Trends in Muscle-Strengthening Exercise Among Nationally Representative Samples of United States Adults Between 2011 and 2017

in Journal of Physical Activity and Health

Background: Muscle-strengthening exercise (MSE) is a component of the World Health Organization’s “2010 Global Recommendations on Physical Activity for Health.” However, its participation trends are seldom examined in physical activity surveillance. This study describes the prevalence, trends, and correlates of MSE among a large sample of US adults. Methods: The data were analyzed from the 2011, 2013, 2015, and 2017 US Behavioral Risk Factor Surveillance System surveys. Self-reported MSE participation was assessed using the same validated survey item. Population-weighted proportions were calculated for (1) “insufficient” (0–1 time/wk) or (2) “sufficient MSE” (≥2 times/wk). Prevalence ratios of those reporting sufficient MSE across sociodemographic characteristics were calculated using multivariate Poisson regression. Results: The data were available for 1,735,626 participants (≥18 y). Over the 7-year monitoring period, the prevalence of sufficient MSE showed a small (1.2%) but statistically significant increase (2011 = 29.1%; 2013 = 29.4%; 2015 = 30.2%; and 2017 = 30.3%, P < .001 for linear trend). Older adults, women, and those with lower education/income were consistently less likely to report sufficient MSE, compared with their counterparts. Conclusions: From 2011 to 2017, between 69.7% and 70.9% of US adults did not meet the MSE guidelines. Consistently low participation levels highlight the need to provide support for uptake of or adherence to MSE at the population level.

Strong epidemiological evidence shows that regular physical activity reduces the risk of all-cause and chronic disease–specific mortality and multiple chronic health conditions, such as cardiovascular disease, diabetes, and breast/colon cancer.1,2 Since the mid-1970s and until recently, physical activity guidelines for public health were exclusively based on promoting moderate- to vigorous-intensity aerobic activity (eg, walking, jogging, cycling). However, over the last decade, muscle-strengthening exercise (MSE; weight/strength training) has been incorporated into public health guidelines.3

Muscle-strengthening exercise was first included in the 2008 Physical Activity Guidelines for Americans4 and was subsequently adopted in the World Health Organization’s (WHO) 2010 Global Recommendations on Physical Activity for Health.5 The WHO guidelines state that adults ≥18 years should have “two or more days per week of muscle strengthening activity involving major muscle groups.”5 The addition of MSE into the physical activity guidelines is due to strong clinical and epidemiological evidence showing that this activity has multiple independent health benefits. In brief, meta-analyses of short-duration (typically 6–12 wk) clinical exercise studies have shown multiple health outcomes, including increased skeletal muscle mass/strength,6 bone mineral density,7 enhanced ability to perform activities of daily living,8 and improved cardiometabolic health.9 Importantly, in many of these studies, the benefits of MSE occur either independent of, or are more effective than, participation in moderate- to vigorous-intensity aerobic activity alone. A recent meta-analysis of 11 prospective cohort studies showed that, compared with no exercise, MSE was independently associated with a 21% lower risk of all-cause mortality.10

Despite its multiple health benefits, physical activity surveillance rarely assesses population-level trends in MSE participation.11 In the United States (US), for example, prevalence estimates from population studies conducted between 2004 and 2017 show that between 6.0% and 30.2% of adults (≥18 y) meet MSE guidelines (≥2 times/wk).1215 However, data on the trends over time of MSE levels are limited. One study analyzing the US National Health Interview Survey (NHIS) showed that, between 1998 and 2008, the proportion of adults meeting MSE guidelines increased from 17.7% to 21.9%.16 More recently, a technical report from the US Healthy People 2020 Midcourse Review showed that, between 2008 and 2014, the prevalence of those meeting MSE guidelines increased from 21.9% to 24.4%.17

To our knowledge, no studies since then have assessed the more recent trends in MSE among US adults. Furthermore, there has been a limited examination of trends in MSE across multiple population subgroups based on sociodemographics (eg, age, education level, income, employment status) and US census regions. Importantly, from a public health perspective, the existing studies on MSE trends do not typically conduct a multivariate-adjusted analysis.17,18 The development of relevant public health interventions and policies requires the regular assessment of physical activity-related behaviors to monitor trends over time and determine the most at-risk populations.19

The primary aim of this study, therefore, was to describe the prevalent trends in MSE among a large sample of US adults between 2011 and 2017. The secondary aim was to describe how trends vary between sociodemographic factors and by US census region.

