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Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 german adults.
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Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 German adults. Jason A Bennie , Megan Teychenne , Susanne Tittlbach PII: DOI: Reference:
S0165-0327(19)32050-6 https://doi.org/10.1016/j.jad.2020.01.172 JAD 11621
To appear in:
Journal of Affective Disorders
Received date: Revised date: Accepted date:
22 September 2019 21 January 2020 28 January 2020
Please cite this article as: Jason A Bennie , Megan Teychenne , Susanne Tittlbach , Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 German adults., Journal of Affective Disorders (2020), doi: https://doi.org/10.1016/j.jad.2020.01.172
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Highlights
Among a sample 23,602 adults, 58.3% reported no muscle-strengthening exercise. Compared to those doing none, lower depressive symptoms were observed among those doing any muscle-strengthening exercise. The strength of association between muscle-strengthening exercise and depression increased with increasing levels of depression symptom severity Strategies to prevent depression should promote muscle-strengthening exercise.
Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 German adults. Jason A Bennie1*, Megan Teychenne2, and Susanne Tittlbach3. 1. Physically Active Lifestyles Research Group (USQ PALs), Institute for Resilient Regions, University of Southern Queensland, Springfield, Queensland, Australia. 2. Deakin University, Geelong, Australia, Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences. 3. Social and Health Sciences in Sport, Institute of Sport Science, University of Bayreuth, Bavaria, Germany.
*Corresponding author Jason Bennie, PhD, Physically Active Lifestyles Research Group (USQ PALs), Institute for Resilient Regions, University of Southern Queensland, Education City, 37 Sinnathamby Boulevard, Springfield Central, QLD 4300, Australia. Email: [email protected] P: +61 (7) 3470 4136 (office).
Declarations of interest: none
Abstract Background: There is strong epidemiological evidence that physical activity is associated with lower likelihood of depression. Yet, most existing large population studies have investigated aerobic physical activity (e.g. walking/running), with few epidemiological studies examining the association between muscle-strengthening exercise (MSE; push ups, using weight machines) with depression. The aim of this study is to examine associations between MSE and depressive symptoms among a representative sample of German adults.
Methods: Cross-sectional analyses were conducted on the 2014 German Health Update. Validated questionnaires were used to assess MSE and depression symptom severity (eightitem Personal Health Questionnaire Depression Scale). Generalized linear models with Poisson regression with a robust error variance were used to assess prevalence ratios of depression symptom severity (mild, moderate, moderately severe/severe) across weekly MSE frequency (None [reference]; 1, 2, 3-4 and ≥5), adjusting for potential cofounders (e.g. age, sex, socioeconomic status, self-rated health, smoking, hazardous alcohol consumption, aerobic exercise).
Results: Data were available on 23,635 adults (≥18 years). When compared with those reporting no MSE, for all levels of depressive symptom severity, there were reduced prevalence ratios across all MSE frequencies. Compared to the higher MSE frequency groups (3-≥5 times/week), the prevalence ratios (range: 0.53-0.85) were similar among lower frequency groups (1-2 times/week) (range: 0.46-0.85). All associations remained after adjustment for sociodemographic, lifestyle characteristics and aerobic physical activity.
Limitations: Findings may be biased by the self-reporting of MSE and depressive symptom severity.
Conclusion: Any increase in MSE at the population-level may be beneficial for the prevention and treatment of depression
INTRODUCTION Physical activity is a key modifiable, non-pharmacological and relatively side-effect free therapeutic approach for the prevention and management of depression (1). The current clinical and epidemiological evidence on the associations between physical activity and depression is largely generated from research assessing the therapeutic effects of aerobic moderate-to-vigorous physical activity (MVPA; e.g. walking, cycling, running) (1, 2).
Recent evidence suggests that muscle-strengthening exercise (resistance exercise/weight training) may also be beneficial for reducing depressive symptom severity (3, 4). A metaanalysis of 33 randomized clinical trials showed that muscle-strengthening exercise had a moderate-sized mean effect (∆= 0.66; 95% CI, 0.48-0.83) on reducing depressive symptom severity among adults (4). In that meta-analysis, compared to MVPA, muscle-strengthening exercise had similar therapeutic effects on depressive symptom severity (4). However, current data are limited by the recruitment of small and non-representative samples (4). There is presently limited research examining the independent associations between musclestrengthening exercise and depressive symptom severity among community-based samples (1, 4, 5), and no studies among German adults.
The aim of this study is to examine the associations between weekly frequency of musclestrengthening exercise and depressive symptom severity among a nationally representative sample of German adults.
METHODS German Health Update 2014
Data were drawn from the 2014 German Health Update (hereafter: GEDA 2014). An overview of the GEDA 2014 has been described elsewhere (6). In brief, conducted between November 2014 and July 2015, a two-stage stratified cluster sampling approach was implemented to recruit a nationally representative sample of adults aged ≥18 years. Originally, 90,102 invitations to participate were sent, with 24,016 initially responding (response rate= 27.6%) (6). We excluded those who did not complete the Personal Health Questionnaire Depression Scale (n=414; 1.7% of the total sample).
Muscle-strengthening exercise To assess participation in muscle-strengthening exercise, 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?”. Respondents were requested to consider a variety of muscle-strengthening exercise--related activities, such as strength exercises (using weights, elastic band, own body weight, etc.), knee bends (squats), push-ups (press-ups), sit-ups, etc. This item has shown evidence of concurrent validity (using the ≥ 2 times/week threshold against metabolic syndrome) (7), and „fair‟ test-retest reliability (Intraclass Correlation Coefficient = 0.55) (8). Using classifications consistent with a previous study (9), muscle-strengthening exercise was categorised into five groups: „0‟; „1‟; „2‟; „3-4‟ and „≥5 times/week‟.
The Personal Health Questionnaire Depression Scale (PHQ-8) The eight-item Personal Health Questionnaire Depression Scale (PHQ-8) was used to examine depressive symptom severity (10). The PHQ-8 has shown evidence of convergent validity (with the Health-Related Quality of Life questionnaire as the standard), and considered a reliable and valid tool to assess depressive symptom severity in population-
based studies (10). Participants reported the frequency (ranging from „not at all‟ to „nearly every day‟) of experiencing eight different depressive symptoms (8-items) in the past two weeks”. As per protocol, „not at all‟ (i.e. 0 to 1 day) was recoded as „0‟; „several days‟ (i.e. 2 to 6 days) was recoded as „1‟; „more than half the days‟ (i.e. 7 to 11 days) was recorded as „2‟; and „nearly every day‟ (i.e. 12 to 14 days) was recoded as „3‟ (10). Responses to all eight items were then summed to create a total score, with 0-4 representing „no significant depressive symptoms‟; 5-9 representing „mild depressive symptoms‟; 10-14, „moderate‟; 1519, „moderately severe‟; and 20-24, „severe‟(10). Due to small numbers, we collapsed „moderately severe‟ and „severe‟. Four categories of depressive symptom severity are used in the present analysis: (i) no significant depressive symptoms; (ii) mild; (iii) moderate; and (iv) moderately severe/severe.
