Trend and Prevalence Estimates Based on the 2008 Physical Activity Guidelines for Americans

Trend and Prevalence Estimates Based on the 2008 Physical Activity Guidelines for Americans

Trend and Prevalence Estimates Based on the 2008 Physical Activity Guidelines for Americans Susan A. Carlson, MPH, Janet E. Fulton, PhD, Charlotte A. ...

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Trend and Prevalence Estimates Based on the 2008 Physical Activity Guidelines for Americans Susan A. Carlson, MPH, Janet E. Fulton, PhD, Charlotte A. Schoenborn, MPH, Fleetwood Loustalot, PhD Background: According to the 2008 Physical Activity Guidelines for Americans, adults need to engage in at least 150 minutes/week of moderate-intensity activity or its equivalent (defıned as aerobically active) to obtain substantial health benefıts and more than 300 minutes/week (defıned as highly active) to obtain more extensive health benefıts. In addition to aerobic activity, the 2008 Guidelines recommend that adults participate in muscle-strengthening activities on 2 or more days/week.

Purpose: This study examined the prevalence and trends of meeting the activity criteria defıned by the 2008 Guidelines among U.S. adults. Methods: Prevalence and trends of participation in leisure-time physical activity were estimated from the 1998 –2008 National Health Interview Survey (analyzed in 2010).

Results: In 2008, 43.5% of U.S. adults were aerobically active, 28.4% were highly active, 21.9% met the muscle-strengthening guideline, and 18.2% both met the muscle-strengthening guideline and were aerobically active. The likelihood of meeting each of these four activity criteria was similar and were associated with being male, being younger, being non-Hispanic white, having higher levels of education, and having a lower BMI. Trends over time were also similar for each part of the 2008 Guidelines, with the prevalence of participation exhibiting a small but signifıcant increase when comparing 1998 to 2008 (difference ranging from 2.4 to 4.2 percentage points). Conclusions: Little progress has been made during the past 10 years in increasing physical activity levels in the U.S. There is much room for improvement in achieving recommended levels of physical activity among Americans, particularly among relatively inactive subgroups. (Am J Prev Med 2010;39(4):305–313) Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine

Introduction

T

he USDHHS recently released the 2008 Physical Activity Guidelines for Americans (2008 Guidelines),1 an evidence-based update on the benefıts of physical activity.2 The 2008 Guidelines recommend that for substantial health benefıts, including lower risk for premature death, coronary heart disease, stroke, hypertension, type 2 diabetes, and depression, adults should participate weekly in at least 150 minutes of moderateintensity aerobic activity, 75 minutes of vigorous-intensity

From the National Center for Chronic Disease Prevention and Health Promotion (Carlson, Fulton, Loustalot), CDC, Atlanta, Georgia; and the National Center for Health Statistics (Schoenborn), CDC, Hyattsville, Maryland Address correspondence to: Susan A. Carlson, MPH, Division of Nutrition, Physical Activity, and Obesity, CDC, 4770 Buford Highway NE, MS K-46, Atlanta GA 30341. E-mail: [email protected]. 0749-3797/$17.00 doi: 10.1016/j.amepre.2010.06.006

aerobic activity, or an equivalent combination, and that for increased and additional health benefıts, including lower risk for colon and breast cancer and prevention of unhealthy weight gain, they should participate weekly in more than 300 minutes of moderate-intensity activity, 150 minutes of vigorous-intensity activity, or an equivalent combination. The 2008 Guidelines also recommend that adults participate in muscle-strengthening activities involving all seven major muscle groups on 2 or more days/week to increase bone strength and muscular fıtness. To fully meet the 2008 Guidelines, adults must engage in at least the equivalent of 150 minutes/week of moderate-intensity aerobic activity and in musclestrengthening activities on 2 or more days/week. Currently, physical activity levels in the U.S. are monitored for the assessment of progress toward meeting national health objectives in Healthy People 2010.3 Criteria used to defıne levels of aerobic activity in Healthy

Published by Elsevier Inc. on behalf of American Journal of Preventive Medicine

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People 2010 are based on the 1995 CDC/ACSM recommendations and the 1996 Surgeon General’s Report on Physical Activity and Health that followed4,5 and are different from 2008 Guidelines criteria. In Healthy People 2010 (objective 22-2), being active is defıned as participating in at least 30 minutes/day of moderate-intensity aerobic activity 5 or more days/week or in at least 20 minutes of vigorous aerobic activity 3 or more days/week, whereas in the 2008 Guidelines, being active is defıned on the basis of the total amount of activity in 1 week (at least 150 minutes of moderate-intensity aerobic activity, 75 minutes of vigorous-intensity aerobic activity, or an equivalent combination per week). The 2008 Guidelines criteria do not include a minimum frequency requirement or a duration requirement other than that physical activity must be for at least 10 minutes at a time, and they allow moderate- and vigorous-intensity activity to be combined. It is important to examine the effects that use of different criteria may have on national prevalence estimates of aerobic activity and trends in these estimates. The National Health Interview Survey (NHIS) is the data source used to monitor national progress toward meeting Healthy People 2010 physical activity objectives. In the present study, NHIS data were used to estimate the prevalence of U.S. adults (overall and by selected demographic characteristics) who, in 2008, (1) were aerobically active according to Healthy People 2010 criteria and according to 2008 Guidelines criteria; (2) were highly aerobically active according to 2008 Guidelines criteria; (3) engaged in adequate muscle-strengthening activity as defıned by Healthy People 2010 and 2008 Guidelines; and (4) both engaged in adequate muscle-strengthening activity and were aerobically active as defıned by the 2008 Guidelines. Trends in prevalence estimates from 1998 through 2008 were also assessed.