Methods

We analyzed data from the 2011, 2013, 2015, and 2017 US Behavioral Risk Factor Surveillance System (BRFSS) surveys.1 Initiated in 1984, the BRFSS collects state-specific data on health-risk behaviors that are pertinent to public health among the US adult population.1 Because assessments of MSE have only been included since the 2011 BRFSS, we analyzed the data across 4 survey time points, from the 2011 BRFSS to the most recently publicly available data in 2017. A description of the background and methodology utilized in the BRFSS is available elsewhere.1 In brief, the BFRSS collects data from the health departments of all 50 US states, and each BRFSS survey was approved by the National Center for Health Statistics Research Ethics Review Board.1 The median response rate was 49.7%, 45.9%, 47.2%, and 45.9% for the 2011, 2013, 2015, and 2017 telephone interview surveys, respectively.1

For the present analysis, the participants were excluded if data were missing for MSE (n = 308,172; 15.5% of the total sample). Consistent with our previous study,14 to enhance generalizability, we did not use any other exclusion criteria. Furthermore, since the WHO physical activity guidelines recommend MSE on 2 or more days per week for both adults (aged 18–64 y) and older adults (aged ≥65 y),5 we included adults aged ≥18 years in our analysis.

Detailed information on the physical activity survey items used in the BRFSS is available elsewhere.20 To assess the MSE levels, the respondents were asked the following questions: “During the past month, how many times per week or per month did you do physical activities or exercises to strengthen your muscles? Do not count aerobic activities like walking, running, or bicycling. Count activities using your own body weight like yoga, sit-ups or push-ups and those using weight machines, free weights, or elastic bands.” These survey items have shown evidence of reliability (Cohen k = 0.85–0.92) and convergent validity (using the ≥2 times/wk threshold against all-cause mortality).10

The respondents were given the option of reporting their MSE frequency as either (1) “times per week” or (2) “times per month.” Consistent with previous studies,14,15 for those reporting times per month, this number was divided by 4 to provide estimates for weekly frequency. As with our previous study,14 to limit the possibility of unrealistic responses, the weekly frequency of MSE was truncated at 14 times/wk (<1.0% of the sample). These MSE data were reduced in 2 ways. First, the MSE levels were classified into 5 categories (0, 1, 2, 3, and ≥4 times/wk). Second, according to the WHO guidelines,5 the sample was dichotomized as (1) “insufficient MSE” (0–1 times/wk) or (2) “sufficient MSE” (≥2 times/wk).

The sociodemographic characteristics (sex, age, education level, employment status, and income categories) were assessed using standard questions. These sociodemographic characteristics were chosen due to their established association with MSE.1214 Each sociodemographic characteristic subcategory is consistent with both standardized BRFSS reporting1 and previous studies reporting on BRFSS MSE.14,15

To examine how MSE is patterned among the US population at the geographical level, we stratified the sample according to US Census Bureau regions.21 Using a standardized approach,21 4 regions were defined as follows: (1) Midwest (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin); (2) Northeast (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont); (3) South (Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia); and (4) West (Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming).

All analyses were conducted with the complex samples module of SPSS (version 22; SPSS Inc, IBM, Chicago, IL). In the analysis for the primary aim, weighting factors to correct for nonresponse, stratification, and clustering were implemented to enhance population representativeness.1

To examine the primary aim, for the individual 2011, 2013, 2015, and 2017 samples, weighted prevalence levels (in percentage) and their 95% confidence intervals (95% CI) were calculated for weekly MSE frequency first for 5 categories (0, 1, 2, 3, and ≥4 times/wk) and second for 2 categories: (1) “insufficient” (0–1 times/wk) and (2) “sufficient MSE” (≥2 times/wk). In addition, the prevalence levels of those reporting sufficient MSE for each individual sample are presented across sociodemographic characteristics and by US Census regions. Trends in the prevalence of reporting sufficient MSE (dependent) over time (independent) were assessed using linear regression analysis. A P value < .05 indicated statistical significance.

