To our knowledge, this is the first study that evaluated objectively measured PA patterns using accelerometry in children across the different weight categories overweight, obesity and morbid obesity, and also evaluated the modifying effect of age and gender. The present study shows that children with morbid obesity performed in total more PA (cpm) than children with obesity. In addition, children with obesity spent a lower percentage of time being sedentary and a higher percentage of time in LPA. The difference in total PA (cpm) between these two weight categories exists during both weekdays and weekend days. In addition, children with morbid obesity spent less ST during a week day compared to children with obesity. These results are in contrast with our hypothesis that PA decreases with increasing overweight severity.
Previous studies showed that children with obesity were less physically active compared to children with normal weight (25, 26). Extension of these results to the assumption that children with morbid obesity are less physically active than children with obesity was refuted by the results of the present study. Several explanations for this remarkable finding can be considered. First, children with morbid obesity might be more aware of a healthy and active lifestyle than children with less morbid obesity after being referred to the obesity centre for treatment and might be more motivated to improve PA already before the start of the intervention. In addition, the development of overweight or obesity is multifactorial and complex. Not only PA, but also nutrition, metabolic, environmental, psychosocial, and cultural factors are considered to play a key role in obesity development and maintenance. For example, according to Nemet et al. (2010) food consumption increased after moderate intensity PA in children with overweight. However, food intake decreased after moderate intensity PA in children with normal weight (27). Based on these findings, it could be suggested that even though children with morbid obesity were more physically active, they may compensate higher PA with a higher calorie intake. One could also question whether the degree of obesity may somehow affect the accuracy of the accelerometer to assess PA. However, the Actigraph accelerometer, which was used in the present study, was shown before to measure activity counts equally accurate across different weight categories (28).
In agreement with previous studies, the present study shows that boys are more physically active compared to girls and PA levels increase with age, up to an age of 10–11 years old, and then decrease at > 11 years when children head into puberty (29, 30). Specifically, primary school-aged children (< 12 years) showed higher total PA compared to secondary school-aged children (≥ 12 years). The higher level of total PA in boys could be explained by a higher intrinsic motivation and experiencing more pleasure from exercise compared to girls (31). Furthermore, previous studies found gender differences concerning different PA types (32, 33). The results of the study of Reimers et al. (2018) showed that boys were more likely to engage in sports and active games, while girls prefer walking and/running or to play in a playground (33). It is recommended to provide tailored PA types in order to stimulate and improve PA. Additionally, the negative association between PA and age highlights the importance of early PA promotion since the presence of comorbidities is already evident in primary school children with obesity (34). A methodological strength of this study is the use of objectively measured PA using accelerometry to measure PA in children across different weight categories (overweight, obesity and morbid obesity). Previous studies used self-reported PA or used objectively measured PA but did not differentiate between weight categories. The present study also evaluated differences between PA patterns in boys and girls and in different age categories in children with overweight and (morbid) obesity. Limitations were the cross-sectional design of the study and the absence of a power-calculation. In addition, children were instructed to remove the accelerometer during water activities and some contact sports, which may have impacted the accelerometry data. This is common for accelerometer-derived data. However, the time spent on these activities is generally very small compared to the entire observation interval.
The results of the current study provide new insights for medical specialists, health professionals, sport coaches and physical educational teachers, who can stimulate and motivate children to perform PA. Extra attention is needed for children with obesity, female gender and children from > 12 years. Consequently, interventions which include the school environment and parents are needed to increase PA during school as well in the home environment during weekends and after school hours. More insight in the specific needs and possibilities to increase PA and decrease ST in this subgroup is warranted.
Follow -up data of children participating in the COACH program are continuously being collected to determine the effect of the lifestyle intervention on PA across overweight categories including age and gender. The evaluation of PA and ST over time during this intervention will demonstrate whether PA can be changed in the different subgroups.