Twenty-seven pairs of children matched on age, gender and ethnicity, ages 5 to 9 years were recruited from a sample of 115 children. One child in each pair was overweight (at or above the 85th percentile for BMI) and one was normal weight (between 20th and 70th percentile for BMI) at the beginning of the study. Anthropometric measurements (waist, hip, upper arm and calf circumference; femur and humerus breadth; triceps, calf, suprailiac, etc. skinfolds; stature and mass), percent fat (Bod Pod); physical fitness (Fitnessgram and submaximal cycle ergometer) and physical activity (self-report) were measured at baseline and nine months later at the end point of the study to track growth, fitness and physical activity across time. Fifty-three of the participants completed the study. Six (20%) of the overweight participants were no longer overweight at the end of the study (e.g., above 85th percentile for BMI); no normal weight participants reached the 85th percentile during the study time. All of the overweight participants with significant changes in BMI percentile were at or below the 90th percentile.

Group comparisons (overweight and normal weight) based on BMI produced large differences in mass, lean body mass, waist circumference, femur & humerus breadth, percent fatness, and subcutaneous fat. On variables that are important measures of growth both groups increased significantly in stature, mass, lean body mass, humerus breadth, and subcutaneous fat. Thus, the growth measures not associated with fatness followed the same pattern in overweight and normal weight groups. For measures of fatness, both groups regressed toward the mean over time. Somatotype revealed that overweight participants were more mesomorphic (increased muscle and bone) as well as endomorph (increased fat) when compared to normal weight participants. Mesomorphy increased over time and endomorphy decreased, and the trend was for all participants to shift toward a balanced somatotype.

Using percent body fat (estimated from Bod Pod) to group participants into normal (below 20 and 30% for males and females respectively) and overweight (at or above 20 and 30% body fat) produced different classifications than those created using BMI in 35% of the participants and agreement with BMI in 65% of the sample. Percent body fat changed in 13.5 % of the participants from baseline to endpoint, with 5 no longer too fat and 2 becoming too fat. Fewer participants were classified as overweight using percent fat than BMI.

Considering the participants where BMI and percent fat agreed (n=34), differences between the normal weight and obese groups were identified for Pacer laps (moderate effect size) and push-ups (large effect size) with small or no differences for curl-ups, self-reported physical activity, kjoules (work), and heart rate. The obese participants were equally fit based on total work output, exercise heart rate, and curl-ups at baseline and endpoint. The overweight group did not complete as many push-ups, had an 80-83% of participants in the healthy zone for Pacer while the number of laps was fewer on average, reported similar amounts of organized physical activity and generally lost the ground over time when compared with the normal weight group. These findings were generally consistent when comparing the entire sample (n=53).

Based on BMI groups overweight and normal weight children demonstrated the similar growth patterns across time (7 months) with the exception of mass. Body fat groupings suggested that BMI may misclassify some participants who have greater lean body mass and are mesomorphic. Running tests result in more difference between overweight and normal weight participants than cycle ergometer exercise tests. Overweight and normal weight children are more alike than different for growth and physical activity parameters.