To examine the secondary aim, a series of multivariate analyses were performed separately for the 2011, 2013, 2015, and 2017 BRFFS samples. In these analyses, Poisson regression with a robust-error variance was applied to calculate prevalence ratios (PR). In cross-sectional epidemiological studies, providing PR derived from Poisson regression is considered a more statistically robust method than the generally used logistic regression.22 In each model, the associations of reporting/not reporting “sufficient MSE” (≥2 times/wk: “yes” vs “no”) with the sociodemographic characteristics and US Census region (explanatory variables) were assessed. To adjust for yearly variations, the year of study was included as a covariate.

Results

The weighted sample characteristics for each year’s sample are shown in Supplementary Table S1 (available online). Overall, between 2011 and 2017, the mean yearly sample size was 433,907 (range: 393,746–477,663). In brief, over half were aged ≥45 years, just under half earned ≥$50,000 per year, and over one-quarter had graduated from college.

Figure 1 shows the weighted percentages for MSE for the 2011, 2013, 2015, and 2017 samples. Over the study period, the prevalence slightly decreased among those reporting no MSE (2011 = 59.0% vs 2017 = 57.7%). In contrast, the prevalence increased marginally among those doing MSE ≥4 times/wk (2011 = 11.9% vs 2017 = 13.4%). However, across the remaining MSE frequencies, the prevalence levels remained stable across each survey (Figure 1).

Figure 1
Figure 1

—Proportions (weighteda; 95% CI) of Behavioral Risk Factor Surveillance System respondents (2011–2017) reporting muscle-strengthening exercise (times/wk) (n = 1,735,626). CI indicates confidence interval. aData weighted using stratum weight provided by the CDC.23 CDC indicates Centers for Disease Control and Prevention; CI, confidence interval.

Citation: Journal of Physical Activity and Health 17, 5; 10.1123/jpah.2019-0472

Overall, the proportions reporting sufficient MSE (≥2 times/wk) showed a small (1.2%) but significant increased linear trend over time (P < .001), with 29.1% (95% CI, 28.8–29.4), 29.4% (95% CI, 29.1–29.7), 30.2% (95% CI, 29.9–30.5), and 30.3% (95% CI, 30.0–30.6) for the 2011, 2013, 2015, and 2017 BFRSS, respectively (Table 1). Significant linear trends were observed across most sociodemographic characteristics and all US Census regions (P < .001, for most comparisons). However, across specific population subgroups, there were some patterns observed. First, in 2015, the prevalence of those meeting the MSE guideline peaked among students and those aged 18–24 years, but declined in 2017. Second, between 2011 and 2017, MSE guideline adherence declined among the lowest income group (<$15,000).

Table 1

Proportions (weighteda) Reporting Sufficient Muscle-Strengthening Exercise Among Behavioral Risk Factor Surveillance System Respondents (2011–2017): By Sociodemographic Characteristics and US Census Regionb