Methods Survey Description The NHIS is a multistage probability sample survey of U.S. households that is conducted annually and designed to be representative of the civilian, non-institutionalized U.S. population. The NHIS collects basic health and demographic information from all family members and additional information, such as information about leisure-time physical activity, from one randomly selected adult (aged ⱖ18 years). During 1998 –2008, annual NHIS sample sizes for completed interviews of sampled adults ranged from 21,781 (2008) to 32,440 (1998), and fınal unconditional sample adult response rates ranged from 62.6% (2008) to 74.3% (2002). Further details about the survey can be accessed from NHIS websites.6,7

Measures Aerobic activity. Randomly selected adults were asked two series of questions that assessed how often during leisure time they participated, for ⱖ10 minutes at a time, in (1) vigorous-intensity

activities that cause heavy sweating or large increases in breathing or heart rate and (2) light- or moderate-intensity activities that cause only light sweating or slight to moderate increases in breathing or heart rate. Participants provided both frequency of their participation (per day, week, month, or year) and duration of each session (minutes or hours). Using Healthy People 2010 criteria,3 respondents were classifıed as aerobically active if they reported ⱖ30 minutes of light- or moderate-intensity leisure-time physical activity on fıve or more times/week or ⱖ20 minutes of vigorous-intensity leisure-time physical activity on three or more times/week. Using 2008 Guidelines criteria,1 respondents were classifıed as aerobically active if they reported ⱖ150 minutes/week of light- to moderate-intensity activity, 75 minutes/week of vigorous-intensity activity, or an equivalent combination of the two. Based on 2008 Guidelines,1 minutes of vigorous-intensity activity were given twice the credit of minutes of moderate-intensity activity when combining moderate and vigorous intensity to calculate the equivalent combination. Aerobic physical activity was also examined in four levels based on the 2008 Guidelines: highly active (⬎300 minutes/week of light- to moderate-intensity activity, ⬎150 minutes/week of vigorousintensity activity, or an equivalent combination); suffıciently active (150 –300 minutes/week of light- to moderate-intensity activity, 75–150 minutes/week of vigorous-intensity activity, or an equivalent combination); insuffıciently active (some activity but not enough to meet the active defınition); and inactive (no light-tomoderate- or vigorous-intensity activity of ⱖ10 minutes).1

Muscle-strengthening activities. Respondents were also asked about their participation in leisure-time physical activities specifıcally designed to strengthen their muscles, such as lifting weights or doing calisthenics. Respondents were classifıed as meeting the muscle-strengthening guideline if they reported engaging in muscle-strengthening activity two or more times/week. Demographic characteristics. Respondents were categorized into fıve age groups (i.e., 18 –24, 25–34, 35– 44, 45– 64, and ⱖ65 years) using reported age. Educational attainment was assessed in terms of the highest grade or year of school completed and adults were categorized into four education levels (i.e., less than high school, high school, some college, and college).8 To assess race/ethnicity, respondents were fırst asked to identify whether they consider themselves Hispanic or Latino. All respondents were then asked to select from a list what race or races they consider themselves, and for people who choose more than one race, a question was asked about the one race that best describes them. Adults were classifıed into four race/ethnic groups (i.e., white, non-Hispanic; black, non-Hispanic; Hispanic; and other, non-Hispanic).8 Geographic region was defıned in terms of the four major regions identifıed by the U.S. Census Bureau: Northeast, Midwest, South, and West.9 BMI, calculated from self-reported height and weight, was categorized as underweight/normal weight (⬍25 kg/m2); overweight (25–⬍30 kg/ m2); and obese (ⱖ30 kg/m2).10

Statistical Analysis The age-adjusted prevalence of U.S. adults who, in 2008, (1) were aerobically active according to both Healthy People 2010 and 2008 Guidelines criteria; (2) were highly aerobically active according to 2008 Guidelines criteria; (3) engaged in muscle-strengthening activities two or more times/week; and (4) met criteria for both www.ajpm-online.net

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a

Table 1. Estimated prevalence of being aerobically active according to Healthy People 2010 criteria and estimated prevalence according to 2008 Guidelines criteria among U.S. adults, by select characteristics, NHIS 2008 Active

Difference

Healthy People 2010 criteriab (% [95% CI])

2008 Guidelines criteriac (% [95% CI])

Absolute (Percentage point)

Relatived (%)

32.6 (31.6, 33.5)

43.5 (42.4, 44.6)

10.9

33.6

Male

34.8 (33.5, 36.1)

47.4 (45.9, 48.9)

12.6

36.2

Female

30.5 (29.5, 31.6)

39.9 (38.7, 41.1)

9.4

30.7

18–24

38.5 (35.6, 41.4)

52.4 (49.4, 55.5)

14.0

36.3

25–34

37.7 (35.8, 39.6)

