Mild Cognitive Impairment Is Associated With Reduced Dynamic Balance Performance and Altered Lower-Extremity Kinematics During the Four Square Step Test.

Background purpose: Cognitive deficits associated with mild cognitive impairment (MCI) likely impact balance control, especially during dynamic tasks. The Four Square Step Test (FSST) presents concurrent obstacle step-over and multi-directional stepping tasks to clinically interrogate dynamic balance. The primary FSST outcome, completion time, delivers a coarse measure of dynamic balance control, but cannot reveal underlying kinematic strategies that may further characterize MCI-related balance deficits. The objective of this study was to use an augmented FSST to characterize aging and MCI effects on both dynamic balance performance and lower-extremity kinematic execution strategies.

Methods: Younger adults (YA, mean age = 23.7y; n = 7), older adults (OA, mean age = 67.4y; n = 20), and individuals with MCI (MCI, mean age = 71.7y; n = 17) performed the FSST in an observational study. We compared overall group effects, then performed 2-way, post-hoc comparisons to identify age (YA vs OA) and cognitive (OA vs MCI) differences in: (1) FSST completion times indicating dynamic balance performance, and (2) lower-extremity peak joint angles during leading and trailing steps in anterior-posterior and lateral directions, indicating kinematic execution strategies.

Results discussion: The FSST completion time was impaired in OA compared to YA (31% slower; p < .001) and in MCI compared to OA (18% slower, p = .008). Both YA and OA exhibited similar kinematics throughout. Individuals with MCI exhibited reduced knee flexion across steps compared to OA (p ≤ .002). Reduced knee flexion was associated with degraded FSST performance (Pearson's r < -0.44) and is generally less amenable to the obstacle step-over sub-task. While longer FSST completion times revealed aging-and MCI-related impacts on dynamic balance performance, kinematic analyses further revealed altered dynamic balance strategies only in individuals with MCI.

Conclusions: Deficits associated with MCI impair FSST performance. Altered lower-extremity kinematics suggest that individuals with MCI may be especially challenged by the complexity of concurrent multi-directional stepping and obstacle step-over FSST sub-tasks. Clinicians should consider both impaired overall performance and underlying kinematic strategies when characterizing altered dynamic balance control during complex tasks (eg, FSST) in individuals with MCI.