Examination of balance measures produced by the biodex stability system

Objective: Our purpose was to establish normal patterns and relationships of stability using the Biodex Stability System. Design and Setting: The design of this study used both nonexperimental and quasi-experimental methods. All testing was performed in a university sports medicine laboratory. Subjects: Nineteen healthy subjects (8 males, 11 females, age = 24.4 ± 4.2 years; wt = 70.5 ± 20 kg; ht = 171.2 ± 11.7 cm) with no history of lower extremity injury participated in this study. Measurements: For data analysis, the medial/lateral stability index (MLSI), anterior/posterior stability index (APSI), overall stability index (OSI), and time-in-balance scores were recorded. Results: Multiple regression revealed that APSI and MLSI significantly contributed to the OSI, with the APSI accounting for 95% of the OSI variance. Additionally, the percentage of time spent between 0° and 5° from level was significantly greater than the time spent between 6° and 10°, 11° and 15°, and 16° and 20°. Furthermore, the percentage of time spent between 6° and 10° was significantly greater than the time spent between 16° and 20°. Conclusions: These data suggest that uninjured individuals spent the majority of the time balanced within 0° to 5° from level and progressively less time at greater angles. Additionally, the data suggest that the OSI is very closely related to the APSI and receives a relatively small contribution from the MLSI. Because of this small contribution, if the clinician is interested in both anterior-posterior and medial-lateral motions, it may be best to use the MLSI and APSI separately rather than the OSI.