50.3 (48.1, 52.5)

12.6

33.5

35–44

33.6 (31.7, 35.5)

45.4 (43.2, 47.5)

11.8

35.2

45–64

31.8 (30.5, 33.1)

41.6 (40.1, 43.1)

9.8

30.7

ⱖ65

22.6 (21.1, 24.2)

30.4 (28.7, 32.1)

7.8

34.3

White, non-Hispanic

35.9 (34.8, 37.1)

47.6 (46.3, 49.0)

11.7

32.5

Black, non-Hispanic

24.7 (22.8, 26.7)

33.9 (31.7, 36.2)

9.2

37.5

Hispanic

25.1 (23.1, 27.3)

33.4 (31.0, 35.8)

8.3

32.8

30.5 (27.4, 33.7)

41.9 (38.7, 45.2)

11.4

37.6

18.7 (17.1, 20.5)

25.6 (23.6, 27.7)

6.9

36.6

High school

26.4 (24.9, 28.0)

35.6 (33.8, 37.3)

9.1

34.6

Some college

33.3 (31.8, 34.7)

45.6 (44.0, 47.2)

12.4

37.1

College

44.8 (43.0, 46.7)

59.0 (57.3, 60.7)

14.2

31.6

Northeast

32.0 (29.8, 34.4)

42.1 (40.1, 44.2)

10.1

31.5

Midwest

33.8 (31.8, 35.9)

45.3 (42.8, 47.8)

11.5

34.0

South

29.7 (28.3, 31.2)

40.3 (38.5, 42.2)

10.6

35.6

West

36.0 (34.2, 37.9)

47.4 (45.3, 49.4)

11.4

31.6

Underweight/normal weight (⬍25)

37.2 (35.9, 38.5)

47.8 (46.3, 49.2)

10.5

28.3

Overweight (25–⬍30)

34.2 (32.6, 35.7)

46.1 (44.6, 47.7)

12.0

35.0

Obese (ⱖ30)

25.6 (24.0, 27.2)

36.5 (34.6, 38.4)

10.9

42.6

Characteristic Total Gender

Age (years)

Race/ethnicity

e

Other, non-Hispanic Education level

Less than high school f

Census region

BMI category

Note: Percentages may not add up to 100.0 because of rounding. a Estimates are age-adjusted to the 2000 U.S. projected population using five age groups (18 –24, 25–34, 35– 44, 45– 64, and ⱖ65 years) except for estimates by age group. b At least 30 minutes of moderate-intensity physical activity five or more times per week or ⱖ20 minutes of vigorous-intensity physical activity three or more times per week. The activity status of 618 respondents could not be determined because of missing data. c At least 150 minutes of moderate-intensity aerobic activity, 75 minutes of vigorous-intensity aerobic activity, or an equivalent combination per week. The activity status of 583 respondents could not be determined because of missing data. d Relative to Healthy People 2010 estimates (2008 Guidelines criteria estimate minus the Healthy People 2010 criteria estimate divided by the Healthy People 2010 criteria estimate ⫻ 100). e Other race/ethnicity includes American Indian, Alaska Native, Asian, Native Hawaiian, and Other Pacific Islander. f Includes individuals with a General Educational Development test or equivalent NHIS, National Health Interview Survey

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muscle-strengthening and being aerobically active as defıned by 2008 Guidelines criteria were estimated by gender, age, race/ethnicity, education, census region, and BMI category. Survey participants with missing data on education (n⫽149) and BMI (n⫽919) were excluded from analyses by these factors. Overall prevalence of activity among U.S. adults during each survey year (1998 –2008) was estimated. SUDAAN, version 9.0, was used for data analysis to account for the complex sample design. Estimates (except where stratifıed by age) were age-adjusted to the 2000 U.S. projected population using the fıve age groups.11 Pairwise t-tests (pairwise statement in SUDAAN’s proc descript) were used to determine whether differences in estimates by gender, race/ethnicity, education, census region, BMI category, and year were signifıcant and orthogonal polynomial contrasts (polynomial statement in SUDAAN’s proc descript) were used to test for linear and quadratic trends. Differences and contrasts were considered signifıcant at p⬍0.05, and only signifıcant differences were discussed.

Results In 2008, using Healthy People 2010 criteria 32.6% of U.S. adults were aerobically active during their leisure time compared with 43.5% using 2008 Guidelines criteria (Table 1). Reasons for the 10.9 percentage point shift are (1) upwards shift of 4.2 percentage points due to removal of the Healthy People 2010 frequency and duration requirements only; (2) upwards shift of 2.7 percentage points due to the combination of moderate- and vigorous-intensity activity only; (3) upwards shift of 4.2 percentage points due to both Reason 1 and Reason 2; and (4) downwards shift of 0.3 percentage points due to respondent reporting 60 –74 minutes/week of vigorous-intensity activity, which qualifıed as active using Healthy People 2010 criteria but did not qualify using criteria set by the 2008 Guidelines. With either set of criteria, prevalence of aerobic activity in 2008 was higher among men than women; higher among non-Hispanic whites than among non-Hispanic blacks, Hispanics, and those of other race/ethnicity; higher among those of other race/ethnicity than among non-Hispanic blacks and Hispanics; higher among adults in the West than among those in the South and Northeast; and higher among those in the Midwest than among those in the South. Trends by age group and education were both signifıcantly linear and signifıcantly quadratic (demonstrating nonlinear variation in addition to an overall increase with decreasing age and increasing education). Using either set of criteria, the percentage of adults who were aerobically active was higher among underweight/normal-weight adults than obese adults and also higher among overweight adults than among obese adults. However, only when using Healthy People 2010 criteria was there a signifıcant difference in activity levels of underweight/normal-weight adults versus overweight adults.

