Apparatus-free, high-intensity intermittent training (HIIT) for the regulation of appetite, energy balance and metabolic health in inactive, overweight and obese females

Abstract

Globally, one in four males and one in three females self-report not meeting physical activity guidelines (150 minutes of moderate-intensity physical activity per week or 75 minutes of vigorous-intensity physical activity per week, or a combination of moderate and vigorous physical activity). In turn, levels of overweight and obesity continue to rise which are resultant of prolonged and repeated periods of positive energy balance, where energy intake exceeds energy expenditure. High-intensity intermittent exercise (HIIE) consists of brief, repeated bursts of relatively intense exercise interspersed with periods of rest and, specifically, low volume HIIE protocols are those totalling ≤30 minutes. As appetite and energy intake can be transiently reduced following low volume high-intensity intermittent exercise, strategically timing such exercise bouts prior to meal times may promote energy deficit. Over the longer term, this could be of benefit to weight management in an overweight and/or obese population. However, while often perceived as time efficient, the affective and enjoyment responses to high-intensity exercise in an inactive and overweight/obese population are contentious. Other barriers to physical activity, including lack of access to apparatus and facilities need to be considered if low volume high-intensity intermittent exercise is to be adopted in a free-living setting by an inactive population. Therefore, the aim of this thesis was to assess appetite, energy balance, physiological, affective and enjoyment responses to acute and chronic apparatus-free high intensity intermittent exercise in inactive, overweight/obese females. Study 1 demonstrated that not only were the physiological responses to 4 x 30 seconds of “all out” star jumping (jumping jacks) comparable to 4 x 30 seconds of “all out” (maximal effort) cycling, this mode of exercise also induced preferable affective and enjoyment responses. Findings of study 2 then showed a tendency for a condition effect with on relative energy intake (p=0.064; n2 p=0.221) such that there was a reduction in relative energy intake with a medium effect size of 121kcal following 4 x 30 seconds of “all out” star jumping compared with the resting condition (p=0.086; d=0.52). Importantly, participants were free to request to eat at any point following the condition, as opposed to energy intake being assessed at a pre-determined time point. When 4 x 30 seconds of “all out” star jumping (jumping jacks) was undertaken twice daily on three days per week for eight weeks, either within thirty minutes (‘pre-meal’ group) or outside of one hour prior to a meal time (‘anytime group’), no differences in body mass or mean daily energy intake were found (study 3; all p>0.05). However, during week eight of the intervention mean daily energy intake was reduced on exercise days across both groups by a mean of 426kcal, compared with non-exercise days (p=0.033), although this occurred in both groups and was therefore independent of exercise timing. Compared with baseline, change in subjective appetite increased following the intervention in those undertaking exercise within thirty minutes prior to a meal (p=0.033), while postprandial subjective appetite decreased at 120 minutes following the standardised meal (p=0.026) in those undertaking exercise outside of one hour prior to a meal. In the ‘anytime’ group only, GLP AUC concentration was significantly increased by 21% following the intervention (p=0.037). Regardless of exercise group, mean cardiorespiratory fitness improved by a mean of 8% (p=0.007) and mean waist circumference reduced by a mean of 1.3cm (p=0.011), highlighting possible reductions in abdominal fat. Mean hip circumference improved by a mean of 1.4cm in the ‘anytime’ group only (p=0.04). No changes in glycaemic control or fasted lipid profiles occurred (all p>0.05). Preferable enjoyment responses were seen in the ‘anytime’ group in weeks 6 (p=0.033), 7 (p=0.002) and 8 (p=0.018) in the group undertaking exercise outside of one hour prior to a meal. This thesis concludes that 4 x 30 seconds of “all out” star jumping, twice a day on three days per week over eight weeks improves cardiorespiratory fitness, waist circumference and daily energy intake on exercise days regardless of exercise timing, while inducing positive affective responses. Timing exercise outside of one hour prior to meal times induces preferable modulations in postprandial subjective appetite as well as greater improvements in hip circumference and more preferable enjoyment responses. Such findings inform strategies to effectively improve markers of health and regulation of energy balance on exercising days in a manner that addresses commonly-reported barriers in inactive, overweight and obese females. Future research is warranted, specifically for further insight into the effects of exercise timing around meal times, as well as the optimisation of low volume HIIT for health in a free-living setting that offers greater flexibility with regards to exercise mode and timing, while it could also interrupt prolonged sedentary behaviour. Interventions that incorporate HIIE modes that also promote improvements in lean mass and muscle strength are also merited