Forced use of paretic leg induced by constraining the non-paretic leg leads to motor learning in individuals post-stroke

Abstract

The purpose of this study was to determine whether applying repetitive constraint forces to the non-paretic leg during walking would induce motor learning of enhanced use of the paretic leg in individuals post-stroke. Sixteen individuals post chronic (> 6 months) stroke were recruited in this study. Each subject was tested in two conditions, i.e., applying a constraint force to the non-paretic leg during treadmill walking and treadmill walking only. For the constraint condition, subjects walked on a treadmill with no force for 1 min (baseline), with force for 7 min (adaptation), and then without force for 1 min (post-adaptation). For the treadmill only condition, a similar protocol was used but no force was applied. EMGs from muscles of the paretic leg and ankle kinematic data were recorded. Spatial-temporal gait parameters during overground walking pre and post treadmill walking were also collected. Integrated EMGs of ankle plantarflexors and hip extensors during stance phase significantly increased during the early adaptation period, and partially retained (15-21% increase) during the post-adaptation period for the constraint force condition, which were significantly greater than that for the treadmill only (3-5%) condition. The symmetry of step length during overground walking significantly improved (p = 0.04) after treadmill walking with the constraint condition, but had no significant change after treadmill walking only. Repetitively applying constraint force to the non-paretic leg during treadmill walking may lead to a motor learning of enhanced use of the paretic leg in individuals post-stroke, which may transfer to overground walking.

Keywords: Constraint force; EMG; Forced use; Locomotion; Stroke.

Conflict of interest statement

Conflict of Interest Statement:

None of the authors have potential conflicts of interest to be disclosed.

Figures

Figure 1.

Experimental setup. A backward resistance force was applied to the non-paretic leg of individuals post-stroke through a motorized cable and cable spool.

Figure 2.

Experimental paradigm. Blocks of overground tests are depicted in gray. Blocks of treadmill walking with no force are depicted in white. Blocks of treadmill walking with force are depicted in light blue, and blocks of standing break are depicted in pattern fill.

Figure 3.

EMG data from one subject during baseline, early adaptation period, late adaptation period, and early post-adaptation period for the constraint force condition, A, and treadmill only condition, B. EMG data were normalized to peak values of each muscle while the subject walked at the maximum walking speed, and were averaged across 20 steps for baseline, and 5 steps for early adaptation, late adaptation, early post-adaptation periods.

Figure 3.

EMG data from one subject during baseline, early adaptation period, late adaptation period, and early post-adaptation period for the constraint force condition, A, and treadmill only condition, B. EMG data were normalized to peak values of each muscle while the subject walked at the maximum walking speed, and were averaged across 20 steps for baseline, and 5 steps for early adaptation, late adaptation, early post-adaptation periods.

Figure 4.

Step-by-step integrated EMG of the paretic leg during the course of treadmill walking for the conditions with a constraint force applied to the non-paretic leg and treadmill only (control). Data shown are average across 15 subjects post-stroke (data from one subject were excluded due to large artifacts). The step numbers were different across subjects during adaptation period because the treadmill speeds were different. Thus, the data from the first 160 steps and last 30 steps during the adaptation period were used to calculate the average of integrated EMG.

Figure 5A.

Group average of integrated EMG of the paretic leg for the condition when a constraint force was applied to the non-paretic leg. Data shown are average and standard deviation across subjects. B. Group average of the changes in integrated EMG of the paretic leg when the constraint force was removed during the early post-adaptation period, i.e., the first 5 steps after load release, and the late post-adaptation period, i.e., the last 5 steps. The changes in integrated EMG at the same time period for the condition of treadmill only are also shown for comparison. * indicates significance.

Figure 5A.

Group average of integrated EMG of the paretic leg for the condition when a constraint force was applied to the non-paretic leg. Data shown are average and standard deviation across subjects. B. Group average of the changes in integrated EMG of the paretic leg when the constraint force was removed during the early post-adaptation period, i.e., the first 5 steps after load release, and the late post-adaptation period, i.e., the last 5 steps. The changes in integrated EMG at the same time period for the condition of treadmill only are also shown for comparison. * indicates significance.

Figure 6.

Group average of the symmetry index of step length during overground walking pre, immediate post, and 10-minute post treadmill walking for the constraint force and treadmill only conditions. Data shown are average and standard error of symmetry index of step length across subjects. * indicates significance.