Key Points
Question
What are the current physical activity levels among US adolescents and young adults by income, race/ethnicity, and sex?
Findings
In this cross-sectional study of data from 9472 adolescent and young adult respondents in the National Health and Nutrition Examination Survey from 2007 through 2016, females were significantly less physically active than their male counterparts. Minority race/ethnicity and low income were associated with lower physical activity in most groups.
Meaning
Disparities may exist in the rates of physical activity among adolescents and young adults, with lower initiation and duration of activity among racial/ethnic minorities and those living in poverty.
Abstract
Importance
Physical activity in youth is associated with adult health. Understanding the prevalence and factors of moderate to vigorous physical activity among adolescents and young adults will guide public health and policy efforts.
Objectives
To describe the current patterns of physical activity and duration among adolescents and young adults and to identify the direction and magnitude of associations between physical activity and income, race/ethnicity, and sex.
Design, Setting, and Participants
This cross-sectional secondary data analysis used the self-reported physical activity data of adolescents and young adults from the National Health and Nutrition Examination Survey from 2007 through 2016. This data set is a multistage probability sample of the noninstitutionalized US population and allows estimates that represent the US population. The years 2007 through 2016 were selected because of the consistent physical activity questions during this period. Adolescents and young adults aged 12 to 29 years who responded to the survey were included. Individuals who were underweight were excluded. Data analysis was performed from October 17, 2017, to April 27, 2018.
Main Outcomes and Measures
Self-reported physical activity duration and intensity.
Results
Of the 9472 participants, 4771 (50.4%) were males, and the weighted mean age (range) was 20.6 (12-19) years. Across all demographic categories, females reported less physical activity than did their male counterparts. White adolescent males were most likely (89.3%; 95% CI, 86.5%-92.1%) and black females aged 18 to 24 years were least likely (45%; 95% CI, 39.0%-51.0%) to report any physical activity. Among those who were active, black males aged 18 to 24 years reported the longest duration of activity (77.9 minutes per day; 95% CI, 66.4-89.3 minutes per day), and black females aged 25 to 29 years reported the shortest duration of activity (33.2 minutes per day; 95% CI, 28.1-38.2 minutes per day). In adjusted models, younger age, white race, and higher income were associated with greater physical activity.
Conclusions and Relevance
Female adolescents and young adults were not meeting the recommended guidelines for physical activity, and substantial disparities by race and income levels were noted. These data highlight opportunities for targeted physical activity programming and policy efforts.
This cross-sectional study analyzes the association between physical activity and income, race/ethnicity, and sex among US adolescents and young adults by using self-reported data included in the National Health and Nutrition Examination (NHANES) Survey from 2007 through 2016.
Introduction
Physical activity is a priority health behavior and leads to decreased morbidity and mortality.1 High levels of physical activity are associated with decreased risk for obesity, type 2 diabetes, specific types of cancer, cardiovascular disease, and premature death among adolescents and young adults.2,3,4,5,6 Adolescence and young adulthood are critical periods of establishing healthy lifestyle habits to sustain activity patterns and prevent obesity.7
The 2008 Physical Activity Guidelines for Americans (the most recent guidelines for youth available) recommend that adolescents engage in a minimum of 60 minutes of moderate to vigorous physical activity per day.8 At age 20 years, the applicable adult guidelines for physical activity are considerably lower, with a recommended 150 minutes of moderate physical activity, 75 minutes of vigorous physical activity, or an equivalent combination of moderate and vigorous physical activity per week.8 Note that the recommended physical activity decreases from 420 minutes per week to 150 minutes per week in this adolescent-to-adult shift. Physical activity among youths in the United States has increased in the past decade, but only 27% of high school students adhere to physical activity guidelines.1,9 There is evidence of a decline in physical activity as adolescents grow older,9,10,11,12,13 and approximately one-third of adults do not meet their recommended physical activity guidelines despite the reduced duration.14,15
In previous studies, physical activity levels have varied by race/ethnicity, income, and sex. Black and Hispanic adolescents report less physical activity on average than do white adolescents and are more likely to report no physical activity on any day in the past week.1,9 Limited evidence suggests that low-income adolescents engage in less physical activity than higher-income peers; however, this association has not achieved significance when accounting for weight status.16,17,18 Similar income associations are observed among US adults.13,15,19 The most recent report on physical activity among youths by these key sociodemographic descriptors was in 2010, and it did not include young adults in the sample.10
The present study reports physical activity data from the National Health and Nutrition Examination Survey (NHANES) from 2007 through 2016. Our objectives were to describe the current patterns of physical activity and duration during adolescence and young adulthood and to identify the direction and magnitude of associations between physical activity and income, race/ethnicity, and sex.
