Learning and consolidation of postural skills by exercise on balance board

INTRODUCTIONThe use of oscillating boards is very common in various rehabilitation protocols to improve upstanding postural stability. The destabilizing effect generated by the platform drives the nervous system to encode new patterns of motor control so that muscles and joints can produce adequate postural mechanics. How much does it really know of the process of learning and memory that underlie the beneficial effects of these devices on the rehabilitation outcomes? In order to study these mechanisms, we quantified the postural improvement during the use of a balance board oscillating along all directions. We identified the timing of postural learning its long-term consolidation and, in particular, we examined whether the distribution of the practice could significantly influence the level of learning. The results of this research can provide the normative basis for optimizing the timing and patterns of application of these devices in postural rehabilitation programs.MATERIALS AND METHODSWe have recruited 16 healthy, male adults. The task was to maintain the oscillating board (diameter 40 cm) in the horizontal position for 20 seconds. The experimental protocol included two practice sessions each of 8 trials (S1 and S2) and, a week after the completion of practice, a retention test of 8 trials, was performed to verify the consolidation of the performance. The subjects were randomly distributed into two groups: one group executed practice sessions separated by 20 minutes (1-day), while for the second group, S1 and S2 were separated by 24 hours interval (2-days). Eight reflecting markers applied to the board were captured by 8 infrared cameras (SMART-D, BTS Milan), to allow the following reconstruction of three-dimensional oscillations. The amplitude and the variability of the board oscillations were measured comparing the normal vector of the board with the normal vector of the horizontal plane. The vectors were calculated by solving the equation of the plane based on the coordinates values of 3 of 8 markers. The amplitude of the board oscillations was expressed as the angle between the board and the horizontal plane while the variability was assessed by computing the root mean square error (RMSE) and the approximate entropy. Statistical analysis was performed by comparing trials, sessions and groups by three-way ANOVA for repeated measures on trials and sessions.RESULTSAll subjects greatly improved the performance during the two practice sessions. However, from S1 to S2, the mean amplitude of board oscillations, measured independently from the direction, reduced more in members of group 2-days than in those of group 1-day. The main effects of session (F = 66.19, p <0.0001), and trial (F = 10.07, p <0.0001), were highly significant, but the main effect of group (F = 3.17, p = 0.09) was not significant. In addition, the interaction of group × session was significant (F = 5.63, p <0.05), indicating that the changes of the amplitude of the platform swings, between S1 and S2, were influenced by the difference between the groups. Furthermore, during the retention test the average angle of oscillation of group 2-days was lower than those of group 1-day (p <0.01). The main changes of board angular excursions occurred along the anterior-posterior direction both for the amplitude and the variability. The results of the statistical analysis for anterior-posterior direction were similar to those obtained from the analysis of oscillations measured independently from the direction. Instead, in the medial-lateral direction, the angular variations and the analysis of the variability were not statistically significant between the two groups. CONCLUSIONSThe statistical results showed that the use of balance boards can strongly improve postural stability in a few trials. Moreover, the distribution of practice, with rest periods between sessions of one day, further improves the learning process of new postural skill and contributes to its maintenance in the long-term memory. Finally, the changes of angular oscillations along the anterior-posterior axis are more sensitive to learning with respect to the variations in medial-lateral direction. Our intent for the future is to apply the basic knowledge obtained from these experiments to implement new protocols for the rehabilitation of balance disorders associated with neurological or orthopedic impairments.