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

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.