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

ABSTRACT

Balance assessment plays a major role in treatment and rehabilitation of patients. Recently scientists have designed a new device with a dynamic multi-axial tilting platform to aid in joint rehabilitation and enhance proprioceptive mechanisms and postural assessment, called Biodex balance system [BBS]. Repetition of exposure to the BBS causes learning or familiarization. Therefore, it can't be sure that the changes seen in the stability index, are due to the effect of the learning or intervention. The purpose of this study was to evaluate the learning effects of test-retest postural task and to set the learning curve and test-retest reliability of dynamic standing balance using BSS. Ten healthy non-athletic persons participated in this study. The volunteers were asked to stand on BBS with two levels of difficulty on their dominant leg with open eyes. Two trials of 10 repetitions were applied at difficulty level of 4 and 8 with 30 minutes rest between each test and 30 minutes rest between two trials. Total stability index [TSI], anteroposterior [APSI] and mediolateral [MLSI] were registered. The effect of repetition of hard postural task on biodex was significantly different in trial 6 from 1-5 [P<0.05]. The effect of repetition of easy postural task on biodex was significantly different in trial of 5 from 1-4 [P<0.05]. After learning, we found no significant difference in mean stability index of test condition of each trials in reliability assessment so the intra-class correlation coefficients ranged from 0.83 to 0.92. Tests at lower stability level produced the higher ICCs [0.90-0.92]. There was a very strong correlation between total stability index and AP stability index using Pearson correlation coefficient [P<0.01, r = 88%]. The results showed that repeating a task on the BBS for five times or more have learning effects. 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 have learning effects