The effects of aging and functional level on balance
Kumar, Neeraj Ashok
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The purpose of this study was to determine if there 1.) are age-and functional level-related sensory-motor changes in community dwelling older adults with no history of falls and its association with fall risk as measured by the Timed "Up & Go" (TUG) and Dynamic Gait Index (DGI) tests (Experiment I), 2.) are age- and functional level-related differences in balance responses to platform translations (Experiment II), and 3.) is an association between the balance responses to platform translations and fall risk as measured by the TUG (Experiment II). Fifty-eight subjects participated in Experiment I: 16 young adults (mean age = 26.86 ± 5.36 years) and 42 older adults (mean age = 73 ± 7.38 years). For Experiment II, 51 of the 58 subjects participated: 13 young adults (mean age = 26.38 ± 5.08 years) and 38 older adults (mean age = 72.66 ± 7.7 years). The older adult group was classified into high (HF), medium (MF), or low functioning level (LF) based on a functional ability test. For Experiment I, lower extremity muscle force (MF), range of motion (ROM), vibratory (VB) and light touch sensation (LT), visual acuity (VA), dynamic visual acuity (DVA), gaze stabilization test (GST), visual contrast sensitivity (VCS), performance on the Timed "Up & Go" test (TUG) and the Dynamic Gait Index (DGI) were measured. Independent t-tests and Chisquare test of independence were performed to evaluate sensory-motor differences between young and older adults. The effect of functioning level on sensory- motor measurements was analyzed using one-way ANOVA with Tukey's Honestly Significant Differences post hoc analysis. A Spearman's Rho ( r s ) correlation analysis was performed between the sensory-motor variables and fall risk based on the TUG and DGI. A forward stepwise logistic regression analysis was conducted on those variables that had moderate to high correlations to determine which variables accurately classified subjects into at-risk or not-at-risk for falls. Significant differences (p < 0.05) were found between young and older adults on MF, ROM, VB, LT, VA, GST and VCS. Hip extension MF and hip abduction ROM were associated with a greater likelihood of being at risk for falls based on the TUG and DGI. For Experiment II, all subjects were presented with two sets of 10 sinusoidal platform translations (0.25 Hz & 0.50 Hz EO & EC, 0.75 Hz EO). To evaluate the effect of platform translation condition, age, functional level, and vision on trunk sway responses, a 3-way ANOVA was performed. A Spearman's Rho ( r s ) correlation analysis was performed between the dependent variables (trunk amplitude, velocity, and their variability) during platform translations and the subjects' fall risk (TUG score > 11.1 sec). When moderate to high correlations were found ( r s >0.40), receiver operating characteristic (ROC) curve analysis was used to determine cutoff scores for those variables. Sensitivity, specificity, positive and negative likelihood ratios (LR) for detecting fall risk were calculated. Older adults demonstrated increased trunk sway amplitude, velocity, and associated variability during all frequencies of platform translations, with LF falling frequently during translations and having the greatest sway amplitude and velocity response. This may be related to the age related changes seen in the sensory-motor systems, which were more impaired in LF. Sway velocity variability during slow ML platform translations correlated the strongest with fall risk. This may be explained by the decreased hip extension muscle force and hip abduction ROM that were associated with falls. Age-related changes in the sensory motor function may contribute to the mechanisms underlying loss of balance and falling in community-dwelling older adults.