Reliability of Behavioral and fNIRS Neural Responses: Assessments During Posture–Inhibitory Control Dual Tasking

Background: Posture–inhibitory control dual-tasking is critical for safe daily functioning. Although functional near-infrared spectroscopy (fNIRS), a non-invasive neuroimaging tool, is increasingly used to examine neural mechanisms of dual-tasking, its reliability across posture transitions remains unclear. This study examined the reliability of behavioral and neural measures during sit-to-stand transitions and explored the neural mechanisms underlying posture–inhibitory control dual-tasking. Methods: Eighteen healthy adults (M age 42.8, SE = 3.3) completed tasks with varying posture challenges (sitting, standing, and tandem stance) and inhibitory demands (no task, congruent, and incongruent). Cortical activation was measured using fNIRS and reassessed after a 1 min sit-to-stand task. Results: Under lower task demands, activation in prefrontal and pre/postcentral regions increased with greater postural and inhibitory load, whereas this pattern reversed under higher demands. Behavioral performance demonstrated poor-to-excellent reliability (ICC range: 0.24 to 0.95; |r| = 0.33–0.97), whereas fNIRS measures showed poor-to-good reliability following sit-to-stand transitions (ICC range: <0 to 0.72; |r| = 0.02–0.79). Exploratory analyses suggested a shift from under- to over-additive cortical activation after posture transitions. Conclusions: Findings support the Capacity Sharing Theory, suggesting that postural and cognitive tasks compete for shared resources. Additionally, our findings reveal variable reliability of behavioral and neural measures across posture transitions. Future studies should account for postural changes when interpreting behavioral and neural findings.