Methods
This analysis used only deidentified secondary data and was deemed exempt from further review by the Duke University Institutional Review Board. No patient informed consent was required.
Data Source
When using the NHANES data, we chose 2007 through 2016 for inclusion because of the consistent physical activity questions in those years. The NHANES, which is described in detail elsewhere,20 is a multistage probability sample of the noninstitutionalized US population and allows estimates that represent the US population. It includes several components, including the mobile examinations and the in-home interviews analyzed in this study. Data analysis was performed from October 17, 2017, to April 27, 2018.
Population
We included individuals aged 12 to 29 years who responded to questions regarding physical activity. We excluded individuals who were underweight on the basis of their body mass index (calculated as weight in kilograms divided by height in meters squared) because of concerns regarding underlying illness that might affect activity levels.
Measures
Physical activity was self-reported. Adolescents aged 12 to 15 years were asked questions during the mobile examination (ie, not in the home) and without parent assistance. Participants 16 years or older responded for themselves during the in-home interview. We used 2 questions focused on moderate and vigorous recreational activity (individuals were first asked about work-related activities). The vigorous activity question was as follows:
“The next questions exclude the work and transport activities that you have already mentioned. Now I would like to ask you about sports, fitness, and recreational activities. In a typical week, do you do any vigorous-intensity sports, fitness, or recreational activities that cause large increases in breathing or heart rate, like running or basketball, for at least 10 minutes continuously?”
The moderate activity question was as follows:
“In a typical week, do you do any moderate-intensity sports, fitness, or recreational activities that cause a small increase in breathing or heart rate, such as brisk walking, bicycling, swimming, or volleyball, for at least 10 minutes continuously?”
After each question, individuals were asked about how many days per week they are active and then how many minutes they are active on a typical day. We categorized individuals who reported either any or no activity for either moderate or vigorous activity. We then characterized the mean daily activity as (number of days per week × average minutes on a typical day)/7. We did this for each of the moderate and vigorous activities and summed them for an overall mean daily activity level.
Race/ethnicity was self-reported using these classifications: non-Hispanic white, non-Hispanic black, Hispanic, or other race/ethnicity. Income was classified according to household income as a ratio of the federal poverty level, ranging from less than 100% of the federal poverty level to 500% of the federal poverty level or greater. Household income was reported by the household reference person—a person 18 years or older who owned or rented the dwelling unit. Age was categorized as 12 to 17 years, 18 to 24 years, and 25 to 29 years. We separated the young adult age category into 2 subgroups (aged 18-24 years and 25-29 years) to allow for a discussion of life factors (eg, college, first job) that may differ among these 3 age groups.
Statistical Analysis
We present all results stratified by age and sex. We collapsed the moderate and vigorous physical activity categories in the 2008 Physical Activity Guidelines for Americans8 for analysis. We conducted bivariate analyses examining race/ethnicity and income by physical activity. All comparisons were tested using adjusted Wald tests. Only the test of difference across all categories is provided here, with 95% CIs. Multivariable analyses were conducted using ordinary least squares regression (continuous outcomes) or generalized linear models with a log link (binary outcomes). For the generalized linear models, coefficients were exponentiated and presented as risk ratios. In these models, we controlled for age, weight status (ie, healthy weight; overweight; and obesity class I, II, or III),21 and education level (ie, high school diploma, less than high school, and college) for those 18 years or older. Consistent with the NHANES analytical guidelines, all multivariable analyses also controlled for the NHANES cycle. All analyses were adjusted for the complex survey design in the NHANES, including strata, primary sampling units, and probability weights, conducted using the svy commands in Stata, version 15 (StataCorp LLC). All binary comparisons used adjusted Wald tests to calculate 2-sided P values. For these and the P values from generalized linear models results, we considered 2-sided P < .05 to be statistically significant.
Results
The sample (N = 9472) included 4771 males (50.4%) and 4701 females (49.6%), with a weighted mean age (range) of 20.6 (12-19) years, who participated in the NHANES, responded to questions regarding physical activity, and were not underweight. Table 1 reports the descriptive characteristics of the population stratified by sex and by age and is representative of the US population of adolescents and young adults.
