Neural mechanisms for bilateral force asymmetry during supine lower limb extensions in neurologically intact individuals and individuals with post -stroke hemiparesis.

摘要

When individuals with post-stroke hemiparesis train with upper or lower extremity robotic devices, they increase muscle recruitment and strength specific to the joints exercised. Although current robotic devices address muscle weakness in individuals post-stroke, they do not address patients' impaired force scaling abilities. In this dissertation I examined foot forces produced during lower limb extensions and designed and tested the use of a novel control mode (symmetry-based resistance) for improving individuals' force-scaling abilities. With symmetry-based resistance, exercise resistance increases with increasing lower limb force asymmetry. Subjects who train with symmetry-based resistance perform the least work when they produce symmetric forces. In the first and second experiments, I investigated foot reaction forces in neurologically intact and post-stroke individuals. When both subject populations were asked to produce equal isometric forces in their lower limbs, they generated less force in their weaker limb even though they believed their forces were equal. Normalizing force by each limbs' bilateral maximum voluntary contraction force revealed no significant differences between limbs. These results suggest that individuals relied primarily on sense of effort, rather than proprioceptive feedback, for gauging isometric lower limb force production. Results suggest that sense of effort is also major factor determining force production during isotonic, or dynamic, movements in subjects post-stroke. In the third experiment, I demonstrated that neurologically intact individuals can successfully use the robotic device with symmetry-based resistance to improve their force scaling abilities and increase lower limb force symmetry from ∼46% to ∼50% (where 50% indicates perfect symmetry). In the final experiment, individuals with post-stroke hemiparesis were able to improve their lower limb symmetry from an initial average value of ∼29% to ∼36% during exercise with symmetry-based resistance. Improvements in lower limb symmetry, however, were not maintained during the one day training session when the controller was turned off. Subjects who trained for four weeks showed a trend towards retention of improved symmetry as initial lower limb symmetry values were improved from Day 1 to Day 4. Overall these studies provide information about the neural mechanisms for lower limb force generation and suggest an innovative controller for stroke rehabilitation.