Different Error Size During Locomotor Adaptation Affects Transfer to Overground Walking Poststroke

Abstract

Background: Studies in neurologically intact subjects suggest that the gradual presentation of small perturbations (errors) during learning results in better transfer of a newly learned walking pattern to overground walking. Whether the same result would be true after stroke is not known.

Objective: To determine whether introducing gradual perturbations, during locomotor learning using a split-belt treadmill influences learning the novel walking pattern or transfer to overground walking poststroke.

Methods: Twenty-six chronic stroke survivors participated and completed the following walking testing paradigm: baseline overground walking; baseline treadmill walking; split-belt treadmill/adaptation period (belts moving at different speeds); catch trial (belts at same speed); post overground walking. Subjects were randomly assigned to the Gradual group (gradual changes in treadmill belts speed during adaptation) or the Abrupt group (a single, large, abrupt change during adaptation). Step length asymmetry adaptation response on the treadmill and transfer of learning to overground walking was assessed.

Results: Step length asymmetry during the catch trial was the same between groups ( P = .195) confirming that both groups learned a similar amount. The magnitude of transfer to overground walking was greater in the Gradual than in the Abrupt group ( P = .041).

Conclusions: The introduction of gradual perturbations (small errors), compared with abrupt (larger errors), during a locomotor adaptation task seems to improve transfer of the newly learned walking pattern to overground walking poststroke. However, given the limited magnitude of transfer, future studies should examine other factors that could impact locomotor learning and transfer poststroke.

Keywords: locomotion; motor learning; rehabilitation; stroke.

Figure 1.

Time course for the experimental paradigm showing Baseline, Adaptation, Catch and Washout periods in over ground and treadmill walking. A) Belt speed time course for experimental group 1 (gradual adaptation). B) Belt speed time course for experimental group 2 (abrupt adaptation).

Figure 2.

Flow diagram of study.

Figure 3.

Individual representative data of step length (a)symmetry for all sequential strides taken during treadmill (3A and 3B) and over ground walking (3C and 3D). Representative subjects that underwent an abrupt split-belt paradigm (A and C) and a gradual paradigm (B and D) are shown. A value of zero represents step length symmetry (normalized by baseline). Note that the placement of the over ground walking periods are indicated in Figures 3A and 3B, but this data is shown in Figures 3C and 3D. Abbreviations: TM, Treadmill; OG post, Over ground post adaptation.

Figure 4.

Comparisons between groups Gradual (gray bars) and Abrupt (black bars) for step length symmetry differences between time points. To ensure that the initial perturbation was different between groups, we compared the symmetry value at early adaptation (EA1) between groups (A). To confirm that the catch trial did not differently influence the groups, we compared the difference between the late adaptation pre catch (LA1) and the early adaptation post catch (EA2) between groups (B). The difference between the early adaptation (EA2) and late adaptation (LA2) post catch were also compared across groups (C). Zero on the y-axis for (A) is relative to baseline (a)symmetry and for (B) and (C) represents no difference across treadmill testing periods within the group. Error bars indicate ± standard deviation. Asterisk indicates a significant difference between groups.

Figure 5.

Comparisons between groups Gradual (gray bars) and Abrupt (black bars) for step length symmetry. (A) The same magnitude of aftereffect (catch trial) on the treadmill was observed between groups. Note that the after effect is normalized by step length symmetry during treadmill baseline, therefore a zero value equals no difference compared to baseline. (B) The transfer index indicates the amount of adaptation transfer from the treadmill to over ground walking in each group. (C) Washout represents if the OG walking washed out the treadmill effects on locomotor learning. A greater value equals better transfer / washout. Note that no differences were observed between groups (p>0.05). Error bars indicate ± standard deviation. Asterisk indicates a significant difference between groups.