Several different national surveys track physical activity in many age groups and at several levels for the United States national public health objectives. Understanding and comparing each of these surveys requires background information about physical activity assessment.
Domain: Physical activities are often classified into domains that reflect the purpose of the activity. A common four-category classification is
Domestic (housework, yard work, physically-active child care, chores)
Transportation (walking or bicycling for the purposes of going somewhere)
Leisure-time (discretionary or recreational time for hobbies, sports, and exercise).
Existing physical activity assessment questionnaires differ as to which domains are measured and few assess multiple domains. Historically, strategies to promote physical activity have emphasized increases in leisure-time physical activity and consequently, many questionnaires focus on only this domain. More recently, strategies to promote physical activity have emphasized the health benefits of all kinds of physical activity. Consequently, more physical activity assessment questionnaires are being designed to measure more than one, if not all four, domains of activity.
Physical Activity Recommendations: Adults attain recommended levels of physical activity by meeting either a moderate-intensity physical activity recommendation, a vigorous intensity physical activity recommendation, or both. Historically, the health benefits of vigorous physical activity were recognized and promoted first, leading to the recommendation in the mid-1980s that adults should be physically active three or more days per week for 20 or more minutes each occasion. The public health benefits of moderate physical activity first came prominent in the mid 1990s with the publication of the physical activity and public health recommendations from the CDC and the American College of Sports Medicine in 1995 and the U.S. Surgeon General's Report on Physical Activity and Health in 1996. Both reports indicate that adults can be classified as meeting the moderate physical activity recommendation if they participate in moderate activity for at least 30 minutes per day on most days of the week.
Physical Activity Assessment: Physical activity can be assessed in three general ways: questionnaire, observation and direct measurement, or diary. Physical activity questionnaires measure activities by asking a respondent to recall and report recent or usual participation in activities or in sedentary behaviors, usually over a set period of time. Methods of observation and direct measurement include electronic devices (e.g., pedometers, motion detectors, heart rate monitors) designed to record an individual's movements or physiological responses to movement and direct observation (e.g., watching and recording playground use during school recess). Diary assessment of physical activity involves an individual recording all activity for a defined period of time (usually a week or a day). Once data from each of these assessment methods are gathered, estimates or indicators of energy expenditure or indices of physical activity are obtained.
United States national health surveys that assess and track physical activity in individuals typically include short sets of questions as just one of many sets of health-related questions. No national surveys currently use a longer, more detailed physical activity questionnaire, such as those typically used in research studies. Further, no national physical activity or health surveys have yet employed observational methods of physical activity assessment, although such methods are being pilot tested. In addition to cardiovascular-related physical activities, some national health surveys also query muscle strengthening and flexibility activities. Travel and transportation surveys, designed to track individual transportation and movement habits, rely on diaries for information on daily walking and bicycling habits.
Physical Activity Questionnaire Scoring: Once assessment is completed, responses must be summarized for reporting and research purposes. Methods to create summary scores from physical activity questionnaires can result in either continuous scores (such as total kilocalories expended in physical activity over a given time period) or categorical scores (e.g., low, medium, or high levels of physical activity). A frequently used scoring algorithm in U.S. national surveys relies on an external standard (a pre-established physical activity recommendation or recommendations such as those established by the CDC and ACSM). Individual survey respondents are classified into three basic levels: sufficiently active (meeting either physical activity recommendation); insufficiently active (some reported physical activity but not enough to meet existing recommendations); and inactive (no reported physical activity). All public health indicators used for tracking progress toward meeting the Healthy People 2010 objectives, including measures of physical activity, are categorical summary measures (meets/does not meet the objective).
In 2002, five separate national surveys provide information on physical activity levels of the U.S. population and one survey contains relevant data on policies for physical activity promotion. Each survey uses a different set of questions because the purposes of each survey differ. Compiling and evaluating data from all sources allows a more complete picture of the physical activity levels and trends among Americans than can be obtained from evaluating results from a single survey alone.
Results from these surveys paint a similar picture — most Americans are not physically active at recommended levels. Each survey however shows slightly different results and this, taken collectively, has the potential for confusion. Each of the surveys are detailed below. To reduce confusion when citing results, it is recommended that the name of the survey, the year of the results and the domains of physical activity that were assessed be detailed.
Behavioral Risk Factor Surveillance System (BRFSS): Begun in 1984, BRFSS is a telephone survey that provides ongoing statistics on major behavioral risk factors among American adults, with an emphasis on state-level surveillance and comparisons across states. BRFSS collects data from approximately 210,000 people in 50 states, the District of Columbia, Puerto Rico, the U.S. Virgin Islands and Guam. The main purpose of the physical activity portion of the BRFSS is to track the proportion of respondents who meet or exceed the CDC recommendations for sufficient physical activity. Historically, there have been two sets of physical activity questions in BRFSS. Between 1984 and 2000, the questions focused on measurement of only one domain of physical activity — specifically leisure-time — using open-ended questions. Beginning in 2001, a new set of BRFSS questions was implemented to capture data on three key physical activity domains: leisure-time, domestic, and transportation. Occupational physical activity is also queried in the BRFSS survey but, because of technical reasons, does not contribute to a physical activity summary score. The main results from the survey are the proportions of American adults that are sufficiently active, insufficiently active, and inactive.