Potential cofounders All potential cofounders were chosen a priori, with previous literature showing that each are plausibly associated with engagement in muscle-strengthening exercise (4, 11, 12) and depressive symptoms (10, 13). Sociodemographic (sex, age, socioeconomic position), lifestyle characteristics (self-rated health, hazardous alcohol consumption [>20 grams/day for women, >40 grams/day for men], aerobic MVPA, self-reported body mass index [BMI], smoking) were assessed using previously validated questionnaires (6, 8, 14, 15). Socioeconomic position (low, medium or high) was assessed using the previously validated, German-specific, Socioeconomic SES index (SES Index) (14). In brief, the SES Index is based on information from three constructs: [i] formal education/vocational training; [ii] occupational status; and [iii] equivalenced to net household income. As per protocol, a distribution-based distinction of three status groups is made for the analyses, with the low and high status groups each comprising 20% and the medium status group 60% of the population
(14). We also adjusted for those reporting “being restricted by chronic disease in the past 6 months”.
Statistical analysis Analyses were conducted using the Complex Samples module of SPSS version 23. To allow for valid population estimates, weighting factors were included to correct for non-response (16). Descriptive statistics were used to describe the weighted percentages (%) across all potential cofounders, weekly frequency of muscle-strengthening exercise and depressive symptom severity.
Generalized linear models with Poisson regression with robust error variance were used to calculate prevalence ratios (PR) assessing the associations categories of depressive symptom severity (dependant variable) across muscle-strengthening exercise groups (explanatory variable). For these analyses, the reference group was those reporting no musclestrengthening exercise „0‟ times/week. In cross-sectional studies, the presenting adjusted prevalence ratios (APRs) calculated via Poison regression is considered a more robust statistical approach than the conventionally used logistic regression reporting of odds ratios (17). Separate models were conducted for: (i) mild (yes vs. no; reference [ref] = no significant depressive symptoms); (ii) moderate (yes vs. no; ref = no significant depressive symptoms); and (iii) moderately severe/severe depressive symptoms (yes vs. no; ref = no significant depressive symptoms).
We conducted three separate generalized linear models across each level of depressive symptom severity: (i) „Model A‟ (unadjusted); (ii) „Model B‟ (adjusted for sex, age, socioeconomic position, hazardous alcohol consumption, smoking, self-rated health, BMI
and being restricted by chronic disease in the past 6 months); and (iii) „Model C‟ (adjusted for Model B + aerobic MVPA). Since muscle-strengthening exercise (3, 9), and depressive symptom severity (13) differ by sex, we conducted a sex-stratified analysis. In addition, to reduce the risk of reverse causation, we conducted a sensitivity analyses stratifying by those who reporting being restricted by chronic disease in the past 6 months” („yes‟ vs. ‟no‟).
RESULTS Sample description The final sample was 23,635 (≥18 years). The GEDA 2014 sample characteristics are shown in Appendix Table 1. As shown in Table 1, 58.3% reported muscle-strengthening exercise 0 times/week, 12.3% 1 time/week, 12.1% 2 times/week, 10.3% 3-4 times/week and 6.9% ≥5 times/week. Compared to those who engaged in any muscle-strengthening exercise, those reporting none were older, had a lower socioeconomic status, were more obese, were daily smokers and had lower aerobic MVPA levels.
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Table 1: Sample characteristics and depressive symptom severitya according to weekly frequency of muscle-strengthening exercise among adults from the in the German Health Update 2014 survey (n=23,635). Muscle-strengthening exercise (times/week) 0 1 2 3-4 ≥5 Total sample n (%b) n=23,635 13,367 (58.3) 3,085 (12.3) 2,990 (12.1) 2,531 (10.3) 1,662 (6.9) Participant characteristics % (n) %b (95% CI) Males 49.2 (10,735) 50.1 (49.1-50.2) 37.5 (35.4-39.7) 47.0 (44.8-49.2) 55.7 (53.4-58.1) 56.5 (53.5-59.3) Aged ≥65 years 23.5 (5,566) 24.4 (23.5-25.3) 21.4 (20.5-22.3) 21.5 (19.7-23.4) 18.4 (16.8-20.2) 19.7 (17.9-2.6) c Low socioeconomic status 19.9 (3,980) 23.8 (22.8-24.7) 12.5 (11.1-14.2) 13.2 (11.7-15.0) 16.6 (14.7-18.7) 17.3 (15.2-19.8) Daily smoker 18.6 (3,980) 22.0 (21.2-22.9) 11.2 (9.8-12.7) 13.6 (12.0-15.3) 16.2 (14.4-18.2) 15.1 (13.0-17.4) Hazardous alcohol consumptiond 4.7 (1,111) 5.1 (4.6-5.5) 3.6 (2.9-4.4) 3.5 (2.8-4.4) 4.8 (3.9-5.9) 5.0 (3.8-6.6) „Very poor‟ self-rated health 0.7 (140) 1.0 (0.8-1.3) 0.2 (0.1-0.4) 0.4 (0.2-1.0) 0.2 (0.1-0,5) 0.8 (0.4-1.6) 2 Body mass index ≥30 kg/m „obese‟ 18.0 (3,957) 21.7 (20.8-22.6) 15.1 (13.5-16.8) 12.7 (11.3-14.3) 12.2 (10.7-14.0) 10.5 (8.8-12.4) Restricted by chronic disease in the past 6 months 6.5 (1,352) 7.6 (7.1-8.2) 3.2 (2.5-4.1) 5.3 (4.3-6.5) 4.2 (3.3-5.3) 8.3 (6.8-10.1) Did not meet the aerobic MVPA guidelinesc 54.7 (12,022) 72.9 (72.0-73.8) 43.3 (41.1-45.5) 24.7 (22.8-26.8) 19.5 (17.6-21.6) 25.0 (22.6-27.7) a b Depressive symptom severity % (95% CI) No significant depressive symptoms 67.0 (15,877) 64.4 (63.4-65.4) 71.4 (69.3-73.3) 69.5 (67.3-71.5) 70.6 (68.3-72.8) 71.9 (69.1-74.5) Mild depressive symptoms 22.9 (5,231) 23.8 (22.9-24.7) 21.3 (19.5-23.1) 23.0 (21.9-24.9) 21.3 (19.3-23.4) 20.4 (18.1-22.9) Moderate 6.8 (1,477) 7.8 (7.2-8.4) 5.5 (4.5-6.7) 5.6 (4.7-6.8) 5.6 (4.5-6.9) 4.7 (3.6-6.1) Moderately severe/severe 3.3 (674) 4.1 (3.7-4.5) 1.9 (1.4-2.5) 1.9 (1.4-2.7) 2.5 (1.8-3.5) 3.0 (2.1-4.3) a Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8). b c Sample weights provided by the GEDA 2014 (16). Socioeconomic status (low, medium and high) calculated by German-specific „SES Index‟(14); and includes information on formal education/vocational training, occupational status and equivalenced to net household income. d Hazardous alcohol consumption classified as >20 grams pure alcohol daily for women, and >40 grams daily for men (15). e To not meet the aerobic MVPA guidelines, a respondent had to report <150 moderate-intensity minutes/week or <75vigorous-intensityminutes/week, or an equivalent combination of both.