Table 1. Description of the Population and Weighted Proportions Overall and by Age .
| Variable | Male (n = 4771) | Female (n = 4701) | ||||||
|---|---|---|---|---|---|---|---|---|
| No. (%) | Weighted Proportion by Age, % | No. (%) | Weighted Proportion by Age, % | |||||
| 12-17 y | 18-24 y | 25-29 y | 12-17 y | 18-24 y | 25-29 y | |||
| Age, y | ||||||||
| 12-17 | 2123 (33.4) | NA | NA | NA | 2015 (33.8) | NA | NA | NA |
| 18-24 | 1679 (38.1) | NA | NA | NA | 1626 (36.5) | NA | NA | NA |
| 25-29 | 969 (28.5) | NA | NA | NA | 1060 (29.7) | NA | NA | NA |
| Race/ethnicity | ||||||||
| White | 1559 (58.0) | 56.9 | 57.8 | 59.5 | 1491 (58.4) | 59.0 | 56.0 | 60.7 |
| Black | 1144 (13.0) | 14.5 | 13.4 | 10.7 | 1123 (14.1) | 13.8 | 15.8 | 12.4 |
| Hispanic | 1458 (20.5) | 20.6 | 20.6 | 20.1 | 1504 (19.1) | 19.5 | 19.5 | 18.1 |
| Other | 610 (8.5) | 8.1 | 8.1 | 9.7 | 583 (8.4) | 7.8 | 8.7 | 8.8 |
| Income, FPL, % | ||||||||
| <100 | 1469 (23.0) | 20.6 | 29.0 | 17.7 | 1553 (25.2) | 20.3 | 34.1 | 19.9 |
| 100-199 | 1303 (22.8) | 22.5 | 24.9 | 20.5 | 1272 (24.0) | 23.9 | 25.2 | 22.7 |
| 200-299 | 670 (15.4) | 15.7 | 14.2 | 16.6 | 701 (16.7) | 17.8 | 15.1 | 17.3 |
| 300-399 | 473 (12.3) | 14.0 | 9.4 | 14.3 | 426 (11.5) | 12.4 | 9.7 | 12.8 |
| 400-499 | 321 (9.0) | 9.2 | 7.3 | 11.3 | 255 (7.0) | 7.9 | 5.4 | 8.1 |
| ≥500 | 535 (17.5) | 18.1 | 15.2 | 19.7 | 494 (15.5) | 17.6 | 10.6 | 19.2 |
| Weight status | ||||||||
| Healthy weight | 2492 (49.9) | 62.7 | 47.8 | 37.9 | 2367 (51.0) | 62.7 | 47.3 | 42.3 |
| Overweight | 1130 (25.9) | 16.2 | 30.1 | 31.7 | 1016 (21.6) | 17.2 | 23.0 | 24.8 |
| Obesity | ||||||||
| Class I | 668 (15.1) | 12.9 | 13.1 | 20.4 | 692 (13.7) | 13.2 | 14.2 | 13.7 |
| Class II | 283 (5.2) | 5.3 | 4.9 | 5.7 | 351 (7.5) | 4.4 | 8.5 | 9.9 |
| Class III | 198 (3.8) | 2.9 | 4.2 | 4.4 | 275 (6.2) | 2.4 | 7.1 | 9.3 |
| Education level | ||||||||
| Less than HS | 648 (18.5) | NA | 22.2 | 13.7 | 546 (15.4) | NA | 18.4 | 11.8 |
| HS diploma | 740 (26.9) | NA | 30.0 | 22.9 | 655 (22.5) | NA | 26.2 | 17.9 |
| College | 1260 (54.5) | NA | 47.8 | 63.5 | 1485 (62.1) | NA | 55.5 | 70.3 |
Abbreviations: FPL, federal poverty level; HS, high school; NA, not applicable.
In unadjusted analyses (Table 2), males reported moderate or vigorous physical activity more often than did females in all age and race/ethnicity categories. White adolescent males were most likely (89.3%; 95% CI, 86.5%-92.1%) and black females aged 18 to 24 years were least likely (45%; 95% CI, 39.0%-51.0%) to report any physical activity. The prevalence of any moderate or vigorous physical activity decreased sharply after adolescence for both males and females. Minority race/ethnicity and low income were associated with low moderate or vigorous physical activity in most groups except among adolescent males (among whom race differences were not significant) and among 25- to 29-year-old males (among whom income differences were not significant).