Sufficient muscle-strengthening exercise (≥2 times/wk)
2011201320152017
%a (95% CI)%a (95% CI)%a (95% CI)%a (95% CI)Trend Pc
Total29.1 (28.8–29.4)29.4 (29.1–29.7)30.2 (29.9–30.5)30.3 (30.0–30.6)<.001
Sex
 Men34.2 (33.8–34.7)34.6 (34.1–35.0)34.8 (34.4–35.3)34.4 (34.0–34.9)<.001
 Women24.3 (23.9–24.6)24.5 (24.1–24.8)25.8 (25.5–26.2)26.4 (25.9–26.8)<.001
Age, y
 18–2443.8 (42.7–45.0)46.2 (45.1–47.2)46.3 (45.2–47.4)45.3 (44.2–46.5)<.001
 25–3434.3 (33.5–35.1)35.0 (34.3–35.8)36.8 (36.0–35.1)36.9 (36.0–37.7)<.001
 35–4429.1 (28.4–29.8)29.3 (28.6–30.0)29.1 (28.4–29.8)30.8 (30.0–31.7)<.001
 45–5425.9 (25.4–26.5)25.9 (25.4–26.5)26.6 (25.9–27.2)26.6 (25.9–27.3)<.001
 55–6423.7 (23.2–24.2)23.7 (23.2–24.3)23.8 (23.3–24.4)24.1 (23.5–24.7)<.001
 65–7423.0 (22.4–23.5)22.9 (22.3–23.5)24.3 (23.7–24.9)24.8 (24.1–25.5)<.001
 ≥7519.8 (19.2–20.3)19.8 (19.2–20.4)21.0 (20.3–21.8)21.4 (20.6–22.2)<.001
Education levelb
 Did not graduate high school19.7 (18.8–20.5)18.9 (18.0–19.7)19.9 (19.0–20.9)18.3 (17.4–19.3).600
 Graduated high school25.0 (24.5–25.5)25.5 (25.0–30.0)25.8 (25.3–26.3)26.0 (25.4–26.6).010
 Attended college31.6 (31.0–32.1)31.7 (31.2–32.2)32.1 (31.5–32.6)32.2 (31.6–32.8)<.001
 Graduated college36.4 (35.9–36.8)36.7 (36.3–37.2)37.7 (37.3–38.2)37.9 (37.4–38.4)<.001
Employment status
 Student45.2 (43.5–46.9)47.4 (45.7–49.0)48.3 (46.6–49.9)45.9 (44.2–47.7)<.001
 Employed31.2 (30.8–31.6)31.7 (31.3–32.0)32.8 (32.4–33.2)33.2 (32.7–36.6)<.001
 Unemployed29.5 (28.5–30.6)29.3 (28.1–30.4)28.2 (26.9–29.5)26.7 (25.4–28.0).170
 Homemaker22.1 (21.3–23.0)22.0 (21.0–23.0)22.5 (21.5–23.5)22.1 (20.9–23.4).014
 Retired23.5 (23.0–23.9)23.3 (22.8–23.8)24.4 (23.9–24.9)24.6 (24.1–25.2)<.001
 Unable to work17.7 (16.8–18.6)17.6 (16.8–18.5)18.0 (17.1–18.9)18.4 (17.5–19.4).013
Income categoriesb
 <$15,00023.1 (22.2–24.0)23.3 (21.5–23.1)21.7 (20.8–22.6)21.7 (20.7–22.7)<.001
 $15,000–$24,99924.0 (23.3–24.7)24.7 (24.0–25.4)24.6 (23.8–25.4)25.0 (24.2–25.9)<.001
 $25,000–$34,99926.6 (25.7–27.4)26.1 (25.2–27.0)27.4 (26.4–28.4)25.9 (24.9–27.0)<.001
 $35,000–$44,99927.8 (27.0–28.5)29.4 (28.6–30.2)29.9 (29.0–30.7)29.5 (28.6–30.4)<.001
 ≥$50,00034.8 (34.3–35.2)34..9 (34.4–35.4)35.7 (35.2–36.1)35.6 (35.1–36.1)<.001
US Census regionb
 Midwest28.8 (28.2–29.4)28.6 (28.0–29.1)29.7 (29.1–30.3)29.6 (29.1–30.2)<.001
 South29.7 (29.1–30.3)30.1 (29.6–30.7)30.3 (29.7–30.9)30.5 (29.9–31.2)<.001
 Northeast27.9 (27.4–28.4)28.1 (27.6–28.6)27.9 (27.4–28.4)29.2 (28.7–29.8)<.001
 West32.0 (31.4–32.6)32.8 (32.1–33.6)32.0 (32.4–33.1)33.5 (32.7–34.3)<.001

Abbreviation: CI, confidence interval. aData weighted using stratum weight provided by the Centers for Disease Control and Prevention (CDC).24 bUS Census Bureau regions are defined as the Midwest (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin); Northeast (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont); South (Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia); and West (Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming). cP value for linear regression analysis of the proportion over time (2011–2017).

