Physical Activity in U.S. Adults

Physical Activity in U.S. Adults Compliance with the Physical Activity Guidelines for Americans Jared M. Tucker, PhD, Gregory J. Welk, PhD, Nicholas K. Beyler, PhD Background: To date, no study has objectively measured physical activity levels among U.S. adults according to the 2008 Physical Activity Guidelines for Americans (PAGA).

Purpose: The purpose of this study was to assess self-reported and objectively measured physical activity among U.S. adults according to the PAGA. Methods: Using data from the NHANES 2005–2006, the PAGA were assessed using three physical activity calculations: moderate plus vigorous physical activity ⱖ150 minutes/week (MVPA); moderate plus two instances of vigorous physical activity ⱖ150 minutes/week (M2VPA); and time spent above 3 METs ⱖ500 MET-minutes/week (METPA). Self-reported physical activity included leisure, transportation, and household activities. Objective activity was measured using Actigraph accelerometers that were worn for 7 consecutive days. Analyses were conducted in 2009 –2010.

Results: U.S. adults reported 324.5⫾18.6 minutes/week (M⫾SE) of moderate physical activity and 73.6⫾3.9 minutes/week of vigorous physical activity, although accelerometry estimates were 45.1⫾4.6 minutes/week of moderate physical activity and 18.6⫾6.6 minutes/week of vigorous physical activity. The proportion of adults meeting the PAGA according to M2VPA was 62.0% for self-report and 9.6% for accelerometry. Conclusions: According to the NHANES 2005–2006, fewer than 10% of U.S. adults met the PAGA according to accelerometry. However, physical activity estimates vary substantially depending on whether self-reported or measured via accelerometer. (Am J Prev Med 2011;40(4):454 – 461) © 2011 American Journal of Preventive Medicine

Introduction

T

he Physical Activity Guidelines for Americans (PAGA) released by the USDHHS provide defınitive public health recommendations for physical activity.1 The PAGA recommend that adults obtain at least 150 minutes/week of moderate-intensity physical activity (MPA), 75 minutes/week of vigorous-intensity physical activity (VPA), or a combination of moderate and vigorous physical activity (MVPA). The guidelines are conceptually similar to previous recommendations,2,3 but provide more flexibility in how physical activity is accumulated across the week. Another distinction is that

From the Department of Health, Nutrition and Exercise Sciences, North Dakota State University (Tucker), Fargo, North Dakota; the Department of Kinesiology, Iowa State University (Welk), Ames, Iowa; and Mathematica Policy Research, Inc (Beyler), Washington DC Address correspondence to: Jared M. Tucker, PhD, Department of Health, Nutrition, and Exercise Sciences, North Dakota State University, P.O. Box 6050, Fargo ND 58108-6050. E-mail: [email protected]. 0749-3797/$17.00 doi: 10.1016/j.amepre.2010.12.016

454 Am J Prev Med 2011;40(4):454 – 461

the PAGA increased the VPA guideline from 60 minutes/ week (20 minutes ⫻ 3 days/week) to 75 minutes/week. The advisory committee that developed the PAGA made these recommendations based on accumulating evidence that the health benefıts from physical activity are primarily dependent on total energy expenditure.4 The committee concluded that the amount of energy expenditure necessary to achieve many of the health benefıts was in the range of 500 –1000 MET-minutes/week. Based on the standard MET thresholds (3 METs for MPA and 6 METs for VPA), this can be achieved with approximately 150 minutes/week of MPA or 75 minutes/week of VPA. The use of MET-minutes allows the guidelines to focus on total energy expenditure in physical activity. For effective public health surveillance, it is important to determine the proportion of U.S. adults that meet the guidelines outlined in the PAGA. Compliance with the PAGA was evaluated in one recent study,5 but this relied on self-report data. An earlier study6 examined compliance with previous physical activity recommendations using accelerometry. Although the PAGA are similar to

© 2011 American Journal of Preventive Medicine • Published by Elsevier Inc.

