The results from this study supported the hypothesis that a single bout of SDEX or LDEX at the VeT does not increase short-term food intake in children. Thus the application of SDEX during the school day may contribute to healthier body weights in children.
In the current study, walking on a treadmill at a moderate intensity for 15 min and 45 min duration at an estimated energy expenditure of approximately 260 kJ and 790 kJ respectively did not significantly affect food intake at a test meal thirty minutes after exercise when compared with the resting control, consistent with the literature in both children [4, 5] and adults [18–21]. As a result, the energy expended during exercise resulted in a lower net energy balance for the duration of the experimental period. Fifteen and forty-five minutes of exercise reduced NEB in boys by approximately -418 kJ and -928 kJ, respectively and in girls by approximately -297 kJ and -432 kJ, respectively.
There is some indication, however, that girls compared with boys, have a lower or diminished ability to tolerate energy deficits caused by LDEX. Subjective appetite was similarly increased by LDEX in boys and girls, but there was a trend in girls only to increase food intake after LDEX by approximately 297 kJ. Unfortunately, our study was slightly underpowered (0.69) to provide confidence that intake did not increase. Four more subjects would be required to achieve a power of 0.80. On average, girls compensated for approximately 42% and boys for -13% of the energy expended during forty-five minutes of exercise. Similarly, women were found to increase intake following a single bout of high-intensity exercise  and moderate to large amounts of repeated exercise [23, 24] for up to 19 days  but a lack of compensation has been observed in men after two bouts of high-intensity exercise , or even after completing three 40 min exercise sessions per day for 7 days .
The greater ability of girls to compensate for energy deficits is also suggested by the observation that appetite ratings were strongly correlated with the amount of food consumed by girls, but much weaker in boys (Tables 4 and 5). In girls, subjective appetite scores were positively correlated with food intake at each time point for both SD (r > 0.48) and LD (r > 0.38) sessions. In boys, subjective appetite was only correlated with food intake at fifteen minutes (r = 0.40, p < 0.05) during the LD, but not during any of the SD measurement time points. This may reflect a higher sensitivity to appetite or greater care during completion of VAS questionnaires in girls. In boys, correlation analysis suggests that increased food intake is more strongly related to increased body weight, fat free mass, aerobic fitness (VeT) and levels of disinhibition.
The lack of effect of exercise on food intake was not explained by water intake at the test meal, but provides some indication that the children were more sensitive to physiologic signals of thirst than to hunger after exercise. Unfortunately, thirst was not assessed in this study. Even though all children were asked to drink 250 mL of water immediately after both rest or exercise periods, which was 30 min before the meal was served, water intake at the meal (Table 2) was higher by an average of 60 ml during LDEX but not SDEX. Thus, it can be suggested that 45 min, but not 15 min of exercise was sufficient to lead to a physiologic signal to rehydrate due to loss of body water . The implication of this observation is that non-caloric beverages should be readily available because thirst could drive excess caloric intake if the beverages available are those containing calories.
Intensity of exercise and perhaps thirst may also explain the contrasting results in subjective appetite found in a previous study conducted by our laboratory when compared to this one. In the study reported previously, average appetite and PFC increased following a submaximal fitness test assessing VeT in 9 to 14 year old boys . The fitness test protocol required progression from very low- to high-intensity exercise of approximately 80 - 85% maximum HR over a period of 12 min. However during the current study, children maintained steady state exercise at the VeT, which corresponds to moderate intensity exercise for 15 min. It may be that a higher level of exercise stimulates appetite in the boys, or perhaps they expressed a feeling of thirst rather than hunger when they completed the appetite rating scales. To determine VeT, subjects are fitted with a two-way non re-breathing valve which can dry out the mouth, in addition to water and electrolytes lost due to perspiration. It has been suggested that confusion of thirst with hunger signals may be the cause of excessive energy intake from caloric beverages .
This study provides three reasons to suggest SDEX is preferable over LDEX and less frequent activity in a school setting. First, SDEX at the VeT attenuated the increase in average appetite, desire to eat, and hunger that occurred during resting, which suggests that before lunch may be a good time to encourage a SD exercise program. In contrast, LDEX sessions resulted in an increase in average appetite, desire to eat, and hunger in boys and girls. These reported differential effects on subjective appetite did not affect food intake at a meal served 30 min following exercise. However, it is unknown whether the increase in subjective appetite following LDEX would ultimately result in increased food intake if the subsequent meal were served later.
Second, it is possible that three repeated bouts of SDEX at the VeT over the day would elicit a greater net negative energy balance than 1 bout of LDEX, but the long-term significance of this approach to energy balance has not been determined. In boys, one bout of SDEX resulted in a net negative energy balance of -418 kJ during the study measurement period in comparison to -928 kJ following one bout of LDEX. However, repeating SDEX three times daily could result in a greater net negative energy balance of -1254 kJ in boys. Furthermore, the significance of repeated SDEX compared with 1 bout of LDEX is potentially more beneficial in girls compared with boys. In girls, one bout of SDEX resulted in a comparable net negative energy balance to 1 bout of LDEX (-297 kJ vs. -432 kJ) during the study measurement period. However, repeating SDEX three times daily could result in a larger net negative energy balance of -891 kJ.
Third, subjects perceived LDEX to be "harder" than SDEX, as evidenced by reported RPE values during exercise (Table 3), which means they may be less likely to continue a program employing LD exercise. Reported RPE values ranging from 12 to 14 are generally considered a moderate level of exercise and correspond to work perceived as "fairly light to somewhat hard" . Those values correspond closely to mean values from our study (11 - 15). In addition, mean RPE values from the current study are consistent with a previous study that reported a mean RPE of 13.6 during exercise at the VeT in 11 year old children .
Last, our study supports the use of VeT as a target intensity for exercise training programs. Exercise at the VeT is practical for implementation as that intensity can easily be assessed without the use of equipment by using the Breath Sound Check (BSC) or the Talk Test. The BSC refers to an intensity at which one can just hear their breathing  indicating that they are training at an exercise intensity within 15% of their own VeT. The Talk Test, describes the VeT as when subjects are "just capable of talking"  and has a high correlation with the VeT during both treadmill and cycle ergometer exercise in men and women . Both methods are appealing because they do not require equipment and can be applied to different exercise modalities. Furthermore, the VeT corresponds to a moderate level of exercise, which is the intensity recommended to the public by the Canadian government. The Public Health Agency of Canada recommends that each child and adolescent build up physical activity over a period of a few months to achieve at least 60 more min of daily physical activity [32, 33]. In addition, increased amounts of moderate activity is associated with reduced body fat and BMI in children  which supports use of this intensity in children and adolescents.