60

Age-adjusted prevalence

308

40

20

0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Year Healthy People 2010a

2008 Guidelinesa

Figure 1. Estimated prevalence of being aerobically active according to Healthy People 2010 criteria and estimated prevalence according to 2008 Guidelines criteria among U.S. adults, National Health Interview Survey 1998 –2008 Note: Error bars represent the upper and lower bounds of the 95% CI. a Significant quadratic effect (p⬍0.05)

Prevalence estimates of recommended aerobic activity ranged from 29.7% (1998) to 32.9% (2003) on the basis of Healthy People 2010 criteria and from 40.1% (1998) to 43.4% (2003) on the basis of 2008 Guidelines criteria (Figure 1). Differences between annual prevalence estimates based on 2008 Guidelines criteria and those based on Healthy People 2010 criteria ranged from 10.4 percentage points (1998) to 11.4 percentage points (2004). With both sets of criteria, a signifıcant quadratic trend (i.e., a signifıcant nonlinear trend) was observed in prevalence rates between 1998 and 2008, and the difference between 1998 and 2008 was signifıcant using either criterion: 2.9 percentage points (95% CI⫽1.7, 4.0) using Healthy People 2010 criteria and 3.4 percentage points (95% CI⫽2.1, 4.8) using 2008 Guidelines criteria. Using 2008 Guidelines criteria, 28.4% of U.S. adults were highly aerobically active in 2008 during their leisure time (Table 2). Demographic variations in these estimates were identical to those for being at least minimally aerobically active except that the estimate was also signifıcantly higher for adults in the Midwest than for those in the Northeast and the trend by education was signifıcantly linear. From 1998 to 2008, annual age-adjusted estimates of the percentage of U.S. adults who were highly active ranged from 26.0% (1998) to 28.6% (2003) (Figure 2). There was a signifıcant quadratic trend from 1998 through 2008 and the difference between 1998 and 2008 was 2.4 percentage points (95% CI⫽1.3, 3.6). Approximately one in fıve U.S. adults participated in muscle-strengthening leisure-time physical activities two or more times/week in 2008 (Table 3). The perwww.ajpm-online.net

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a

Table 2. Estimated prevalence (% [95% CI]) of four levels of aerobic activity among U.S. adults as defined in the 2008 Guidelines, by selected characteristics, NHIS 2008 2008 Guidelinesb Active Characteristic

Highly active

Sufficiently active

Insufficiently active

Inactive

28.4 (27.5, 29.4)

14.9 (14.3, 15.6)

20.1 (19.4, 20.9)

36.6 (35.3, 37.8)

Male

33.0 (31.8, 34.3)

14.3 (13.4, 15.3)

18.4 (17.4, 19.4)

34.3 (32.7, 36.0)

Female

24.2 (23.2, 25.2)

15.5 (14.8, 16.3)

21.8 (20.8, 22.8)

38.5 (37.2, 39.8)

18–24

36.3 (33.4, 39.2)

16.1 (14.1, 18.3)

18.8 (16.8, 21.0)

28.8 (26.1, 31.7)

25–34

34.2 (32.3, 36.2)

15.9 (14.5, 17.3)

19.2 (17.6, 20.9)

30.7 (28.6, 32.9)

35–44

28.8 (27.0, 30.6)

16.4 (15.0, 17.9)

21.4 (19.9, 23.0)

33.4 (31.2, 35.6)

45–64

26.8 (25.5, 28.2)

14.6 (13.6, 15.7)

21.0 (19.8, 22.1)

37.6 (35.9, 39.3)

ⱖ65

18.6 (17.2, 20.1)

11.6 (10.4, 12.9)

18.9 (17.5, 20.4)

50.9 (49.0, 52.9)

White, non-Hispanic

31.5 (30.3, 32.7)

16.0 (15.2, 16.8)

20.2 (19.4, 21.2)

32.3 (30.9, 33.7)

Black, non-Hispanic

21.3 (19.4, 23.4)

12.5 (11.2, 13.9)

18.7 (17.0, 20.5)

47.5 (45.1, 50.0)

Hispanic

21.0 (19.3, 22.9)

12.3 (10.9, 13.8)

19.1 (17.4, 20.8)

47.7 (45.1, 50.2)

27.0 (24.1, 30.1)

14.9 (12.8, 17.3)

23.1 (20.5, 26.1)

35.0 (31.6, 38.5)

16.5 (14.9, 18.3)

9.1 (7.9, 10.5)

17.0 (15.4, 18.8)

57.4 (55.1, 59.7)

High school

23.5 (22.1, 25.1)

11.9 (10.9, 13.0)

18.6 (17.2, 20.0)

46.0 (44.0, 48.0)

Some college

29.4 (27.9, 30.9)

