Reliability of Biodex Balance System Measures

This study examined the reliability of measures of dynamic balance obtained using the Biodex Balance System (BBS). Twenty male (n = 10) and female (n = 10) active adults engaged in weight-bearing sports volunteered for this study. Dynamic balance was assessed using measures obtained from the BBS at a spring resistance level of 2. Spring resistance levels range from 1 (least stable) to 8 (most stable). The BBS uses a circular platform that is free to move in the anterior-posterior and medial-lateral axes simultaneously, which permits three measures to be obtained: an overall stability index (OSI), an anterior-posterior stability index (APSI), and a medial-lateral stability index (MLSI). Measures were obtained from 20-sec trials during which participants were asked to maintain an upright standing position on their dominant limb on the unstable surface of the BBS. An examination of measures obtained across 8 trials indicated that the BBS produced reliable measures as indicated by R = .94 (OSI), R = .95 (APSI), and R = .93 (MLSI). Based on findings in this study, the testing protocol recommended providing 2 practice trials (Trial 1 and Trial 2) followed by 2 test trials (Trial 3 and Trial 4). Reliability estimates for Trials 3 and 4 were R = .90 (OSI), R = .86 (APSI), and R = .76 (MLSI). Replication of this protocol with a separate group of 27 collegiate athletes resulted in reliability estimates of R = .92 (OSI), R = .89 (APSI), R = .93 (MLSI).