Health-enhancing physical activity in Germany: findings from a national sample of 24,016 adults

Background The German ‘ National Recommendations for Physical Activity and Physical Activity Promotion ’ state that adults (≥18 years) should engage in: [i] ≥150 minutes of aerobic moderate-to-vigorous-intensity physical activity/week (MVPA); and [ii] ≥2 days/week of muscle-strengthening exercise (MSE). However, there is limited research on the adherence to these guidelines among German adults. The present purpose was to describe the prevalence and correlates of physical activity guideline adherence among a nationally representative sample of German adults. Methods Data were drawn from the 2014 German Health Update survey, collected via a combination of web-based and mail surveys. Self-reported physical activity levels were assessed using the previously validated European Health Interview Survey Physical Activity Questionnaire. Weighted prevalence levels of the sample meeting the aerobic MVPA (≥150 minutes/week), MSE (≥2 times/week) and combined MVPA-MSE guidelines were calculated. Poisson regressions were used to assess prevalence ratios for physical activity guideline adherence categories across sociodemographic (age, sex, socioeconomic status) and lifestyle-related (self-rated health, BMI) variables.


Abstract Background
The German ' National Recommendations for Physical Activity and Physical Activity Promotion ' state that adults (≥18 years) should engage in: [i] ≥150 minutes of aerobic moderate-to-vigorous-intensity physical activity/week (MVPA); and [ii] ≥2 days/week of muscle-strengthening exercise (MSE). However, there is limited research on the adherence to these guidelines among German adults. The present purpose was to describe the prevalence and correlates of physical activity guideline adherence among a nationally representative sample of German adults.

Methods
Data were drawn from the 2014 German Health Update survey, collected via a combination of web-based and mail surveys. Self-reported physical activity levels were assessed using the previously validated European Health Interview Survey Physical Activity Questionnaire. Weighted prevalence levels of the sample meeting the aerobic MVPA (≥150 minutes/week), MSE (≥2 times/week) and combined MVPA-MSE guidelines were calculated. Poisson regressions were used to assess prevalence ratios for physical activity guideline adherence categories across sociodemographic (age, sex, socioeconomic status) and lifestyle-related (self-rated health, BMI) variables.

Conclusions
As almost 80% of German adults do not meet the nationally recommended aerobic combined MVPA-MSE physical activity guidelines, there is a necessity for large-scale public health interventions promoting both aerobic MVPA and MSE.

Background
Globally, approximately three quarters of deaths are attributable to chronic diseases [1]. In high-income countries, such as Germany, chronic diseases including ischemic heart disease, Alzheimer's disease, stroke and diabetes are the leading causes of mortality and morbidity [2]. Physical inactivity is an independent risk factor for the prevention/management of chronic diseases, with epidemiological evidence showing that physical activity decreases the risk of all-cause mortality, and the incidence of chronic health conditions [3].
Since the 1970's, most physical activity guidelines have focused on promoting moderate-to-vigorous aerobic physical activity (MVPA; e.g. walking, cycling, running) [4]. More recently, muscle-strengthening exercise (MSE; e.g. resistance exercise/weight training) has been added into global [5] and many national public health guidelines [6][7][8]. The 2016 German 'National Recommendations for Physical Activity and Physical Activity Promotion' based on an expert survey and an appraisal of researched studies [9], was the first German national guidelines to include both aerobic MVPA and MSE. These stated that adults (≥ 18 years) should participate in: [i] at least 150 minutes/week of moderate physical activity (e.g. walking) or 75 minutes/week of vigorous physical activity (e.g. jogging), or an equivalent combination of both; and [ii] 2 or more days per week of MSE involving major muscle groups [9].
The addition of combined MVPA-MSE into physical activity guidelines is due to the clinical and epidemiological evidence showing each activity mode has independent and cumulative health benefits [10]. In brief, aerobic MVPA is principally associated with a reduced risk of cardiovascular disease, diabetes, colon/breast cancer and depression [11]. MSE is largely linked to increased skeletal mass/strength, bone density, ability to perform activities of daily living and reduced risk of falls [12]. In addition, recent epidemiological studies have shown that compared to meeting one guideline alone, meeting both aerobic MVPA-MSE guidelines is prospectively associated with lower risk of all-cause mortality [13,14].
Despite joint aerobic MVPA-MSE being nationally recommended, there is limited available data describing its prevalence and correlates among German adults.
German public health surveillance studies have typically solely examined the population-levels of aerobic MVPA guideline adherence [9], with self-report estimates suggesting that ~ 50% of adults meet the aerobic MVPA guideline [15,16]. A recent report showed that 29.4% of German adults reported meeting the MSE guideline, and 22.6% met the combined MVPA-MSE guidelines, with guideline adherence declining with age and education and males having a higher prevalence, compared to females [17]. However, limitations of that report, were first, physical activity guideline adherence across other key sociodemographic/lifestyle factors were not included (e.g. socioeconomic status, self-rated health, body mass index) [18], and second, a multivariable analysis was not conducted. Reporting of physical activity levels by population sub-groups is vital for determining the most 'at-risk' populations [19], and essential to inform/guide optimal public health policy.
The primary aim of this study is to determine the prevalence of MVPA, MSE and Institute and all participants provided informed consent to participate. The purpose of the GEDA is to provide a health monitoring survey that produces reliable information on the actual German adult population's health status, health determinants and health care utilization [20].
A overview of the methods used in the GEDA 2014 is available elsewhere [20].
Conducted between November 2014 and July 2015, a two-stage stratified cluster sampling approach was used to recruit persons aged ≥ 18 years with permanent residence in Germany. Two modes of data collection were used: [i] self-administered web questionnaire (SAQ-Web); and [ii] self-administered paper questionnaire (SAQ-Paper). Initially, 90,102 invitations to participate were sent, with 24,016 fully completed (response rate = 26.9%), with 11,253 via SAQ-Web (45.3%) and 13,571 via SAQ-Paper (54.7%) [17,20].
In the current study, we only included data from those who fully responded to the physical activity items. To increase generalisability, we did not apply any further inclusion/exclusion criteria [21][22][23][24]. Additionally, since the German physical activity guidelines for MVPA and MSE apply to both adults (aged 18-64 years) and older adults (aged ≥ 65 years) [9], we included adults aged ≥ 18 years.
Physical activity assessments Self-reported physical activity levels were assessed using the European Health Interview Survey Physical Activity Questionnaire (EHIS-PAQ) [25]. The EHIS-PAQ has been shown to be a reliable and valid physical activity assessment tool for use in public health surveillance, and an overview of the development, design and psychometric testing this instrument has been described elsewhere [25] Aerobic MVPA Consistent with standardised protocols [25], to count towards meeting the aerobic MVPA guideline, we included physical activity accrued within the domains of: [i] moderate-to-vigorous aerobic recreational physical activity (e.g. Nordic walking, brisk walking, ball games, jogging, bicycling, swimming, aerobics, rowing, badminton); and [ii] transport-related physical activity (e.g. walking/cycling). For these two domains, respondents were asked to consider physical activity during a 'typical week', with the bout of activity having to last for ≥ 10 minutes. In each domain, respondents also were asked to report the number of days per week and total time spent (hours/minutes). MVPA was then summed the reported in the two domains to provide a weekly aerobic MVPA estimate. A validation study showed that when assessing moderate-to-vigorous aerobic recreational and transport-related

