Dynamic balance during walking adaptability tasks in individuals post-stroke

Abstract

Maintaining dynamic balance during community ambulation is a major challenge post-stroke. Community ambulation requires performance of steady-state level walking as well as tasks that require walking adaptability. Prior studies on balance control post-stroke have mainly focused on steady-state walking, but walking adaptability tasks have received little attention. The purpose of this study was to quantify and compare dynamic balance requirements during common walking adaptability tasks post-stroke and in healthy adults and identify differences in underlying mechanisms used for maintaining dynamic balance. Kinematic data were collected from fifteen individuals with post-stroke hemiparesis during steady-state forward and backward walking, obstacle negotiation, and step-up tasks. In addition, data from ten healthy adults provided the basis for comparison. Dynamic balance was quantified using the peak-to-peak range of whole-body angular-momentum in each anatomical plane during the paretic, nonparetic and healthy control single-leg-stance phase of the gait cycle. To understand differences in some of the key underlying mechanisms for maintaining dynamic balance, foot placement and plantarflexor muscle activation were examined. Individuals post-stroke had significant dynamic balance deficits in the frontal plane across most tasks, particularly during the paretic single-leg-stance. Frontal plane balance deficits were associated with wider paretic foot placement, elevated body center-of-mass, and lower soleus activity. Further, the obstacle negotiation task imposed a higher balance requirement, particularly during the trailing leg single-stance. Thus, improving paretic foot placement and ankle plantarflexor activity, particularly during obstacle negotiation, may be important rehabilitation targets to enhance dynamic balance during post-stroke community ambulation.

Keywords: Angular momentum; Biomechanics; Community ambulation; Gait; Obstacle; Stability.

Fig. 1

The net external moment components are shown in the sagittal, frontal and transverse planes during single-leg-stance. Whole-body center-of-mass (CoM) is shown with ‘ ’. The ground-reaction-force (GRF) vectors and their corresponding moment arms appear in the same color. During single-leg-stance, only the stance leg contributes to the net external moment about the body CoM. In each plane, the net external moment consists of two moment arm and GRF components. For instance, in the frontal plane, only the vertical and mediolateral moment arms and GRFs contribute to the net external moment and the regulation of whole-body angular-momentum. Here, we focus on analyzing the moment arms to further understand the regulation of whole-body angular-momentum.

Fig. 2

Walking adaptability tasks were as follows, obstacle-trail (OBT): obstacle negotiation during the trailing leg single-stance; obstacle-lead (OBL): obstacle negotiation during the leading leg single-stance; step-up-trail (SUT): step-up during the trailing leg single-stance; step-up-lead (SUL): step-up during the leading leg single-stance. Each one of the adaptability tasks were repeated for the paretic leg leading as well as the nonparetic leg leading. For example in the OBT, during the paretic single-leg-stance, the nonparetic leg leads to clear the obstacle and vice versa.

Fig. 3

The mean, normalized trajectories of whole-body angular-momentum in each of the three anatomical planes for all the tasks (SS: self-selected; FC: fastest-comfortable; BW: backward walking; Obstacle: obstacle clearance; Step-up: stepping up a box). Trajectories represent average data across participants post-stroke ( ) and healthy controls ( ). The post-stroke data is shown in the paretic leg reference frame (i.e., 0% gait cycle represents paretic leg heel strike). For brevity, only the obstacle and step-up trials leading with the nonparetic leg are shown. Shaded regions represent the healthy control single-leg-stance (SLS) phase of the gait cycle (exact values shown in Fig. 6). Positive directions of angular-momentum are (sagittal: backward; frontal: towards the reference leg; transverse: from the reference leg to the contralateral leg).

Fig. 4

The mean (SD), normalized range of H (H_R) in each of the three anatomical planes during single-leg-stance (SLS) of the nonparetic leg ( ), paretic leg ( ), and average of both legs in healthy controls ( ). Tasks included self-selected (SS), fastest-comfortable (FC) and backward (BW) walking, obstacle negotiation during trailing (OBT) and leading (OBL) leg support, and step-up during trailing (SUT) and leading (SUL) leg support. Significant differences (P < α/2, α < 0.05) are shown between the paretic- and nonparetic-SLS (§) as well as paretic- and healthy control-SLS (ψ). The largest group differences in H_R are in the frontal plane. Note the smaller scale in the transverse plane.

Fig. 5

The mean (SD), normalized range of H (H_R) in the sagittal ( ), frontal ( ) and transverse ( ) planes during the paretic and healthy control single-leg-stance (SLS). Significant differences across the tasks are shown in the tables with ‘*’ (for P < α/6, α < 0.01) and ‘†’ (for P < α/6, 0.01<α < 0.05). The colors of the significance symbols correspond to the anatomical planes. In the sagittal plane, in both groups H_R during the trailing phase of the obstacle (OBT) and step-up (SUT) tasks was higher than other tasks (task demand). In the frontal plane, only in adults post-stroke H_R during the obstacle negotiation (OBT and OBL) was higher than other tasks (difference in regulation).

Fig. 6

The mean (SD) rate of change of H (Ḣ) in the frontal plane (left) and single-leg-stance (SLS) duration (right) during the nonparetic ( ), paretic ( ), and healthy control ( ) SLS. Significant differences (P < α/2, α < 0.05) are shown between the paretic- and nonparetic-SLS (§) as well as the paretic- and healthy control-SLS (ψ). Significant differences in Ḣ across tasks are shown in the table with ‘*’ (for P < α/6, α < 0.01) and ‘†’ (for P < α/6, 0.01<α < 0.05). The colors of the significance symbols correspond to the limbs. During the paretic-SLS, Ḣ was higher than the nonparetic- and healthy control-SLS, while paretic-SLS duration was lower than the non-paretic and healthy control-SLS. Adults post-stroke regulated H differently across tasks than healthy controls.

Fig. 7

The mean (SD) mediolateral moment arm (top left); vertical moment arm (top right), soleus (SOL) activation (bottom left); medial gastrocnemius (GAS) activation (bottom right) during the nonparetic ( ), paretic ( ), and healthy control ( ) single-leg-stance (SLS). Significant differences (P < α/2, α < 0.05) are shown between the paretic- and nonparetic-SLS (§) as well as the paretic- and healthy control-SLS (ψ). Significant differences across tasks are shown in the tables with ‘*’ (for P < α/6, α < 0.01) and ‘†’ (for P < α/6, 0.01<α < 0.05). The colors of the significance symbols correspond to the limbs. Although the direction (increase or decrease) of changes in the moment arms between tasks were similar in both groups, adults post-stroke had significantly larger moment arms than healthy controls. Soleus activation during the obstacle and step-up tasks was significantly higher in healthy controls than post-stroke.