Author(s): KIM, M., SONG, H., BAE, J., YOON, H., Institution: GYEONGGUK NATIONAL UNIVERSITY, Country: KOREA, SOUTH, Abstract-ID: 1371

INTRODUCTION:
In older adults, gait requires substantial cognitive processing and attentional regulation, and declines under dual-task (DT) conditions are closely linked to increased fall risk and loss of functional independence. Previous studies have shown that increased oxygenated hemoglobin (HbO) in the prefrontal cortex (PFC) during DT reflects compensatory recruitment of cognitive resources. However, significant individual differences exist in these neural responses. From a physical reserve perspective, it remains unclear how physical function indicators, such as muscle strength, relate to PFC activation during DT. This study investigated determinants of the difference in PFC HbO activation between single-task (ST) and DT and examined whether muscle strength moderates the relationship between dual-task cost (DTC) and neural response.
METHODS:
Gait performance (TUG 2-lap time) and PFC HbO (fNIRS) were measured in 59 community-dwelling older women (age: 77.93±6.60 years; educational years: 4.72±2.84; CIST: 19.67±6.67) during Timed Up and Go 2-lap ST and DT (verbal fluency task). The primary outcome was the difference in PFC activation between TUG DT and TUG ST(Delta_PFC_HbO). Independent variables included age, cognitive function (CIST), TUG-DTC, and upper-body (hand grip) and lower-body (30-second chair stand test) muscle strength. Multiple linear regression and hierarchical regression analyses were conducted to identify predictors of Delta_PFC_HbO and to test the moderating effects of strength (p < .05).
RESULTS:
Age significantly predicted the increase in PFC HbO activation during DT (B = 0.017, β = 0.418, p = .002), suggesting greater neural resource mobilization with advancing age. General cognitive function and behavioral DTC did not show significant associations with Delta_PFC_HbO. Handgrip strength showed a significant, independent association with Delta_PFC_HbO even after controlling for age, cognition, and TUG-DTC. No significant interaction or main effects were found for lower-body strength in the hierarchical regression models. PFC activation during DT was influenced by age, while handgrip strength independently explained individual differences in neural mobilization beyond behavioral performance.
CONCLUSION:
The major finding of this study was that while age-related increases in PFC HbO reflect compensation for reduced neural efficiency, strength-related increases reflect the capacity for neural resource mobilization. Aligning with the physical reserve perspective, our findings suggest that muscle strength, similar to cardiorespiratory reserve, represents a physiological capacity to recruit additional neural resources in response to task demands. Rather than simply alleviating task burden, muscle strength may determine the potential for neural compensation under cognitive-motor stress. Due to the cross-sectional design and specific sample profile (older women), future longitudinal studies are required to improve generalizability and clarify causal relationships.