Assessment of Physical Activity
As with dietary assessment (see Chapter 5), there are many challenges in the valid and reliable assessment of physical activity in individuals. This is especially true in the populations served by WIC to whom the Dietary Guidelines would apply—children ages 2 to 5 years and pregnant or postpartum women. This chapter describes the challenges and summarizes what is currently known about the patterns of physical activity in these populations and the methods available for assessing their physical activity. It makes recommendations about the role of physical activity assessment in the WIC program and about future research needs in this area.
CHALLENGES IN ASSESSING PHYSICAL ACTIVITY
Physical Activity in Preschoolers
The Dietary Guidelines and thus the physical activity guideline contained within them, apply only to children 2 years of age and older. There are no published guidelines for activity in children 12 to 23 months of age. While the Dietary Guidelines recommend 60 minutes of “moderate” daily physical activity for 2- to 5-year-old children, there is not a definition provided of what constitutes moderate activity for children.
Direct observation of activity is the best criterion measure for any instrument to assess physical activity in children 2 to 5 years of age. Such observations reveal that as children play, they have short and intermittent, rather than continuous, bouts of activity with frequent rest periods (Bailey et al., 1995).
These bouts rarely last more than 10 minutes. This difference in activity patterns between adults and children is also seen in many animal species. The difference is thought to result from differing needs of the developing brain to provide itself, through activity, with a pattern of stimulation from the environment that subserves its own optimal development (Rowland, 1998). Compared to adults, children have more spontaneous activity, a shorter attention span, less interest in sustaining a single activity, more interest in trying new activities, and the need for more frequent rest periods. Therefore, assessing physical activity in young children, as compared to adults, requires child-specific definitions of what constitutes moderate physical activity. Furthermore, children 2 to 5 years of age are not cognitively capable of recalling their own physical activity in terms of activity type, frequency, duration, or intensity. This is analogous to the inability of children this age to recall sufficient details of their own dietary intake for a valid assessment of diet. Thus, as with dietary assessment, parent (or other adult caretaker) reporting is required, which poses other challenges to conducting valid assessment of physical activity.
Physical Activity in Women
Much of the physical activity of women of child-bearing age, especially those already raising young children, occurs in the context of walking for transportation, the workplace, childcare, and household tasks, rather than in leisure-time physical activity (Ainsworth, 2000a, 2000b; Eyler et al., 1998; Masse et al., 1998). Thus, many self-report measures developed for adults (and many with a focus on men) do not contain the necessary questions about nonleisure-time physical activity that would allow for a full accounting of the activity of many women. This appears especially true for ethnic minorities and women with young children, such as those receiving WIC services, who are reported in many physical activity surveys to have very low levels of leisure-time physical activity and who appear quite sedentary. These women, however, may be involved in moderate physical activity while doing things such as household chores, walking at work, taking care of children or other family members, shopping, and gardening (Ainsworth et al., 1999).
Any physical activity assessment tool aimed at accurately classifying physical activity levels in women enrolled in the WIC program would need to include a variety of activities performed by these women in their everyday lives. For example, including household activities in physical activity questionnaires has been shown to dramatically alter the classification of women’s activity levels in relationship to men (Ainsworth et al., 1993b). However, capturing women’s moderate-intensity physical activity with several brief questions may be an insurmountable challenge for some of the same reasons that it is with preschool children. For women and young children, many of these moderate-intensity activities occur outside of structured settings, in short bouts, and
admixed with other activities of lesser intensity (Masse et al., 1998). Activities are quite varied and differ among women by age and ethnicity (e.g., the lesser role of walking in urban African-American women than in rural Native-American women [Ainsworth et al., 1999]). Thus, it is not clear which or how many examples or cues should be given to prompt the recall of moderate-intensity physical activity on the brief survey questions that are aimed at making global physical activity assessments (Ainsworth, 2000a).
