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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.