Tucker et al / Am J Prev Med 2011;40(4):454 – 461

previous recommendations, it is important to understand how the guidelines in PAGA may affect national data for public health surveillance. The purpose of the current study was to assess selfreported and objectively measured physical activity levels among U.S. adults according to the 2008 PAGA. To date, no studies have compared the physical activity levels of Americans measured from both self-report and accelerometer. Therefore, an ancillary objective of the study was to compare self-report and accelerometer physical activity outcomes, in order to gain insight into the relationship between these two assessment tools.

455

On return, monitors were downloaded and checked to determine whether they were still correctly calibrated.

Demographic and anthropometric measures. Participants’ physical activity levels were categorized by gender, age, race/ethnicity, and BMI in order to allow for comparisons among these groups. Age was categorized into 6 groups: 20 –29 years, 30 –39 years, 40 – 49 years, 50 –59 years, 60 – 69 years, and ⱖ70 years. Race/ethnicity was self-reported and for the current study included three groups: non-Hispanic white, non-Hispanic black, and Mexican American. Trained health technicians measured height and weight using a calibrated stadiometer and digital scale, respectively. Participants were categorized by weight status as either normal weight (BMI ⬍25), overweight (BMI⫽25–29.9), class I obese (BMI⫽30–34.9), or class II obese and above (BMI ⱖ35).

Methods Study Population Data for the current study were obtained from the National Health and Nutrition Examination Survey (NHANES) 2005–2006.7 The NHANES uses a multi-stage probability cluster sampling design to provide nationally representative data on a variety of health risks and behaviors, including both self-reported and objective estimates of physical activity. All counties within the U.S. served as the sampling frame for the NHANES. Within these counties, clusters of households were selected, after which one or more people within each household were recruited for participation. Oversampling of certain subpopulations was done to increase the reliability and accuracy of health estimates for these groups. In order to account for this oversampling design, NHANES provides weights for each respondent, which indicate the probability of being sampled.

Measures Self-report physical activity. Self-reported physical activity was assessed during the household interview and included a series of questions that required participants to recall physical activity behaviors during the past 30 days. Questions focused on the typical frequency and duration of physical activity performed during transportation, household, and leisure activities. Estimated intensity levels were assigned to all reported transportation activities (4.0 METs) and household activities (4.5 METs) based on the Compendium of Physical Activities and communication between NHANES and the Compendium’s authors.8 Therefore, all reported transportation and household physical activity was considered moderate intensity (i.e., ⱖ3 METs) in the current study. For leisure-time physical activity, respondents were asked to report the level of exertion (moderate or vigorous) for each reported activity. Each leisure activity was assigned one of two predetermined MET scores unique to each mode of activity, depending on whether reported as moderate or vigorous intensity.9 For example, moderate-intensity cycling was considered 4 METs and vigorous-intensity cycling was considered 8 METs.

Accelerometer physical activity. Objective physical activity was assessed in NHANES using 7-day accelerometry (Actigraph model 7164 (LLC). Participants were instructed to begin wearing the monitor the day after it was distributed, and to remove the device only during sleep and water-based activities. The monitors were programmed to record data in 1-minute intervals (epochs). April 2011

Data Processing Self-report physical activity. The self-report data were processed using three different methods to evaluate the impact of these approaches on resultant physical activity. The fırst approach (labeled MVPA) was calculated by adding reported minutes of moderate physical activity to minutes of vigorous physical activity. The second approach (labeled M2VPA) used the weighting procedure recommended in the appendix of the PAGA, in which 1 minute of VPA is equivalent to 2 minutes of MPA.8 The minutes of VPA were doubled and added to minutes of MPA to compute the score. For MVPA and M2VPA, participants were categorized into three activity levels based on total weekly minutes calculated for each approach: no reported MVPA (0 minutes/week); insuffıcient MVPA to meet the guidelines (1–150 minutes/week); and suffıcient MVPA to meet the guidelines (ⱖ150 minutes/week). In the third approach, physical activity levels were calculated using MET-minutes (labeled METPA). Total MET-minutes of physical activity were calculated by multiplying the weekly physical activity volume (duration ⫻ frequency) of each activity by its corresponding MET value. Participants were categorized into one of the following three guideline-based activity levels according to their total weekly METPA: none (0 MET-minutes/week), insuffıcient to meet the guidelines (1– 499 MET-minutes/week), and suffıcient to meet the guidelines (ⱖ500 MET-minutes/week). Accelerometer physical activity. Accelerometer-based physical activity was processed similarly to the self-reported physical activity to provide direct comparisons among the three methods of evaluating the PAGA (i.e., MVPA, M2VPA, and METPA). However, the accelerometer data required additional processing procedures to check subject compliance and to determine the physical activity intensities. Accelerometer processing was conducted using adapted versions of SAS programs released by the National Cancer Institute.10 Consistent with standard processing in NHANES, participants were considered compliant if they wore the monitor for at least 10 hours/day on at least 4 of the 7 days. Non-wear periods were defıned as times during which no movement was detected for 60 consecutive minutes, as has been done in previous NHANES accelerometer research.6 Minutes of MVPA were estimated from accelerometer counts using cut points established from a weighted average of four previously published thresholds11–14 for moderate (2020 –5998 counts/minute) and vigorous (ⱖ5999 counts/minute) physical activity, as per previous research.6,15