Table 2: Prevalence ratios (PR)a of depressive symptom severityb according to weekly frequency of muscle-strengthening exercise among German adults from the in the German Health Update 2014 survey (n=23,635). Depressive symptom severityb Muscle-strengthening Model Ac Model Bd Model Ce exercise (times/week) Prevalence ratio (95% CI) Prevalence ratio (95% CI) Prevalence ratio (95% CI) Mildf 0 1 (reference) 1 (reference) 1 (reference) 1 0.86 (0.79-0.94) 0.85 (0.78-0.93) 0.85 (0.78-0.93) 2 0.93 (0.86-1.01) 0.94 (0.87-1.03) 0.94 (0.87-1.03) 3-4 0.85 (0.77-0.93) 0.85 (0.77-0.93) 0.85 (0.77-0.94) ≥5 0.80 (0.71-0.90) 0.81 (0.72-0.91) 0.82 (0.73-0.92) f Moderate 0 1 (reference) 1 (reference) 1 (reference) 1 0.62 (0.52-0.73) 0.61 (0.52-0.73) 0.62 (0.52-0.73) 2 0.66 (0.56-0.79) 0.67 (0.56-0.80) 0.66 (0.56-0.79) 3-4 0.72 (0.60-0.86) 0.73 (0.61-0.88) 0.72 (0.60-0.86) ≥5 0.61 (0.48-0.76) 0.59 (0.46-0.75) 0.61 (0.48-0.76) f Moderately severe/severe 0 1 (reference) 1 (reference) 1 (reference) 1 0.47 (0.35-0.61) 0.44 (0.32-0.58) 0.46 (0.34-0.60) 2 0.50 (0.38-0.66) 0.49 (0.37-0.65) 0.49 (0.37-0.65) 3-4 0.57 (0.42-0.75) 0.54 (0.40-0.71) 0.53 (0.39-0.71) ≥5 0.66 (0.47-0.89) 0.65 (0.46-0.89) 0.65 (0.45-0.89) a Prevalence ratio calculated using Poisson regression with a robust error variance. b Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8). c Model A: unadjusted PR d Model B: adjusted PR: sex, age, socioeconomic status, hazardous alcohol consumption, self-rated health, body mass index and being restricted by chronic disease in the past 6 months: e Model C: adjusted for Model B + aerobic MVPA f Reference category = no significant depressive symptoms.
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Odds ratios for depressive symptom severity by weekly frequency of musclestrengthening exercise The unadjusted and adjusted prevalence ratios (APR) for depressive symptom severity by weekly frequency of muscle-strengthening exercise (ref = „0 times/week‟) are shown in Table 2. All associations remained similar after adjusting for sociodemographic/lifestyle characteristics and aerobic MVPA.
For the total sample, in the fully adjusted model („Model C‟), for mild depressive symptoms, (with the exception of muscle-strengthening exercise 2 times/week), all other musclestrengthening exercise frequencies were significantly associated with lower likelihood of mild depressive symptoms, with similar APRs (Range: 0.82-0.85). There was a similar trend of a non-linear association between weekly frequency of muscle-strengthening exercise and the reporting of moderate depressive symptoms, with all APRs generally similar across all MSE frequencies (range: 0.61-0.72). Among the most depressed group, compared to those doing no muscle-strengthening exercise, there was trend for an inverse linear association. Those reporting muscle-strengthening exercise 1, 2, 3-4, and ≥5 times/week were 54%, 51%, 47% and 35% less likely to report moderately severe/severe depressive symptoms, respectively. In a sex-stratified analysis, the APRs were mostly concordant between males and females (Appendix 2). In a sensitivity analyses, when compared to those who reported “being restricted by a chronic disease is the last six months”, those who were not had lower likelihood of reporting depressive symptoms (Appendix 2).
DISCUSSION
Among a large community-based sample of German adults, compared to those who engage in no muscle-strengthening exercise, there was a lower likelihood of reporting depression symptom severity among those engaging in any muscle-strengthening exercise. Particularly, there was a trend for the strength of association between muscle-strengthening exercise and depression to increase with increasing levels of depression symptom severity. While prospective evidence is needed to confirm these initial cross-sectional observations, the present study suggests that muscle-strengthening exercise may be an effective lifestyle behaviour in preventing high levels of depression.
This is the first epidemiological evidence suggesting that muscle-strengthening exercise among adults may be associated with lower levels of mild, moderate and severe levels of depressive symptoms, independent of aerobic MVPA. While our cross-sectional study design limits interpretations on the direction of these associations, these findings are supportive of those from recent meta-analyses of randomized clinical trials showing that musclestrengthening exercise has therapeutic benefits on symptoms of depression (4) and anxiety (5). These mental health benefits from muscle-strengthening exercise could be due to several possible underlying mechanisms, including psychosocial (e.g. enhanced self-efficacy, selfesteem and, social connectedness), and neurobiological (e.g. changes in neuroplastic mechanisms, increasing cerebral blood flow, reducing oxidative stress and inflammation) (18). Although, given the complexity of mental health problems such as depression, it is likely the mechanisms are multifactorial. Furthermore, contrasted to the decades of mechanistic research on the anti-depressive effects of aerobic exercise, comparative research on muscle-strengthening exercise is limited (4, 5), and hence warrants further study.
A further key finding was that the lower likelihood of depression symptom severity appeared not to be dose-dependent. Across all levels of depression severity, there were similar APRs among the low-to-moderate muscle-strengthening exercise frequency groups (1-2 times/week), compared to higher frequencies (3-4 and ≥5 times/week). This finding is somewhat consistent with meta-analytical evidence from clinical exercise studies that suggests that muscle-strengthening exercise results in a reduction in depressive symptoms irrespective of program or session duration, intensity, frequency, or total prescribed volume (4). While conscious of limitations of the cross-sectional nature of these data, to our understanding, this is the first study to show these associations among a large sample of adults. Our study suggests that high levels of muscle-strengthening exercise, which may be unattainable among those with no previous muscle-strengthening exercise experience (19), and those experiencing poor mental health, may not be necessary to improve mental-healthrelated outcomes at the population-level.
The fact that ~60% of our sample did not do any muscle-strengthening exercise underscores the importance of promoting this behaviour in future German public health initiatives. However, as with other Countries (20), in contrast to aerobic MVPA, muscle-strengthening exercise has received comparatively little attention in physical activity promotion within the German context (21). The current study and strong clinical evidence (4, 5), suggests that interventions that support muscle-strengthening exercise uptake/adherence at the population level are likely to have community-wide mental health benefits.
