The effects of different sensory augmentation on weight-shifting balance exercises in Parkinson's disease and healthy elderly people: a proof-of-concept study

Abstract

Background: Earlier versions of biofeedback systems for balance-related applications were intended primarily to provide "alarm" signals about body tilt rather than to guide rehabilitation exercise motion. Additionally, there have been few attempts to evaluate guidance modalities for balance rehabilitation exercises. The purpose of this proof-of-concept study is to evaluate the effects of guidance modalities during common dynamic weight-shifting exercises used in clinical settings.

Methods: A motion guidance system providing visual biofeedback, vibrotactile biofeedback, or both, was used during weight-shifting exercises. Eleven people with idiopathic Parkinson's disease (PD) and nine healthy elderly people participated. Each participant wore a six-degree-of-freedom inertial measurement unit (IMU) located near the sacrum and four linear vibrating actuators (Tactors) attached to the skin over the front, back, and right and left sides of the abdomen. The IMU measured angular displacements and velocities of body tilt in anterior-posterior (A/P) and medial-lateral (M/L) directions. Participants were instructed to follow a slow moving target by shifting their weight in either the A/P or M/L direction up to 90 % of their limits of stability (LOS). Real-time position error was provided to participants in one of three sensory modalities: visual, vibrotactile, or both. Participants performed 5 trials for each biofeedback modality and movement direction (A/P and M/L) for a total of 30 trials in a random order. To characterize performance, position error was defined as the average absolute difference between the target and participant movements in degrees.

Results: Simultaneous delivery of visual and vibrotactile biofeedback resulted in significantly lower position error compared to either visual or vibrotactile biofeedback alone regardless of the movement direction for both participant cohorts. The pairwise comparisons were not significantly different between visual and vibrotactile biofeedback.

Conclusion: The study is the first attempt to assess the effects of guidance modalities on common balance rehabilitation exercises in people with PD and healthy elderly people. The results suggest that combined visual and vibrotactile biofeedback can improve volitional responses during postural tracking tasks. Index Terms - sensory augmentation, weight-shifting balance exercise, guidance modality, vibrotactile biofeedback, visual biofeedback, Parkinson's disease.

Fig. 1

A system configuration. a Sensing system. b Custom software. c C2 tactor and tactor control unit. d Visual biofeedback. A white and light blue object depicts the target and participant’s movements in A/P and M/L directions

Fig. 2

a Sensor and tactor location. b Representative sample data from one participant with PD during the A/P dynamic weight-shifting exercise. Images shown in the top panel indicate movement directions corresponding to the movement trajectories shown in the bottom panel. Solid blue and red lines shown in the bottom panel represent the target motion (generated by custom software after measuring the participant’s 90 % of LOS in the A/P direction) and participant’s motion, respectively. Dashed black lines represent the participant’s 90 % of LOS in both the anterior and posterior directions

Fig. 3

Average SOT scores for the PD (n = 11) and control (n = 9) group

Fig. 4

Average range of LOS in the A/P and M/L direction as a function of the group before and after dynamic weight-shifting balance exercises guided by biofeedback. Error bars indicate standard error of the corresponding average (* p < 0.05, ** p < 0.0001)

Fig. 5

Average position error as a function of the direction, modality, and group. Error bars indicate standard error of the corresponding average (* p < 0.05, (** p < 0.001, ** p < 0.0001)