16.0 (14.9, 17.1)

22.8 (21.6, 24.0)

31.9 (30.3, 33.5)

College

38.2 (36.4, 40.0)

20.7 (19.2, 22.3)

21.0 (19.4, 22.7)

20.1 (18.6, 21.7)

Northeast

25.5 (23.5, 27.7)

16.3 (14.7, 18.0)

20.8 (19.0, 22.6)

37.4 (34.9, 40.1)

Midwest

29.7 (27.6, 31.9)

15.5 (14.0, 17.1)

22.1 (20.5, 23.8)

32.7 (30.4, 35.2)

South

26.8 (25.3, 28.4)

13.4 (12.5, 14.4)

18.5 (17.3, 19.7)

41.3 (39.0, 43.6)

West

31.7 (29.9, 33.6)

15.5 (14.4, 16.8)

20.2 (18.8, 21.6)

32.6 (30.2, 35.1)

Underweight/normal weight (⬍25)

32.3 (31.0, 33.6)

15.3 (14.3, 16.4)

19.2 (18.2, 20.3)

33.2 (31.8, 34.7)

Overweight (25–⬍30)

30.3 (28.8, 31.8)

15.7 (14.6, 16.9)

19.8 (18.7, 20.9)

34.3 (32.6, 36.0)

Obese (ⱖ30)

22.9 (21.2, 24.7)

13.5 (12.4, 14.7)

21.9 (20.4, 23.4)

41.7 (39.8, 43.7)

Total Gender

Age (years)

Race/ethnicity

c

Other, non-Hispanic Education level

Less than high school d

Census region

BMI category

Note: Percentages may not add up to 100.0 because of rounding. a Estimates are age-adjusted to the 2000 U.S. projected population using five age groups (18 –24, 25–34, 35– 44, 45– 64, and ⱖ65 years) except for estimates by age group. b Highly active was defined as ⬎300 minutes of moderate-intensity aerobic activity, ⬎150 minutes of vigorous-intensity aerobic activity, or an equivalent combination of moderate- and vigorous-intensity physical activity per week. Sufficiently active was defined as 150 –300 minutes of moderate-intensity aerobic activity, 75–150 minutes of vigorous-intensity aerobic activity, or an equivalent combination of moderate- and vigorous-intensity aerobic activity per week. Insufficiently active was defined as some aerobic activity but not enough to meet the highly or sufficiently active definition. Inactive was defined as no moderate- or vigorous-intensity aerobic activity for ⱖ10 minutes. The activity status of 644 respondents could not be determined because of missing data. c Other race includes American Indian, Alaska Native, Asian, Native Hawaiian, and Other Pacific Islander. d Includes individuals with a General Educational Development test or equivalent NHIS, National Health Interview Survey

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Discussion

Age-adjusted prevalence

60

40

20

0 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Year Highly activea Insufficiently activea

Sufficiently activeb Inactiveb

Figure 2. Estimated prevalence of four levels of aerobic activity among U.S. adults as defined in the 2008 Guidelines, National Health Interview Survey 1998 –2008 Note: Error bars represent the upper and lower bounds of the 95% CI. a Significant quadratic effect (p⬍0.05) b Significant linear effect (p⬍0.05)

centage of those who did so was higher among men than women, negatively associated with age, highest among non-Hispanic whites and lowest among Hispanics, positively associated with education, lower in the South than in other regions, and lower among obese people than among those in other BMI categories. Only 18.2% of U.S. adults met both the musclestrengthening criteria and the criteria for being aerobically active in the 2008 Guidelines; 3.7% met the muscle-strengthening criteria but were not aerobically active; and 25.2% were aerobically active but did not meet the muscle-strengthening criteria. Demographic patterns in the percentage of adults meeting both sets of criteria were similar to those for muscle strengthening alone. Annual estimates of the percentage of U.S. adults who met the muscle-strengthening criteria from 1998 through 2008 ranged from 17.7% (1998) to 21.9% (2008), and estimates of the percentage who met both the muscle-strengthening and aerobic criteria ranged from 14.4% (1998) to 18.2% (2008) (Figure 3). During this period, signifıcant linear and quadratic trends (demonstrating nonlinear variation in addition to an overall increase over time) were observed in the percentage of U.S. adults who met the musclestrengthening criteria, and the difference in this percentage between 1998 and 2008 was signifıcant (4.2 percentage points; 95% CI⫽3.3, 5.2). The percentage of those who met both the muscle-strengthening and aerobic criteria exhibited a signifıcant increasing linear trend, and the difference in prevalence between 1998 and 2008 was signifıcant (3.9 percentage points; 95% CI⫽3.0, 4.8).

