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Background: Regular physical exercise can counteract age-relatedphysiological and cognitive decline, reduce the risk of disease, andimprove quality of life. Even so, a considerable proportion of older adultsare insufficiently physically active. Supramaximal high-intensity intervaltraining (HIT) is a potential time-efficient, effective, and appealingalternative to longer duration moderate-intensity training (MIT).Research also indicates promising effects from supramaximal HIT forolder adults, but the interpretation of these results is limited to a fewsmall studies, highlighting a need for larger, high-quality randomizedcontrolled trials (RCT) for this population. The aims of this thesis wereto investigate motivational aspects of physical exercise, and controlledsupramaximal HIT in particular; and to examine the applicability andeffects of controlled supramaximal HIT in comparison to aerobic MIT,among older adults not engaged in regular physical exercise.

Methods: This thesis comprises four research papers, totaling 117participants (64-79 years old, 56% women). Paper I used cross-sectionaldata from 49 participants to investigate a neurobiological link betweendopamine and exercise-related motivation. Papers II-IV used data fromthe Umeå HIT Study, an RCT with 68 participants, to examineapplicability and effects from 3 months of twice-weekly controlledsupramaximal HIT (10×6-sec intervals, 20 minutes in total) compared toMIT (3×8-min intervals, 40 minutes in total). Both groups exercised onstationary bicycles in a group setting. All participants in the Umeå HITstudy received medical clearance before the training started. Paper IIdescribed the applicability of controlled supramaximal HIT and its effecton exercise-related motivation. Paper III examined the effects onphysiological and cognitive functions, such as cardiorespiratory fitnessand global cognitive function. Paper IV used data from 42 participantson structural and functional magnetic resonance imaging (MRI) toinvestigate the effects of the exercise on the hippocampus and episodicmemory.

Results: Paper I indicated a positive association between self-reportedexercise motivation and dopamine D2-receptor availability in the frontalparts of the brain. Paper II showed that non-exercising, but otherwiserelatively healthy older adults were able to exercise at supramaximaltraining intensities without compromising their physical and mentalwell-being during the training, or their exercise motivation. Theparticipation was high, and no serious adverse events occurred. Notably,the participants performing supramaximal HIT reported more positiveivand fewer negative exercise-related events compared to the participantsperforming MIT. The results from Paper III showed that three months ofcontrolled supramaximal HIT resulted in similar but also additionaleffects compared to MIT, despite the total training time being halved.Both groups improved fitness and cardiovascular function, and in favorof supramaximal HIT there was an improvement in muscular function.Neither group showed an effect on global cognitive function, but apotential improvement in working memory was observed in favor ofsupramaximal HIT. While the effects on episodic memory were mixed,Paper IV observed associations between change in cardiorespiratoryfitness and change in hippocampus function for the CA4/DG subfieldduring pattern completion, which in turn was associated with episodicmemory improvements in pattern completion.

Conclusion: Overall, this thesis supports controlled supramaximal HIT as an effective and appealing training method for older adults, which canmake meaningful contributions to their independence in daily lifeactivities. Although the connection between motivation, dopamine, andaging requires further research, an interesting observation in this thesiswas that, contrary to previous concerns, controlled supramaximal HIThad no negative impact on the participants' motivation. Controlledsupramaximal HIT can be a meaningful addition to the exerciseprograms commonly available for older adults, as providing moretailored and individualized training may contribute to promotingphysical exercise for health and well-being. The cognitive effects ofsupramaximal HIT were mixed, and future studies should aim for longerinterventions and more pronounced physiological changes. Further,research should evaluate controlled supramaximal HIT in a broaderpopulation, including individuals with chronic conditions and diseases,and explore how this form of exercise can be effectively implemented ineveryday settings.

Background: Age-related cognitive and physiological decline can in part be mitigated by increasing older adults’ physical exercise, but individuals respond differently, for example in cognitive domains such as working memory (WM). This thesis examines how high intensity exercise affects cognitive, neural, and physiological measures in older adults and explores how clinical findings can be translated into real world settings. 

Methods: This thesis includes four papers, and is based on the Umeå HIT study, which compared supramaximal high intensity interval training (HIT) to moderate intensity training (MIT) for older adults. Papers I-III used data from the Umeå HIT randomized controlled trial (RCT), while Paper IV used data from the Umeå HIT Home Study. The Umeå HIT RCT assessed the effects of 12 weeks of twice-weekly supramaximal HIT (20 minutes total, including 10 x 6 second intervals) compared to MIT (40 minutes total, including 3 x 8-minute bouts) among non-exercising older adults (n = 68, 66-79 years old, 56% women). Exercise intensity was individualized and controlled. Specifically, Paper I assessed cognitive, physiological, well-being and adverse event outcomes, of supramaximal HIT vs MIT. Paper II assessed effects of supramaximal HIT vs MIT on a functional magnetic resonance imaging WM task and examined the relationship between improved leg strength and WM manipulation task-related blood oxygen level dependent (BOLD) response and performance in an MRI subsample. Paper III tested baseline- and change-factors related to WM improvement. Paper IV, based on the Umeå HIT Home study (n = 11, 69-74 years old, 55% women) explored how the original supramaximal HIT protocol could be adapted to home use through a co-creation study involving participants who had exercised in the supramaximal HIT-group of the RCT. 

Results: Paper I found that irrespective of group, cardiorespiratory fitness and systolic and diastolic blood pressure were significantly improved, while global cognitive function was not affected. A significant group x time interaction was found in WM performance and isometric leg extensor strength in favor of supramaximal HIT. Paper II found that increased isometric leg extensor strength in the supramaximal HIT group was positively related to dorsolateral prefrontal cortex  BOLD response, which in turn was related to increased WM performance. Paper III showed that the link between increased isometric leg extensor strength and improved WM also applied to a broader WM composite and the relationship was found in both exercise groups. It further showed that baseline white matter lesion load did not limit WM improvements following supramaximal HIT, unlike MIT. Upregulated brain derived neurotrophic factor was related to WM improvements, but differed by group, suggesting a stronger relationship in MIT. Paper IV identified alternative modalities to stationary bicycling and several adaptations to the supramaximal HIT protocol, including extending intervals to ten seconds, using an audio metronome to control intensity, and a mobile application for exercise delivery. Of the suggested modalities, chair stand intervals elicited similar acute physiological responses to supramaximal HIT on a stationary bicycle, intensity could be systematically modulated using a metronome, and the modality was considered safe.  

Conclusion: This thesis found that supramaximal HIT elicits similar- to superior effects on physiological and cognitive outcomes compared to MIT, despite half the exercise time. Furthermore, leg strength improvements were related to increased BOLD response in a key WM area, which in turn was related to improved WM performance in supramaximal HIT. Leg strength gains were further related to broader WM improvements irrespective of exercise group, indicating that muscular adaptations may be an important target for future exercise-cognition studies. Unlike MIT, supramaximal HIT-related WM gains were not limited by baseline white matter lesion load, and future studies should test this hypothesis directly. Adapting HIT for home use, especially with chair stand intervals, appears promising for future implementation, potentially enabling both cardiorespiratory and muscular gains. Future research should test the feasibility and effects of home-based supramaximal chair stand, as a step toward future implementation to real-world settings for older adults.