In a session moderated by Howell Wechsler, Kathleen Janz and Shari Barkin explored the current state of the science regarding the impact of physical activity on the prevention and treatment of obesity in youth. This chapter summarizes their presentations and the discussion that followed.
Researchers involved with the Iowa Bone Development Study, a 16-year longitudinal study, found that children and adolescents who are more moderately to vigorously active have lower adiposity. Janz, who was involved in that study, identified it as one of several observational studies on the association between physical activity and adiposity in youth. Other prospective studies, but not all, have likewise shown high levels of adiposity associated with low levels of physical activity. The relationship between adiposity and physical activity, Janz continued, is bidirectional, with other evidence indicating that adiposity leads to less moderate- to vigorous-intensity activity (MVPA). The good news, Janz opined, is that some families are doing it right—their children are maintaining healthy levels of activity and adiposity throughout childhood. She encouraged learning from them and underscored the importance of starting early, before children begin school.
Focusing on these youngest children, Barkin and her research team found that preschoolers average more than 100 minutes per day of MVPA, but they get that activity in spurts and sporadically over a period of up to 11 hours. These findings suggest to Barkin that providing “structured” time to play does not capitalize on normal preschool child development. She stressed the importance of aligning policies with childrens’ natural
movement patterns. She then went on to describe promising results from three intervention trials on physical activity in preschool and kindergarten school settings regarding the sustainability of the beneficial effects of physical activity interventions. Shifting her focus from the school setting to the community at large, Barkin highlighted the importance of teaching families—not just children but also adults—how to use nearby parks and recreation facilities and other physical activity–promoting features of their built environment. Merely having features of the built environment that are supportive of physical activity is necessary but not sufficient; families must understand how to use these facilities to promote and sustain family health behaviors.
Value of Observational Studies for Understanding Physical Activity and Adiposity
The two most common study designs used to study healthy children, Kathleen Janz began, are cross-sectional and prospective longitudinal designs. Cross-sectional studies measure the explanatory variable (i.e., physical activity) and the outcome (i.e., adiposity) at the same time. In contrast, prospective longitudinal studies measure the explanatory and outcome variables on two or more occasions. Think of cross-sectional studies as “snapshots,” Janz suggested, and longitudinal studies as “feature films.” While prospective longitudinal studies do not necessarily prove cause and effect, they do support inferences about cause and effect. They also complement randomized controlled trials by providing information on real-world or everyday physical activity dimensions (e.g., frequency, intensity, duration), domains (e.g., active transport, leisure activity), and patterns in relationship to adiposity.
Importantly, in Janz’s opinion, both types of studies provide unique information about real-world associations, with implications for both the prescription of individual-level exercise strategies to prevent obesity (i.e., with respect to dose–response) and population-level public health guidelines (i.e., with respect to practicality as well as dose–response).
1 This section summarizes information and opinions presented by Kathleen F. Janz, Ed.D., University of Iowa, Iowa City.
Physical Activity as an Explanatory Variable for Adiposity
Among the many studies conducted over the past few decades on the association between high levels of physical activity and low levels of adiposity, Janz focused first on the Iowa Bone Development Study, a 16-year follow-up study with which she has been involved since its inception. She and her colleagues have been following 500 children who were 5 years old at the start of the study, in 1998, having conducted eight clinical exams of each child as of the time of this workshop.
This was one of the first studies able to afford, with funding from the National Institutes of Health (NIH), an accelerometer with which to measure physical activity objectively. Additionally, Janz and her team have been using physical activity questionnaires to collect self-report data on participation in organized sports, sports lessons, television viewing, and videogame playing.
With respect to adiposity measures, Janz’s team has been using dual-energy X-ray absorptiometry (DXA) to sort the body into three components—lean tissue, fat tissue, and bone tissue—and measure the amount of each. Today, the technology has advanced to the point where it is also possible to measure visceral adipose tissue. One of the useful features of DXA technology, suggested Janz, is that the scanner is backward compatible, so that her research team has been able to rerun old DXA scans and distinguish between visceral and subcutaneous adipose tissue.
To provide the workshop audience with a sense of how adiposity changes in children as they age, Janz showed DXA images of two Iowa Bone Development Study participants, a girl and a boy, over a 10-year time span (see Figure 2-1). The girl entered the study at the age of 4 years and at a weight of 13.4 kg with 3 kg fat, so 23.1 percent body fat. That is normal, Janz said, for a young child. As the girl aged, both her weight and adiposity increased, but her percent body fat stayed approximately the same. At the end of 10 years, she had what Janz considered a healthy level of adiposity. The boy was 5 years old when he entered the study, and he had a healthy level of adiposity for a boy of his age. Between the ages of 5 and 9, however, something dramatic happened: his weight increased significantly, his percent adiposity increased threefold, and he became obese.
