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J Athl Train. 1998 Oct;33(4):323-7.

Examination of balance measures produced by the biodex stability system.

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Curry School of Education, University of Virginia, Charlottesville, VA 22903.



Our purpose was to establish normal patterns and relationships of stability using the Biodex Stability System.


The design of this study used both nonexperimental and quasi-experimental methods. All testing was performed in a university sports medicine laboratory.


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.


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.


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 degrees and 5 degrees from level was significantly greater than the time spent between 6 degrees and 10 degrees , 11 degrees and 15 degrees , and 16 degrees and 20 degrees . Furthermore, the percentage of time spent between 6 degrees and 10 degrees was significantly greater than the time spent between 16 degrees and 20 degrees .


These data suggest that uninjured individuals spent the majority of the time balanced within 0 degrees to 5 degrees 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.


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