Abstract: With digitalization and virtual entertainment being the megatrends of the 21st century, there is reasonable concern about the role of physical activity (PA) in the daily life of children and adolescents. To identify risk-groups with insufficient PA and to guide interventions, continuous and representative tracking of PA is crucial. In this paper, representative PA data of children and adolescents from the Motorik-Modul (MoMo) baseline study (2003–2006, N = 4,528) is compared to those of Wave 2 (2014–2017, N = 3,708). Participants aged 4–17 were drawn out of 167 sample points in Germany and the data was weighted to ensure representativeness for Germany. Organized (sports clubs and schools) and unorganized (unorganized sports and playing outside) PA was measured by questionnaire and stratified by sex, age, and socioeconomic status. Contrary to common expectation, overall PA remained stable among youths in the past ten years, however, there is an ongoing trend towards organized forms of PA at the expense of unorganized sports and playing outside. Besides different trends in settings, there is inequality in PA distribution among socioeconomic status and gender, unequally pronounced in different settings.
4 Discussion
The MoMo Wave 2 data confirm the trend of decreasing unorganized PA and increasing organized PA among children and adolescents living in Germany. The results are consistent with the results of Wave 1 (2009–2012) data [8]. However, a slight overall increase in PA that has been found in the data from 2003 to 2012 [8] could not be confirmed. Additionally, a closer look at the settings and disadvantaged groups revealed significant, setting-specific socioeconomic inequalities in PA behavior that should be used to tailor target-group and setting-specific interventions.
4.1 Organized physical activity
Whereas time spent in curricular sports remained stable from 2003 to 2017, the overall time spent in extracurricular sports increased from 6.1 to 16.6 minutes per week. This finding verifies the trend we observed from Wave 1 data [8], evolving extracurricular activities to an important setting for organized PA in Germany. One reason for this development might be the extensive implementation of daytime schools in Germany in the last years. The fear of a "PA cannibalism" at the expense of PA in sports clubs with increasing PA in schools and other extracurricular activities [26] is not confirmed. However, this study shows evidence for a general PA cannibalism, but at the expense of unstructured PA. Boys reported slightly higher amounts of extracurricular PA in school compared to girls, especially at the age of 11 to 13, but mean differences between genders are small. Taking into account the apparent gender inequality in sports clubs, extracurricular sports could be used as a vehicle to promote PA among girls in the school setting.
Considering the 15-year trend from Baseline to Wave 2, an increase in participation rates from 53.5% to 60.0% and 89.4 to 99.1 minutes PA in sports clubs was observed. Official numbers from the DOSB also report relatively stable rates of sports club memberships during the 2000s and 2010s with rates peaking at 79.8% among 7-to-14-year-old boys and 61.1 among 7-to-14-year-old girls [10]. In sum, a total of 60.0% of children and adolescents living in Germany report to participate in PA in sports clubs (Table 1). Overall rates of participation in sports clubs peak as early as between the age of six to ten and then decline slowly until adulthood. This decline in PA participation during adulthood is also reported in Canadian studies [27, 28]. Studies with non-humans show that a decline in PA of up to 50% appears at the maturation from adolescence to adulthood in nearly every living being [29]. However, Farooq and colleagues stated in a recent study that PA declines as early as from the age of 7 years in western civilizations and that there was no evidence indicating a substantially smaller decline during childhood than during the transition between adolescence and adulthood [30]. Considering the overall average time spent with PA per week (Table 2) compared to PA participation rates, a decline is delayed to late adolescents, as training volumes increase with age which, in turn, compensate for drop-outs. However, sports clubs are still the most important setting for the PA of children and adolescents in Germany and become more important worldwide [31]. A critical question is how to foster the active participation of adults in sports clubs. Offering a broader range of sports, including new trend sports and sports-related activities, as well as age-appropriated forms of motivation and competition are just some of many possible examples for interventions in the setting sports club.
4.2 Unorganized physical activity & playing outside
Data from Wave 1 showed that in Germany, unorganized sports activity as well as playing outside decreased between 2003 and 2012. This decline could be confirmed by our recent Wave 2 data. Other international studies also reported a declining trend in active play [32]. Reviews state that active, unstructured play in developed countries is decreasing for various reasons, including increased screen time, safety concerns (e.g. traffic, stranger danger), emphasis on organized youth sports, and parental work [5]. Although studies show that PA, particularly unorganized activity, is an effective way to decrease obesity in children [33], active play is likely of light intensity and to date, still, the significance of light and/or incidental PA among children and adolescents, is widely unknown [5]. One promising approach in promoting unorganized PA such as playing outside or active commuting is to improve walkability [34]. Walkability is, in turn, linked to unorganized sports activity and outside play in children [34]. Even though, there is some evidence that active commuting is not, or even negatively linked to organized PA in children under 10 years of age [35]. However, it may be a source of unorganized PA for older children and adolescents, just because of the fact they cross and use playgrounds on their way [36].
