The objective of the study is to evaluate the impact of physical activity in obese and nonobese prepubertal children on:

1. biological stress responses during a psychosocial stress test
2. snacking and feeling of hunger in response to the same psychosocial stress test
3. the moderating factor of attachment on the biological stress responses and on snacking

Children will be investigated on one study day during 3.5 hours.

Hypotheses In this study, 3 primary hypotheses will be tested.

1. Moderate physical activity during 25 min in children decreases the cortisol levels in response to the Trier Social Stress Test TSST-C (for children).
2. Moderate physical activity during 25 min in children decreases the snacking (calorie consumption when corrected for expenditure and switch in quality of food intake) in response to the Trier Social Stress Test TSST-C (for children).
3. A secure attachment will be a moderating factor for the general increase in cortisol and the snacking in response to the psychosocial stress test (Trier Social Stress Test TSST-C).

Secondary objectives:

1. To test if the impact of physical activity on stress responses and snacking differs between obese and non-obese children
2. To test the impact of physical activity on the cardiovascular stress reactivity (blood pressure, heart rate) and the perceived stress (scale) in response to the Trier Social Stress Test TSST-C?
3. To test if the stress reactivity and its modulation by physical activity is different in anxious and in impulsives/labile children
4. To test if serious life events and parental worries and parental educational style influence the stress reactivity

Inclusion Criteria:

• 7-10 year old children

Exclusion Criteria:

• Severe illness
• Medications interfering with study