A key limitation is that the cross-sectional design limits inferences of causality for the main outcomes. However, our sensitivity analyses provide some indication that these associations might be causal. For example, as shown in Appendix 2, compared to those who felt restricted
by chronic disease, the associations between muscle-strengthening exercise and depression were more favourable among those who did not. A further limitation was the use of selfreport assessments of muscle-strengthening exercise and depression, which may have resulted in recall bias (e.g. social desirability, or under/over reporting). Other limitations included the modest GEDA 2014 response rate, the non-assessment of anti-depressant medication, sedentary behaviour and the chance that other unmeasured factors may have biased results. Strengths include the recruitment of a large community-based sample of German adults, and the use of standardised measures of depression symptom severity (10), muscle-strengthening exercise (8) and socioeconomic position (14).
CONCLUSION Among a large sample of German adults, muscle-strengthening exercise was associated with a lower likelihood of depressive symptoms severity. Although longitudinal studies are needed to better understand the direction of associations, our preliminary epidemiological evidence suggests that any level of muscle-strengthening exercise may be sufficient to improve mental health related outcomes at the population-level, and hence may contribute to reducing the significant public health burden of depression.
Conflict of interest statement All authors declare that there is no current conflict of interest to disclose with any organizations that might have an interest in the submitted work.
Financial disclosure All authors declare that there is no financial relationships with any organizations that might have an interest in the submitted work.
Author Statement Contributors Contributors Bennie conceptualised the study and developed the initial research plan. Bennie conducted the data analysis and drafted the initial manuscript. Tittlbach and Teychenne provided expertise on the analysis and interpretation of data and assisted in drafting the manuscript. Teychenne provided guidance on the study and critically reviewed the manuscript. All authors read and approved the final version of the manuscript for publication. Role of the Funding Source All authors declare that there is no financial relationships with any organizations that might have an interest in the submitted work. Acknowledgements Acknowledgements We thank all GEDA 2014 participants for their generous donation of time when taking part in this study. This research was funded by the Social and Health Sciences in Sport Institute of Sport Science, University of Bayreuth that provided funding for an overseas visiting scholar. Conflict of interest statement All authors declare that there is no current conflict of interest to disclose with any organizations that might have an interest in the submitted work.
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Appendix Table 2: Adjusted prevalence ratiosa (APR) of depressive symptom severityb according to levels of weekly frequency of muscle-strengthening exercise (MSE): stratified by sex and being restricted by chronic disease in the last 6 months. Sex Depressive symptom severityb MSE (times/week) Males APRd (95% CI) Females APRd (95% CI) c Mild 0 1 1 1 0.84 (0.71-0.98) 0.82 (0.75-0.91) 2 0.89 (0.77-1.02) 0.95 (0.86-1.06) 3-4 0.88 (0.76-1.02) 0.83 (0.73-0.95) ≥5 0.84 (0.70.0.99) 0.84 (0.71-1.00) Moderatec 0 1 1 1 0.66 (0.46-0.91) 0.56 (0.45-0.69) 2 0.78 (0.57-1.03) 0.58 (0.46-0.73) 3-4 0.74 (0.54-0.99) 0.75 (0.59-0.94) ≥5 0.62 (0.42-0.89) 0.61 (0.43-0.84) Moderately severe/severec 0 1 1 1 0.38 (0.20-0.66) 0.45 (0.31-0.62) 2 0.25 (0.12-0.45) 0.61 (0.43-0.83) 3-4 0.67 (0.43-0.99) 0.44 (0.26-0.66) ≥5 0.60 (0.34-0.96) 0.74 (0.46-1.12) Felt restricted by chronic disease in the last 6 months No Yes APRe (95% CI) APRe (95% CI) Mildc 0 1 1 1 0.66 (0.54-0.80) 0.78 (0.46-1.23) 2 0.75 (0.61-0.92) 0.93 (0.59-1.39) 3-4 0.74 (0.61-0.89) 0.47 (0.25-0.79) ≥5 0.53 (0.39-0.70) 1.02 (0.61-1.59) Moderatec 0 1 1 1 0.66 (0.54-0.80) 1.02 (0.61-1.59) 2 0.74 (0.61-0.89) 0.47 (0.25-0.79) 3-4 0.65 (0.61-0.92) 0.93 (0.59-1.39) ≥5 0.53 (0.39-0.70) 0.78 (0.46-1.23) Moderately severe/severec 0 1 1 1 0.73 (0.47-1.07) 0.69 (0.31-1.24) 2 0.64 (0.44-0.89) 0.60 (0.34-1.06) 3-4 0.53 (0.36-0.75) 0.50 (0.35-0.94) ≥5 0.59 (0.42-0.82) 0.63 (0.31-1.02) a Prevalence ratio calculated using Poisson regression with a robust error variance. b Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8). c Reference category = no significant depressive symptoms. d adjusted for age, socioeconomic status, hazardous alcohol consumption, self-rated health, body mass index, being restricted by chronic disease in the past 6 months and aerobic MVPA. e adjusted for sex, age, socioeconomic status, hazardous alcohol consumption, self-rated health, body mass index and aerobic MVPA.
Appendix 1: Sample characteristics of German Health Update 2014 n 23,635 Total Sex Weighted %a (n) Male 49.2 (10,735) Female 50.8 (12,900) Age (years) 18-29 17.1 (3,866) 30-44 22.4 (5,298) 45-64 36.7 (8,905) ≥65 23.8 (5,566) Socioeconomic statusb Low 19.9 (3,980) Medium 59.9 (13,245) High 20.2 (6,592) Self-rated health Very good 14.9 (3,774) Good 53.7 (12,824) Moderate 26.0 (5,797) Poor 4.7 (933) Very poor 0.7 (140) Body Mass Index (kg/m2) Underweight (<18.5) 1.8 (439) Normal (≥18.5-<25) 44.3 (10,871) Overweight (25– <30) 35.8 (8,156) Obese (≥30) 18.0 (3,957) Smoking status Never 76.0 (18,268) Occasional 5.4 (1,338) Daily 18.6 (3,980) Hazardous alcohol consumptionc Yes 4.7 (1,111) No 95.3 (22,132) Restricted by chronic disease in the past 6 months Yes 6.5 (1,352) No 93.5 (22,034) Aerobic MVPA leveld (minutes/week) 0-149 minutes/week „inactive‟ 54.7 (12,022) ≥ 150 minutes/week „active‟ 45.3 (10,800) Muscle-strengthening exercise (times/week) 0 58.3 (13,337) 1 12.3 (3,085) 2 12.1 (2,990) 3-4 10.3 (2,531) ≥5 6.9 (1,662) Depressive symptom severitye No significant depressive symptoms 67.0 (15,877) Mild depressive symptoms 22.9 (5,231) Moderate 6.8 (1,477) Moderately severe/severe 3.3 (674) a Sample weights provided by the GEDA 2014 (17) b Socioeconomic status (low, medium and high) calculated by German-specific „SES Index‟(12); and includes information on formal education/vocational training, occupational status and equivalenced to net household income c Hazardous alcohol consumption classified as >20 grams pure alcohol daily for women, and >40 grams daily for men. d To not meet the aerobic MVPA guidelines, a respondent had to report <150 moderate-intensity minutes/week or <75vigorous-intensityminutes/week, or an equivalent combination of both. e Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8).
Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 German adults. Jason A Bennie , Megan Teychenne , Susanne Tittlbach PII: DOI: Reference:
S0165-0327(19)32050-6 https://doi.org/10.1016/j.jad.2020.01.172 JAD 11621
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Journal of Affective Disorders
Received date: Revised date: Accepted date:
22 September 2019 21 January 2020 28 January 2020
Please cite this article as: Jason A Bennie , Megan Teychenne , Susanne Tittlbach , Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 German adults., Journal of Affective Disorders (2020), doi: https://doi.org/10.1016/j.jad.2020.01.172
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Highlights
Among a sample 23,602 adults, 58.3% reported no muscle-strengthening exercise. Compared to those doing none, lower depressive symptoms were observed among those doing any muscle-strengthening exercise. The strength of association between muscle-strengthening exercise and depression increased with increasing levels of depression symptom severity Strategies to prevent depression should promote muscle-strengthening exercise.
Muscle-strengthening exercise and depressive symptom severity among a nationally representative sample of 23,635 German adults. Jason A Bennie1*, Megan Teychenne2, and Susanne Tittlbach3. 1. Physically Active Lifestyles Research Group (USQ PALs), Institute for Resilient Regions, University of Southern Queensland, Springfield, Queensland, Australia. 2. Deakin University, Geelong, Australia, Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences. 3. Social and Health Sciences in Sport, Institute of Sport Science, University of Bayreuth, Bavaria, Germany.
*Corresponding author Jason Bennie, PhD, Physically Active Lifestyles Research Group (USQ PALs), Institute for Resilient Regions, University of Southern Queensland, Education City, 37 Sinnathamby Boulevard, Springfield Central, QLD 4300, Australia. Email: [email protected] P: +61 (7) 3470 4136 (office).
Declarations of interest: none
Abstract Background: There is strong epidemiological evidence that physical activity is associated with lower likelihood of depression. Yet, most existing large population studies have investigated aerobic physical activity (e.g. walking/running), with few epidemiological studies examining the association between muscle-strengthening exercise (MSE; push ups, using weight machines) with depression. The aim of this study is to examine associations between MSE and depressive symptoms among a representative sample of German adults.
Methods: Cross-sectional analyses were conducted on the 2014 German Health Update. Validated questionnaires were used to assess MSE and depression symptom severity (eightitem Personal Health Questionnaire Depression Scale). Generalized linear models with Poisson regression with a robust error variance were used to assess prevalence ratios of depression symptom severity (mild, moderate, moderately severe/severe) across weekly MSE frequency (None [reference]; 1, 2, 3-4 and ≥5), adjusting for potential cofounders (e.g. age, sex, socioeconomic status, self-rated health, smoking, hazardous alcohol consumption, aerobic exercise).
Results: Data were available on 23,635 adults (≥18 years). When compared with those reporting no MSE, for all levels of depressive symptom severity, there were reduced prevalence ratios across all MSE frequencies. Compared to the higher MSE frequency groups (3-≥5 times/week), the prevalence ratios (range: 0.53-0.85) were similar among lower frequency groups (1-2 times/week) (range: 0.46-0.85). All associations remained after adjustment for sociodemographic, lifestyle characteristics and aerobic physical activity.
Limitations: Findings may be biased by the self-reporting of MSE and depressive symptom severity.
Conclusion: Any increase in MSE at the population-level may be beneficial for the prevention and treatment of depression
INTRODUCTION Physical activity is a key modifiable, non-pharmacological and relatively side-effect free therapeutic approach for the prevention and management of depression (1). The current clinical and epidemiological evidence on the associations between physical activity and depression is largely generated from research assessing the therapeutic effects of aerobic moderate-to-vigorous physical activity (MVPA; e.g. walking, cycling, running) (1, 2).
Recent evidence suggests that muscle-strengthening exercise (resistance exercise/weight training) may also be beneficial for reducing depressive symptom severity (3, 4). A metaanalysis of 33 randomized clinical trials showed that muscle-strengthening exercise had a moderate-sized mean effect (∆= 0.66; 95% CI, 0.48-0.83) on reducing depressive symptom severity among adults (4). In that meta-analysis, compared to MVPA, muscle-strengthening exercise had similar therapeutic effects on depressive symptom severity (4). However, current data are limited by the recruitment of small and non-representative samples (4). There is presently limited research examining the independent associations between musclestrengthening exercise and depressive symptom severity among community-based samples (1, 4, 5), and no studies among German adults.
The aim of this study is to examine the associations between weekly frequency of musclestrengthening exercise and depressive symptom severity among a nationally representative sample of German adults.
METHODS German Health Update 2014
Data were drawn from the 2014 German Health Update (hereafter: GEDA 2014). An overview of the GEDA 2014 has been described elsewhere (6). In brief, conducted between November 2014 and July 2015, a two-stage stratified cluster sampling approach was implemented to recruit a nationally representative sample of adults aged ≥18 years. Originally, 90,102 invitations to participate were sent, with 24,016 initially responding (response rate= 27.6%) (6). We excluded those who did not complete the Personal Health Questionnaire Depression Scale (n=414; 1.7% of the total sample).
Muscle-strengthening exercise To assess participation in muscle-strengthening exercise, 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?”. Respondents were requested to consider a variety of muscle-strengthening exercise--related activities, such as strength exercises (using weights, elastic band, own body weight, etc.), knee bends (squats), push-ups (press-ups), sit-ups, etc. This item has shown evidence of concurrent validity (using the ≥ 2 times/week threshold against metabolic syndrome) (7), and „fair‟ test-retest reliability (Intraclass Correlation Coefficient = 0.55) (8). Using classifications consistent with a previous study (9), muscle-strengthening exercise was categorised into five groups: „0‟; „1‟; „2‟; „3-4‟ and „≥5 times/week‟.
The Personal Health Questionnaire Depression Scale (PHQ-8) The eight-item Personal Health Questionnaire Depression Scale (PHQ-8) was used to examine depressive symptom severity (10). The PHQ-8 has shown evidence of convergent validity (with the Health-Related Quality of Life questionnaire as the standard), and considered a reliable and valid tool to assess depressive symptom severity in population-
based studies (10). Participants reported the frequency (ranging from „not at all‟ to „nearly every day‟) of experiencing eight different depressive symptoms (8-items) in the past two weeks”. As per protocol, „not at all‟ (i.e. 0 to 1 day) was recoded as „0‟; „several days‟ (i.e. 2 to 6 days) was recoded as „1‟; „more than half the days‟ (i.e. 7 to 11 days) was recorded as „2‟; and „nearly every day‟ (i.e. 12 to 14 days) was recoded as „3‟ (10). Responses to all eight items were then summed to create a total score, with 0-4 representing „no significant depressive symptoms‟; 5-9 representing „mild depressive symptoms‟; 10-14, „moderate‟; 1519, „moderately severe‟; and 20-24, „severe‟(10). Due to small numbers, we collapsed „moderately severe‟ and „severe‟. Four categories of depressive symptom severity are used in the present analysis: (i) no significant depressive symptoms; (ii) mild; (iii) moderate; and (iv) moderately severe/severe.
