Validity and Reliability of a Portable Balance Tracking System, BTrackS, in Older Adults

Falls are the leading cause of disability, injury, hospital admission, and injury-related death among older adults. Balance limitations have consistently been identified as predictors of falls and increased fall risk. Field measures of balance are limited by issues of subjectivity, ceiling effects, and low sensitivity to change. The gold standard for measuring balance is the force plate; however, its field use is untenable due to high cost and lack of portability. Thus, a critical need is observed for valid objective field measures of balance to accurately assess balance and identify limitations over time. The purpose of this study was to examine the concurrent validity and 3-day test-retest reliability of Balance Tracking System (BTrackS) in community-dwelling older adults. Minimal detectable change values were also calculated to reflect changes in balance beyond measurement error.

Postural sway data were collected from community-dwelling older adults (N = 49, mean [SD] age = 71.3 [7.3] years) with a force plate and BTrackS in multitrial eyes open (EO) and eyes closed (EC) static balance conditions. Force sensors transmitted BTrackS data via a USB to a computer running custom software. Three approaches to concurrent validity were taken including calculation of Pearson product moment correlation coefficients, repeated-measures ANOVAs, and Bland-Altman plots. Three-day test-retest reliability of BTrackS was examined in a second sample of 47 community-dwelling older adults (mean [SD] age = 75.8 [7.7] years) using intraclass correlation coefficients and MDC values at 95% CI (MDC95) were calculated.

BTrackS demonstrated good validity using Pearson product moment correlations (r > 0.90). Repeated-measures ANOVA and Bland-Altman plots indicated some BTrackS bias with center of pressure (COP) values higher than FP COP values in the EO (mean [SD] bias = 4.0 [6.8]) and EC (mean [SD] bias = 9.6 [12.3]) conditions. Test-retest reliability using intraclass correlation coefficients (ICC2.1 was excellent (0.83) and calculated MDC95 for EO (9.6 cm) and EC (19.4 cm) and suggested that postural sway changes of these amounts are meaningful.

BTrackS showed some bias with values exceeding force plate values in both EO and EC conditions. Excellent test-retest reliability and resulting MDC95 values indicated that BTrackS has the potential to identify meaningful changes in balance that may warrant intervention.

BTrackS is an objective measure of balance that can be used to monitor balance in community-dwelling older adults over time. It can reliably identify changes that may require further attention (eg, fall-prevention strategies, declines in physical function) and shows promise for assessing intervention efficacy in this growing segment of the population.