Most currently available wearable devices to noninvasively detect hypoxia use the spatially resolved spectroscopy (SRS) method to calculate cerebral tissue oxygen saturation (StO₂). This study applies the single source—detector separation (SSDS) algorithm to calculate StO₂. Near-infrared spectroscopy (NIRS) data were collected from 26 healthy adult volunteers during a breath-holding task using a wearable NIRS device, which included two source—detector separations (SDSs). These data were used to derive oxyhemoglobin (HbO) change and StO₂. In the group analysis, both HbO change and StO₂ exhibited significant change during a breath-holding task. Specifically, they initially decreased to minimums at around 10 s and then steadily increased to maximums, which were significantly greater than baseline levels, at 25–30 s (p-HbO < 0.001 and p-StO₂ < 0.05). However, at an individual level, the SRS method failed to detect changes in cerebral StO₂ in response to a short breath-holding task. Furthermore, the SSDS algorithm is more robust than the SRS method in quantifying change in cerebral StO₂ in response to a breath-holding task. In conclusion, these findings have demonstrated the potential use of the SSDS algorithm in developing a miniaturized wearable biosensor to monitor cerebral StO₂ and detect cerebral hypoxia.

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.