Today, about two-thirds of the Iowa Bone Development Study cohort have maintained a healthy level of adiposity as they have aged, like the girl in the top row of Figure 2-1. Regrettably, Janz said, 22 percent of the cohort were obese by the age of 19, defined as 32 percent body fat in females and 25 percent body fat in males. Another 12 percent of the cohort were already obese at the age of 5.
Something to keep in mind when conducting longitudinal research with children, in Janz’s opinion, is that the timing and tempo of growth
FIGURE 2-1 Dual-energy X-ray absorptiometry (DXA) images of two Iowa Bone Development Study participants, a girl (top row) and boy (bottom row), over a 10-year time span.
NOTE: % = percent body fat; BF = body fat; BW = body weight; F = female; kg = kilogram; M = male; yr = year.
SOURCE: Presented by Kathleen Janz on April 14, 2015.
and development are variable among individuals. Twelve-year-old girls, for example, can look very different from one another with respect to not only body height and weight but also maturation. Janz cautioned that when one is evaluating the epidemiological literature on physical activity and adiposity, it is important to look carefully to ensure that variation in timing and tempo is being represented.
Because the Iowa Bone Development Study data were collected on the same children across time, the investigators have been able to control for individual variation in both timing and tempo, making this a very powerful
study, in Janz’s opinion. They controlled for individual variation by using a multilevel regression analysis that involved first building an individualized growth curve for each child explaining adiposity changes over time, and then predicting total and visceral adiposity from measures of MVPA and sedentary time (i.e., obtained through accelerometry) and self-reported television (TV) viewing time.
The researchers found that total sedentary time does not matter in predicting adiposity, but TV viewing time (a subset of sedentary time) does matter, as does MVPA. More specifically, Janz explained, when her team examined the MVPA of a typical 11-year-old, that is, an 11-year-old average in terms of height, maturity, sedentary time, TV viewing, and every other measured variable (except MVPA), they found a 7.5 percent difference in adiposity between girls with high and low levels of MVPA, and a 5 percent difference in boys. When they conducted the same analysis but averaging all variables except, in this case, TV viewing time, they found a 5 percent difference in adiposity between girls who watched a great deal of TV and girls who watched the least amount of TV, and a 9.3 percent different in boys. Averaging all variables except both MVPA and TV viewing time yielded an 11.8 percent difference in adiposity between girls with low activity levels and high TV viewing time and girls with high activity levels and low TV viewing time, and a 21.3 percent difference in boys.
Other research groups also have been examining the association between physical activity and adiposity. In a 2013 review of studies that have used accelerometers to measure physical activity, Pate and colleagues (2013) identified seven prospective studies on the association between physical activity and adiposity, six of which found negative associations (i.e., that high levels of adiposity were associated with low levels of physical activity and vice versa), and one found no association. Of the seven studies, however, only two used criterion (i.e., DXA) adiposity measures. This is problematic, Janz said, because relying on body mass index (BMI) (instead of using DXA) can hinder precise interpretation of the data, given that boys and girls with the same BMI, even at the same age, can have different amounts of fat tissue. Additionally, Pate and colleagues (2013) identified four prospective studies on the association between sedentary time and adiposity, only one of which found a positive association (i.e., high levels of sedentary time associated with high levels of adiposity); the other three found no association. Again, however, only one of the four studies used a criterion (i.e., DXA) measure of adiposity.
In a similar review, Ekelund and colleagues (2014) identified nine longitudinal studies on the association between sedentary time and adiposity. All used accelerometers to measure sedentary time. Of the nine studies, eight showed no association, and one showed an association but only at higher levels of adiposity. Additionally, the reviewers identified eight longitudinal
studies on the association between TV viewing time and adiposity. All relied on self-reported TV viewing time, but only one used a criterion (i.e., DXA) measure of adiposity. Of the eight, five showed a positive association, and three showed no association. Janz interpreted these results to mean that in general, sedentary time does not appear to be associated with adiposity, but a subset of sedentary time—probably TV viewing time—does appear to matter. Janz cautioned, though, that some of the findings related to TV viewing time could be a reflection of researchers having measured this component of sedentary time more than others.
Using a cross-sectional study design, Katzmarzyk and colleagues (2015) examined physical activity, sedentary time, and obesity in more than 6,000 children aged 9 to 11 years at 12 sites worldwide. The children wore accelerometers, and World Health Organization (WHO) BMI standards were used to determine obesity. The researchers found that across all 12 sites, all with very different economic statuses, according to Janz, the best predictor of lower obesity was MVPA, as opposed to either vigorous-intensity physical activity or sedentary behavior. Specifically, 55 minutes per day of MVPA was the best predictor of lower obesity. These results support what has been observed longitudinally, Janz remarked.