Table 2 shows the results of the multivariate-adjusted analyses of individual BRFSS surveys. Generally, across sociodemographic characteristics and US Census regions, the adjusted PRs (APRs) were similar for all time points. The lowest APRs were among those who were “unable to work” (APR range: 0.40–0.44). Compared with men, women were less likely to report sufficient MSE. Across each individual survey, APRs decreased with age, but increased with income and education level. When compared with students, all other employment categories were less likely to report sufficient MSE. When compared with those living in the West US Census region, according to the 2017 analysis, those living in the South, Midwest, and Northeast regions were less likely to report sufficient MSE (APR range: 0.80–0.93).

Table 2

Adjusteda Prevalence Ratiosb and 95% CI for Reporting Sufficient Muscle-Strengthening Exercise for the 2011, 2013, 2015, and 2017 Behavioral Risk Factor Surveillance System Samples

Sufficient muscle-strengthening exercise (≥2 times/wk)
2011 (n = 474,463)2013 (n = 448,075)2015 (n = 393,746)2017 (n = 405,212)
APRa (95% CI)APRa (95% CI)APRa (95% CI)APRa (95% CI)
Sex (ref: Men)
 Women0.80 (0.79–0.81)0.78 (0.77–0.79)0.82 (0.81–0.83)0.81 (0.80–0.82)
Age, y (ref:18–24 y)
 25–340.76 (0.73–0.78)0.77 (0.75–0.79)0.77 (0.75–0.80)0.79 (0.77–0.82)
 35–440.68 (0.66–0.70)0.65 (0.63–0.66)0.65 (0.63–0.67)0.66 (0.65–0.68)
 45–540.61 (0.59–0.63)0.58 (0.56–0.59)0.58 (0.56–0.60)0.58 (0.57–0.60)
 55–640.57 (0.55–0.58)0.53 (0.51–0.54)0.53 (0.52–0.55)0.53 (0.52–0.55)
 65–740.55 (0.53–0.56)0.52 (0.50–0.53)0.54 (0.52–0.55)0.54 (0.53–0.56)
 >750.47 (0.46–0.48)0.45 (0.44–0.47)0.47 (0.46–0.49)0.49 (0.48–0.50)
Education level (ref: graduated college)
 Attended college0.77 (0.76–0.78)0.78 (0.77–0.79)0.78 (0.77–0.80)0.77 (0.76–0.78)
 Graduated high school0.58 (0.57–0.59)0.60 (0.59–0.61)0.60 (0.59–0.62)0.61 (0.60–0.62)
 Did not graduate high school0.47 (0.45–0.48)0.47 (0.45–0.48)0.48 (0.46–0.49)0.45 (0.44–0.47)
Employment status (ref: student)
 Employed0.70 (0.68–0.73)0.67 (0.65–0.69)0.66 (0.64–0.68)0.67 (0.66–0.70)
 Unemployed0.62 (0.59–0.65)0.59 (0.57–0.62)0.57 (0.55–0.60)0.57 (0.54–0.59)
 Homemaker0.58 (0.55–0.60)0.53 (0.51–0.56)0.54 (0.52–0.56)0.52 (0.49–0.54)
 Retired0.57 (0.55–0.60)0.54 (0.52–0.56)0.55 (0.53–0.60)0.55 (0.53–0.57)
 Unable to work0.44 (0.42–0.46)0.40 (0.38–0.42)0.40 (0.38–0.42)0.40 (0.38–0.42)
Income categories (ref: ≥$50,000)
 $35,000–$44,9990.77 (0.76–0.79)0.80 (0.78–0.81)0.79 (0.78–0.81)0.80 (0.78–0.81)
 $25,000–$34,9990.71 (0.69–0.72)0.72 (0.70–0.73)0.73 (0.72–0.75)0.70 (0.69–0.72)
 $15,000–$24,9990.63 (0.62–0.65)0.66 (0.64–0.67)0.66 (0.65–0.68)0.66 (0.65–0.68)
 <$15,0000.59 (0.57–0.60)0.62 (0.60–0.65)0.62 (0.60–0.64)0.61 (0.60–0.63)
US Census regionc (ref: West)
 Midwest0.84 (0.82–0.85)0.84 (0.82–0.85)0.87 (0.86–0.89)0.84 (0.83–0.86)
 South0.92 (0.91–0.94)0.90 (0.89–0.92)0.92 (0.91–0.94)0.93 (0.91–0.95)
 Northeast0.80 (0.79–0.82)0.81 (0.80–0.82)0.85 (0.83–0.86)0.84 (0.83–0.86)

