Background
The increase in prevalence of overweight and obesity in children and adolescents is a major public health concern in industrialised countries [
1] and physical activity (PA) is inversely related to being overweight and obesity [
2]. Especially for children and adolescents, regular PA is a prerequisite for normal growth and maturation, health, and fitness. Compared to inactive young people, physically active children and adolescents have higher levels of cardiorespiratory fitness, muscular endurance and muscular strength, more favourable cardiovascular and metabolic disease risk profiles, enhanced bone health, and reduced symptoms of anxiety and depression [
3]. In addition, limited PA during childhood and adolescence may predispose development of a sedentary life style in adulthood [
4,
5].
Because of the growing evidence of the health benefits of regular PA, several public health organisations have established PA guidelines [
6‐
11]. These organisations claim that children and adolescents aged between 5 and 17 years should perform at least 60 minutes of moderate to vigorous PA (of 5 to 8 metabolic equivalent of task) each day. Data from the HBSC-Study (Health Behaviour in School-aged Children) showed that in most European countries most adolescents aged 11, 13 and 15 years do not engage in moderate-to-vigorous PA every day [
12], and similar results were reported for the United States [
13], Australia [
14] and Brazil [
15].
Three comprehensive reviews concluded that socio-demographic variables are consistently correlated with PA in children and adolescents and that boys are more active than girls [
16‐
18]. However, data on age-related levels of PA are inconclusive. For instance, while Sallis et al. [
16] reported that younger children were more active than older children, the results by Uijtdewillingen et al. [
17] were opposite. In addition, van der Horst et al. [
18] did not find enough evidence that would suggest that age is a determinant of PA. Further, being of African-American descent has been associated with lower PA levels [
17] and adolescents of Euro-American race are more physically active [
16] suggesting that ethnicity influences PA level. Finally, while the review of Sallis et al. [
16] concluded that socioeconomic status is not related to PA, Stalsberg and Pedersen [
19] reported that 58% of the reviewed articles found that adolescents from families with higher socioeconomic status tend to be more physically active than those from families with lower socioeconomic status.
To date, representative data on comparative prevalence rates and potential predictors for compliance with the PA guideline in German children and adolescents are lacking. Previous studies had several limitations including (i) lack of a representative nationwide study sample, (ii) prevalence estimates only provided for specific and narrow age groups and (iii) use of non-validated measures to estimate compliance with the PA guideline. Hence, statements on compliance with the PA guideline and potential predictors of children and adolescents in Germany can not be generalised, and are incomplete and unreliable.
The purpose of this study was to assess the percentage of children and adolescents in Germany who meet the PA guideline of 60 minutes of moderate-to-vigorous PA each day and to evaluate the socio-demographic correlates of guideline compliance using nationwide representative data, a broad age range and reliable and validated measurement instruments.
Discussion
The purposes of this study were to show representative prevalence rates for complying with the PA guideline of 60 minutes of moderate-to-vigorous PA every day in children and adolescents in Germany and to evaluate socio-demographic correlates of compliance with the PA guideline. The results of this study showed that only 15.3% of children and adolescents aged between 4 and 17 years meet the current PA guideline of 60 minutes of moderate-to-vigorous PA every day. These estimates are comparable to results of the HBSC-Study for Germany [
12]. The results of both studies emphasise the importance of interventions aimed at enhancing the level of PA in children and adolescents in Germany. The gender differences in compliance with PA guidelines in this study are in agreement with earlier reports for other countries including European countries [
12] and the United States [
13,
27,
28]. Both in children and adolescents, boys show higher compliance rate than girls. These differences are especially large in preschool children (4–5 years) where 35.4% of boys and 28.4% of girls meet the PA guideline. For schoolchildren and adolescents, the difference between both gender groups decreases.
A progressive decrease in the prevalence of compliance with the PA guideline with age was observed. Similar age-related decreases have been reported in several international studies with subjective [
12] and objective [
29] measures of PA. For girls, there is a continuous decrease during childhood and adolescence. In childhood, the chance to meet the PA guideline decreased by 17% every year and during adolescence 19%. Therefore, PA interventions should be employed for girls of all ages. For boys, there was a significant decrease in the prevalence of meeting the PA guideline only during childhood but not during adolescence. Especially, strong decrease in the compliance rate was observed during the transition from childhood to adolescence and hence this stage of life seems to be a particularly critical period for the maintenance of PA levels [
30]. In the German school system, most children change from primary school to secondary school around 10 years of age, requiring a reorganisation of everyday activities and friendships. Hence, PA programs need a special focus on this age period.