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Two accelerometer outcome measures included MVPA and M2VPA, which were calculated as described in the data processing procedures for self-reported physical activity. The third accelerometer outcome measure was computed to create a measure that would parallel the self-report MET-minute variable (METPA). Accelerometer counts were fırst converted into MET-minutes using a published equation developed for the Actigraph.12 Accelerometer counts below the computed threshold for moderate physical activity (3 METs) were not included in the MET-minutes total. The PAGA recommends that aerobic activity be performed in bouts of at least 10 minutes or more. For self-report physical activity, participants were instructed to report only activities that lasted at least 10 minutes. Therefore, all self-reported activities can, in theory, be interpreted as physical activity performed in sustained bouts. For accelerometer physical activity, MVPA and M2VPA were calculated using only physical activity performed in 10-minute bouts. In order to account for occasional stoppages in sustained physical activity sessions, at least 8 of 10 consecutive minutes at or above moderate intensity were required to be included in the total, as has been done in previous research.6 It was assumed that participants similarly ignored brief 1–2-minute stoppages when selfreporting bouts of physical activity. For METPA, total MET-minutes was used to assess guideline compliance.

Data Analysis All data processing and statistical analyses were performed using SAS, version 9.1, in 2009 –2010. Analyses incorporated sampling weights to allow for nationally representative physical activity estimates. The current study sample was limited to adults, aged ⱖ20 years at the time of NHANES 2005–2006, with compliant accelerometer data (i.e., 4 days with ⱖ10 hours/day of wear time). Descriptive analyses included adjusted means for each physical activity assessment method (MVPA, M2VPA, and METPA) for both self-report and accelerometer measures. Adjusted frequencies for the proportion of U.S. adults meeting the PAGA were also calculated in total and by demographic group. Agreement between accelerometer physical activity and the self-reported domains of MVPA were examined using Spearman correlation coeffıcients because of the skewed data distribution.

Results A total of 4773 adults completed both the accelerometer and self-report physical activity measures. Of those, a subsample of 3082 (64.6%) adults met the compliance criteria for Actigraph wear time and did not have any missing data. Nationally representative estimates from the current study were based on this subsample (n⫽3082).

Physical Activity Guidelines for Americans According to self-report, the proportions of adults meeting the PAGA were 59.6%, 62.0%, and 65.7% using the MVPA, M2VPA, and METPA methods, respectively (Table 1). The proportion of Americans meeting the PAGA according to accelerometry were much lower, with only 8.2% (MVPA); 9.6% (M2VPA); and 44.6% (METPA) of U.S. adults meeting the guidelines (Table 2). The propor-

tion of adults meeting the PAGA was highest when using the METPA method and lowest when using the MVPA method, regardless of physical activity measurement method or demographic group. The proportion of adults meeting the PAGA differed very little between the MVPA and M2VPA calculation methods for both self-report (1.4%) and accelerometry (2.4%). The small differences reflect the relatively low levels of vigorous physical activity in the population. However, slightly larger differences between the MVPA and M2VPA estimates were found among some subpopulations (⬃3%–5%), because of relatively greater levels of vigorous physical activity.