Abbreviations: APR, adjusted prevalence ratios; CI, confidence intervals. aAdjusted for year of study, and all explanatory variables in the table. bPrevalence ratio calculated using Poisson regression with a robust-error variance. cUS Census Bureau regions are defined as the Midwest (Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, South Dakota, and Wisconsin); Northeast (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont); South (Alabama, Arkansas, Delaware, District of Columbia, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia); and West (Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming).

Discussion

Among a sample of almost 1.8 million US adults between 2011 and 2017, ~70% did not meet the MSE guideline. The persistently low recent population prevalence levels, in combination with established independent multiple health benefits associated with this behavior,2,69 emphasize the need for public health action to support the uptake and adherence of MSE among US adults.

The finding that the MSE levels were low but appeared to increase slightly from 29.1% in 2011 to 30.3% in 2017 is consistent with previous studies.16,17 For example, data from the US NHIS showed that the proportion of US adults meeting the MSE guidelines increased from 17.7% in 1998 to 21.9% in 2008.16 However, we urge caution when interpreting these trends as increasing from 21.9% in 2008 (NHIS) to 30.3% in 2017 (BRFSS). These variances in MSE prevalence estimates between the BRFSS and NHIS samples are likely due to a combination of factors, including differences in (1) data collection methods (eg, telephone vs face-to-face interviews), (2) survey items (eg, the use of different terminology to define MSE), and (3) sample sizes (eg, samples of the individual waves of the BRFSS being ∼5-fold greater than those from the NHIS).

The marginal increases in meeting the MSE guideline (≥2 times/wk) observed in the present study are likely due to increasing numbers engaging in high levels of this exercise mode. As shown in Figure 1, the prevalence of those reporting the highest MSE frequency (≥4 times/wk) increased by 1.4% from 2011 to 2017. Due to the study design, we are unable to determine the cause(s) of this observation. However, this may be due to the increase in popularity in MSE-related fitness trends, such as training with free weights, body weight training, and functional fitness training.25 Nonetheless, we emphasize that, across studies, 70% to 80% of US adults were not meeting the MSE guidelines over the last decades. Notably, compared with the proportion of the pooled BRFSS sample reporting no self-reported moderate- to vigorous-intensity aerobic activity (∼30%),1 almost double reported no MSE (∼60%).

The key sociodemographic correlates of MSE guideline adherence identified in the present study are generally consistent with previous research. Studies from the US,1214 Australia,11,26 and the United Kingdom27 have also shown that the population subgroups least likely to meet the MSE guidelines include women, older adults, and those with low income and education levels. These consistent cross-country findings underscore the importance of establishing the barriers and enablers to MSE among these population subgroups, both within the United States and globally. The patterns of MSE by US census region showed that, compared with those in the West region, populations within the Midwest, South, and Northeast regions are less likely to report sufficient MSE.

