Sub-sensory electrical or mechanical stimulation can enhance the sensitivity of the human somatosensory system to improve the balance control capabilities of elderly. In addition, clinical studies suggest that visual-auditory biofeedback can improve sensory compensation for the elderly. This study hypothesizes that the static balance and gait performance of single leg quiet standing and treadmill walking could be improved for providing proprioceptive neuromuscular facilitation using sub-sensory stimulation and visual-auditory biofeedback in amputee subjects. To test this, a computerized foot pressure biofeedback sensory compensation system using sub-threshold low-level electrical stimulation combined with visualauditory biofeedback was developed. Seven unilateral trans-tibial amputees who wore prostheses over 2 years were recruited. The subjects performed multiple single leg quiet standing trials with sub-sensory electrical stimulation applied at the quadriceps muscle during half of the trials. Static balance performance was characterized by using a Zebris motion analysis system to measure the sway distance and duration of the centre of mass on the second sacral (S2) of the subjects. In addition, multiple treadmill ambulatory trials with or without visual-auditory biofeedback was performed. Dynamic gait performance was characterized with a Zebris instrumented insole to measure the temporal responses of foot pressure sensors. Experimental results showed an improvement in three balance performance indices (Holding Time Index, HTI, Maximum Sway Distance Index, MSDI, and Average Sway Distance Index, ASDI) during single leg quiet standing by applying sub-sensory stimulation. The improvement ratio of these balance performance indices across subjects for single leg quiet standing tests resulted in 132.34% in HTI, 44.61% in MSDI, and 61.45% in ASDI. With visual-auditory biofeedback as a cue for heel contact and toe push-off condition during treadmill ambulation, the improvement of four dynamic gait performance measures (Double Support Period, DSP, Constant Time Cadence, CTC, Single Support Period, SSP, and Stance/Swing Ratio, SSR) in amputees was verified. This resulted in 7.89% in DSP (affected side), 5.09% in CTC, 16.67% in SSP (sound side), 45.30% in SSR (sound side), and 40.30% in SSR (affected side) respectively. These findings suggest that sub-threshold electrical stimulation and visual-auditory biofeedback rehabilitation strategies may be effective in compensating sensory loss and improving static balance and dynamic ambulation performance for amputees.

ABSTRACT

Sub‐threshold electrical stimulation can enhance the sensitivity of the human somatosensory system to improve the balance control capability of elderly was shown in recent rehabilitation articles. The purpose of this study was to evaluate the postural sway of trans‐tibial amputees when performing single leg quiet standing on firm surface. Four unilateral trans‐tibial amputees who consecutively wore prosthetics over 2 years were recruited in this study. Subjects performed single leg quiet standing trails with sub‐threshold electrical stimulation applied at the quadriceps muscle during the trails. Spatial co‐ordinates for the determination kinematic data (sway distance) of the center of mass (COM) on second sacral (S2) were collected using an ultrasound‐based Zebris CMS‐HS system. The single leg quiet standing test is measure considered to assess postural steadiness in a static position by a spatial measurement. The common notion is that a better postural steadiness, i.e. less postural sway, allows for longer time single leg quiet standing. However, there is lack of evidence how postural steadiness during single leg quiet standing changes over time. In this article, we hypothesized that the static balance of single leg quiet standing could be improved for providing proprioceptive neuromuscular facilitation using sub‐sensory stimulation in amputees. To test this hypothesis, a computerized sub‐threshold low‐level electrical stimulation device was developed and proposed for clinical study. Experimental results show that reduction in all of the postural sway indices (constant time sway length, max sway distance and average sway distance) and increase in single leg support time index during single leg quiet standing by applying sub‐sensory stimulation. The single leg quiet standing test findings suggest that sub‐threshold electrical stimulation rehabilitation strategies may be effective in improving static balance performance for amputees.

The ability to control postural steadiness is an important determinant of overcoming the internal and external environmental stimulus across the falls for stoke patients. Traditionally, assessments of postural steadiness are based on patient's ability to control the angular deviation of the center of mass (COM) within the base of support. In this study, a wireless inertial-based sensing modality with augmented biofeedback training protocol was developed and used for clinical evaluation. Eighteen cerebral vascular accident patients were recruited for the assessment.The experimental results revealed that biofeedback strategy together with motor skill learning protocol appears to be an important variable for improving postural steadiness during tandem stance.Keywords-postural steadiness, center of mass, knowledge of performance, knowledge of result I.

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