Author(s): LIN, C., LIN, C.F., Institution: NATIONAL CHENG KUNG UNIVERSITY, Country: TAIWAN, Abstract-ID: 2704

INTRODUCTION:
Chronic ankle instability (CAI) has been associated with altered sensorimotor control, particularly when postural tasks are challenged by sensory deprivation or cognitive load.
The purpose of this study was to examine how cognitive dual-tasking and visual conditions modulate the relationship between postural sway (center of pressure; COP) and cortical hemodynamics (concentration of oxyhemoglobin (HbO), de-oxyhemoglobin (HbR), total hemoglobin (HbT)) in individuals with CAI, copers (i.e., history of ankle sprain with full recovery), and healthy controls during single-leg standing.
METHODS:
Eighteen individuals with CAI (26.5±6 y/o, 9M9F), 13 copers (27±6.9 y/o, 5M8F), and 12 healthy controls (24.4±4.6 y/o, 5M7F) participated. Participants performed single-leg standing under four conditions: eyes-open (EO), eyes-closed (EC), EO with cognitive dual-task, and EC with cognitive dual-task.
COP metrics (anterior-posterior (AP)/medial-lateral (ML) maximal displacement, variability and total trajectory) were recorded using a forceplate. Mean cortical hemodynamics were measured via fNIRS over bilateral prefrontal (PF), premotor (PM), primary motor (M1), and somatosensory (S1) cortices.
Spearman correlations were calculated between COP variables and cortical hemodynamics within each group and condition. Statistical significance was set at p<0.05.
RESULTS:
COP-cortical coupling was condition- and group-specific. During EO single-task, copers showed positive COP-HbO coupling in sensorimotor regions (M1 r=0.582; S1 r=0.676), whereas healthy controls demonstrated negative associations between sway and HbO/HbT (e.g., ML displacement vs M1 HbO r=-0.671; total trajectory vs M1 HbO r=-0.713).
During EC single-task, CAI exhibited positive correlations between total trajectory and HbO in premotor and motor cortices (r=0.470-0.496), while copers showed positive associations between AP sway variability and prefrontal HbO (r=0.577-0.593).
Under EO dual-task, CAI and healthy control demonstrated negative sway, HbT/HbO coupling (CAI r=-0.585 to -0.513; HC r=-0.685 to -0.748).
In contrast, during EC dual-task, copers displayed widespread positive coupling across sensorimotor regions (S1 HbO r=0.615-0.748; M1/S1 HbT r=0.650-0.699), with additional positive associations between HbT and AP sway variability (r=0.615-0.678).
CONCLUSION:
The relationship between postural sway and cortical hemodynamics during single-leg standing is highly task-dependent and differs among CAI, copers, and healthy controls. Sensory deprivation and cognitive dual-tasking reveal distinct cortical-postural control strategies. Copers demonstrate robust and widespread positive sensorimotor coupling under the most challenging condition (EC dual-task), suggesting adaptive cortical engagement, whereas CAI and healthy controls exhibit different or region-specific coupling patterns.