The low prevalence of MSE presented in this study suggests that this behavior warrants immediate public health action. However, compared with aerobic activity, MSE has been of limited focus in public health approaches to chronic disease prevention.27 This may be due to, first, MSE having been a component of the physical activity guidelines only within the last decade, and second, getting large proportions of the population to become engaged in this behavior is likely to be more challenging than moderate-to-vigorous intensity aerobic activity.28,29 Synchronized and multilevel health promotion strategies are required to increase population-level MSE engagement. Potential future concurrent approaches may include providing physical environmental support (eg, equipment in open spaces and subsidized community health center memberships), providing equipment (eg, resistance bands) to promote this activity in the multiple settings (eg, home/workplace/community), subsidizing access to exercise professionals who have the capacity to safely instruct those with no previous experience (eg, strength and conditioning professionals/fitness trainers), and using mass media campaigns to promote this physical activity mode.

Insights may be gained from developing a better understanding of the key factors influencing MSE among populations who have high-prevalence levels. An example from the present study is that, across the BFRSS surveys, student populations regularly had the highest MSE prevalence levels. Although our study design limits the ability to accurately establish the temporal relationship, these data suggest that once student populations transition into employment their MSE levels subsequently decline. Understanding the key individual (eg, time allocation, motivation, cost), social (peer support/social modeling), and physical environmental factors (access to facilities/equipment) that cause declines in MSE during major events across the life span will provide unique insights into the key determinants of this behavior. Although much research has focused on the tracking of aerobic physical activity though the life span,30 comparative research on MSE is nonexistent. A lifespan approach to MSE is particularly important, considering that age-related declines in muscle mass or muscle function are predicted to be among the key 21st-century public health challenges.23,31

A strength of this study includes the recruitment of large representative samples of US adults. In addition, the use of standardized data collection processes ensure that our results can be compared with findings from future waves of the BRFSS. The analysis of several public surveillance data sets is also a strength, and we are not aware of any epidemiological study on MSE with a comparable sample size.

Limitations are also recognized. Foremost is the use of self-report assessments of MSE. This assessment method may have resulted in recall bias issues, such as social desirability and overreporting and/or underreporting. However, at present, unlike aerobic physical activity, there is no accepted device-based method (eg, accelerometery) to assess MSE. Consequently, MSE is routinely assessed by self-report in public health surveillance.14 A further limitation was the use of a single self-report item assessing weekly or monthly frequency only, and not the “intensity” or “type” of MSE. Last, given that 15.5% of the BRFSS sample did not report their MSE levels, our prevalence estimates should be viewed with caution. It is probable that nonresponders to the MSE item are the most physically inactive. Which, in turn, despite the data being weighted for nonresponse, is likely to affect the prevalence estimates. Consequently, the MSE prevalence estimates presented here are likely to be conservative.

Conclusion

Among nearly 1.8 million US adults, between 2011 and 2017, ∼70% did not meet the MSE guideline. Consistently low MSE levels accentuate the need for public health action to support the uptake/adherence of this important health behavior at the population level. US populations most at risk of not engaging in sufficient MSE include older adults, women, those with low income/education levels, and those living in the Midwest and Northeast regions. There was a time trend for the reporting of sufficient MSE to steadily increase between 2011 and 2017.

References

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Bennie, Kolbe-Alexander, Biddle, and De Cocker are with the Physically Active Lifestyles Research Group (USQ PALs), Centre for Health, Informatics, and Economic Research, Institute for Resilient Regions, University of Southern Queensland, QLD, Australia. Kolbe-Alexander is also with the School of Health and Wellbeing, Faculty of Health, Engineering and Sciences, Southern Queensland, QLD, Australia. Seghers is with the Department of Movement Sciences, Physical Activity, Sports and Health Research Group, KU Leuven, Leuven, Belgium.

Bennie (Jason.bennie@usq.edu.au) is corresponding author.

Supplementary Materials

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    —Proportions (weighteda; 95% CI) of Behavioral Risk Factor Surveillance System respondents (2011–2017) reporting muscle-strengthening exercise (times/wk) (n = 1,735,626). CI indicates confidence interval. aData weighted using stratum weight provided by the CDC.23 CDC indicates Centers for Disease Control and Prevention; CI, confidence interval.

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