Self-Report Versus Accelerometer Physical Activity Average minutes/week of MPA, VPA, and total METPA are displayed by measurement method and demographic characteristics in Table 3. Levels of physical activity varied substantially between measurement methods with self-report estimates exceeding accelerometer estimates in all cases. The self-report data yielded estimates of 324.5⫾18.6 minutes/week (mean⫾SE) of MPA and 73.6⫾3.9 minutes/week of VPA. The corresponding estimates from the Actigraph data were 45.1⫾4.6 minutes/ week of MPA and 18.6⫾6.6 minutes/week of VPA. Despite estimate differences, patterns for weekly physical activity were similar across measurement methods for most demographic characteristics. According to both self-report and accelerometry, MVPA levels were higher in men than women, higher in non-Hispanic whites than non-Hispanic blacks, and higher in normal-weight adults than overweight and obese adults (Table 3). Additionally, adults at or above the obese class II threshold had the lowest physical activity levels of all weight-status categories according to self-report and accelerometry. Physical activity levels among different age groups also shared similar patterns between instruments, with those aged 20 –29 years obtaining the most MVPA of any age group, and those aged 30 –39 years obtaining 22.0% less MVPA according to self-report and 17.3% less MVPA according to accelerometry. Also, those aged 40 – 49 years obtained the second-most MVPA according to both measures when compared to adults in other age groups. Although most physical activity patterns among demographic groups were similar between self-report and accelerometer measures, some discrepancies were evident. Most notably, self-reported levels of MVPA were lowest among Mexican Americans (259.4⫾20.7 minutes/ week) when compared to MVPA levels for non-Hispanic whites (423.0⫾27.9 minutes/week) and non-Hispanic blacks (354.1⫾28.8 minutes/week). In contrast, MVPA levels were highest among Mexican Americans (90.7⫾ www.ajpm-online.net

Tucker et al / Am J Prev Med 2011;40(4):454 – 461

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Table 1. Proportion of U.S. adults meeting the Physical Activity Guidelines for Americans by MVPA, M2VPA, and METPA according to self-report MVPA None

Inadequate

M2VPA Adequate

None

Inadequate

METPA Adequate

None

Inadequate

Adequate

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

12.5

1.05

27.9

0.93

59.6

1.50

12.5

1.05

25.6

0.81

62.0

1.48

12.5

1.05

21.9

0.99

65.7

1.43

Male

10.7

1.24

25.5

1.30

63.9

1.90

10.7

1.24

23.2

1.29

66.1

1.86

10.7

1.24

19.4

1.31

69.9

1.88

Female

14.1

1.05

30.2

1.09

55.8

1.61

14.1

1.05

27.7

0.99

58.2

1.59

14.1

1.05

24.2

1.25

61.7

1.56

20–29

10.5

1.85

25.6

2.17

63.9

3.25

10.5

1.85

22.3

2.38

67.2

3.39

10.5

1.85

18.3

2.13

71.2

2.88

30–39

10.0

1.54

30.9

2.42

59.0

2.55

10.0

1.54

27.1

1.68

62.9

2.12

10.0

1.54

23.4

1.57

66.6

2.01

40–49

10.5

2.05

25.1

1.84

64.4

3.13

10.5

2.05

23.6

1.70

65.8

3.02

10.5

2.05

20.2

1.47

69.3

2.99

50–59

9.3

1.49

31.9

1.73

58.8

2.55

9.3

1.49

28.6

1.96

62.1

2.58

9.3

1.49

24.3

1.73

66.4

2.25

60–69

13.8

3.01

26.6

1.57

59.7

3.71

13.8

3.01

25.6

1.56

60.6

3.67

13.8

3.01

22.9

1.86

63.3

3.87

ⱖ70

25.9

2.62

27.2

2.14

46.9

3.36

25.9

2.62

27.2

2.14

47.0

3.36

25.9

2.62

23.3

2.65

50.8

3.12

27.0

1.93

32.3

1.31

40.7

2.33

27.0

1.93

29.3

1.70

43.7

2.77

27.0

1.93

24.6

1.84

48.4

2.89

Non-Hispanic white

9.6

1.18

27.5

1.08

63.0

1.71

9.6

1.18

25.5

0.89

65.0

1.69

9.6

1.18

21.6

1.08

68.8

1.61

Non-Hispanic black

18.3

1.74

34.0

1.71

47.7

2.28

18.3

1.74

29.6

1.84

52.1

2.57

18.3

1.74

26.6

1.87

55.1

2.69

Total Gender

Age (years)