With regard to women who are either pregnant, postpartum, or lactating, the Dietary Guidelines do not make specific exclusions or modifications of the quantitative physical activity recommendation. There have been no recommendations from the American College of Obstetricians and Gynecologists (ACOG) since 1994 regarding physical activity in pregnant and postpartum women (ACOG, 1994). The 1994 ACOG recommendations stated that in uncomplicated pregnancies “there are no data in humans to indicate that pregnant women should limit exercise intensity and lower target heart rates because of potential adverse effects.” While these recommendations are not quantitative, they still allow the target of “30 minutes of moderate physical activity most days of the week, preferably daily.” A recent review of studies examining the maternal and fetal effects of maternal exercise during pregnancy suggests that even strenuous exercise regimens are associated with improved outcomes for mother and fetus (Clapp, 2000). In summary, there is no evidence or conflicting “expert” recommendation suggesting that the quantitative physical activity guideline in the Dietary Guidelines does not apply to pregnant, postpartum, or lactating women who are not experiencing medical complications of these physiologic states.
Epidemiology of Physical Activity in the WIC Population
Published studies describing the physical activity patterns of WIC recipients are very limited. Because of the inherent difficulties with measuring physical activity in preschool children, as discussed previously, there are no available data comparing physical activity levels across socioeconomic gradients in preschool children. Even among school-age children, there is no clear evidence that children of lower socioeconomic status have lower levels of physical activity. In a recent analysis of Third National Health and Nutrition Examination Survey data, ethnic minority children (non-Hispanic blacks and Mexican Americans) who were 8 to 16 years of age reported being less physically active than non-Hispanic white children (Andersen et al., 1998). However, these activity data were not examined by family income or parental education.
In a nationally representative sample of pregnant women, the prevalence of exercise during pregnancy did not differ significantly by household income, although women with more than high school education were slightly more active (Zhang and Savitz, 1996). In a study of Pittsburgh, Pennsylvania residents
that examined job-related, household, and leisure-time physical activity, Ford and colleagues (1991) noted less physical activity for women of lower socioeconomic status. This is consistent with others studies showing that activity levels are lower in adults with lower socioeconomic status (Macera and Pratt, 2000; Troiano et al., 2001), particularly as measured by educational level (Bild et al., 1993; White et al., 1987). However, these studies all focused largely on leisure-time physical activity. Only one study was identified that specifically examined physical activity levels among women enrolled in WIC, but this assessment was only for leisure-time physical activity (Jeffery and French, 1998). In that study, baseline data were reported from a weight gain prevention trial that involved both high- and low-income groups of women. The low-income women were recruited from WIC and, compared to the high-income group, tended to watch more television but did not report significantly less physical activity. In this low-income group, television viewing was strongly related to body mass index but not to physical activity.
METHODS TO ASSESS PHYSICAL ACTIVITY
Overview of Methods
Several comprehensive reviews have been written on the different methods to assess physical activity in adults and children (Baranowski et al., 1992; Goran, 1998; Kohl et al., 2000; Kriska and Caspersen, 1997; Pate, 1993; Sallis and Saelens, 2000; Welk and Wood, 2000). Of the many methods, only recall questionnaires (interviewer- or self-administered) have potential feasibility for application in WIC. All such self-report measures, including proxy reporting from parents or adult caregivers, are subject to bias. All other nonrecall methods are not feasible, primarily because of expense or burden on WIC staff or clients.
Although the committee reviewed the current dietary assessment tools used in WIC (see Chapter 2), WIC agencies were not requested to submit all general questionnaires used in WIC clinics. These general questionnaires may have also contained items on physical activity. Nonetheless, among the 54 agencies supplying assessment tools for review (dietary and/or general), none had any physical activity questions for children and only 4 had any physical activity questions for women (self-report). Only 1 state had a question about television viewing and this was aimed at children.
Assessment of physical activity involves many of the same challenges as assessment of food intake (Baranowski, 1985, 1988; Baranowski and Simons-Morton, 1991). Therefore, the committee believed it was appropriate to use the same eight criteria in the framework for evaluating tools to assess dietary risk (see Chapter 4) to evaluate each of the methods deemed potentially feasible for physical activity assessment in WIC. Thus, any suitable instrument must be brief, easy to administer, and valid. In particular, where validity is concerned, the instrument must be able to determine whether the children (≥ 24 months of
age) and women served by WIC are meeting the quantitative recommendation for physical activity outlined in the Dietary Guidelines. Furthermore, the instrument must be valid across the different populations served by WIC (e.g., rural and urban or African American and white).