Muscle-strengthening exercise
To assess participation in MSE, respondents were asked, "In a typical week, on how many days do you carry out physical activities specifically designed to strengthen your muscles such as doing resistance training or strength exercises? Include all such activities even if you have mentioned them before.". When considering this question, respondents were prompted to consider a range of MSE-related activities, such as resistance training, strength exercises (using weights, elastic band, own body weight, etc.), knee bends (squats) and push-ups (press-ups). This item has shown to have 'fair' test-retest reliability (ICC = 0.55) [25], and similar items have shown evidence of concurrent validity, using the two or more MSE days/week threshold against metabolic syndrome [26].
According to the German physical activity guidelines [9], participants were Sociodemographic, socioeconomic status and lifestyle variables Sociodemographic (sex, age, nationality, socioeconomic status) and lifestyle variables (self-rated health, body mass index [BMI]) were assessed using standard survey items. Each sociodemographic/lifestyle variable was chosen due to its known association with combined MVPA-MSE [21][22][23][24], and sub-categories were created to be consistent with previous studies from the GEDA 2014 [27]. Socioeconomic status (low, medium or high) was assessed using the previously validated, Germanspecific, Socioeconomic SES index (SES Index) [27]. An overview of development of the SES Index can be found elsewhere [27].

Sample description
Data from 24,016 adults aged were included in the analysis. Socioeconomic and lifestyle characteristics of participants are shown in Table 1. Among the weighted sample, over half were female, over one third were aged 45-64 years, and the majority were of German nationality. Over half rated their health as 'good' and just under half had a 'normal' BMI (≥ 18.5 to < 25 kg/m 2 ).

Correlates of physical activity guideline adherence
In the multivariate adjusted analysis, across each sociodemographic and lifestyle factor, the adjusted PRs (APRs) were generally concordant for all physical activity guideline adherence categories (Table 2) The likelihood of meeting each physical activity guideline category decreased by decreasing socioeconomic status and self-rated health. The APRs for both aerobic MVPA-MSE guidelines were lowest among those with 'very poor', 'poor', and 'moderate' self-rated health (APR range = 0.20-0.46), and those with 'low' socioeconomic status (APR = 0.53; 95% CI:0.48-0.59). Compared to those with 'normal' BMI, those classified as 'overweight' and 'obese' were 31% and 52% less likely to meet the combined guidelines, respectively.