Table 2. Percentage of Individuals Reporting Any Moderate or Vigorous Physical Activity by Age, Race/Ethnicity, and Income.
| Variable | Age 12-17 y | Age 18-24 y | Age 25-29 y | |||
|---|---|---|---|---|---|---|
| Individuals, % (95% CI) | P Value | Individuals, % (95% CI) | P Value | Individuals, % (95% CI) | P Value | |
| Malea | ||||||
| Overall | 87.9 (86.0-89.9) | NA | 72.6 (69.4-75.9) | 70.7 (67.1-74.2) | NA | |
| Race/ethnicity | ||||||
| White | 89.3 (86.5-92.1) | .19 | 74.3 (69.5-79.1) | <.001 | 73.0 (68.2-77.7) | .02 |
| Black | 87.8 (85.0-90.7) | 76.4 (72.1-80.7) | 66.4 (59.4-73.4) | |||
| Hispanic | 86.0 (83.7-88.3) | 62.1 (56.7-67.4) | 63.7 (57.7-69.7) | |||
| Other | 83.6 (76.2-91.1) | 81.5 (75.7-87.3) | 75.9 (66.0-85.8) | |||
| Income, FPL, % | ||||||
| <100 | 83.2 (79.2-87.2) | 67.1 (59.0-75.2) | .22 | 59.2 (51.8-66.5) | .002 | |
| 100-199 | 85.0 (81.5-88.5) | 72.7 (67.4-78.0) | 63.3 (55.7-70.9) | |||
| 200-299 | 90.2 (85.5-94.9) | 76.0 (69.3-82.7) | 77.1 (69.6-84.5) | |||
| 300-399 | 90.7 (85.8-95.7) | 78.1 (69.8-86.3) | 80.4 (72.4-88.3) | |||
| 400-499 | 87.6 (81.3-94.0) | 68.7 (56.9-80.4) | 69.9 (58.1-81.7) | |||
| ≥500 | 93.1 (89.1-97.1) | 78.5 (71.3-85.8) | 76.7 (68.4-84.9) | |||
| Femaleb | ||||||
| Overall | 78.1 (75.8-80.5) | NA | 61.5 (58.2-64.9) | NA | 61.2 (57.2-65.1) | NA |
| Race/ethnicity | ||||||
| White | 82.4 (79.2-85.7) | <.001 | 70.8 (66.1-75.6) | <.001 | 66.6 (61.3-71.8) | <.001 |
| Black | 69.0 (64.2-73.8) | 45.0 (39.0-51.0) | 45.3 (38.7-52.0) | |||
| Hispanic | 70.0 (65.9-74.2) | 51.7 (46.7-56.7) | 55.1 (48.8-61.4) | |||
| Other | 82.2 (76.7-87.7) | 53.7 (43.3-64.1) | 58.5 (47.8-69.2) | |||
| Income, FPL, % | ||||||
| <100 | 68.5 (63.9-73.0) | .001 | 54.8 (48.5-61.0) | <.001 | 44.7 (37.5-51.9) | <.001 |
| 100-199 | 76.0 (71.8-80.2) | 57.7 (50.7-64.6) | 51.6 (44.4-58.9) | |||
| 200-299 | 78.3 (73.0-83.6) | 62.7 (54.8-70.6) | 70.2 (61.9-78.5) | |||
| 300-399 | 80.4 (73.8-87.0) | 62.1 (52.3-72.0) | 58.9 (47.3-70.6) | |||
| 400-499 | 81.0 (71.4-90.6) | 75.2 (63.5-87.0) | 68.8 (56.9-80.8) | |||
| ≥500 | 89.2 (83.2-95.3) | 83.3 (75.8-90.8) | 79.4 (72.5-86.4) | |||
Abbreviations: FPL, federal poverty level; NA, not applicable.
For age 12-17 years, n = 2123; age 18-24 years, n = 1679; and age 25-29 years, n = 969.
For age 12-17 years, n = 2015; age 18-24 years, n = 1626; and age 25-29 years, n = 1060.
Physically active males reported more daily minutes of activity (Table 3) than did females in all age categories. Among those who were active, black males aged 18 to 24 years reported the longest duration of activity (77.9 minutes per day; 95% CI, 66.4-89.3 minutes per day), and black females aged 25 to 29 years reported the shortest duration of activity (33.2 minutes per day; 95% CI, 28.1-38.2 minutes per day). The duration of moderate or vigorous physical activity decreased as the age category increased for both males and females. Overall, there were limited differences in the duration of physical activity by race/ethnicity and income. Lower income and minority race/ethnicity were associated with lower activity among 12- to 17-year-old females. The association of income with activity duration for 18- to 24-year-old males was statistically significant but had an inconsistent pattern.
