Comparison of Soleus H-Reflexes in Two Groups of Individuals With Motor Incomplete Spinal Cord Injury Walking With and Without a Walker

Phadke, Chetan P.; Flynn, Sheryl; Kukulka, Carl G; Thompson, Floyd J.; Behrman, Andrea L.

doi:10.1310/sci2016-0007

Cited by 1 publication

(1 citation statement)

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“…For example, do humans favor trajectories producing lower and less variable contraction velocities? By extension, such an approach can help us understand how disruption of reflex mechanisms could lead to pathological movements such as spasticity, tremor and clonus (Zehr and Stein, 1999; Hultborn, 2006; Hidler and Rymer, 1999; Laine et al, 2016) in neurological conditions including cerebral palsy, stroke, Parkinsons disease and spinal cord injury (Sanger et al, 2010; de Vlugt et al, 2016; Phadke et al, 2016; Agapaki et al, 2016). Similarly, perhaps one can design arm movement trajectories that are more effective for rehabilitation because they require less time-critical modulation of stretch reflexes.…”

Section: Discussionmentioning

confidence: 99%

Similar movements are associated with drastically different muscle contraction velocities

Hagen

Valero-Cuevas

2017

Journal of Biomechanics

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We investigated how kinematic redundancy interacts with the neurophysiological control mechanisms required for smooth and accurate, rapid limb movements. Biomechanically speaking, tendon excursions are over-determined because the rotation of few joints determines the lengths and velocities of many muscles. But how different are the muscle velocity profiles induced by various, equally valid hand trajectories? We used an 18-muscle sagittal-plane arm model to calculate 100,000 feasible shoulder, elbow, and wrist joint rotations that produced valid basketball free throws with different hand trajectories, but identical initial and final hand positions and velocities. We found large differences in the eccentric and concentric muscle velocity profiles across many trajectories; even among similar trajectories. These differences have important consequences to their neural control because each trajectory will require unique, time-sensitive reflex modulation strategies. As Sherrington mentioned a century ago, failure to appropriately silence the stretch reflex of any one eccentrically contracting muscle will disrupt movement. Thus, trajectories that produce faster or more variable eccentric contractions will require more precise timing of reflex modulation across motoneuron pools; resulting in higher sensitivity to time delays, muscle mechanics, excitation/contraction dynamics, noise, errors and perturbations. By combining fundamental concepts of biomechanics and neuroscience, we propose that kinematic and muscle redundancy are, in fact, severely limited by the need to regulate reflex mechanisms in a task-specific and time-critical way. This in turn has important consequences to the learning and execution of accurate, smooth and repeatable movements—and to the rehabilitation of everyday limb movements in developmental and neurological conditions, and stroke.

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