Locomotor adaptation is influenced by the interaction between perturbation and baseline asymmetry after stroke

Abstract

Stroke survivors without cerebellar involvement retain the ability to adapt to the split-belt treadmill, however it has been suggested that their rate of adaptation may be slowed compared to those who are neurologically intact. Depending on limb placement, the split-belt treadmill can be configured to either exaggerate baseline asymmetry, or reduce it, which may affect the behavior of adaptation or de-adaptation. The objectives of this study were to characterize the rate and magnitude of locomotor (de)adaptation in chronic stroke survivors compared to healthy matched subjects, and to evaluate whether exaggeration or reduction of baseline asymmetry impact the responses. Seventeen stroke survivors and healthy subjects completed 10 minutes of split-belt treadmill walking, then 5 minutes of tied-belt walking. Stroke survivors completed this once with each leg on the fast belt. Magnitude and rate of (de)adaptation were evaluated for step length and limb phase asymmetry. There were no differences between the groups with the exception of the reduced step length asymmetry configuration, in which case there was a significantly reduced magnitude (p=<0.000) and rate (p=0.011) of adaptation when compared to controls. There was a similar trend observed during post-adaptation for the exaggerated asymmetry group. The rate and magnitude of locomotor (de)adaptation is similar between chronic stroke survivors and neurologically intact controls, except when the adaptation or de-adaptation response would take the stroke survivors away from a symmetric step length pattern. This suggests that there may be some benefit to symmetry that is recognized by the system.

The influence of high intensity exercise and the Val66Met polymorphism on circulating BDNF and locomotor learning

“…Step length was labeled as Left or Right based on leading leg. Stride by stride symmetry data for step length was calculated as: $$\frac{false(boldnormal\mathrm{Step}boldnormal\mathrm{Length}boldnormalofboldnormal\mathrm{Leg}boldnormalonboldnormal\mathrm{Slow}boldnormal\mathrm{Belt}-boldnormal\mathrm{Symmetrical}boldnormal\mathrm{Step}boldnormal\mathrm{Length}false)}{boldnormal\mathrm{Symmetrical}boldnormal\mathrm{Step}boldnormal\mathrm{Length}}$$Where symmetrical step length = (Left step length + Right step length)/2 (Tyrell et al, 2014; Tyrell, Helm, & Reisman, 2015). …”

“…The temporal measure of limb phasing was calculated as previously reported (Helm et al, 2015; Tyrell et al, 2014, 2015). Briefly, a calculation of limb phase for each leg provides a measure of the difference in time between the contralateral limb’s peak flexion and the ipsilateral limb’s peak extension, normalized by the ipsilateral limb’s stride duration.…”

“…This was performed by subtracting the average of the last 30 strides of the baseline condition from each raw symmetry value (Tyrell et al, 2014, 2015; Vasudevan, Torres-Oviedo, Morton, Yang, & Bastian, 2011). Subtraction of the baseline symmetry pattern from each raw symmetry value allows for comparison of data across subjects who may demonstrate different levels of baseline (a)symmetry.…”

The presence of a single-nucleotide polymorphism in the BDNF gene affects the rate of locomotor adaptation after stroke

“…Where symmetrical step length = (paretic step length + non-paretic step length)/2 (Tyrell et al, 2014; Tyrell, Helm, & Reisman, 2015). …”

“…The temporal measure of limb phasing was calculated as previously reported (Tyrell et al, 2014, 2015). Briefly, a calculation of limb phase for each leg provides a measure of the difference in time between the contralateral limb’s peak flexion and the ipsilateral limb’s peak extension, normalized by the ipsilateral limb’s stride duration.…”