Nicholas, Rosemary
(2023)
Using MRI to elucidate the importance of physical activity to brain health and motor function in ageing.
PhD thesis, University of Nottingham.
Abstract
We live in an increasingly ageing population where people are living longer, but quality of life is not keeping up with increased lifespan. Concerns contributing to poor health in ageing include cognitive impairment and frailty driven by neurodegeneration and declining musculoskeletal health. Inactivity is also a significant driver of poor health in ageing and this may divulge important mechanisms of age-related decline. This thesis aims to differentiate whether activity in ageing impacts on physiological responses by studying trained and untrained individuals.
Lifelong highly active male cyclists (Older Trained, OT), age-matched healthy older untrained (OU) males and young untrained (YU) males participants underwent cognitive and physiological tests, and MRI structural and functional scans of the muscle, heart and brain. Brain and heart functional measures were collected at rest, during supine exercise using a Ergospect Cardio-Step module, and during a recovery period post-exercise. A semi-automatic muscle segmentation method was developed to extract measures of leg muscle volume and fat fraction from wholebody mDIXON MRI scans. In general age was the primary driver of differences found rather than training.
In the muscle, lower muscle strength was associated with older age. Additionally, the older untrained (OU) had greater fat percentages within their calf muscles than the young untrained (YU). The OT group were more similar to the YU group than the OU group in muscle quality during isokinetic contractions.
For cardiac measures, peak heartrate during the VO2 test, aortic stroke volume and stroke distance were all lower in the OT and OU groups. Aortic stroke volume was higher in the older OT and OU groups than the YU group during supine exercise. Heartrate increased during exercise in all participants, but for the YU group this was the primary driver of their increase in cardiac output with no increase in stroke volume, whereas the older OT and OU groups compensated for lower increases in heartrate with concurrent increases in stroke volume. Aortic backflow was greater in older groups at rest, without increased aortic stiffening, suggesting greater peripheral vasculature resistance in the older groups.
In the brain measures, gmCBF at baseline and cerebral vessel velocity at both baseline and during supine exercise were lower with age. OEF was higher in the OU group than YU group. As expected, white matter, cortical and subcortical grey matter volume, as well as cortical thickness were lower in the older groups than the young group. Modest correlations existed between cerebral velocity during supine exercise and cortical and sub-cortical grey matter, white matter and cortical thickness. Structural connectivity measured was greater in the young than older groups, along with the cognitive scores from the MOCA and Trail A tests.
Some effects of a long term high physical activity were seen, where the OT group were more similar to the YU group than the OU group. This lifestyle effect was exhibited in maintained muscle quality during isokinetic contractions, higher VO2peaks, and greater velocity of cerebral blood flow at rest. All of the older volunteers in this thesis were non-frail, non-sedentary and healthy, and therefore differences of activity levels may not have been large enough to reveal significant impacts of a highly active lifestyle in a small sample size. Future work will increase the sample size, examine more differentiated groups or introduce an intervention and improve acquisition techniques for better data quality.
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