, amplitudes during combined arm and leg
movement instead were in between those for modulation produced by arm movement and
leg movement alone. Further a significant contribution for arm movement was revealed
only in trials when hand stimulation was used to condition H-reflex amplitudes.
Therefore a measurable interaction between neural activity regulating arm and leg
movement during locomotion is specifically enhanced when cutaneous input from the
hand is present.
Fourth, we explored interlimb interactions during a locomotor-like, 3 limb stepping
paradigm involving movement of both arms and one leg while eliciting an H-reflex in the
stationary test limb. The conditioning effect of contralateral leg movement, bilateral arm movement, and combined bilateral arm and contralateral leg movement on H-reflex amplitude was evaluated at different phases across all tasks. Significant interactions between arm and leg activity could be revealed using the 3-limb paradigm. Further, across phases we observed differential suppressive effects of separate and combined arm and leg movement suggesting phase dependent contributions of arm and leg activity to overall 3-limb suppression. These results support the role of the arms in modulating activity in the legs during human locomotor tasks.
Fifth, the mechanical effects of stimulating a cutaneous nerve innervating the dorsum of
the hand during arm cycling were quantified. The results show that mechanical responses
to cutaneous stimulation of the hand during arm cycling are related to the task and phase
and consistent with the anatomical location of the stimulus (local sign). Therefore, these responses are comparable to functionally relevant responses in the legs during lower limb rhythmic movement. However, unlike the responses in the lower limbs, the mechanical responses cannot be easily described in the neuromechanical context of arm cycling.
Therefore we suggest that the superimposed task constraints and control variable of arm
cycling limit the kinematic reflex expression and make it difficult to decipher the true functional role of the reflexes. Overall, these results provide evidence for mechanical correlates to neural responses during arm cycling and further support parallels between the neural regulation of arm and leg rhythmic movement.
Sixth, a combined neural and mechanical measurement approach was used to compare
three rhythmic arm movement tasks: arm cycling; arm swing while standing; and arm
swing while treadmill walking. The results highlight important neural and mechanical
features that distinguish differences between tasks. Overall, differences in neural control between tasks (i.e., pattern of muscle activity) reflected changes in the mechanical constraints unique to each task while the results are consistent with conserved common central motor control mechanisms operational for arm cycling, arm swing while walking, and arm swing alone yet appropriately sculpted to demands unique to each task.
Taken together the data in this thesis suggest that, in addition to understanding details of neural interlimb coupling, mechanical considerations may play an important role in the coordination of locomotor movements. Additionally, the use of rhythmic arm movement as a locomotor adjunct in rehabilitation is revealed through combined neural and mechanical measurement.
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Keywords
Mechanics, Neuroscience