|Abstract:||Lower heart rate reserve, a major risk factor for hypertension, can affect cognitive decline in similar way as seen in hypertensive individuals, but if it has an effect on cognitive performance and impairment in oxygenation of the prefrontal cortex (PFC), leading to cognitive impairment in these individuals is still unknown. Unfortunately, how heart rate reserve can affect these measures while dual-task walking is still not understood as cognitive and motor decline in older adults is related to their dual task performance. Additionally, the relationship between heart rate reserve and cognitive motor interference (CMI), which is a direct of measure of dual-task performance related to falls in older adults, has not been examined. It is important to understand these relationships because falls related to dual-task walking is very common in older adults and causes major consequences that negatively affect their daily living.
Thus, the objective of this dissertation was to examine the effect of heart rate reserve on dual task walking in middle aged to older aged adults by examining dual task cost (measure of CMI), error rate (measure of cognitive performance), and PFC activation among the dual tasks which was compared with single task walking. All studies involved assessing heart rate reserve, cardiovascular endurance through Naughton Submaximal test and performance of the Trail Walking Task (TWT) on an instrumented treadmill. Spatiotemporal measures were used to measure dual task cost and the error rate was used as the measure for cognitive performance. Chapter 1 found that individuals exhibited higher dual-task cost when going from single-task walking to dual-task walking. Furthermore, when compared to the easiest TWT condition, all participants exhibited decrease in dual-task cost during the difficult TWT condition. Chapter 2 found that higher heart rate reserve individuals exhibited higher PFC activation (i.e., increase in oxyhemoglobin and decrease in deoxyhemoglobin) going from single task walking to dual task walking for all the dual task conditions. Additionally, we found the differences in recruitment of PFC activation (i.e., greater changes in PFC when going from single-task walking to dual-task walking) during the easiest TWT condition when compared to the difficult TWT condition. Chapter 3 found that individuals with lower heart rate reserve were overall walking slowly in all tasks compared to higher heart rate reserve individuals, there was increase in speed going from single to difficult TWT condition for both groups. In addition, there were no significant differences in cognitive performance while dual task walking among the cohorts when going from easier to difficult TWT condition. Overall, the findings from this study indicated that while dual-task walking, individuals with lower heart rate reserve exhibited greater decrements in physical dual-task performance and greater recruitment of attentional resources showing increase in delta PFC while dual tasking which is consistent with the Compensation related utilization of neural circuits hypothesis (CRUNCH) model and “supply and demand” theory. As a whole, these study’s findings add to the current literature establishing the beneficial effects of heart rate reserve for dual-task walking. While this study was the first to examine the overall effects of heart rate reserve on measures directly and indirectly related to dual tasking, no causal relationships can be formed. Thus, it is recommended for research to examine the effects of an intervention program on these measures in adults with impaired heart rate reserve. Such findings will elucidate the importance of healthy heart rate reserve in middle aged to older aged adults to improve dual-tasking ability and decrease the risk of falls.