Paretic propulsion as a measure of walking performance and functional motor recovery post-stroke: A review

Abstract

Background: Although walking speed is the most common measure of gait performance post-stroke, improved walking speed following rehabilitation does not always indicate the recovery of paretic limb function. Over the last decade, the measure paretic propulsion (Pp, defined as the propulsive impulse generated by the paretic leg divided by the sum of the propulsive impulses of both legs) has been established as a measure of paretic limb output and recently targeted in post-stroke rehabilitation paradigms. However, the literature lacks a detailed synthesis of how paretic propulsion, walking speed, and other biomechanical and neuromuscular measures collectively relate to post-stroke walking performance and motor recovery.

Objective: The aim of this review was to assess factors associated with the ability to generate Pp and identify rehabilitation targets aimed at improving Pp and paretic limb function.

Methods: Relevant literature was collected in which paretic propulsion was used to quantify and assess propulsion symmetry and function in hemiparetic gait.

Results: Paretic leg extension during terminal stance is strongly associated with Pp. Both paretic leg extension and propulsion are related to step length asymmetry, revealing an interaction between spatiotemporal, kinematic and kinetic metrics that underlies hemiparetic walking performance. The importance of plantarflexor function in producing propulsion is highlighted by the association of an independent plantarflexor excitation module with increased Pp. Furthermore, the literature suggests that although current rehabilitation techniques can improve Pp, these improvements depend on the patient's baseline plantarflexor function.

Significance: Pp provides a quantitative measure of propulsion symmetry and should be a primary target of post-stroke gait rehabilitation. The current literature suggests rehabilitation techniques that target both plantarflexor function and leg extension may restore paretic limb function and improve gait asymmetries in individuals post stroke.

Keywords: Biomechanics; Gait; Hemiparesis; Symmetry.

Conflict of interest statement

Conflict of interest statement: The authors have no conflicts of interest to declare.

Copyright © 2018 Elsevier B.V. All rights reserved.

Figures

Figure 1:

Comparison of the average propulsion (expressed as a percentage of the total propulsion) generated by the paretic (red bars; Pp) and nonparetic legs (yellow bars) of subjects of differing hemiparetic severity. There are substantial differences in the percent of Pp in those with severe and moderately severe hemiparesis when compared with those with mild severity. Compensation by the nonparetic leg is noticeable in the asymmetry shown by the moderate and severe groups. Error bars indicate SD for each variable. Adapted from [6].

Figure 2:

Individual walking speed data for subjects in each of the hemiparetic severity groups. Although there is a weak overall trend for walking speed to decrease with severity, the variability is substantial and the speed ranges in each of the groups overlap substantially. Five participants with severe hemiparesis are still able to achieve normal walking speeds (>0.8 m/s), but all demonstrate substantial impaired Pp (filled red markers). Conversely, 3 participants with mild hemiparesis walked 49%; filled green markers). Adapted from [6].

Figure 3:

Relationship between step length ratio and Pp. The solid vertical line indicates symmetric steps (SLR=1), vertical dashed lines indicate the SLR subdivisions at SLR equal to 0.9 and SLR=1.1. Solid horizontal line indicates symmetric propulsive force generation by the paretic leg (Pp=50%), horizontal dashed lines indicate differing levels of paretic leg propulsion (10%, 30%, and 70% PP). Step length ratio quantifies step length asymmetry and Pp quantifies the contribution of the paretic leg to the task of propulsion. Note the decreasing Pp as SLR increases. Abbreviations: Pp, paretic leg propulsion (in percent); NP, nonparetic leg; P, paretic leg. Adapted from [19].

Figure 4:

Greater leg extension angles are associated with greater anterior ground reaction forces. Leg extension angle was calculated as the angle between the vertical axis and a line from the pelvis COM to the foot COM [22].

Figure 5:

Average contributions to the normalized GRF (GRF normalized by body weight (BW); contribution computed per unit muscle force) during the 1st and 2nd half of stance in the AP direction for the non-impaired control (black), Group A (red, merged plantarflexor module) and Group B (yellow, independent plantarflexor module) simulations. Hemiparetic values in Groups A and B correspond to muscle groups on the paretic leg. Muscle groups: hamstrings (HAM), soleus (SOL), gastrocnemius (GAS), rectus femoris (RF), vasti (VAS), and gluteus medius (GMED). During the 2nd half of stance, Group A’s increased braking from RF + VAS coupled with reduced propulsion from SOL + GAS compared to controls leads to the reduced net propulsion observed when the plantarflexor module is merged with the early stance extensor module (RF + VAS). Adapted from [49].

Figure 6:

Muscle contributions from the paretic leg to the anterior posterior ground reaction forces during the paretic propulsive phase for A) Subject A who increased Pp with rehabilitation and B) Subject B who decreased Pp with rehabilitation. Adapted from [24].