In 2008, an estimated 43.5% of U.S. adults were aerobically active during their leisure time according to 2008 Guidelines criteria, and 32.6% were according to Healthy People 2010 criteria. With both sets of criteria, being male, being of younger age, being non-Hispanic white, having higher levels of education, and having a lower BMI were associated with being aerobically active. And with both sets of criteria, a small but signifıcant positive difference between 1998 and 2008 in the percentage of adults who were aerobically active was observed. In 2008, 28.4% of U.S. adults were highly active according to 2008 Guidelines criteria and 18.2% met the criteria both for muscle strengthening and for being aerobically active. Findings from this report provide baseline data that can be used to monitor changes in physical activity participation among U.S. adults and as a basis for setting new national health objectives based on physical activity criteria in the 2008 Guidelines. Findings that the estimated percentage of U.S. adults who were aerobically active according to 2008 Guidelines criteria was higher than that according to Healthy People 2010 criteria was largely the result of 2008 Guidelines criteria not including any activity frequency requirement and allowing moderate- and vigorous-intensity activity to be combined. Although the Behavioral Risk Factor Surveillance System (BRFSS) assesses physical activity differently than NHIS,12 a similar difference in estimates

Figure 3. Estimated prevalence of U.S. adults who met the muscle-strengthening guideline and the musclestrengthening guideline combined with aerobically active as defined in the 2008 Guidelines, National Health Interview Survey 1998 –2008 Note: Error bars represent the upper and lower bounds of the 95% CI. a Significant linear effect (p⬍0.05) b Significant quadratic effect (p⬍0.05) www.ajpm-online.net

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a

Table 3. Estimated prevalence (% [95% CI]) of U.S. adults who met the muscle-strengthening guideline and the muscle-strengthening guideline combined with aerobically active as defined in the 2008 Guidelines, by selected characteristics, NHIS 2008 Did not meet musclestrengthening guideline and activec

Did not meet musclestrengthening guideline and not activec

Met musclestrengthening guidelineb

Met musclestrengthening guideline and activec

Met musclestrengthening guideline and not activec

21.9 (21.2, 22.7)

18.2 (17.5, 19.0)

3.7 (3.4, 4.1)

25.2 (24.4, 26.0) 52.8 (51.7, 53.9)

Male

25.7 (24.6, 26.8)

21.7 (20.6, 22.8)

4.1 (3.6, 4.6)

25.7 (24.6, 26.8) 48.5 (47.1, 50.0)

Female

18.3 (17.4, 19.3)

14.9 (14.1, 15.8)

3.4 (3.0, 3.8)

24.9 (23.9, 26.0) 56.7 (55.5, 57.9)

18–24

29.3 (26.7, 32.1)

26.1 (23.6, 28.8)

3.3 (2.5, 4.3)

26.2 (23.9, 28.7) 44.3 (41.4, 47.3)

25–34

26.6 (24.8, 28.4)

22.6 (20.8, 24.4)

3.9 (3.2, 4.8)

27.6 (25.8, 29.5) 45.9 (43.8, 48.0)

35–44

22.7 (21.1, 24.4)

19.4 (17.8, 21.1)

3.3 (2.7, 4.1)

25.9 (24.2, 27.7) 51.4 (49.3, 53.5)

45–64

19.9 (18.9, 20.9)

16.3 (15.3, 17.3)

3.7 (3.2, 4.2)

25.3 (24.0, 26.6) 54.7 (53.2, 56.2)

ⱖ65

14.1 (12.8, 15.5)

9.5 (8.4, 10.7)

4.6 (3.9, 5.4)

20.9 (19.4, 22.4) 65.1 (63.2, 66.8)

White, non-Hispanic

24.2 (23.3, 25.2)

20.7 (19.7, 21.7)

3.6 (3.2, 4.1)

26.9 (26.0, 27.9) 48.8 (47.5, 50.1)

Black, non-Hispanic

19.0 (17.3, 21.0)

14.7 (13.1, 16.6)

4.3 (3.5, 5.2)

19.1 (17.4, 20.9) 61.9 (59.6, 64.1)

Hispanic

15.0 (13.6, 16.5)

11.3 (9.9, 12.7)

3.8 (3.0, 4.7)

22.2 (20.3, 24.1) 62.8 (60.4, 65.2)

19.3 (17.0, 21.7)

14.8 (12.7, 17.3)

4.5 (3.3, 6.0)

26.9 (24.1, 29.9) 53.8 (50.7, 56.9)

2.9 (2.3, 3.7)

18.2 (16.4, 20.1) 71.6 (69.4, 73.7)

Characteristic Total Gender

Age (years)

Race/ethnicity

d

Other, non-Hispanic Education level

Less than high school e

10.3 ( 9.0, 11.7)

7.3 (6.2, 8.7)

High school

15.6 (14.5, 16.9)

12.2 (11.1, 13.4)

3.5 (2.9, 4.2)

23.3 (21.9, 24.8) 61.0 (59.3, 62.7)

Some college

23.8 (22.6, 25.0)

19.9 (18.7, 21.1)

4.0 (3.4, 4.6)

25.7 (24.4, 27.1) 50.4 (48.8, 52.0)

College

32.4 (30.8, 34.1)

27.9 (26.3, 29.6)

4.5 (3.8, 5.4)

31.0 (29.5, 32.6) 36.5 (34.9, 38.2)

Northeast

22.3 (20.6, 24.2)

18.2 (16.4, 20.1)

4.1 (3.3, 5.1)

24.0 (22.5, 25.5) 53.7 (51.8, 55.7)

Midwest

24.1 (22.7, 25.6)

19.9 (18.6, 21.3)

4.3 (3.6, 5.1)

25.4 (23.5, 27.3) 50.4 (48.1, 52.8)

South

19.8 (18.6, 21.1)

16.6 (15.4, 17.8)