Table 3. Mean Time of Moderate or Vigorous Physical Activity Among Individuals Reporting Any Activity.
| Variable | Age 12-17 y | Age 18-24 y | Age 25-29 y | |||
|---|---|---|---|---|---|---|
| Mean Time, min (95% CI) | P Value | Mean Time, min (95% CI) | P Value | Mean Time, min (95% CI) | P Value | |
| Malea | ||||||
| Overall | 71.1 (67.3-74.9) | NA | 64.3 (59.2-69.4) | NA | 50.3 (46.1-54.4) | NA |
| Race/ethnicity | ||||||
| White | 71.3 (65.8-76.7) | .39 | 60.6 (53.2-68.0) | .06 | 49.3 (43.5-55.2) | .05 |
| Black | 76.0 (69.0-83.0) | 77.9 (66.4-89.3) | 63.7 (52.0-75.3) | |||
| Hispanic | 68.1 (61.9-74.4) | 64.3 (52.5-76.1) | 50.8 (43.0-58.6) | |||
| Other | 68.4 (61.0-75.8) | 67.2 (56.6-77.9) | 42.0 (32.1-51.8) | |||
| Income, FPL, % | ||||||
| <100 | 67.2 (61.0-73.4) | .72 | 81.0 (71.0-91.0) | .001 | 56.2 (46.0-66.4) | .76 |
| 100-199 | 69.8 (63.6-76.0) | 56.6 (50.5-62.7) | 49.8 (40.6-59.0) | |||
| 200-299 | 75.6 (62.8-88.4) | 58.0 (44.9-71.0) | 47.0 (36.5-57.4) | |||
| 300-399 | 69.5 (61.5-77.5) | 64.8 (52.1-77.5) | 51.9 (41.6-62.3) | |||
| 400-499 | 73.2 (59.1-87.3) | 69.6 (54.1-85.0) | 44.9 (33.9-55.9) | |||
| ≥500 | 72.9 (65.3-80.6) | 52.2 (42.9-61.4) | 50.9 (41.4-60.4) | |||
| Femaleb | ||||||
| Overall | 56.0 (52.2-59.8) | NA | 44.9 (40.4-49.4) | NA | 39.2 (34.6-43.8) | NA |
| Race/ethnicity | ||||||
| White | 60.3 (54.9-65.7) | <.001 | 44.7 (39.6-49.8) | .24 | 39.1 (33.0-45.1) | .16 |
| Black | 54.4 (47.9-60.9) | 52.4 (40.3-64.5) | 33.2 (28.1-38.2) | |||
| Hispanic | 47.4 (43.0-51.8) | 42.6 (35.9-49.3) | 44.6 (34.0-55.2) | |||
| Other | 43.7 (37.7-49.8) | 40.2 (29.2-51.2) | 36.6 (25.7-47.4) | |||
| Income, FPL, % | ||||||
| <100 | 46.3 (40.0-52.5) | .002 | 51.2 (39.9-62.5) | .25 | 42.4 (29.1-55.6) | .96 |
| 100-199 | 50.9 (45.2-56.5) | 39.0 (33.3-44.6) | 37.2 (28.8-45.5) | |||
| 200-299 | 62.9 (52.3-73.4) | 45.2 (34.0-56.4) | 36.8 (26.9-46.7) | |||
| 300-399 | 61.5 (48.9-74.1) | 43.2 (33.8-52.7) | 39.2 (28.8-49.6) | |||
| 400-499 | 50.5 (39.6-61.4) | 33.9 (23.0-44.8) | 41.9 (30.0-53.7) | |||
| ≥500 | 63.2 (55.8-70.5) | 47.2 (34.8-59.7) | 39.9 (31.8-48.0) | |||
Abbreviations: FPL, federal poverty level; NA, not applicable.
For age 12-17 years, n = 1832; age 18-24 years, n = 1208; and age 25-29 years, n = 657.
For age 12-17 years, n = 1486; age 18-24 years, n = 902; and age 25-29 years, n = 612.
Adjusted analyses (Table 4), controlling for weight status, yielded results that were similar to those of bivariate analyses. No significant differences by race/ethnicity among males of any age were noted. Higher income was associated with greater likelihood of any activity in adolescents, whereas higher education level was associated with physical activity in both categories of young adults (aged 18-29 years). Younger age was also associated with greater likelihood of activity among males. In contrast, among females of all ages, minority race/ethnicity was significantly associated with lower likelihood and higher income was associated with greater likelihood of any moderate or vigorous physical activity.
Table 4. Generalized Linear Model of Likelihood of Reporting Any Moderate or Vigorous Physical Activitya.