Although there are several physical activity questionnaires for adults that have undergone extensive validity testing (Sallis and Saelens, 2000), the staff or client burden of most questionnaires is too great to meet the operational constraints of WIC. This is mainly because of the time involved in capturing all the characteristics of specific physical activity behaviors (i.e., type, frequency, duration, and intensity of each activity) that are necessary for a valid physical activity assessment of an individual. Furthermore, in physical activity assessment, it is even less clear than in diet assessment what reporting period (past day, week, or month) is required to reliably assess habitual activity levels of an individual (Baranowski and de Moor, 2000; Trost et al., 2000). Thus, the cognitive demands of recalling the performance of varied activities over time, while also including the dimensions of frequency, duration, and intensity, is likely to make the valid classification of any individual’s physical activity an unachievable goal, regardless of that individual’s available time or educational level.
Complicating physical activity assessment is the fact that the Dietary Guidelines emphasize moderate, as opposed to vigorous, physical activity. This emphasis arises appropriately from the evidence of the health benefits of moderate levels of physical activity (HHS, 1996). However, the level of moderate activity, as compared to vigorous activity, is far more difficult to determine for an individual because individuals differ greatly in their perceptions of what constitutes moderate activity and in their memory of that activity (Baranowski et al., 1992).
For the target adult population served by WIC, low-income women who are pregnant and/or who are caring for infants and preschool children, a large amount of physical activity may come from housework, childcare activities, occupational activity, or walking for transportation (rather than as a leisure-time activity). To the extent that a physical activity assessment tool does not adequately characterize these moderate activities, the levels of physical activity in WIC women may be greatly underestimated (Ainsworth, 2000a, 2000b; Ainsworth et al., 1999).
In summary, there are no currently available instruments for assessing physical activity in adults that meet the operational constraints of WIC and that can also accurately assess whether an individual is meeting the quantitative physical activity guideline in the Dietary Guidelines. Limitations in human cognition make it unlikely that an instrument could ever be developed that
would accurately classify an individual’s physical activity level for purposes of WIC certification. As with diet recall, accurately recalling and characterizing the varied behaviors that constitute an individual’s physical activity level is too complex for the human mind.
The cognitive limitations of preschool children require a parent or other adult caretaker to report on a child’s physical activity. Thus, the physical activity instruments used for children are more properly referred to as “parent” or “caretaker” reports than as “self” reports. The two available instruments in which an adult reports on the child’s activity were included as part of a recent comprehensive review of self-report instruments for assessing physical activity (Sallis and Saelens, 2000). Both instruments used logs or diaries rather than recalls of the child’s activity (Harro, 1997; Manios et al., 1998). Furthermore, only one study (Harro, 1997) involved 4- and 5-year-olds, and neither involved children younger than 4 years of age. Thus, there are no published activity recall instruments for preschool children that could be evaluated by the committee for assessing the physical activity guideline for children that is provided in the Dietary Guidelines.
CONCLUSIONS REGARDING THE ROLE OF PHYSICAL ACTIVITY ASSESSMENT FOR ELIGIBILITY DETERMINATION
The committee concludes that there are not now, nor will there likely ever be, valid physical activity assessment tools that can distinguish ineligible individuals from eligible individuals for WIC based on their physical activity levels. Thus, failure to meet the recommend levels of physical activity in the Dietary Guidelines should not be used to determine eligibility of individuals for WIC services.
However, as with assessment of food intake, there are still at least two possible roles of physical activity assessment in WIC. These roles would help support WIC’s mission in the primary prevention of nutrition-related chronic disease, especially the prevention of overweight and obesity. One role of physical activity assessment would be to aid in education and counseling. A second role would be in monitoring groups of individuals or target populations within WIC who may be at higher risk for low physical activity levels and/or who may benefit most from interventions within WIC to increase physical activity levels.