3.2 (2.8, 3.7)

23.7 (22.3, 25.0) 56.5 (54.7, 58.4)

West

22.6 (21.0, 24.2)

19.0 (17.6, 20.6)

3.7 (3.0, 4.5)

28.3 (26.9, 29.8) 49.0 (47.0, 51.0)

Underweight/normal weight (⬍25)

25.4 (24.2, 26.6)

21.8 (20.6, 23.0)

3.7 (3.3, 4.2)

26.0 (24.7, 27.3) 48.5 (47.1, 50.0)

Overweight (25–⬍30)

23.7 (22.4, 25.0)

19.4 (18.1, 20.6)

4.3 (3.8, 5.0)

26.7 (25.4, 28.1) 49.6 (48.0, 51.2)

Obese (ⱖ30)

17.0 (15.7, 18.4)

13.6 (12.4, 15.0)

3.3 (2.7, 3.9)

22.9 (21.4, 24.4) 60.2 (58.3, 62.1)

Census region

BMI category

Note: Percentages across the last four columns may not add up to 100.0 because of rounding. a Estimates are age-adjusted to the 2000 U.S. projected population using five age groups (18 –24, 25–34, 35– 44, 45– 64, and ⱖ65 years) except for estimates by age group. b Defined as performing muscle-strengthening activities two or more times per week. There were 335 respondents missing data on muscle-strengthening activities. c Muscle-strengthening guideline was defined as performing muscle-strengthening activities two or more times per week. Active was at least 150 minutes of moderate-intensity aerobic activity, at least 75 minutes of vigorous-intensity aerobic activity, or an equivalent combination of moderateand vigorous-intensity aerobic activity per week. The activity status of 638 respondents could not be determined because of missing data. d Other race/ethnicity includes American Indian, Alaska Native, Asian, Native Hawaiian, and Other Pacific Islander. e Includes individuals with a General Educational Development test or equivalent NHIS, National Health Interview Survey

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of prevalence of recommended aerobic activity was found13 using data from the BRFSS. The less restrictive nature of the physical activity criteria in the 2008 Guidelines is allowing health promotion programs to promote aerobic activity with such slogans as “Be active your way.”14 In addition, activity criteria in the 2008 Guidelines are being used as the basis for the next generation of national and state physical activity objectives.15 By either set of aerobic activity criteria, the same demographic subgroups (e.g., women, older adults, nonHispanic blacks, Hispanics, adults with lower levels of education) had relatively low levels of participation. Eliminating health disparities among segments of the U.S. population continues to be a challenge for health promotion efforts.3 In addition to providing minimum criteria for adult aerobic activity (the equivalent of 150 minutes/week of moderate-intensity aerobic activity), the 2008 Guidelines provide criteria for aerobic activity associated with more-extensive health and fıtness benefıts (the equivalent of ⬎300 minutes/ week of moderate-intensity activity).1 In 2008, only about one in four U.S. adults achieved this level. Previous recommendations and national health objectives have not identifıed levels of physical activity associated with more extensive benefıts, which include lower risk for colon and breast cancer and for unhealthy weight gain. The 2008 Guidelines also recommend that adults engage in muscle-strengthening activities for all major muscle groups at least 2 days/week alone and in combination with aerobic activity.1 However, in 2008, only 18.2% of U.S. adults participated both in at least the equivalent of 150 minutes of moderate-intensity aerobic activity and at least two sessions of muscle-strengthening activities per week. Participation in muscle-strengthening activities improves musculoskeletal strength and endurance and can increase bone density; these changes can lead to fewer falls and fractures, as well as a better ability to carry out everyday activities—particularly among older adults.2 Previous national health objectives have included separate objectives for aerobic and muscle-strengthening activities, but adults are now being encouraged to participate in both types of activities to meet the full 2008 Guidelines.1 Surveillance systems need to consistently assess all parts of the 2008 Guidelines to fully monitor the health of the population. Little progress has been made over the past 10 years in increasing physical activity levels among U.S. adults. The 2008 Guidelines state that physical activity promotion efforts should use evidence-based approaches that are tailored to the needs of individual communities.1 The Guide to Community Preventive Services provides examples of such approaches that communities can implement, including community-wide activity-promotion

campaigns, efforts to increase community members’ access to physical activity opportunities in conjunction with informational outreach, and street-scale urban-design and land-use policies that support physical activity.16,17 There are limitations and strengths in using NHIS physical activity data. First, all data are derived from self-reports of survey participants. Using accelerometers to estimate physical activity levels in the National Health and Nutrition Examination Survey, Troiano and colleagues found lower levels of physical activity among U.S. adults than the present study did,18 and reporting bias has been shown to result in overly high estimates of physical activity.19 However, the amount of physical activity recommended in the 2008 Guidelines was based on epidemiologic studies of the association between self-reported physical activity and health benefıts.2 If accelerometers were used to estimate the percentage of adults who met activity criteria in the 2008 Guidelines, the construct being monitored would differ from the construct on which the criteria were based. In addition, accelerometers do not capture all activities (e.g., swimming, biking). Another problem with NHIS physical activity data is that they are derived from responses to questions that ask about combined participation in light-intensity and moderate-intensity activity, whereas the 2008 Guidelines do not mention light-intensity activity. Including lightor moderate-intensity activity likely contributes to an overestimation of prevalence. Another study limitation is that NHIS data on muscle-strengthening activities did not reflect whether reported activity involved the seven major muscle groups specifıed in the 2008 Guidelines, and this may have resulted in an overestimation of the prevalence of participation in muscle-strengthening activities as defıned in the 2008 Guidelines. A fınal limitation in results involved a change in the NHIS physical activity questions beginning in 2004 when the leisuretime qualifıer was added to each question instead of being mentioned in only an introductory phrase. There is no way to quantify what effect this change had on trend analysis. A major strength of the study is that the use of NHIS data allowed the monitoring of changes in physical activity levels among U.S. adults over a 10-year period, thereby demonstrating the value of NHIS data in monitoring progress toward current and future Healthy People objectives. Another strength is that the current study is the fırst to examine all parts of the adult 2008 Guidelines in a representative sample of the U.S.

