Soleus Loading Response During Walking

Plain-language summary

Stroke survivors experience motor deficits, weak voluntary muscle activations, and low weight-bearing capacity that impair ambulation. Restoring motor function is a priority for people post-stroke, whose gait patterns are slow, and metabolically inefficient. The role of the ankle is crucial for locomotion because it stores mechanical energy throughout the stance phase, leading to a large activation of plantarflexor muscles during push-off for propulsion. After a stroke, paretic plantarflexors undergo changes in their mechanics and activation patterns that yield diminished ankle power, propulsion, and gait speed. Recovery of lost plantarflexor function can increase propulsion and mitigate unnatural gait compensations that occur during hemiparetic walking. In the stance phase, dorsiflexion is imposed at the ankle and the plantarflexors are loaded, which results in excitation of group Ia and II afferents, and group Ib afferents. Load sensing Ib afferents are active in mid-late stance, and through spinal excitatory pathways, reinforces the activation of plantarflexors and propulsive force generation at the ankle. Targeting the excitability of the load sensitive Ib excitatory pathway, propulsive soleus activity and resulting force generation (and thereby gait speed) can be improved after stroke. The long-term research goal is to develop a novel hybrid gait paradigm integrating operant conditioning and powered wearable devices to advance neuro-behavioral training and enhance locomotor ability after stroke. The overall objectives are to 1) modulate the soleus muscle loading response within the stance phase, and 2) develop a dynamic protocol to operantly condition the soleus response in stroke survivors. The central hypothesis is that enhancing the soleus loading response in mid-late stance phase through operant up-conditioning can increase plantarflexor power and forward propulsion after stroke. In working towards attaining the research objective and testing the central hypothesis, the objective of this pilot study is to modulate the soleus loading response in the stance phase during treadmill walking. The specific aims in this study are to 1) apply ankle perturbations in mid-late stance phase combining a control algorithm and a powered device to characterize the changes in soleus EMG between perturbed and unperturbed (i.e., when no perturbations are applied) step cycles in 15 able-bodied individuals; and 2) determine the feasibility of the wearable ankle device and its algorithm in 5 participants with hemiparesis and gait deficits due to a stroke. The testing of the device and its algorithm will provide foundational evidence to adjust the soleus stimuli continuously and reliably, and develop the new walking operant conditioning protocol for stroke survivors. An expected outcome in this pilot is to lay the groundwork to develop the soleus up-conditioning protocol as a potential strategy to improve paretic leg function. If successfully developed, this new protocol proposed in a subsequent study will be the first neurobehavioral training method that targets spinal load-sensitive pathways to improve ankle plantarflexor power and forward propulsion after stroke.

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