| Variable | Age 12-17 y | Age 18-24 y | Age 25-29 y | |||
|---|---|---|---|---|---|---|
| RR (95% CI) | P Value | RR (95% CI) | P Value | RR (95% CI) | P Value | |
| Maleb | ||||||
| Race/ethnicity | ||||||
| White | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Black | 1.02 (0.97-1.07) | .46 | 1.07 (0.98-1.17) | .12 | 1.00 (0.88-1.13) | .94 |
| Hispanic | 1.00 (0.95-1.05) | .99 | 0.92 (0.82-1.02) | .11 | 1.02 (0.90-1.15) | .79 |
| Other | 0.95 (0.87-1.04) | .25 | 1.10 (1.00-1.20) | .047 | 1.02 (0.89-1.17) | .75 |
| Income | 1.02 (1.01-1.03) | .001 | 1.02 (0.99-1.04) | .14 | 1.02 (0.99-1.05) | .19 |
| Age | 0.99 (0.98-1.00) | .04 | 0.96 (0.94-0.98) | <.001 | 0.97 (0.93-1.00) | .06 |
| Education level | ||||||
| HS diploma | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Less than HS | NA | NA | 0.96 (0.85-1.07) | .42 | 0.84 (0.67-1.05) | .12 |
| College | NA | NA | 1.27 (1.17-1.38) | <.001 | 1.24 (1.08-1.43) | .003 |
| Weight status | ||||||
| Healthy weight | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Overweight | 1.00 (0.94-1.06) | .97 | 1.01 (0.94-1.08) | .79 | 0.97 (0.87-1.09) | .64 |
| Obesity | ||||||
| Class I | 0.96 (0.90-1.03) | .27 | 0.91 (0.80-1.04) | .17 | 0.82 (0.69-0.97) | .02 |
| Class II | 0.95 (0.88-1.04) | .27 | 0.87 (0.72-1.04) | .13 | 1.00 (0.85-1.18) | .98 |
| Class III | 0.97 (0.86-1.10) | .61 | 0.91 (0.75-1.09) | .29 | 0.88 (0.66-1.17) | .37 |
| Femalec | ||||||
| Race/ethnicity | ||||||
| White | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Black | 0.87 (0.80-0.95) | .002 | 0.68 (0.60-0.77) | <.001 | 0.77 (0.66-0.89) | .001 |
| Hispanic | 0.89 (0.83-0.95) | .001 | 0.81 (0.73-0.90) | <.001 | 0.97 (0.86-1.09) | .58 |
| Other | 1.00 (0.93-1.08) | .98 | 0.75 (0.61-0.91) | .005 | 0.85 (0.71-1.03) | .09 |
| Income | 1.04 (1.02-1.06) | .001 | 1.05 (1.02-1.08) | <.001 | 1.06 (1.02-1.09) | .001 |
| Age | 0.97 (0.96-0.99) | .003 | 0.99 (0.96-1.01) | .29 | 1.01 (0.98-1.04) | .61 |
| Education level | ||||||
| HS diploma | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Less than HS | NA | NA | 0.84 (0.72-0.97) | .02 | 0.89 (0.63-1.27) | .53 |
| College | NA | NA | 1.17 (1.05-1.30) | .005 | 1.60 (1.30-1.97) | <.001 |
| Weight status | ||||||
| Healthy weight | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Overweight | 1.01 (0.94-1.09) | .73 | 0.98 (0.88-1.10) | .77 | 0.97 (0.85-1.10) | .59 |
| Obesity | ||||||
| Class I | 0.99 (0.91-1.09) | .91 | 0.88 (0.76-1.01) | .06 | 1.07 (0.92-1.24) | .38 |
| Class II | 0.96 (0.85-1.09) | .52 | 0.91 (0.75-1.10) | .32 | 0.94 (0.77-1.14) | .49 |
| Class III | 0.89 (0.61-1.32) | .57 | 0.90 (0.72-1.13) | .36 | 0.99 (0.81-1.21) | .93 |
Abbreviations: HS, high school; NA, not applicable; RR, risk ratio.
Also controlling for the National Health and Nutrition Examination Survey cycle.
For age 12-17 years, n = 2123; age 18-24 years, n = 1679; and age 25-29 years, n = 969.
For age 12-17 years, n = 2105; age 18-24 years, n = 1626; and age 25-29 years, n = 1060.
Additional adjusted analyses (Table 5) revealed the duration of activity in mean daily minutes among those reporting any activity. Black males aged 18 to 29 years reported longer activity duration. Other findings showed no other consistent patterns among males. Among adolescent females, Hispanic ethnicity was associated with shorter activity duration compared with their white peers. No other single race/ethnicity differences were noted. Income was negatively associated with activity duration among 18- to 24-year-old males, but no association was noted among females.
