Using Biofeedback to Reduce Step Length Asymmetry Impairs Dynamic Balance in People Poststroke

Abstract

Background: People poststroke often walk with a spatiotemporally asymmetric gait, due in part to sensorimotor impairments in the paretic lower extremity. Although reducing asymmetry is a common objective of rehabilitation, the effects of improving symmetry on balance are yet to be determined.

Objective: We established the concurrent validity of whole-body angular momentum as a measure of balance, and we determined if reducing step length asymmetry would improve balance by decreasing whole-body angular momentum.

Methods: We performed clinical balance assessments and measured whole-body angular momentum during walking using a full-body marker set in a sample of 36 people with chronic stroke. We then used a biofeedback-based approach to modify step length asymmetry in a subset of 15 of these individuals who had marked asymmetry and we measured the resulting changes in whole-body angular momentum.

Results: When participants walked without biofeedback, whole-body angular momentum in the sagittal and frontal plane was negatively correlated with scores on the Berg Balance Scale and Functional Gait Assessment supporting the validity of whole-body angular momentum as an objective measure of dynamic balance. We also observed that when participants walked more symmetrically, their whole-body angular momentum in the sagittal plane increased rather than decreased.

Conclusions: Voluntary reductions of step length asymmetry in people poststroke resulted in reduced measures of dynamic balance. This is consistent with the idea that after stroke, individuals might have an implicit preference not to deviate from their natural asymmetry while walking because it could compromise their balance. Clinical Trials Number: NCT03916562.

Keywords: angular momentum; asymmetry; balance; biofeedback; gait; stroke; validation.

Figures

Figure 1.

Experimental protocol. We provided online visual feedback to show the position of the ankle markers during swing phase as black dots and a vertical bar on each side, which represented the target step length. Black horizontal lines near the top of each bar in the Baseline asymmetry trial represent the target range which was equal to the standard deviation of the step length measured during baseline. Scores were provided on the top left or right corner of the display to encourage participants to achieve the desired step lengths.

Figure 2.

Angular momentum varies with the level of step length asymmetry. (a) Angular momentum in the sagittal plane across the gait cycle. Participants rotated forward most around non-paretic foot-strike (40 ∼ 60% of a gait cycle) and rotated backward most around non-paretic mid swing (75 ∼ 85 % of a gait cycle). The line represents the average across participants and the shaded area represents the standard deviation. The gait cycle starts with foot-strike on the paretic side. (b) Angular momentum in the frontal plane over the gait cycle. Participants rotated toward the non-paretic side near non-paretic foot-strike (40 ∼ 60% of a gait cycle) and rotated toward the paretic side most near paretic foot-strike (0 ∼ 15 % of a gait cycle).

Figure 3.

Associations between the peak forward and backward angular momentum in the sagittal (L_Sag^min and L_Sag^max) and frontal plane (L_Fr^min) and clinical balance assessments during Baseline. L_Sag^min was positively associated with (a) the Functional Gait Assessment and L_Sag^min was negatively associated with (b) Berg Balance Scale and (c) the Functional Gait Assessment. L_Fr^min was positively associated with (d) Functional Gait Assessment. FGA: Functional Gait Assessment, BBS: Berg Balance Scale

Figure 4.

Association between step length asymmetry and baseline peak angular momentum in the sagittal plane. Participant’s natural SLA magnitude was positively associated with L_Sag^max magnitude as measured during the Baseline trial. This indicates that larger SLA magnitude is associated with larger peak backward angular momentum in the sagittal plane.

Figure 5.

Variation in step length asymmetry (SLA) across trials (a) A representative participant with longer non-paretic step lengths had positive SLA during Baseline, Baseline FB, and ExggAsym. During Sym, the participant reduced step length asymmetry. (b) A representative participant with longer paretic step lengths had negative SLA during Baseline, Baseline FB, and ExggAsym. During Sym, the participant reduced step length asymmetry. (c) Step length asymmetry magnitude for all participants during Baseline, Baseline FB, Sym, and ExggAsym. *p