4.3 Overall PA & socioeconomic inequalities
Our study shows that overall PA among children and adolescents in Germany did not decline significantly during the 2000s and 2010s, although this expectation was expressed in previous research [37]. Other national studies and previous research support this finding [7, 8]. Referring to international PA recommendations [4] overall PA is on an unsatisfying level in Germany [38]. Nevertheless, the signaled crisis in childhood PA [5, 6] did not get worse during the 2000s and 2010s in Germany and there is a lack of representative data from periods before 2000 to discuss earlier trends.
However, as our survey assessed mainly sports activity, shifts in light PA may have been unobserved in our study. A recent Norwegian study among a representative sample of 9-year-olds found, that the prevalence of children and adolescents meeting the Norwegian PA recommendations was similar in 2005–2006 and 2011–2012. Yet, their accelerometer data indicated that both children and adolescents substituted time spent in light PA for time spent sedentary [39].
The decrease of unorganized PA among children and adolescents since the beginning of this study is alarming and needs to be observed meticulously. It is yet unclear, whether the lack of unorganized PA can be compensated in organized settings with the expertise of trained instructors. Although, participants in sports clubs typically spend 40–50% of their time in moderate to vigorous physical activity (MVPA) [40] and intensities of PA during organized sports are relatively high compared to other settings [14, 41]. Current studies indicate that sports clubs become a more and more important source of PA all over the world [31] and sports club participants are more likely to meet PA recommendations (OR 2.4–6.4, [31]). The question of the pros and cons of a mainly structured and guided PA at the expense of unorganized playing outside becomes increasingly important and should be the focus of further experimental research.
Although there is not much change in the total amount of PA, previous research that focused on biological and environmental correlates [42], different settings [8], and socio-structural factors [43] revealed that there is social and environmental inequality in PA attendance and PA behavior in Germany. The SES has been identified as an important correlate of PA and a healthy lifestyle [5, 34]. Socioeconomic disparities in health behavior have been found by numerous studies all over the world and account for a large amount of PA inequality [44–46]. By analyzing different PA-relevant settings, the present study shows that these socioeconomic differences are not evenly pronounced in each setting. For example, there is no gender gap in curricular sports, and gender differences in extracurricular sports are small and age-dependent (Table 2). Adding the SES as a factor, our study shows that a prevalent gender gap in unorganized PA is mainly due to differences between gender among youths from families with low SES (Table 3) and can therefore not be generalized. In families with an intermediate SES, girls do even more unorganized PA compared to their male counterparts. The fact that different social groups participate in different types of settings provides the opportunity for target-group-specific interventions. An example would be the development of additional programs for extracurricular sports in schools utilizing cooperations between schools and sports clubs to reach out especially for girls from low SES families or girls with migration backgrounds. On the other hand, these setting-specific trends sharpen the scope of shifts in the importance of those settings. For example, the shift from unorganized PA to PA in sports clubs may leave boys from low SES families with lesser overall PA.
The large meta-analysis from Althoff et al. (2017) about PA data from smartphones found these inequalities in PA to be crucial for the prevalence of inactivity driven diseases such as overweight and obesity.
4.4 Strength and limitations
The present study is limited to its observational nature and we do not intend to infer causality from paralleled trends or significant correlations. The main goal of MoMo is to track and report PA and fitness of children and adolescents in a nationwide sample, and significant effort was put into collecting representative data from 167 sample points all over the country.
PA was assessed by self-reports. This method has various limitations including recall bias and social desirability. Measuring PA by objective methods such as accelerometers is more accurate in most types of PA, but is always limited to a short time interval, and unless a diary is added, the setting in which the PA took place is not captured. Since accelerometers capture any form of PA in a specific time frame, the correlation with self-reported habitual PA in specific settings is expected to be restricted, even when summarized. An accelerometer is also a very responsive tool towards socially desired behavior, and children drop it for some sports like swimming, martial arts, and sometimes even curricular sports in school. Using a questionnaire offered the chance to assess different types of exercise as well as other PA parameters like setting and sports club membership during a normal week, even when the person is, for example, on vacation or ill.
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