The objective of this study was to determine if a foam testing condition and/or nonlinear analysis methods can be used to identify differences between age stratified subgroups of older adults when conducting the Limits of Stability assessment. Ninety older adults participated in this study. A force plate was used to record center of pressure data during Limits of Stability testing on a firm and foam surface. Participants were grouped into age-stratified subgroups: young-old (60-69 years), middle-old (70-79 years), and old-old (80+ years). Anterior-posterior (A/P) and medial-lateral (M/L) sway ranges and sample entropy values were calculated. The young-old group had significantly larger A/P and M/L sway ranges than the old-old group on both surfaces. A/P sample entropy increased significantly with age. M/L sample entropy increased significantly with age between the young-old and old-old and the middle-old and old-old groups. Sample entropy values between surfaces significantly differed for all groups. These results indicate Limits of Stability differences occur between older adults of different age groups and should be taken into consideration for clinical and research testing. Nonlinear analysis may help further identify differences in Limits of Stability performance while use of a foam surface is of limited additional value.
Keywords: biomechanics; limits of stability; older adults; posturography; sample entropy.