Learning effects of the biodex balance system during assessment of postural task with in test-retest measurements

Introduction: Balance assessment plays a major role in treatment and rehabilitation of patients. Recentlyscientists have designed a new device with a dynamic multi-axial tilting platform to aid in jointrehabilitation and enhance proprioceptive mechanisms and postural assessment, called Biodex balancesystem (BBS). Repetition of exposure to the BBS causes learning or familiarization. Therefore, it can’t besure that the changes seen in the stability index, are due to the effect of the learning or intervention. Thepurpose of this study was to evaluate the learning effects of test-retest postural task and to set the learningcurve and test-retest reliability of dynamic standing balance using BSS.Materials and Methods: Ten healthy non-athletic persons participated in this study. The volunteers wereasked to stand on BBS with two levels of difficulty on their dominant leg with open eyes. Two trials of 10repetitions were applied at difficulty level of 4 and 8 with 30 minutes rest between each test and 30 minutesrest between two trials. Total stability index (TSI), anteroposterior (APSI) and mediolateral (MLSI) wereregistered.Results: The effect of repetition of hard postural task on biodex was significantly different in trial 6 from1-5 (P<0.05). The effect of repetition of easy postural task on biodex was significantly different in trial of 5from 1-4 (P<0.05). After learning, we found no significant difference in mean stability index of testcondition of each trials in reliability assessment so the intra-class correlation coefficients ranged from 0.83to 0.92. Tests at lower stability level produced the higher ICCs (0.90-0.92). There was a very strongcorrelation between total stability index and AP stability index using Pearson correlation coefficient(P<0.01, r = 88%).Conclusion: The results showed that repeating a task on the BBS for five times or more have learningeffects. So, while evaluating postural stability in a simple task which has more than five repetitions,learning effect should be take in to account and in difficult postural task it is sex repetitions that can havelearning effects.