Discussion
Approximately 80% of German adults did not meet the nationally recommended physical activity guidelines of ≥ 150 minutes per week of aerobic MVPA and MSE ≥ 2 days per week. Considering that evidence that combined aerobic MVPA-MSE is independently associated with a multiple beneficial health outcomes [13,14,22,26,30], our findings suggest the need for immediate public health action to address physical inactivity in Germany.
The physical activity prevalence estimates presented in the current paper suggest that inactivity among German adults is currently underestimated. A recent study based on pooled data from several national public health surveillance surveys worldwide from 2002-2016, stated that 42.2% of German adults (≥ 18 years) were classified as inactive [15]. However, the German data analysed in that study included physical activity estimates solely based on meeting/not meeting the aerobic MVPA guideline [15]. The present data suggest that when considering the prevalence of adults not meeting the combined MVPA-MSE guidelines (77.4%), physical inactivity among German adults is almost two-fold greater than estimates exclusively based on aerobic MVPA guideline adherence.
The aerobic MVPA guideline adherence estimated in the current study are consistent with previous studies on German adults [15,16]. Cross-country comparisons show that a slightly higher prevalence of German adults meet the combined guidelines compared to U.S. [22] and U.K. [7] (22.6% vs. ~20.0%). In contrast, lower MVPA-MSE guideline adherence estimates have been observed among Australian [24], and Finnish adults [31] (10.8%-15.0%) For MSE guideline adherence, somewhat similar cross-country patterns to those for meeting the MVPA-MSE guidelines have been observed [22,24,31], with Germany levels comparable to U.S and U.K [7,23], but higher than those from Australian [24] and Finnish studies [31].
With the inclusion of a larger number of sociodemographic/lifestyle factors and the use of a multivariate adjusted analysis, the current study expands on a pervious report from the GEDA 2014 [17]. The lowest likelihood of meeting the combined MVPA-MSE guidelines were identified among those with poorer self-rated health, lower socioeconomic status, the overweight/obese and females. These sociodemographic/lifestyle correlates of combined MVPA-MSE guideline adherence are somewhat congruent with studies from other countries [21,22,24], and indicate that within the German context, these population sub-groups should be the target for future physical activity interventions.
Studies from Australia, Finland and U.S. have shown an inverse age gradient for the likelihood of meeting the combined MVPA-MSE guidelines [21,22,24]. Therefore, it was surprising to observe in our sample of German adults no such age gradient. For example, the second youngest group (30-44 years) had lower APR, when contrasted with their older counterparts (≥ 45 years). The increased physical activity among older populations is consistent with German research -especially for women [32].
While the causes of this are yet to be fully established, it might be that older German adults are better informed and more aware of health benefits of physical activity. This may positively influence being active especially among older populations who are perceiving health problems. Additionally, children leave the parental home (empty-nest-phase), so especially women have more time resources and sports clubs in Germany offer several activities, which are tailored to women [32]. Clearly, more research is needed to first, replicate this finding in prospective studies, and second, to determine its causes, especially for the decrease of physical activity in the younger age group. Nonetheless, the age-specific physical activity patterning shown in the current study might be reflective of increasing demands/life commitments encountered as German population's transition out of young adulthood into middle adulthood.
The finding that ~ 70% of German adults do not meet the MSE guideline indicates that this physical activity may warrant future national public health attention to increase population-level engagement. However, compared to aerobic MVPA, as with other countries [23,24,33], the promotion of MSE has been of limited focus in previous Germany public health promotion [9]. Importantly, our study showed that compared to those reporting insufficient aerobic MVPA, greater proportions report insufficient MSE (70.6% vs. 54.7%). Future large-scale public health MSE promotion approaches should include a combination of approaches [23]. Potential simultaneous and multi-level MSE strategies could include; providing physical environmental support (e.g. access to fitness centres/equipment in open spaces) [34], policy support (e.g. subsiding equipment for home-based activity, gym memberships, access to qualified fitness professionals) and mass-media campaigns challenging the negative stereotypes often linked to MSE (e.g. high injury risk,  [18]. In particular, research on modifiable factors related to MSE will be of interest when developing public health interventions.
A key limitation of this study is the use of self-report MVPA-MSE assessments. We are unable to exclude the possibility this method led to common problems associated with self-report physical activity assessment (e.g. recall bias

Competing interests
All authors declare that they have no competing interests.

Funding
All authors declare that they have no relevant funding to state.

Authors' contributions
Bennie and Tittlbach conceptualised the study and developed the initial research plan. Bennie conducted the data analysis and drafted the initial manuscript.
Tittlbach and De Cocker provided expertise on the analysis and interpretation of data and assisted in drafting the manuscript. All authors read and approved the final version of the manuscript for publication. b To meet the MVPA guideline respondents had to report engaging in at least 150 minutes per week of moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity per week, or an equivalent combination both, and accumulated in bouts of at least 10 consecutive minutes during leisure time and for transport. c To meet muscle-strengthening exercise guideline the guideline respondents had to report engaging in muscle strengthening activity at least two days per week. d Meeting both guidelines.
e Weighted percentage.
f Numbers different to total sample due to missing responses. *p-value for X 2 test.  b Prevalence ratio calculated using Poisson regression with a robust error variance.
c To meet the MVPA guideline respondents had to report engaging in at least 150 minutes per week of moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity per week, or an equivalent combination both, and accumulated in bouts of at least 10 consecutive minutes during leisure time and for transport. d To meet the muscle strengthening exercise guideline respondents had to report engaging in muscle strengthening activity at least two days per week. e Meeting both aerobic MVPA-MSE guidelines.