Table 5. Ordinary Least Squares Regression of Time of Activity on a Typical Day Among Individuals With Any Activitya.
| Variable | Age 12-17 y | Age 18-24 y | Age 25-29 y | |||
|---|---|---|---|---|---|---|
| β (95% CI) | P Value | β (95% CI) | P Value | β (95% CI) | P Value | |
| Maleb | ||||||
| Race/ethnicity | ||||||
| White | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Black | 6.3 (−1.8 to 14.4) | .13 | 15.6 (3.7 to 27.5) | .01 | 14.4 (2.6 to 26.2) | .02 |
| Hispanic | −0.6 (−8.9 to 7.7) | .88 | 0.2 (−15.0 to 15.4) | .98 | 3.1 (−7.2 to 13.3) | .55 |
| Other | −1.3 (−10.6 to 7.9) | .77 | 6.0 (−7.2 to 19.2) | .37 | −9.6 (−20.6 to 1.4) | .09 |
| Income | 1.1 (−0.7 to 3.0) | .22 | −3.3 (−5.7 to −0.9) | .008 | −0.4 (−2.8 to 2.0) | .72 |
| Age | 4.1 (2.4 to 5.8) | <.001 | −4.6 (−6.8 to −2.5) | <.001 | 0.6 (−2.1 to 3.3) | .66 |
| Education level | ||||||
| HS diploma | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Less than HS | NA | NA | 3.2 (−7.7 to 14.1) | .56 | −2.7 (−16.2 to 10.9) | .69 |
| College | NA | NA | 6.6 (−2.6 to 15.8) | .16 | 2.5 (−10.1 to 15.2) | .69 |
| Weight status | ||||||
| Healthy weight | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Overweight | 13.1 (1.7 to 24.4) | .03 | 6.2 (−3.1 to 15.5) | .19 | −4.3 (−14.6 to 6.0) | .41 |
| Obesity | ||||||
| Class I | −5.0 (−12.3 to 2.3) | .18 | −5.1 (−17.4 to 7.2) | .41 | −9.8 (−21.6 to 2.0) | .10 |
| Class II | −6.0 (−21.8 to 9.7) | .45 | −9.3 (−24.4 to 5.8) | .23 | −1.8 (−19.8 to 16.3) | .85 |
| Class III | −1.2 (−19.9 to 17.6) | .89 | −16.1 (−36.5 to 4.3) | .12 | −1.5 (−16.5 to 13.4) | .84 |
| Femalec | ||||||
| Race | ||||||
| White | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Black | −1.3 (−9.9 to 7.4) | .77 | 6.8 (−4.1 to 17.6) | .22 | −4.0 (−12.9 to 4.9) | .38 |
| Hispanic | −8.5 (−15.7 to −1.3) | .02 | −3.7 (−10.5 to 3.1) | .28 | 4.8 (−10.5 to 20.1) | .54 |
| Other | −14.7 (−21.7 to −7.7) | <.001 | −5.9 (−17.6 to 5.8) | .32 | −2.9 (−15.1 to 9.3) | .64 |
| Income | 1.7 (0.0 to 3.4) | .05 | −0.9 (−3.4 to 1.7) | .50 | 0.6 (−1.8 to 3.1) | .60 |
| Age | 3.4 (1.4 to 5.4) | .001 | −1.7 (−3.9 to 0.4) | .11 | −1.1 (−3.6 to 1.4) | .39 |
| Education level | ||||||
| HS diploma | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Less than HS | NA | NA | 3.2 (−7.5 to 13.9) | .55 | 7.0 (−20.9 to 34.8) | .62 |
| College | NA | NA | 0.5 (−9.5 to 10.4) | .93 | −4.3 (−17.6 to 9.0) | .53 |
| Weight status | ||||||
| Healthy weight | 1 [Reference] | NA | 1 [Reference] | NA | 1 [Reference] | NA |
| Overweight | −5.6 (−14.0 to 2.8) | .19 | −6.0 (−15.9 to 4.0) | .23 | −7.7 (−18.8 to 3.4) | .17 |
| Obesity | ||||||
| Class I | −7.0 (−17.4 to 3.5) | .19 | −5.1 (−14.4 to 4.2) | .28 | −12.6 (−22.1 to −3.1) | .01 |
| Class II | −0.8 (−19.8 to 18.2) | .93 | 2.7 (−17.4 to 22.7) | .79 | −1.6 (−22.0 to 18.8) | .88 |
| Class III | −23.0 (−34.8 to −11.2) | <.001 | −14.0 (−27.4 to −0.6) | .04 | −9.9 (−24.0 to 4.3) | .17 |
Abbreviations: HS, high school; NA, not applicable.
Also controlling for the National Health and Nutrition Examination Survey cycle.
For age 12-17 years, n = 1832; age 18-24 years, n = 1208; and age 25-29 years, n = 657.
For age 12-17 years, n = 1486; age 18-24 years, n = 902; and age 25-29 years, n = 612.