Race/ethnicity MexicanAmerican

Weight status (BMI) ⬍25

11.6

1.32

25.3

1.20

63.1

2.11

11.6

1.32

22.9

1.14

65.5

2.03

11.6

1.32

19.3

0.84

69.1

1.59

25–29.9

11.6

1.50

29.8

2.09

58.6

2.08

11.6

1.50

26.4

1.69

62.0

1.89

11.6

1.50

22.1

1.68

66.3

1.85

30–34.9

11.7

1.60

29.2

2.46

59.1

2.84

11.7

1.60

27.7

2.15

60.6

2.54

11.7

1.60

25.0

2.40

63.3

2.67

ⱖ35

17.7

2.31

27.8

2.48

54.5

3.45

17.7

2.32

26.9

2.50

55.4

3.44

17.7

2.32

23.3

2.80

59.0

3.40

Note: MVPA⫽moderate ⫹ vigorous physical activity guideline (150 minutes/week); M2VPA⫽moderate ⫹ 2 ⫻ vigorous physical activity guideline (150 minutes/week); METPA⫽MET physical activity guideline (500 MET-min/week); Freq⫽frequency of U.S. demographic meeting the 2008 Physical Activity Guidelines for Americans METPA, MET physical activity; MVPA, moderate-to-vigorous physical activity; M2VPA, moderate ⫹ 2 ⫻ vigorous physical activity; SEM, standard error of the measure

33.2 minutes/week) according to accelerometry, when compared to non-Hispanic whites (68.0⫾13.1) and nonHispanic blacks (38.2⫾4.7). Physical activity patterns were also very different among Americans aged ⱖ70 years, with self-report MVPA levels lower than all other age groups, whereas accelerometer MVPA in adults aged ⱖ70 years was higher than in both those aged 50 –59 years and 60 – 69 years. The overall correlations between self-reported and accelerometry-based estimates of MVPA were fairly low (r ⫽0.27). When examined across categories of selfreport, accelerometer MVPA exhibited a modest relationship with leisure MVPA (r ⫽0.29); a weak relationship with transportation MVPA (r ⫽0.20); and very weak association with household MVPA (r⫽0.08). April 2011

Discussion The current study found that 9.5% of men and 7.0% of women achieved the PAGA-recommended levels according to the accelerometry MVPA assessment method. Although much lower than self-reported estimates, the proportion of adults meeting the guidelines according to accelerometry was higher than those presented by Troiano and colleagues.6 Using data from NHANES 2003–2004, Troiano et al. reported that according to MVPA performed in 10-minute bouts, only 2.5% (if aged ⬎60 years) to 3.5% (if aged 20 –59 years) of adult men and 2.3% (if aged ⬎60 years) to 3.2% (if aged 20 –59 years) of adult women met previous recommendations.2

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Table 2. Proportion of U.S. adults meeting the Physical Activity Guidelines for Americans by MVPA, M2VPA, and METPA according to accelerometry MVPA None