Potential cofounders All potential cofounders were chosen a priori, with previous literature showing that each are plausibly associated with engagement in muscle-strengthening exercise (4, 11, 12) and depressive symptoms (10, 13). Sociodemographic (sex, age, socioeconomic position), lifestyle characteristics (self-rated health, hazardous alcohol consumption [>20 grams/day for women, >40 grams/day for men], aerobic MVPA, self-reported body mass index [BMI], smoking) were assessed using previously validated questionnaires (6, 8, 14, 15). Socioeconomic position (low, medium or high) was assessed using the previously validated, German-specific, Socioeconomic SES index (SES Index) (14). In brief, the SES Index is based on information from three constructs: [i] formal education/vocational training; [ii] occupational status; and [iii] equivalenced to net household income. As per protocol, a distribution-based distinction of three status groups is made for the analyses, with the low and high status groups each comprising 20% and the medium status group 60% of the population
(14). We also adjusted for those reporting “being restricted by chronic disease in the past 6 months”.
Statistical analysis Analyses were conducted using the Complex Samples module of SPSS version 23. To allow for valid population estimates, weighting factors were included to correct for non-response (16). Descriptive statistics were used to describe the weighted percentages (%) across all potential cofounders, weekly frequency of muscle-strengthening exercise and depressive symptom severity.
Generalized linear models with Poisson regression with robust error variance were used to calculate prevalence ratios (PR) assessing the associations categories of depressive symptom severity (dependant variable) across muscle-strengthening exercise groups (explanatory variable). For these analyses, the reference group was those reporting no musclestrengthening exercise „0‟ times/week. In cross-sectional studies, the presenting adjusted prevalence ratios (APRs) calculated via Poison regression is considered a more robust statistical approach than the conventionally used logistic regression reporting of odds ratios (17). Separate models were conducted for: (i) mild (yes vs. no; reference [ref] = no significant depressive symptoms); (ii) moderate (yes vs. no; ref = no significant depressive symptoms); and (iii) moderately severe/severe depressive symptoms (yes vs. no; ref = no significant depressive symptoms).
We conducted three separate generalized linear models across each level of depressive symptom severity: (i) „Model A‟ (unadjusted); (ii) „Model B‟ (adjusted for sex, age, socioeconomic position, hazardous alcohol consumption, smoking, self-rated health, BMI
and being restricted by chronic disease in the past 6 months); and (iii) „Model C‟ (adjusted for Model B + aerobic MVPA). Since muscle-strengthening exercise (3, 9), and depressive symptom severity (13) differ by sex, we conducted a sex-stratified analysis. In addition, to reduce the risk of reverse causation, we conducted a sensitivity analyses stratifying by those who reporting being restricted by chronic disease in the past 6 months” („yes‟ vs. ‟no‟).
RESULTS Sample description The final sample was 23,635 (≥18 years). The GEDA 2014 sample characteristics are shown in Appendix Table 1. As shown in Table 1, 58.3% reported muscle-strengthening exercise 0 times/week, 12.3% 1 time/week, 12.1% 2 times/week, 10.3% 3-4 times/week and 6.9% ≥5 times/week. Compared to those who engaged in any muscle-strengthening exercise, those reporting none were older, had a lower socioeconomic status, were more obese, were daily smokers and had lower aerobic MVPA levels.
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Table 1: Sample characteristics and depressive symptom severitya according to weekly frequency of muscle-strengthening exercise among adults from the in the German Health Update 2014 survey (n=23,635). Muscle-strengthening exercise (times/week) 0 1 2 3-4 ≥5 Total sample n (%b) n=23,635 13,367 (58.3) 3,085 (12.3) 2,990 (12.1) 2,531 (10.3) 1,662 (6.9) Participant characteristics % (n) %b (95% CI) Males 49.2 (10,735) 50.1 (49.1-50.2) 37.5 (35.4-39.7) 47.0 (44.8-49.2) 55.7 (53.4-58.1) 56.5 (53.5-59.3) Aged ≥65 years 23.5 (5,566) 24.4 (23.5-25.3) 21.4 (20.5-22.3) 21.5 (19.7-23.4) 18.4 (16.8-20.2) 19.7 (17.9-2.6) c Low socioeconomic status 19.9 (3,980) 23.8 (22.8-24.7) 12.5 (11.1-14.2) 13.2 (11.7-15.0) 16.6 (14.7-18.7) 17.3 (15.2-19.8) Daily smoker 18.6 (3,980) 22.0 (21.2-22.9) 11.2 (9.8-12.7) 13.6 (12.0-15.3) 16.2 (14.4-18.2) 15.1 (13.0-17.4) Hazardous alcohol consumptiond 4.7 (1,111) 5.1 (4.6-5.5) 3.6 (2.9-4.4) 3.5 (2.8-4.4) 4.8 (3.9-5.9) 5.0 (3.8-6.6) „Very poor‟ self-rated health 0.7 (140) 1.0 (0.8-1.3) 0.2 (0.1-0.4) 0.4 (0.2-1.0) 0.2 (0.1-0,5) 0.8 (0.4-1.6) 2 Body mass index ≥30 kg/m „obese‟ 18.0 (3,957) 21.7 (20.8-22.6) 15.1 (13.5-16.8) 12.7 (11.3-14.3) 12.2 (10.7-14.0) 10.5 (8.8-12.4) Restricted by chronic disease in the past 6 months 6.5 (1,352) 7.6 (7.1-8.2) 3.2 (2.5-4.1) 5.3 (4.3-6.5) 4.2 (3.3-5.3) 8.3 (6.8-10.1) Did not meet the aerobic MVPA guidelinesc 54.7 (12,022) 72.9 (72.0-73.8) 43.3 (41.1-45.5) 24.7 (22.8-26.8) 19.5 (17.6-21.6) 25.0 (22.6-27.7) a b Depressive symptom severity % (95% CI) No significant depressive symptoms 67.0 (15,877) 64.4 (63.4-65.4) 71.4 (69.3-73.3) 69.5 (67.3-71.5) 70.6 (68.3-72.8) 71.9 (69.1-74.5) Mild depressive symptoms 22.9 (5,231) 23.8 (22.9-24.7) 21.3 (19.5-23.1) 23.0 (21.9-24.9) 21.3 (19.3-23.4) 20.4 (18.1-22.9) Moderate 6.8 (1,477) 7.8 (7.2-8.4) 5.5 (4.5-6.7) 5.6 (4.7-6.8) 5.6 (4.5-6.9) 4.7 (3.6-6.1) Moderately severe/severe 3.3 (674) 4.1 (3.7-4.5) 1.9 (1.4-2.5) 1.9 (1.4-2.7) 2.5 (1.8-3.5) 3.0 (2.1-4.3) a Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8). b c Sample weights provided by the GEDA 2014 (16). Socioeconomic status (low, medium and high) calculated by German-specific „SES Index‟(14); and includes information on formal education/vocational training, occupational status and equivalenced to net household income. d Hazardous alcohol consumption classified as >20 grams pure alcohol daily for women, and >40 grams daily for men (15). e To not meet the aerobic MVPA guidelines, a respondent had to report <150 moderate-intensity minutes/week or <75vigorous-intensityminutes/week, or an equivalent combination of both.