The 2008 Physical Activity Guidelines for Americans8 recommend 60 minutes of moderate or vigorous physical activity per day for youth and 150 minutes of moderate or vigorous physical activity per week for adults. The proportion of individuals who met the adult guidelines ranged from 73.5% of adolescent boys of all ages to only 36.7% of 25- to 29-year-old females. For both sexes, minority race/ethnicity and lower income were associated with lower percentage of individuals meeting guidelines.
Discussion
Most US adolescents and young adults who participated in the NHANES from 2007 through 2016 reported at least some physical activity, which is similar to the findings in other studies of self-reported activity by these age groups.22 However, although most reported engaging in some physical activity, they were not meeting the lower physical activity recommendations for adults. In addition, significant disparities by sex, race/ethnicity, and income were noted in the proportions of individuals who were meeting the national physical activity guidelines. For example, most female adolescents and young adults, particularly those from minority groups, were not meeting the recommendations.
The data show that, at least among 18- to 25-year-old males, those who were active at all tended to be very active, with the mean number of minutes reported at or above the current recommendation for adults (ie, 150 minutes of moderate or vigorous physical activity per week).8 This activity was not true among 25- to 29-year-old males or among females of any age, whose mean activity time was below national guidelines. These self-reported activity estimates were higher than those from national studies that used objectively measured physical activity data.23 For example, 1 analysis of accelerometer data found that only 8% to 9% of adolescents met current national physical activity guidelines (ie, 60 minutes per day for teenagers),13 whereas another study that used an accelerometer found that the mean of moderate or vigorous physical activity was 36 minutes per day for a young adult.24 The discrepancy between self-reported and objectively measured physical activity among various groups of adolescents and young adults represents a key area for future study and has substantial implications for understanding youth population health.25
Consistent with other data, we found that the proportion of adolescents and young adults who were physically active decreased from adolescence to young adulthood.13,26 The observed decrease in activity was steeper from age 12 to 17 years to age 18 to 24 years than to age 25 to 29 years, with age more strongly associated among males than among females. The reasons for the reduced physical activity may include increased demands on adolescent and young adult time (eg, more school work, employment) and fewer opportunities for required daily physical activity in high school and college compared with elementary and middle school.27 Life transitions during adolescence and young adulthood, such as matriculating into higher education, have also been identified as high-risk periods for decreased physical activity, although living on a college campus with nearby exercise facilities may curtail the rate of physical activity decline in young adults.23,28,29 In addition, adolescents and young adults may report new barriers to activity, such as concerns about appearance and image when exercising.30
Females were significantly less likely to start or sustain physical activity than were males. This association persisted across all race/ethnicity and income groups and as participants aged from adolescence to adulthood, a finding similar to that in other studies.10,13,23 In longitudinal studies of adolescent physical activity, the rate of decline of activity has been found to be similar between young men and women.23,31 One study identified that adolescent females decreased below the recommended 60 minutes of moderate or vigorous physical activity per day 1 year earlier than their male counterparts.32 Additional research is needed to fully understand the facilitators and barriers to exercise in females to guide activity promotion in this age group.
Previous studies have demonstrated the association between poverty and physical inactivity across the age span.17,33 Those with lower income are less likely to have gym memberships, and the built environment is also likely a correlate of these findings. Physical activity facilities, sidewalks, connected streets, bike trails, and perceived safe outdoor spaces are more common in neighborhoods where higher-income families live.17 Similar to previous studies, our study found that low-income adolescents in all groups were less likely to be active and reported less overall activity than did their higher-income peers. This association was also true among young adult females.
However, this association was not true among low-income young adult males, who reported being physically active as often as their higher-income peers and engaged in the highest number of daily minutes of activity (77.9 minutes per day).
This finding may be explained, in part, by the difficulty in defining income among young adults. College students who remain as dependents on their parents’ income tax returns and who do not work, work part-time, or work for low wages may have access to high-quality physical activity but report income in the poverty range. Of note, when controlling for poverty, weight status did not consistently have a significant association with reported activity initiation or duration.
Limitations
This study has several limitations. First, the data are cross-sectional and may describe only association, not causation. Second, we cannot adjust for potential colinearity between income and race/ethnicity. Third, the NHANES physical activity data are self-reported and may overstate or understate true physical activity. Last, the NHANES data set does not provide a sufficient level of detail to enable the understanding of the associations among poverty, employment, and physical activity indicators.
Conclusions
Our study found that among adolescents and young adults in the United States from 2007 to 2016, substantial disparities existed in the likelihood to engage in the recommended amount of physical activity. Females, racial/ethnic minorities, and those living in poverty remained most likely to be inactive. These data highlight opportunities for targeted physical activity programming and policy efforts to reduce the risk for chronic diseases and improve overall health throughout the lifespan.
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