Background: A range of metabolic, behavioral, mental and physical health benefits of regular physical activity have been documented in adults and children in the long-term. Yet, relatively little is known about how children's usual daily physical activity patterns (i.e. small bursts throughout the day) affect acute (immediately post-activity) and short-term (72 hours post-activity) metabolic and psychosocial outcomes. Additionally, little is known how this specific pattern of physical activity affects subsequent physical activity levels (i.e. compensatory behavior) and subsequent dietary intake, over the short-term- information critical to designing effective interventions involving the physical environment of the school classroom. Overall Goal: Active Class Space (ACS) will examine the potential influence of intermittent physical activity breaks of various intensities (control, light, moderate, vigorous) on measures of immediate mental performance, mood, hunger and several metabolic outcomes in children aged 7-11 years. We build upon previous work to hypothesize that higher-intensity intermittent physical activity breaks throughout an 8-hour day will improve immediate mental performance, mood, and post-exercise physical activity levels, while reducing hunger and post-exercise food intake. Specific Aims: (1) To determine the effects of intermittent physical activity breaks of varying intensities on immediate mental performance, hunger and satiety; (2) To determine the effects of intermittent activity breaks of varying intensities on ratings of perceived exertion (RPE), perceived exercise enjoyment, in-task mood, post-exercise food intake and post-exercise physical activity levels; and (3) To examine gender differences in the preceding variables in response to low-, moderate, and high-intensity intermittent physical activity. Design: Eighteen healthy males and twenty-one healthy females between the ages of 7-11 years completed completed four experimental conditions in random order: (1) 8 hours of sitting interrupted with 2--minute, light--intensity activity breaks performed at 25% of heart rate reserve (HRR) every 18 minutes; (2) 8 hours of sitting interrupted with 2--minute, moderate--intensity activity breaks (50% HRR); (3) 8 hours of sitting interrupted with 2--minute, high--intensity activity breaks (75% HRR); and (4) 8 hours of sitting interrupted with 2 minutes of sedentary screen time. Standardized meals will be provided during each experimental condition. Dietary intake and physical activity levels were monitored for the remainder of the experimental day and over the subsequent three days for each condition. Dependent Variables: Major outcome variables include: Energy expenditure measured by indirect calorimetry and heart rate; dietary intake measured using a 3-day dietary record; physical activity measured by accelerometry; immediate mental performance assessed using a 90-sec mathematical computation test; hunger and satiety assessed using a visual analog scale; RPE assessed using the Borg scale; perceived exercise enjoyment assessed using the physical activity enjoyment scale (PACES); in-task mood assessed using the Feeling Scale (FS) and Subjective Exercise Experiences Scale (SEES). Data Analysis: A linear mixed model will be fitted for each outcome variable with effects for condition, sex, BMI, and baseline physical activity level. A Bonferroni correction will be used to adjust for multiple comparisons in post hoc tests following the mixed-effect model. A similar linear mixed-model for raw levels of each outcome variable over time will also be fitted to assess temporal differences between conditions. This model will include effects for condition, time, time-by-condition interaction, sex, BMI, and baseline physical activity levels. Significance: ACS will shed new light on the short-term metabolic, behavioral, mental and physical health benefits of intermittent physical activity breaks in children. The results from this study will inform the design of behavioral and environmental interventions to promote physical activity and cognitive development in pediatric populations.