Effectiveness of different visual biofeedback signals for human balance improvement
Introduction
Undisturbed upright stance control is a complex task based on an integration process involving visual, vestibular and proprioceptive information [1]. Postural stability is often evaluated by outputs from the force platform, which measures the centre of foot pressure (CoP) variability. However, posturography has its limitations because human body is multi-segmental and does not always act as an inverted pendulum. Upper body segments are often more independent from lower body segments, especially in challenged situations [2].
Visual biofeedback (VBF) consists of supplying individuals with additional artificial visual information about body motion to supplement the natural visual information and improve human balance [3]. The use of real-time visual biofeedback (VBF) from CoP during a standing task is a common tool incorporated in evaluation and training of the postural control [4]. The CoP position is presented in real time on a monitor screen and the subject is required to confine it to the narrowest possible zone [5].
The sensor of body motion is, besides the processor and interface, one of the main components of each biofeedback device [6]. The question of optimal sensor location for VBF has not been examined yet, despite the fact that accelerometers allow to measure inclination of body segment with respect to the vertical position. They can be attached to any part of the body. Body tilts measured by the accelerometer could be displayed on a monitor screen as well as outputs from a force platform. That offers new possibilities for VBF experiments.
In the present study, the effectiveness of VBF sensed from accelerometers attached to upper and lower trunk and VBF sensed from CoP were investigated. It was hypothesized that VBF from accelerometer attached to lower trunk would have similar influence on the body sway as VBF from CoP, because both reflect similar postural activities.
Section snippets
Methods
Twenty young subjects (9 men and 11 women) within the range of 20–33 years (mean age 22.6 years, mean BMI 21 kg m−2) participated in the study. Subjects did not report any neurological, orthopaedic, or balance impairments. They gave their informed consent in agreement with the Declaration of Helsinki. The study was approved by the local Ethics Committee.
Balance control was measured in eight conditions: standing on a firm (EO)/foam (thickness 10 cm) surface (FEO) with eyes open (control
Results
The results showed a decrease of body sway amplitudes and RMS characterized by CoP displacements and trunk tilts during the condition with VBF. Repeated measures ANOVA revealed a significant effect of VBF location for each evaluated parameter and body segment. There was also a significant interaction between the VBF location and support surface for each parameter of CoP displacements and for some parameters of trunk tilts (Table 1).
Post-hoc comparisons were performed for each VBF condition
Discussion
We confirmed the previous results about stabilizing effect of VBF on balance control. Furthermore, we found that the postural improvement was in relation to the location from which the body sway was sensed due to the visual biofeedback. The results showed that VBF is the most effective in reducing the postural sway of that body segment from which the signal was sensed. The CoP position and L5 position were found to be the best locations for VBF signal.
Visual biofeedback sensed from CoP
Acknowledgement
This work was supported by VEGA grant no. 2/0186/10.
Conflict of interest statement: We certify that none of the authors have a financial or personal relationship with other people or organizations that could inappropriately influence (bias) this work.
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