| Summary: | A physically inactive lifestyle is associated with increased morbidity of non-communicable diseases, with such diseases representing the leading cause of death worldwide. It is well documented that regular participation in physical activity is associated with an improvement in a number of established health markers. However, it has been reported that 34-39 % of UK women aged 25-54 y fail to meet the minimum physical activity recommendations and many conventional exercise training interventions and initiatives are failing to meaningfully increase physical activity levels and adherence in previously inactive premenopausal women. A common barrier preventing premenopausal women from initiating and maintaining increased habitual physical activity is a ‘lack of time’. Physical activity initiation and maintenance can also be affected by the exercise environment with some individuals preferring to exercise alone while others prefer to exercise within a supervised or group environment. Increasing evidence suggests that high-intensity interval training (HIIT) performed independently, under supervision or within a group environment can provide a time-efficient alternative for improving several health markers in different populations. However, limited research has examined the effects of HIIT on health markers in inactive women and the effects of different methods of HIIT on overall health status. Therefore, the purpose of this thesis was to identify how alternative and smaller volumes of higher-intensity exercise influence enjoyment, adherence rates and health markers in previously inactive premenopausal women following 12-16 wks of training. Chapter 4 examined the effects of 16 wks of short duration small-sided football training and whole-body vibration (WBV) training on body composition, aerobic fitness and muscle oxidative capacity of previously inactive premenopausal women. Results from this study demonstrated that short duration small-sided football elicited superior health benefits, which included a reduction in body fat percentage and submaximal exercise heart rate (HR) as well as a decrease in PCr depletion for a given work rate during one-legged knee-extension exercise, compared to WBV training. Chapter 5 demonstrated that 15 wks of high-intensity swim training was an effective and time-efficient alternative exercise modality for the improvement of insulin sensitivity, glucose control and plasma soluble intracellular and vascular cell adhesion molecules compared to prolonged continuous swim training for previously inactive premenopausal women. Chapter 6 revealed that 12 wks of self-paced high-intensity interval and prolonged continuous cycling training both increased cardiorespiratory fitness and cognitive function and reduced resting HR in previously inactive premenopausal women. On the other hand, reductions in resting blood pressure (BP), submaximal HR and body mass and increases in mental well-being were training-type-specific. Finally, Chapter 7 identified that a novel 12 wk home-based DVD-directed exercise programme for previously inactive premenopausal women, encompassing movements commonly found within football training, was beneficial for the improvement of high-density lipoprotein cholesterol concentration and mental well-being when carried out at a moderate- to high-intensity. The exercise training interventions were well tolerated and adhered to by participants and resulted in improvements to some established health markers. However, the improved health profile of premenopausal women after the various training interventions was not uniform, with several training specific adaptations being manifest. Collectively, the combined training studies (n=175 participants) provide some support for shorter-duration, higher-intensity physical exercise training, including football, swimming, cycling and home-based DVD-directed exercise training, but not whole-body vibration training, to improve key health markers in previously inactive premenopausal women. The findings presented in this thesis demonstrate that several HIIT exercise modalities appear to be effective and feasible alternatives to prolonged continuous exercise training for improving health markers in previously inactive premenopausal women.
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