Table 2: Prevalence ratios (PR)a of depressive symptom severityb according to weekly frequency of muscle-strengthening exercise among German adults from the in the German Health Update 2014 survey (n=23,635). Depressive symptom severityb Muscle-strengthening Model Ac Model Bd Model Ce exercise (times/week) Prevalence ratio (95% CI) Prevalence ratio (95% CI) Prevalence ratio (95% CI) Mildf 0 1 (reference) 1 (reference) 1 (reference) 1 0.86 (0.79-0.94) 0.85 (0.78-0.93) 0.85 (0.78-0.93) 2 0.93 (0.86-1.01) 0.94 (0.87-1.03) 0.94 (0.87-1.03) 3-4 0.85 (0.77-0.93) 0.85 (0.77-0.93) 0.85 (0.77-0.94) ≥5 0.80 (0.71-0.90) 0.81 (0.72-0.91) 0.82 (0.73-0.92) f Moderate 0 1 (reference) 1 (reference) 1 (reference) 1 0.62 (0.52-0.73) 0.61 (0.52-0.73) 0.62 (0.52-0.73) 2 0.66 (0.56-0.79) 0.67 (0.56-0.80) 0.66 (0.56-0.79) 3-4 0.72 (0.60-0.86) 0.73 (0.61-0.88) 0.72 (0.60-0.86) ≥5 0.61 (0.48-0.76) 0.59 (0.46-0.75) 0.61 (0.48-0.76) f Moderately severe/severe 0 1 (reference) 1 (reference) 1 (reference) 1 0.47 (0.35-0.61) 0.44 (0.32-0.58) 0.46 (0.34-0.60) 2 0.50 (0.38-0.66) 0.49 (0.37-0.65) 0.49 (0.37-0.65) 3-4 0.57 (0.42-0.75) 0.54 (0.40-0.71) 0.53 (0.39-0.71) ≥5 0.66 (0.47-0.89) 0.65 (0.46-0.89) 0.65 (0.45-0.89) a Prevalence ratio calculated using Poisson regression with a robust error variance. b Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8). c Model A: unadjusted PR d Model B: adjusted PR: sex, age, socioeconomic status, hazardous alcohol consumption, self-rated health, body mass index and being restricted by chronic disease in the past 6 months: e Model C: adjusted for Model B + aerobic MVPA f Reference category = no significant depressive symptoms.
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Odds ratios for depressive symptom severity by weekly frequency of musclestrengthening exercise The unadjusted and adjusted prevalence ratios (APR) for depressive symptom severity by weekly frequency of muscle-strengthening exercise (ref = „0 times/week‟) are shown in Table 2. All associations remained similar after adjusting for sociodemographic/lifestyle characteristics and aerobic MVPA.
For the total sample, in the fully adjusted model („Model C‟), for mild depressive symptoms, (with the exception of muscle-strengthening exercise 2 times/week), all other musclestrengthening exercise frequencies were significantly associated with lower likelihood of mild depressive symptoms, with similar APRs (Range: 0.82-0.85). There was a similar trend of a non-linear association between weekly frequency of muscle-strengthening exercise and the reporting of moderate depressive symptoms, with all APRs generally similar across all MSE frequencies (range: 0.61-0.72). Among the most depressed group, compared to those doing no muscle-strengthening exercise, there was trend for an inverse linear association. Those reporting muscle-strengthening exercise 1, 2, 3-4, and ≥5 times/week were 54%, 51%, 47% and 35% less likely to report moderately severe/severe depressive symptoms, respectively. In a sex-stratified analysis, the APRs were mostly concordant between males and females (Appendix 2). In a sensitivity analyses, when compared to those who reported “being restricted by a chronic disease is the last six months”, those who were not had lower likelihood of reporting depressive symptoms (Appendix 2).
DISCUSSION
Among a large community-based sample of German adults, compared to those who engage in no muscle-strengthening exercise, there was a lower likelihood of reporting depression symptom severity among those engaging in any muscle-strengthening exercise. Particularly, there was a trend for the strength of association between muscle-strengthening exercise and depression to increase with increasing levels of depression symptom severity. While prospective evidence is needed to confirm these initial cross-sectional observations, the present study suggests that muscle-strengthening exercise may be an effective lifestyle behaviour in preventing high levels of depression.
This is the first epidemiological evidence suggesting that muscle-strengthening exercise among adults may be associated with lower levels of mild, moderate and severe levels of depressive symptoms, independent of aerobic MVPA. While our cross-sectional study design limits interpretations on the direction of these associations, these findings are supportive of those from recent meta-analyses of randomized clinical trials showing that musclestrengthening exercise has therapeutic benefits on symptoms of depression (4) and anxiety (5). These mental health benefits from muscle-strengthening exercise could be due to several possible underlying mechanisms, including psychosocial (e.g. enhanced self-efficacy, selfesteem and, social connectedness), and neurobiological (e.g. changes in neuroplastic mechanisms, increasing cerebral blood flow, reducing oxidative stress and inflammation) (18). Although, given the complexity of mental health problems such as depression, it is likely the mechanisms are multifactorial. Furthermore, contrasted to the decades of mechanistic research on the anti-depressive effects of aerobic exercise, comparative research on muscle-strengthening exercise is limited (4, 5), and hence warrants further study.
A further key finding was that the lower likelihood of depression symptom severity appeared not to be dose-dependent. Across all levels of depression severity, there were similar APRs among the low-to-moderate muscle-strengthening exercise frequency groups (1-2 times/week), compared to higher frequencies (3-4 and ≥5 times/week). This finding is somewhat consistent with meta-analytical evidence from clinical exercise studies that suggests that muscle-strengthening exercise results in a reduction in depressive symptoms irrespective of program or session duration, intensity, frequency, or total prescribed volume (4). While conscious of limitations of the cross-sectional nature of these data, to our understanding, this is the first study to show these associations among a large sample of adults. Our study suggests that high levels of muscle-strengthening exercise, which may be unattainable among those with no previous muscle-strengthening exercise experience (19), and those experiencing poor mental health, may not be necessary to improve mental-healthrelated outcomes at the population-level.
The fact that ~60% of our sample did not do any muscle-strengthening exercise underscores the importance of promoting this behaviour in future German public health initiatives. However, as with other Countries (20), in contrast to aerobic MVPA, muscle-strengthening exercise has received comparatively little attention in physical activity promotion within the German context (21). The current study and strong clinical evidence (4, 5), suggests that interventions that support muscle-strengthening exercise uptake/adherence at the population level are likely to have community-wide mental health benefits.
