Effects of Augmented Visual Feedback and Stability Level on Standing Balance Performance Using the Biodex Balance System

Introduction Dynamic balance is critical for the acquisition and execution of motor skills. Balance training is used for injury rehabilitation, fall reduction, and sport and motor skill development. One commercial device used to quantify the degree of dynamic balance is the Biodex Balance System (4). The Biodex Balance System is an instrumented device that allows the tilting of a circular flat platform. The degrees of tilt from horizontal are measured and used to calculate an overall stability index (1). This index is a quantitative estimate used for the evaluation of an individual's neuromuscular control as it pertains to the ability to maintain postural stability on an unstable surface (4). One feature unique to the Biodex Balance System is that the stability of the balance platform can be increased or decreased, thus enabling control of the level of difficulty of the standing balance task. Biodex platform stability levels range from 1 to 8, with 8 being the most stable or least difficult to perform. Another feature of the Biodex Balance System is an attached LCD monitor that provides augmented visual feedback. The monitor provides information, via a screen tracing, concerning the subject's ability to balance on the platform as the subject tries to maintain the cursor in the middle of the screen's grid (4). Theoretical Rationale We were unable to find studies that compared the efficacy of augmented visual feedback at different levels of balance difficulty. As the stabilometer platform becomes less stable and thus more difficult, the ability to effectively process both intrinsic and augmented visual feedback may become increasingly difficult. This would be caused by a decrease in the amount of time available to process feedback information while balancing (11). The increase in time constraints as balance difficulty increases may also bring about a change in the type of motor control strategy used, i.e., open versus closed loop. During open looped motor control, the movement is executed entirely by the motor program without the use of sensory feedback (5,6). During closed looped motor control, an initial command is sent to the muscles which start the movement. The actual execution of closed loop movements, then, depends on sensory feedback which is used to monitor the movement (6). As the balance task becomes increasingly difficult, information processing demands may be increased because of the greater number and rate of balance adjustments that must be monitored. The less stable platform also brings about the rapid initiation of postural responses which limits the effectiveness of feedback mechanisms because of the inherent time delays (11). Horack and Nashner (1986) suggests that rapid postural actions are organized by a limited repertoire of open looped motor programs which do not require feedback for execution. Open looped strategies simplify the process of complex movement by incorporating knowledge of past experiences into motor programs enabling anticipation of events and reducing reliance on the slower feedback mediated responses associated with closed looped monitoring (6). The purpose of this study was to determine the effects of concurrent augmented visual feedback and balance condition on standing balance performance using the Biodex Balance System. We postulate that concurrent augmented visual feedback will not be as effective at the less stable condition (Biodex stability level 2) when compared to the more stable condition (Biodex stability level 7). This hypothesized difference in the effects of visual feedback at the different levels of stability will be demonstrated in the form of a feedback by stability level statistical interaction. Methods Participants Forty healthy, male university students (age = 21.4 [+ or -] 3.6 years, mass = 70.3 [+ or -] 14.3 kg, height = 170 [+ or -] 3.1 cm) volunteered to participate in this study. No participants reported any sensory impairment or physical injury that hindered performance of the balance task, nor did any of the participants have previous experience with balance training on the Biodex Balance System. …