Interestingly, socioeconomic status influenced compliance with the PA guideline only in girls but not in boys. Contrary to our expectations, girls with low socioeconomic status were more likely to comply with the PA guideline than girls with high socioeconomic status. These differences intensify in adolescence. These results contradict the findings of a previous review [
19] that in 58% of the reviewed studies children and adolescents from families with higher socioeconomic status tended to be more physically active than those from families with lower socioeconomic status. We speculate that this discrepancy in results between studies is related to the German school system in which adolescents with higher socioeconomic status more frequently attend a "Gymnasium" (an academic secondary school in the tripartite German secondary school system) and usually spend more time at school especially in the afternoons. Long schooldays, afternoon school and homework presumably pose an organisational challenge for meeting the PA guideline. However, it is unclear why this effect occurs only in girls but not in boys.
Migration background was a predictor of compliance with the PA guideline only for girls but not for boys. Interestingly, coming from a family with migration background had a negative effect on PA compliance in children but a positive effect on PA compliance in adolescents. For girls with migration background, the likelihood of meeting the PA guideline decreased slightly with increasing age. However, for girls without migration background, the compliance with the PA guideline decreased drastically around the transition from childhood to adolescence. Similarly to the socioeconomic effect, we speculate that the German school system may be responsible for these developments. Adolescents without migration background are more likely to attend the "Gymnasium" that is associated with more time spent at school and on homework. However, it remains unclear why the effect of migration background on PA compliance only affects girls but not boys. Further studies are needed to test this assumption and to better understand these gender specific differences.
In contrast to the effects of socioeconomic status and migration background, the effect of residential area significantly influenced compliance with the PA guideline only in boys. We hypothesize that boys who live in rural areas are more likely to use a bicycle and walk longer distances to get to school and to meet with friends. While in cites and medium-sized towns, the public transportation grid is well developed, rural areas suffer from a lack of public transportation. Hence, adolescent boys in rural areas may be forced to be physically active as a means of transportation. One strategy to bring the level of PA up to 60 minutes of moderate-to-vigorous PA per day could be to increase use of active transport by improving the infrastructure (e. g. building safe and convenient bicycle and walking paths) and promoting active transport in schools and communities. Two types of interventions were found to be effective in promoting PA: community-scale and street-scale urban design, as well as land use policies and practices [
31]. Urban planners, policy makers and local communities should be involved in such interventions [
32]. These endeavours should be implemented especially in such regions (e. g. rural areas) where active transport is safe for children and adolescents. Girls should be encouraged to use this kind of transportation in particular [
33].
This work examined the socio-demographic predictors of compliance with the PA guideline. However, one important issue is to question the appropriateness of the PA guidelines. PA guidelines were developed to quantify the amount of PA which is needed to support the normal growth and maturation, health, and fitness of children and adolescents. After reviewing 850 articles on the relationship between PA and health in children and adolescents, Strong et al. [
3] conclude that “school-age youth should participate daily in 60 minutes or more of moderate to vigorous physical activity”. Several international [
6‐
11] organisations have adopted this PA recommendation for children and adolescents. However, these strictly formulated PA recommendations raise the question whether the daily regularity of 60 minutes of moderate to vigorous PA is the most important aspect for health benefits or the accumulation of moderate to vigorous PA within one week. Convincing empirical evidence for the daily regularity of PA has not been yet shown. Because this issue has a serious impact on formulating future PA guidelines further research in this field is required. Especially, longitudinal studies are needed to evaluate the merit of PA recommendations.
The major strength of this study is that the subjective measure of compliance with the PA guideline used in this study is a well established instrument [
16,
25]. In addition, this study reports national level representative data for children and adolescents in Germany for the full age spectrum between 4 and 17 years. However, the results of this study should be interpreted with caution because of some limitations. First, this study has a cross-sectional design, and hence the results of the study do not allow causal inferences of predictors. Second, the results were based on self-report data which has been shown to overestimate the prevalence rates of PA compliance compared to those assessed using objective measures [
34]. In fact, compliance rates measured with objective measures may be even lower than those reported in this study. Third, this study did not provide information on the school obligations and transportation grid that would allow for a better understanding of the effects of socio-demographic variables.
Conclusions
The results of this study showed that a majority of children and adolescents in Germany do not meet the guideline of 60 minutes of moderate-to-vigorous PA every day. Consequently, there is a need for program and policy action as early as possible at the family, community, school, health care, and governmental levels to tackle the problem of decreasing PA with increasing age. The transition from primary school to secondary school appears to be a critical stage of a children’s life with respect to their PA behaviour. Therefore, specific interventions are needed at this stage of life to help young people restructure their daily activities and reimplement PA into daily routines. Especially, boys living in medium seized towns and cities as well as girls with higher socioeconomic status and without migration background were the highest risk groups and need support to develop and maintain habits for daily PA.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
DJ was responsible for the overall conception and design of this manuscript, statistical analysis, interpretation of data and contributed to the design of the study. AKR provided edits to the paper. MOW contributed to the design of the study and provided edits to the paper. AW contributed to the design of the study. All authors read and approved the final manuscript.