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Current physical activity recommendations are being met by less than 21 % of children between 5-15 y. Recent Government initiatives are aiming to increase children’s participation in exercise. However, the effects on an imposed bout of exercise-induced energy expenditure (EE) on energy intake (EI) and appetite (hunger, fullness and prospective consumption) in normal weight children have received a limited research focus to date. Therefore, this thesis aimed to investigate how an imposed bout of exercise-induced energy expenditure (EE) on energy intake (EI) and appetite in normal weight children The first study investigated whether 17 habitually active girls were able to accurately increase their EI to match the EE following 60 min moderate intensity walking exercise. On average 17% of the EE was compensated for by an increase in EI. However, the ranged for EI change was -160% to +166% indicating large individual responses. The second study investigated whether 30 min of maximal sprint intermittent sprint cycling exercise would significantly alter EI or appetite in 13 boys and 13 girls. In the boys, hunger and prospective consumption were suppressed whilst fullness increased immediately following the exercise, whilst EI was significantly increased in response to the exercise condition. No significant changes to appetite or EI were observed in the girls. The third study investigated whether a mid-morning snack, moderate intensity cycling exercise (energy matched to snack) or both would alter EI or appetite in 20 boys and 18 girls. Irrespective of sex, hunger and prospective consumption were suppressed whilst fullness increased following the mid-morning snack, however this change in appetite did not alter EI as no significant differences were found between conditions. The fourth study investigated whether 99 recreational sports players (males/females, adults/children) were able to conceptualise their EE following 1 h habitual training into quantifiable amounts of food (chocolate) or drink (sports drink). Only 36 % of the EE from the exercise was met by the estimated amounts of food or drink. Age, sex nor sports participation significantly altered the participants’ accuracy of estimation. The fifth study investigated whether sex or dietary restraint impacted brain activation responses to visual food stimuli in 15 boys and 14 girls between a fed and fasted condition. Significant differences in brain activation were found between conditions, sexes and dietary restraint, potentially suggesting the differences observed in the previous experimental studies could be attributed to neurological alterations between participants. In conclusion, the findings presented demonstrate the changes in EI between young adolescents in response to an imposed bout of exercise are extremely variable. Whilst eating behaviours failed to correspond to the EI differences observed between participants, potentially brain activation differences may be responsible. The sex of the participant is more likely to impact EI and appetite following maximal sprint intensity exercise, more so than a bout of moderate intensity exercise. Future research should focus on determining what underpins the variable change in EI between participants following a bout of exercise.

Considering current levels of overweight and obesity in the population and the associated adverse health consequences, engaging people with chronic exercise programmes is of heightened importance. During chronic structured exercise programmes, some adults experience adaptive compensatory behavioural responses through increased dietary intake and/or decreased free-living physical activity. These responses can negate the benefits of an exercise-induced energy deficit. However, it is unclear whether young people experience similar responses during chronic structured exercise. Therefore, the experimental research presented in this thesis examined the existence and extent of exercise-induced energy compensation in adolescent girls. To achieve this, a total of 92, 12 to 15 year old girls and 26 adults were recruited into six experimental studies. The Medical Research Council guidance for designing complex interventions was used to structure the experimental chapters into development (Chapters 4 to 7), piloting (Chapter 8) and evaluation (Chapter 9). The first experimental study (Chapter 4) demonstrated that typical daily variation of total energy expenditure (TEE) in adolescent girls is ~3% when estimated by the Actiheart. Physical activity energy expenditure (AEE) variation was found to be ~10%. In the second experimental study (Chapter 5) the agreement and variability of laboratory buffet meals test days was investigated. The results demonstrated typical daily variation of 8.7% in laboratory-based energy intake (EI) in adolescent girls aged 12 to 15 years. Furthermore, a buffet meals familiarisation day is recommended to reduce the variability in EI. Estimation of EI was further explored in Chapter 6 using a digital photography method. This study demonstrated potential for EI assessment using digital photography, but highlighted that, at present, a supplementary written record of EI is required to overcome the limitations associated with missing photographs. Chapter 7 explored themes related to recruitment and retention of adolescent girls to chronic exercise intervention studies. The seven recommendations identified were used to recruit and retain participants in a twelve week pilot exercise intervention study with adolescent girls (Chapter 8). There was no evidence of energy compensation behaviours on a group level; however, high individual variability in both EI and EE behaviours was apparent. The final experimental chapter (Chapter 9) evaluated the fidelity of the exercise intervention and compliance with the measurement of primary outcome variables. Intervention fidelity was largely upheld. On average, participants attended 94% of exercise sessions and 73% of the participants met their individual target heart rate zone. Focus groups with the participants and parents highlighted preference for school-based exercise sessions due to increased variety and convenience, and recommendations for future estimation of free-living EI and EE. Collectively, these studies suggest there is value in pursuing the investigation of energy compensation behaviours in adolescent girls using a mixed methods approach. These studies demonstrate the factors requiring attention when designing and delivering complex interventions to investigate exercise-induced energy compensation in adolescent girls. In particular, methods for estimating free-living EI and EE require further attention before attempting to conduct such research in a larger sample.

Children’s energy requirements may vary during school and summer camp days. To evaluate energy balance during these two periods, seventy-eight children (45% females, 8–10 years) living in Parma, Italy, were enrolled in this observational study. Participants completed a 3-day food diary and wore an activity tracker for three consecutive days during a school- and a summer camp-week to estimate energy intake (EI) and energy expenditure (TEE). Height and body weight were measured at the beginning of each period to define children’s weight status. BMI and EI (school: 1692 ± 265 kcal/day; summer camp: 1738 ± 262 kcal/day) were similar during both periods. Both physical activity and TEE (summer camp: 1948 ± 312; school: 1704 ± 263 kcal/day) were higher during summer camp compared to school time. Therefore, energy balance was more negative during summer camp (−209 ± 366 kcal/day) compared to school time (−12 ± 331 kcal/day). Similar results were observed when males and females were analyzed separately but, comparing the sexes, males had a higher TEE and a more negative energy balance than females, during both periods. The results strongly suggest that an accurate evaluation of children’s energy balance, that considers both diet and physical activity, is needed when planning adequate diets for different situations.

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