Physical activity assessment tools may be valid for assessing physical activity levels within groups even if they are not valid for assessing individuals. This is primarily due to the high levels of day-to-day variability in physical
activity and other reporting errors that greatly affect the validity of assessing physical activity levels in individuals, but do not as greatly affect assessing physical activity levels in groups. Even if valid tools for group assessment were developed in the future, for these tools to be feasible for use in WIC, they would still need to be evaluated in terms of the other criteria within the committee’s framework (see Chapter 4). For example, a valid physical activity assessment tool would also need to be brief and easy to administer.
For preschool children, the committee did not identify a physical activity recall instrument even under development. For women in WIC, perhaps, the most promising tools for group assessment of physical activity are the physical activity modules used in the Centers for Disease Control and Prevention’s Behavioral Risk Factor Surveillance System (BRFSS) (Macera and Pratt, 2000; Troiano et al., 2001; Washburn et al., 2000). In the 2000 BRFSS, there is an 11-item physical activity module with the items in various domains as follows: occupation, 1 item; walking, 3 items; moderate physical activity, 3 items; vigorous physical activity, 3 items; and strength and flexibility, 1 item. Furthermore, there is also a very brief 3-item module now under development (moderate physical activity, 2 items; vigorous physical activity, 1 item) (CDC, 2001). In the development of this brief 3-item module, the questions have undergone cognitive interviewing and subsequent revision based on that interviewing. After these revisions, the questions will be validated in a number of populations against other measures of physical activity and energy expenditure.
While this research process may hold some promise for the development of a useful tool to assess physical activity levels at the group level among women in WIC, the tool will not produce valid measures for determining individual eligibility. It is impossible for three questions to accurately assess an individual’s activity by capturing information about frequency, self-perceived intensity, and duration of activity within a reference period. The correlations between these questions and direct measures of physical activity are unlikely to be greater than 0.4, given the prior work in this area (Ainsworth et al., 1993a; Kriska and Caspersen, 1997). However, these correlations may be adequate for assessment at the group level. Thus, this 3-item module may hold the most promise for WIC because of (1) the extensive effort being placed on its development, including testing in a variety of populations, (2) its brevity, and (3) its ability to classify groups in terms of meeting the quantitative physical activity guideline with the Dietary Guidelines. Additionally, these modules would allow WIC to determine whether groups of enrolled women are meeting the physical activity targets outlined in Healthy People 2010 (HHS, 2000).
RECOMMENDATIONS FOR FUTURE RESEARCH
The principal target groups within WIC for increasing physical activity are children 2 to 5 years of age, and pregnant and postpartum women. As indicated previously, physical activity assessment in WIC, like diet assessment, will have utility only at the group level. This is because even adult women, regardless of their educational level, can not accurately recall their own or their children’s physical activity. Such group assessments, however, are still important for education and monitoring, as described above, and research is required to overcome some of the challenges that exist in the valid, group-level assessment of physical activity in those served by WIC.
Several methods of assessing physical activity that are used in research (e.g., activity diaries or logs, direct observation of activity, motion sensors and heart rate monitoring [Baranowski et al., 1992; Goran, 1998; Kohl et al., 2000; Kriska and Caspersen, 1997; Pate, 1993; Sallis and Saelens, 2000; Welk et al., 2000]) could be used as “gold standard” references to conduct validity and reliability studies of practical instruments for WIC to assess physical activity at the group level using recalls. For example, such research might compare the results of a physical activity recall questionnaire (completed by the mother for her preschool child) against data from motion sensors that assess acceleration of the child’s body in three dimensions (Freedson and Miller, 2000).
Beyond the significant challenge of adequately describing physical activity levels in the WIC population, little is known about the factors influencing physical activity in the WIC population. It is widely perceived, for example, that concern about neighborhood safety is a major barrier to physical activity. However, the research base supporting this notion is small, and little is known about the factors that, if modified, could improve perceptions abut neighborhood safety, and thereby possibly increase physical activity levels. Whether preschool children or their mothers will be more active if they spend more time outdoors or less time watching television is not known.
However, the research to identify potential target indicators of physical activity must come after efforts to improve physical activity assessment, because target indicators cannot be identified without valid physical activity assessment tools. Furthermore, once behavioral targets are identified, interventions to modify these intermediate targets cannot be assessed without some measure of physical activity, which is the ultimate target of change.