Inadequate

M2VPA Adequate

None

Inadequate

METPA Adequate

None

Inadequate

Adequate

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

Freq

SEM

53.0

1.70

38.8

1.47

8.2

0.84

53.0

1.73

37.3

1.53

9.6

0.94

0.4

0.11

55.0

1.64

44.6

1.68

Male

46.5

2.07

44.0

1.52

9.5

1.32

46.5

2.07

42.9

1.56

10.6

1.55

0.1

0.08

42.2

2.00

57.7

2.02

Female

59.1

2.23

33.9

2.20

7.0

0.95

59.1

2.23

32.2

2.36

8.7

1.12

0.6

0.18

66.8

1.71

32.5

1.74

20–29

42.6

4.05

46.6

3.48

10.8

1.64

42.6

4.05

44.7

3.53

12.7

1.68

0.0

0.00

43.3

3.78

56.7

3.78

30–39

47.9

2.90

45.1

2.53

7.0

1.85

47.9

2.90

44.6

2.57

7.5

1.98

0.0

0.00

43.7

1.91

56.3

1.91

40–49

45.0

3.14

45.7

2.92

9.4

1.45

45.0

3.14

42.5

3.27

12.6

1.78

0.0

0.00

42.6

3.01

57.4

3.01

50–59

55.9

3.18

37.6

3.06

6.5

1.43

55.9

3.18

36.0

2.81

8.1

1.43

0.0

0.00

61.4

2.89

38.6

2.89

60–69

62.6

2.03

28.9

2.15

8.5

1.54

62.6

2.03

28.9

2.17

8.5

1.56

0.1

0.10

73.7

2.12

26.2

2.11

ⱖ70

78.4

2.57

15.3

1.92

6.3

1.48

78.4

2.57

15.3

1.92

6.3

1.48

3.2

0.83

86.4

1.66

10.4

1.43

MexicanAmerican

49.4

1.97

41.5

1.39

9.1

1.33

49.4

1.97

40.6

1.34

9.9

1.48

0.1

0.08

53.1

2.64

46.8

2.65

Non-Hispanic white

52.5

1.91

39.3

1.69

8.2

0.99

52.5

1.91

37.4

1.75

10.1

1.16

0.5

0.15

53.3

1.89

46.1

1.95

Non-Hispanic black

58.9

2.36

33.4

2.34

7.7

1.32

58.9

2.36

33.1

2.36

8.0

1.40

0.1

0.08

62.3

2.34

37.6

2.34

Total Gender

Age (years)

Race/ethnicity

Weight status (BMI) ⬍25

46.5

2.49

43.1

2.54

10.3

1.42

46.5

2.49

40.0

2.72

13.4

1.45

0.9

0.26

47.3

2.34

51.8

2.44

25–29.9

50.3

2.28

39.9

1.24

9.8

1.36

50.3

2.28

38.7

1.36

10.9

1.49

0.2

0.12

50.9

2.18

48.9

2.16

30–34.9

56.5

2.80

38.4

2.80

5.1

0.87

56.5

2.80

38.4

2.80

5.1

0.87

0.2

0.19

60.0

3.16

39.8

3.20

ⱖ35

70.6

3.19

26.0

2.46

3.5

1.13

70.5

3.19

26.0

2.46

3.5

1.12

0.0

0.00

76.2

2.36

23.8

2.36

Note: MVPA⫽moderate ⫹ vigorous physical activity guideline (150 minutes/week); M2VPA⫽moderate ⫹ 2 ⫻ vigorous physical activity guideline (150 minutes/week); METPA⫽MET physical activity guideline (500 MET-minutes/week); Freq⫽frequency of U.S. demographic meeting the 2008 Physical Activity Guidelines for Americans SEM, standard error of the measure

There are several potential explanations worth noting for this apparent difference in physical activity levels. One possibility is that average physical activity levels increased slightly between the times data were collected in NHANES 2003–2004 and NHANES 2005–2006. This increase in physical activity is supported by data from the Behavioral Risk Factor Surveillance System (BRFSS), which showed that, according to self-report, the proportion of U.S. adults considered physically active increased by 8.6% in women and 3.5% in men between 2001 and 2005.16 Another factor that likely contributed to the discrepancy is the criteria used to defıne compliance with the physical activity guidelines. The same criterion of 150 minutes/week of MVPA was used for both studies, but the previous guidelines stipulated that individuals must obtain at least 30 min-

utes on a given day to count as an active day.3 In contrast, the PAGA does not require a minimum daily total as long as the physical activity is performed in 10-minute bouts. Therefore, individuals who accumulated 150 minutes/week of MVPA, but did so in ⬍30 minutes/day increments, would have met the PAGA guideline without having met the previously used guideline. Although the accelerometer data reveal low levels of physical activity participation, data from the selfreport instrument yield different results. Approximately 62% of U.S. adults achieved the PAGA when using the M2VPA calculation method recommended by the guidelines’ authors.9 Although substantially higher than accelerometer estimates, the proportion of U.S. adults achieving recommended levels of physical activity is similar to recent self-reported estimates www.ajpm-online.net

