Heart rate reserve effects on brain activation and cognitive-motor performance while doing an instrumented trail walking task in middle-aged to older adults

Heart rate reserve (HRR) has been associated with cardiovascular risk in older adults. Previous studies have shown a decrease in HRR associated with decrease in motor and cognitive function in older adults while doing Stroop walking task. However, the link between HRR and changes in cognitive-motor function while dual tasking merit needs further exploration. The objective of this study was to evaluate the effects of HRR on prefrontal cortex (PFC) activation and on cognitive-motor performance during instrumented trail walking task (TWT). We hypothesized that there will be an increase in PFC activation and better cognitive-motor performance with increase in HRR during TWT. This cross-sectional study included 30 middle-aged to older adults who walked at a comfortable walking speed on an instrumented treadmill. Functional near-infrared spectroscopy was used to quantify relative PFC oxyhemoglobin (HbO₂) and deoxyhemoglobin (Hb) levels. Cognitive performance calculated using error rate (ER) and motor performance calculated using stride length (SL), stride width (SW), stride time (ST). A linear mixed effect was conducted to investigate the effects of HRR, task, and their interaction on primary measures after controlling for covariates. Our results showed that HbO₂ and Hb levels differed significantly, showing increases in PFC activation, i.e. higher HbO₂ and lower Hb during TWT with increase in HRR. This increase in PFC activation was associated with increased speed and higher cognitive-motor performance, suggesting these tasks can distinguish changes in automaticity in adults with varying HRR. We also found a decrease in ST association with a higher HRR.