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INTRODUCTION

The prevalence of overweight among Canadian children has increased dramatically over the past two decades. Currently, an estimated 29.2% of girls and 35.4% of boys are overweight (body mass index [BMI] ≥85th percentile), while 14.6% of girls and 16.6% of boys are obese (BMI ≥95th percentile) (1). This high level of overweight in childhood is cause for concern because increased levels of body fat are known to persist from youth to adulthood (2), and because heavier children are more likely than their leaner peers to possess risk factors for chronic disease (3,4). Such observations may explain the increased risk of morbidity and mortality seen among overweight children who become overweight and obese adults (5). The evidence linking increased weight with unfavourable levels of objective physical health indicators is well supported. However, findings are equivocal when health-related behaviours and perceptions are contrasted according to weight status, especially in younger populations.

Some research suggests that boys and girls with higher levels of body fat consume more total energy (6,7) and dietary fat (8,9), and are less physically active (10,11) and aerobically fit (12) than leaner children. Other studies have failed to show differences in diet (13,14) and physical activity (15) in children stratified by weight status. Although overweight children generally are believed to have lower self-esteem than their normal weight peers, this belief has not been consistently supported in the literature. French and colleagues (16) concluded in their review that overall self-esteem levels in overweight seven- to 12-year-olds were either similar to or just slightly lower than those of normal weight boys and girls.

Because most data linking body fatness in youth with unfavourable lifestyle behaviours and perceptions are derived from cross-sectional investigations, relationships between overweight and lifestyle variables may be transitory. This is a plausible theory because many health-related behaviours and attitudes are established in childhood (17). Thus, the purpose of this study was to examine differences in physical activity, aerobic fitness, self-perception, and dietary intake in a sample of six- to ten-year-olds at risk of overweight, as well as in normal weight boys and girls at zero-, three-, six-, and 12-month intervals.

METHODS

Participants

Thirteen teachers from a convenience sample of seven Edmonton-area elementary schools were asked to have their classrooms (grades 2 to 4) participate in this investigation; the research was not a component of class curricula and participation was voluntary. Parents and children provided informed consent and assent, respectively. Approval for this project was obtained from the University of Alberta Faculty of Agriculture, Forestry and Home Economics human ethics review committee, the Cooperative Activities Program, and the Edmonton Public and Catholic School Districts.

Procedures

Skinfold-thickness measurements were taken at five sites (triceps, biceps, subscapular, suprailiac, and calf) on the right side of the body using Harpenden skinfold calipers (Health Dimensions, Plymouth, MI). Height was assessed to the nearest 0.1 cm using a set square and a wall-mounted tape measure, and weight was determined to the nearest 0.1 kg using a portable medical scale (Health o meter, Inc., Bridgeview, IL); BMI (kg/m^sup 2^) was subsequently calculated. Children were classified as at risk of overweight (BMI ≥ 85th percentile) or normal weight (BMI

Physical activity level was assessed using the Physical Activity Questionnaire for Older Children (PAQ-C), a self-administered, seven-day activity recall that evaluates sports, leisure activities, and games performed during school days, evenings, and weekends (20). The 20-metre shuttle run test (20-MST) was used to determine aerobic fitness levels (21). The test requires subjects to run back and forth between two markers spaced 20 m apart; as the test advances, the time interval between signals decreases so that running speed must increase progressively.

Self-perception was measured using the Self-Perception Profile for Children (SPPC) (22-24). The SPPC consists of the following sub-scales that collectively influence overall self-esteem: scholastic competence, social acceptance, athletic competence, physical appearance, behavioural conduct, and global self-worth. Higher scores represent more positive ratings of self-perception.

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