National Health Interview Survey (NHIS): NHIS provides statistics about the health of Americans with a major emphasis on national-level estimates to track progress toward national health objectives (currently Healthy People 2010). NHIS is a large CDC survey (approximately 40,000 households and 100,000 respondents) that relies on personal interviews for data collection. The main purpose of the physical activity questions on NHIS is to provide information relative to progress to Healthy People 2010 objectives 22-1 through 22-5. Between 1985 and 1996, NHIS periodically assessed physical activity using closed-ended activity questions and in 1997, a revised set of questions, again using a closed-ended format, was implemented. Both versions of NHIS physical activity questions query only the leisure-time physical activity domain. Notably, the current NHIS physical activity questions include an assessment of light-to-moderate intensity physical activities, which is different from other questionnaires that focus only on moderate and vigorous intensity activities.
National Health and Nutrition Examination Survey (NHANES): NHANES provides statistics about the health of Americans through a combination of personal interview and direct physical examination. It is substantially smaller (approximately 10,000 persons in 1999–2000) than either BRFSS or NHIS, but provides much more specialized information than can be collected in the other surveys. Though NHANES collects information on children and adults on many aspects of health, it has traditionally emphasized relationships between dietary intake, nutrition, and health outcomes. The current physical activity questions in NHANES were first used in 1999. For adults, three domains (leisure-time, domestic, and transport) are measured by separate questions in closed-ended format in the survey. For children, leisure-time physical activity is assessed. Sedentary behaviors are also assessed for both children and adults. Of note, the NHANES physical examination currently includes a cardiovascular fitness evaluation (submaximal treadmill test) and a musculoskeletal fitness test (strength testing). These are the only national data available on physical fitness measures in adults.
Youth Risk Behavior Survey (YRBS): YRBS is a national school-based survey of high-school students (grades 9–12). YRBS is a large CDC survey with more than 15,000 respondents. The purpose of the survey is to help determine national prevalence and age-at-initiation of key health risk behaviors. Physical activity data from the YRBS are used to monitor progress toward Healthy People 2010 objectives 22-6 through 22-11. Current YRBS physical activity questions use a closed-ended format and measure factors related to physical activity participation (including moderate-intensity, vigorous-intensity, and muscle strengthening and flexibility), physical education class attendance and availability, and television viewing habits. Three domains of activity (leisure-time, transport, and domestic) are measured in the YRBS. Occupational activity is not thought to be a major source of physical activity in this age group.
National Household Travel Survey (NHTS): NHTS is also formerly known as the Nationwide Personal Transportation Survey and the American Travel Survey. It is a U.S. Department of Transportation survey of travel modes, commuting habits, and long-distance trips. NHTS provides national estimates of daily trip frequency, trip distance, means of transportation, and trip time for persons five years of age and older. The unit of analysis in this survey is the trip rather than the individual respondent. Obviously, NHTS provides information solely in the transport physical activity domain. This survey is periodic (approximately every five years), with survey data available for 1969, 1977, 1983, 1990, 1995, and 2001-2002. Estimates from this survey are used to track progress toward Healthy People 2010 objectives 22-14 and 22-15 regarding walking and bicycling habits in general and to school in particular. Of note, NHTS has dozens of regional counterparts that are conducted by regional transportation authorities, a federal requirement for those regions to receive federal highway funds. Unlike BRFSS (with its state-based estimates), these regional surveys are not coordinated by a federal agency to ensure consistent implementation protocols and quality control. Comparisons of results among regions and with national estimates are therefore not advised.
U.S. National Surveys for Physical Activity — Policy Surveys
School Health Policies and Programs Study (SHPPS): SHPPS is a periodic national mail survey designed to assess school health policies and programs at the state, district, and classroom level in elementary, middle, and high schools. State education agencies, district level representatives and designated school staff classroom faculty provide the respondent base for this survey. Physical activity questions on the SHPPS are designed to assess physical education curriculum offerings, availability of recess and intramural sports programs as well as state and district curricular requirements for physical education. Physical activity data from SHPPS are used to measure progress toward Healthy People 2010 objectives 22-8 and 22-12.
|Survey||Mode of Data Collection||Target Population||Frequency of data collection||Physical Activity Domain (s)|
|BRFSS||Telephone interview||Adults (> 18 years of age) in U.S. states, territories, and the District of Columbia
~210,00 respondents in 2001
|Ongoing - annual||Leisure-time Domestic Transportation|
|NHIS||Personal Interview||Adults and children in U.S. states and the District of Columbia
~100,000 respondents in 2000
|Ongoing - annual||Leisure-time|
|NHANES||Interview/ Examination||Children and adults in U.S.
~10,000 respondents in 1999-2000
|Ongoing - annual||Leisure-time Domestic Transportation|
|YRBS||School-based survey||high-school students in U.S. >15,000 respondents in 2000||Every two years||Leisure-time Domestic Transportation|
|NHTS||Household survey||U.S. households
> 25,000 respondents
|Every 5 – 7 years||Transportation|
|SHPPS||Mail survey||U.S. school districts, state education organizations, and classrooms||Periodic||Physical activity policies and curricula|
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