Conclusion The 2008 Guidelines provide evidence-based recommendations for the amount of physical activity needed to www.ajpm-online.net

Carlson et al / Am J Prev Med 2010;39(4):305–313 1

provide various health benefıts. On the basis of activity criteria in the 2008 Guidelines, in 2008, 56.5% of U.S. adults were not aerobically active during their leisure time, 71.6% were not highly aerobically active, and 81.8% did not participate in minimum recommended levels of both aerobic and muscle-strengthening activities. There is much room for improvement of the level of physical activity in the U.S and as stated in the 2008 Guidelines,1 action is needed at the individual, community, and societal level to help all Americans meet the 2008 Guidelines. The fındings and conclusions in this report are those of the authors and do not necessarily represent the offıcial position of the CDC. No fınancial disclosures were reported by the authors of this paper.

References 1. USDHHS. 2008 physical activity guidelines for Americans. Washington DC: USDHHS, 2008. 2. Physical Activity Guidelines Advisory Committee. Physical Activity Guidelines Advisory Committee report, 2008. Washington DC: USDHHS, 2008. 3. USDHHS. Healthy People 2010, 2nd edition. Washington DC: U.S. Government Printing Offıce, 2000. 4. Pate RR, Pratt M, Blair SN, et al. Physical activity and public health. A recommendation from the Centers for Disease Control and Prevention and the American College of Sports Medicine. JAMA 1995;273(5):402–7. 5. USDHHS. Physical activity and health: a report of the Surgeon General. Atlanta GA: USDHHS, CDC, National Center for Chronic Disease Prevention and Health Promotion, 1996. 6. National Center for Health Statistics, CDC. National Health Interview Survey. www.cdc.gov/nchs/nhis.htm.

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7. National Center for Health Statistics, CDC. Adult physical activity information in the National Health Interview Survey. www.cdc.gov/ nchs/nhis/physical_activity.htm. 8. Pleis JR, Lucas JW, Ward BW. Summary health statistics for U.S. adults: National Health Interview Survey, 2008. National Center for Health Statistics. Vital Health Stat 2009;10(242). 9. U.S. Department of Commerce Economics and Statistics Administration, U.S. Census Bureau. Census regions and divisions of the U.S. www.census.gov/geo/www/us_regdiv.pdf. 10. National Heart, Lung, and Blood Institute. Clinical guidelines on the identifıcation, evaluation, and treatment of overweight and obesity in adults: the evidence report. Bethesda MD: USDHHS, NIH, National Heart, Lung, and Blood Institute, 1998. www.nhlbi.nih.gov/guidelines/ obesity/ob_gdlns.htm. 11. Klein RJ, Schoenborn CA. Age adjustment using the 2000 projected U.S. population. Healthy People 2000 Stat Notes 2001:(20):1–9. 12. Carlson SA, Densmore D, Fulton JE, Yore MM, Kohl HW 3rd. Differences in physical activity prevalence and trends from 3 U.S. surveillance systems: NHIS, NHANES, and BRFSS. J Phys Act Health 2009; 6(S 1):S18 –27. 13. Carlson S, Fulton J, Galuska D, Kruger J, Lobelo F, Loustalot F. Prevalence of self-reported physically active adults—U.S., 2007. MMWR Morb Mortal Wkly Rep 2008;57(48):1297–300. 14. USDHHS. Be active your way: a guide for adults. Washington DC: USDHHS, 2008. 15. USDHHS. Healthy People 2020. www.healthypeople.gov/HP2020. 16. Heath GW, Brownson RC, Kruger J, Miles R, Powell KE, Ramsey LT; Task Force on Community Preventive Services. The effectiveness of urban design and land use and transport policies and practices to increase physical activity: a systematic review. J Phys Act Health 2002; 3(S 1):S55–76. 17. Task Force on Community Preventive Services. Recommendations to increase physical activity in communities. Am J Prev Med 2002; 22(4S 1):67–72. 18. Troiano RP, Berrigan D, Dodd KW, Mâsse LC, Tilert T, McDowell M. Physical activity in the U.S. measured by accelerometer. Med Sci Sports Exerc 2008;40(1):181– 8. 19. Sallis JF, Saelens BE. Assessment of physical activity by self-report: status, limitations, and future directions. Res Q Exerc Sport 2000; 71(2S):S1–14.