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Table 3. Minutes per week (Ms and SEs) of moderate, vigorous, and MET-minute physical activity among U.S. adults by gender, age group, ethnicity, and weight status according to self-report and accelerometer MPA (min/wk)

VPA (min/wk)

n

M

SEM

M

3082

324.5

18.60

73.6

Male

1524

380.5

23.50

Female

1558

272.6

20–29

477

30–39

SEM

METPA M

SEM

3.90

1863.9

81.10

80.6

4.85

2154.5

94.30

18.33

67.1

5.33

1595.2

85.71

313.5

25.17

131.3

12.84

2322.4

149.62

516

274.1

17.98

72.8

7.99

1660.2

80.22

40–49

556

356.6

24.00

68.0

6.16

1948.2

99.40

50–59

454

366.1

32.20

58.5

6.08

1892.0

142.60

60–69

441

348.0

42.24

52.9

13.43

1761.4

220.64

ⱖ70

577

288.1

24.98

37.0

13.17

1403.7

173.68

Mexican-American

635

212.1

21.73

47.3

6.88

1273.4

99.43

Non-Hispanic white

1579

346.9

26.84

76.1

3.58

1961.4

110.78

Non-Hispanic black

661

282.9

26.99

71.2

7.37

1704.1

139.78

940

342.0

29.20

106.2

9.87

2201.6

118.94

25–29.9

1087

322.1

15.67

71.5

6.61

1829.7

94.66

30–34.9

633

328.2

22.94

50.2

4.79

1692.2

94.48

ⱖ35

422

282.3

37.42

32.1

4.52

1364.7

156.31

3082

45.1

4.60

18.6

6.60

907.9

157.76

Male

1524

52.9

8.83

21.2

9.97

1051.0

184.78

Female

1558

37.8

4.61

16.2

9.11

775.5

250.70

20–29

477

57.2

9.47

22.4

16.11

1263.5

454.66

30–39

516

38.4

4.57

27.4

16.49

1127.8

364.45

40–49

556

54.1

12.75

24.9

16.58

1015.0

234.17

50–59

454

35.3

4.11

7.7

3.32

622.2

71.78

60–69

441

32.7

3.64

1.4

0.70

373.3

24.86

ⱖ70

577

45.0

19.40

19.5

14.30

711.3

379.39

635

55.5

7.75

35.2

31.07

1582.8

846.76

SELF-REPORT Total Gender

Age (years)

Ethnicity

Weight status (BMI) ⬍25

ACCELEROMETER Total Gender

Age (years)

Ethnicity Mexican-American

(continued on next page)

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Tucker et al / Am J Prev Med 2011;40(4):454 – 461

460

Table 3. Minutes per week (Ms and SEs) of moderate, vigorous, and MET-minute physical activity among U.S. adults by gender, age group, ethnicity, and weight status according to self-report and accelerometer (continued) MPA (min/wk)

VPA (min/wk)

n

M

SEM

M

Non-Hispanic white

1579

47.3

6.02

20.7

Non-Hispanic black

661

31.8

2.47

940

59.1

25–29.9

1087

30–34.9 ⱖ35

SEM

METPA M

SEM

8.43

925.1

196.10

6.4

3.70

593.5

85.51

9.26

32.5

14.62

1174.8

269.94

46.8

4.85

9.9

2.54

748.1

52.20

633

36.3

8.72

22.6

14.85

1100.1

414.58

422

18.9

3.07

0.2

0.13

374.4

20.75

Weight status (BMI) ⬍25

Note: MVPA⫽minutes/week of moderate physical activity; Vigorous⫽minutes/week of vigorous physical activity; METPA⫽MET- minutes/week of physical activity (METPA⫽⬎3 METs) METPA, MET-minutes physical activity (⬎3 METs); MPA, moderate physical activity; SEM, standard error of the measure; VPA, vigorous physical activity

