Validity and reliability of an unstable board for dynamic balance assessment in young adults

Abstract

Scientific literature is giving greater importance to dynamic balance in fall prevention. Recently, the validity and reliability of the most employed functional tests for dynamic balance assessment has been investigated. Although these functional tests are practical and require minimal equipment, they are inherently subjective, as most do not use instrumented measurement data in the scoring process. Therefore, this study aimed to assess the validity and reliability of an instrumented unstable board for dynamic balance objective assessment in young adults through double-leg standing trials. A test-retest design was outlined with the unstable board positioned over a force platform to collect objective Center of Pressure (CoP) related and kinematic parameters. Fifteen young adults participated in two evaluation sessions (7-day apart) that comprised ten trials per two dynamic conditions (anterior-posterior and medio-lateral oscillations) aiming to maintain the board parallel to the ground. Pearson's correlation coefficient (r) was employed to assess the validity of the kinematic parameters with those derived from the CoP. The test-retest reliability was investigated through Intraclass Correlation Coefficient (ICC), Standard Error of the measurement, Minimal Detectable Change, and Bland-Altman plots. Statistically significant correlations between the CoP and kinematic parameters were found, with r values ranging from 0.66 to 0.95. Good to excellent intrasession (0.89≤ICCs≤0.95) and intersession (0.66≤ICCs≤0.95) ICCs were found for the kinematics parameters. The Bland-Altman plots showed no significant systematic bias. The kinematics parameters derived from the unstable board resulted valid and reliable. The small size of the board makes it a suitable tool for the on-site dynamic balance assessment and a complement of computerized dynamic posturography.

Fig 1. Experimental setup.

Subject secured to a harness standing on the unstable board placed over the force platform (a); detail of the force platform and the unstable board during medio-lateral (b) and anterior-posterior (c) dynamic tests.

Fig 2. Graphical representation of the kinematic parameters (i.e., Full Balance, Gross Balance, and Fine Balance) in a representative AP trial.

Full balance is the area below the rectified raw signal and is represented in grey. Gross Balance is the total time the raw signal stays between +10deg and -10deg, represented in blue. Fine Balance is the total time the raw signal stays between +5deg and -5deg, represented in red.

Fig 3. Bland-Altman plot for Full Balance, Gross Balance, and Fine Balance parameters in the anterior-posterior, medio-lateral, and TDS conditions.

Differences between test and retest scores are plotted against their means. The black line indicates the average of the differences, whereas the dotted ones represent the 95% limits of agreement.