A key limitation is that the cross-sectional design limits inferences of causality for the main outcomes. However, our sensitivity analyses provide some indication that these associations might be causal. For example, as shown in Appendix 2, compared to those who felt restricted
by chronic disease, the associations between muscle-strengthening exercise and depression were more favourable among those who did not. A further limitation was the use of selfreport assessments of muscle-strengthening exercise and depression, which may have resulted in recall bias (e.g. social desirability, or under/over reporting). Other limitations included the modest GEDA 2014 response rate, the non-assessment of anti-depressant medication, sedentary behaviour and the chance that other unmeasured factors may have biased results. Strengths include the recruitment of a large community-based sample of German adults, and the use of standardised measures of depression symptom severity (10), muscle-strengthening exercise (8) and socioeconomic position (14).
CONCLUSION Among a large sample of German adults, muscle-strengthening exercise was associated with a lower likelihood of depressive symptoms severity. Although longitudinal studies are needed to better understand the direction of associations, our preliminary epidemiological evidence suggests that any level of muscle-strengthening exercise may be sufficient to improve mental health related outcomes at the population-level, and hence may contribute to reducing the significant public health burden of depression.
Conflict of interest statement All authors declare that there is no current conflict of interest to disclose with any organizations that might have an interest in the submitted work.
Financial disclosure All authors declare that there is no financial relationships with any organizations that might have an interest in the submitted work.
Author Statement Contributors Contributors Bennie conceptualised the study and developed the initial research plan. Bennie conducted the data analysis and drafted the initial manuscript. Tittlbach and Teychenne provided expertise on the analysis and interpretation of data and assisted in drafting the manuscript. Teychenne provided guidance on the study and critically reviewed the manuscript. All authors read and approved the final version of the manuscript for publication. Role of the Funding Source All authors declare that there is no financial relationships with any organizations that might have an interest in the submitted work. Acknowledgements Acknowledgements We thank all GEDA 2014 participants for their generous donation of time when taking part in this study. This research was funded by the Social and Health Sciences in Sport Institute of Sport Science, University of Bayreuth that provided funding for an overseas visiting scholar. Conflict of interest statement All authors declare that there is no current conflict of interest to disclose with any organizations that might have an interest in the submitted work.
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Appendix Table 2: Adjusted prevalence ratiosa (APR) of depressive symptom severityb according to levels of weekly frequency of muscle-strengthening exercise (MSE): stratified by sex and being restricted by chronic disease in the last 6 months. Sex Depressive symptom severityb MSE (times/week) Males APRd (95% CI) Females APRd (95% CI) c Mild 0 1 1 1 0.84 (0.71-0.98) 0.82 (0.75-0.91) 2 0.89 (0.77-1.02) 0.95 (0.86-1.06) 3-4 0.88 (0.76-1.02) 0.83 (0.73-0.95) ≥5 0.84 (0.70.0.99) 0.84 (0.71-1.00) Moderatec 0 1 1 1 0.66 (0.46-0.91) 0.56 (0.45-0.69) 2 0.78 (0.57-1.03) 0.58 (0.46-0.73) 3-4 0.74 (0.54-0.99) 0.75 (0.59-0.94) ≥5 0.62 (0.42-0.89) 0.61 (0.43-0.84) Moderately severe/severec 0 1 1 1 0.38 (0.20-0.66) 0.45 (0.31-0.62) 2 0.25 (0.12-0.45) 0.61 (0.43-0.83) 3-4 0.67 (0.43-0.99) 0.44 (0.26-0.66) ≥5 0.60 (0.34-0.96) 0.74 (0.46-1.12) Felt restricted by chronic disease in the last 6 months No Yes APRe (95% CI) APRe (95% CI) Mildc 0 1 1 1 0.66 (0.54-0.80) 0.78 (0.46-1.23) 2 0.75 (0.61-0.92) 0.93 (0.59-1.39) 3-4 0.74 (0.61-0.89) 0.47 (0.25-0.79) ≥5 0.53 (0.39-0.70) 1.02 (0.61-1.59) Moderatec 0 1 1 1 0.66 (0.54-0.80) 1.02 (0.61-1.59) 2 0.74 (0.61-0.89) 0.47 (0.25-0.79) 3-4 0.65 (0.61-0.92) 0.93 (0.59-1.39) ≥5 0.53 (0.39-0.70) 0.78 (0.46-1.23) Moderately severe/severec 0 1 1 1 0.73 (0.47-1.07) 0.69 (0.31-1.24) 2 0.64 (0.44-0.89) 0.60 (0.34-1.06) 3-4 0.53 (0.36-0.75) 0.50 (0.35-0.94) ≥5 0.59 (0.42-0.82) 0.63 (0.31-1.02) a Prevalence ratio calculated using Poisson regression with a robust error variance. b Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8). c Reference category = no significant depressive symptoms. d adjusted for age, socioeconomic status, hazardous alcohol consumption, self-rated health, body mass index, being restricted by chronic disease in the past 6 months and aerobic MVPA. e adjusted for sex, age, socioeconomic status, hazardous alcohol consumption, self-rated health, body mass index and aerobic MVPA.
Appendix 1: Sample characteristics of German Health Update 2014 n 23,635 Total Sex Weighted %a (n) Male 49.2 (10,735) Female 50.8 (12,900) Age (years) 18-29 17.1 (3,866) 30-44 22.4 (5,298) 45-64 36.7 (8,905) ≥65 23.8 (5,566) Socioeconomic statusb Low 19.9 (3,980) Medium 59.9 (13,245) High 20.2 (6,592) Self-rated health Very good 14.9 (3,774) Good 53.7 (12,824) Moderate 26.0 (5,797) Poor 4.7 (933) Very poor 0.7 (140) Body Mass Index (kg/m2) Underweight (<18.5) 1.8 (439) Normal (≥18.5-<25) 44.3 (10,871) Overweight (25– <30) 35.8 (8,156) Obese (≥30) 18.0 (3,957) Smoking status Never 76.0 (18,268) Occasional 5.4 (1,338) Daily 18.6 (3,980) Hazardous alcohol consumptionc Yes 4.7 (1,111) No 95.3 (22,132) Restricted by chronic disease in the past 6 months Yes 6.5 (1,352) No 93.5 (22,034) Aerobic MVPA leveld (minutes/week) 0-149 minutes/week „inactive‟ 54.7 (12,022) ≥ 150 minutes/week „active‟ 45.3 (10,800) Muscle-strengthening exercise (times/week) 0 58.3 (13,337) 1 12.3 (3,085) 2 12.1 (2,990) 3-4 10.3 (2,531) ≥5 6.9 (1,662) Depressive symptom severitye No significant depressive symptoms 67.0 (15,877) Mild depressive symptoms 22.9 (5,231) Moderate 6.8 (1,477) Moderately severe/severe 3.3 (674) a Sample weights provided by the GEDA 2014 (17) b Socioeconomic status (low, medium and high) calculated by German-specific „SES Index‟(12); and includes information on formal education/vocational training, occupational status and equivalenced to net household income c Hazardous alcohol consumption classified as >20 grams pure alcohol daily for women, and >40 grams daily for men. d To not meet the aerobic MVPA guidelines, a respondent had to report <150 moderate-intensity minutes/week or <75vigorous-intensityminutes/week, or an equivalent combination of both. e Depressive symptom severity assessed by eight-item Patient Health Questionnaire depression scale (PHQ-8).