from the 2007 BRFSS.17 The BRFSS data showed that 64.5% of U.S. adults obtained suffıcient physical activity to meet the PAGA. These data were obtained according to the M2VPA calculation method, and included the same three domains of physical activity as the NHANES: leisure, transportation, and household activities. However, unlike the NHANES, data from the BRFSS were based on a much larger sample and utilized self-reported physical activity data via telephone surveys. The BRFSS data were collected in 2007 and are, therefore, 1–2 years more recent than the data used in the current study. Despite these differences in methodology and protocol, it is noteworthy that the BRFSS results are similar to those reported here. In the present investigation, the accelerometerestimated proportion of U.S. adults obtaining the PAGA according to METPA varied substantially when compared to the MVPA and M2VPA frequencies. These differences may be caused by various factors, but the most influential factor was that the METPA calculation was assessed by accumulating MET-minutes individually, as opposed to MVPA and M2VPA, which counted only physical activity performed in 10-minutes bouts. The PAGA specify that most physical activity benefıts result from expending a given quantity of energy (500 MET-minutes) in physical activity. However, whether or not these benefıts are contingent on being performed in 10-minute bouts is unclear. Therefore, total METPA levels were of interest in the current study, as a comparison to physical activity estimates performed in bouts. Data from the current study confırm that self-reported physical activity estimates are much greater than accelerometer-based estimates. Several possibilities exist for this discrepancy. First, self-reported physical activity may be

overestimated because of social desirability.18 One study examining this link found that social desirability was the strongest predictor of physical activity frequency in 423 adults (aged 18 –50 years).19 However, other research has shown that social desirability accounted for only 1%–3% of the variance in self-reported physical activity levels (r⫽0.11– 0.17).20 Misinterpretation of survey questions may also lead to biased results. According to Baranowski et al., recalling physical activity is a complex cognitive task, which requires respondents to understand ambiguous terms such as “physical activity,” “leisure-time,” and “moderate-intensity.”21 In the current study, household physical activity was very weakly associated with objectively measured physical activity (r⫽0.08). Therefore, it is possible that some household activities were interpreted as moderate-intensity,22 when in actuality they may be low-intensity. Finally, some participants may have tended to report physical activity of all durations, as opposed to only those activities that occurred in 10-minute bouts or more. It is also possible that accelerometers underestimate true physical activity levels. Because physical activity monitors are typically worn on the hip (as was the case in the NHANES) they cannot accurately assess upper body activities, nor can they account for movements that require extra effort, such as walking uphill or carrying loads. Although some of the published intensity cut-points account for a wide variety of whole-body activities,23,24 many validation studies are based primarily on locomotor movements.11,12,14 Therefore, non-locomotor physical activity, such as biking and many household activities, are likely underestimated by accelerometers. www.ajpm-online.net

Tucker et al / Am J Prev Med 2011;40(4):454 – 461

In summary, physical activity estimates among U.S. adults vary substantially depending on whether measured via self-report or accelerometer. The current study showed that ⬃10% of adults meet the PAGA according to accelerometry. Although these fındings are higher than those of previous studies, they are still well below what is needed to achieve population-level health improvements. No fınancial disclosures were reported by the authors of this paper.

References 1. GovTrack.us. S. 2748 —110th Congress (2008): Physical Activity Guidelines for Americans Act of 2008, GovTrack.us (database of federal legislation). www.govtrack.us/congress/bill.xpd?bill⫽s110-2748& tab⫽analysis. 2. Pate RR, Pratt M, Blair SN, et al. Physical activity and public health. A recommendation from the CDC and the American College of Sports Medicine. JAMA 1995;273(5):402–7. 3. Haskell WL, Lee IM, Pate RR, et al. Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Circulation 2007;116(9):1081–93. 4. USDHHS. Physical Activity Guidelines Advisory Committee fınal report. www.health.gov/PAGuidelines/Report/Default.aspx. 5. CDC. Prevalence of self-reported physically active adults—U.S., 2007. MMWR Morb Mortal Wkly Rep 2008;57(48):1297–300. 6. 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. 7. CDC. National Health and Nutrition Examination Survey 2005–2006. www.cdc.gov/nchs/nhanes/nhanes2005-2006/nhanes05_06.htm. 8. Ainsworth BE, Haskell WL, Whitt MC, et al. Compendium of physical activities: an update of activity codes and MET intensities. Med Sci Sports Exerc 2000;32(9):S498 –516.

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