Adiposity as an Explanatory Variable for Physical Activity
In addition to examining whether physical activity predicts adiposity, Janz has been curious about whether adiposity predicts physical activity. A bidirectional relationship, should it exist, may represent a positive feedback loop, she said. In the first such study of which she is aware that used accelerometers to measure physical activity, Metcalf and colleagues (2011) showed that MVPA at age 7 did not predict change in body fat between the ages of 7 and 10, but percent body fat at age 7 predicted decreases in MVPA between the ages of 7 and 10. Specifically, a 10 percent increase in adiposity at age 7 was associated with 4 fewer minutes per day of MVPA at age 10. Subsequently, three additional studies using accelerometers yielded the same conclusion—that adiposity is a good predictor of decreases in physical activity (Hjorth et al., 2014; Kwon et al., 2011; Richmond et al., 2014).
Developmental Trajectories for Physical Activity and Adiposity
Data from the Iowa Bone Development Study show that across time and for both boys and girls, MVPA decreases, although less so for boys. Using latent class group cluster modeling, Janz and colleagues found that children who were consistently active over time (i.e., engaged in 45 minutes per day of MVPA) were 60 percent less likely to end up obese at the age of 19 than children whose level of MVPA decreased as they aged. Specifi-
cally, 9 percent of children who were consistently active became obese by the age of 19, compared with 24 percent of children whose level of MVPA decreased (from an initial medium level) over time (Kwon et al., 2015).
Implications for Public Policy
In summary, both MVPA and TV viewing predict adiposity; sedentary time is not as important. These findings, Janz said, support the current national guidelines emphasizing 60 minutes per day of MVPA and 2 hours or less of TV viewing.
That adiposity predicts future MVPA implies, in Janz’s opinion, that intervening at the age of 5 years may be too late for some children. She called for more work in preschool children and possibly prenatally, and she encouraged a greater understanding of the possibility of healthy metabolic profiles in overweight and obese children. Finally, because longitudinal studies are enabling researchers to understand the development of obesogenic behavior in youth, including that some children maintain healthy levels of activity and adiposity through childhood to adulthood, Janz encouraged learning from those families who are “doing it right.”
The preschool period of growth is unique, Shari Barkin began. While most preschoolers look chubby at the age of 2 or 3, she said, no one would call their chubby centers “visceral adiposity”—“we would just call it being a preschooler.” Typically, between the ages of 3 and 7, children sprout in height without incurring the same change in weight. This phenomenon is known as “salutatory growth,” with the timing and tempo differing among individuals and impossible to predict. During this period, growth in BMI is typically nonlinear, with a dip in BMI occurring during the salutatory growth years (see Figure 2-2). After age 6 or 7, BMI increases linearly.
Barkin emphasized the importance of understanding nonlinear growth in young children when evaluating intervention studies. For example, suppose that a child who entered a study at age 3 had a BMI greater than 18, which would be considered obese, and when measured again at 4 years, after an intervention, still had a BMI of 18. Without understanding the nonlinear growth that is typical of preschoolers, one might conclude that the intervention had worked. But that is just normal growth, said Barkin.
Not only is normal preschool growth nonlinear, but it also has a wide
2 This section summarizes information and opinions presented by Shari Barkin, M.D., M.S.H.S., Vanderbilt University School of Medicine, Nashville, Tennessee.
FIGURE 2-2 Changes in body mass index over time for boys ages 2 to 20 years.
SOURCE: Presented by Shari Barkin on April 14, 2015 (Centers for Disease Control and Prevention).
range. All of Figure 2-2 between the 5th and 85th percentiles is considered normal, Barkin pointed out. BMIs between the 85th and 95th percentile are considered overweight, and BMIs equal to or greater than the 95th percentile are considered obese.
What Does Physical Activity Look Like in Preschoolers?
“While we may be a chair-loving society, our preschoolers are not,” Barkin said. In fact, preschoolers often need to be forced to sit down. They are meant to move, they move all the time, and how they move is unique. In a study of physical activity in preschoolers, Barkin and her research team placed accelerometers on 50 children aged 3 to 5 years for 7 days (Ruiz et al., 2013). Accelerometers, she explained, pick up muscle movement every second, and validated preschooler threshold values were used to derive time spent in sedentary and light-, moderate-, and vigorous-intensity physical activity (Pate et al., 2006). All of the children were from underserved communities, and 51 percent were African American. By design, none of the children were obese, but 26 percent were overweight and the remaining 74 percent of normal weight. The children wore the accelerometers like princess or superhero belts, Barkin said. They wore them for almost 24 hours per day (an average of 23.4 hours per day) for the entire 7 days. That the children wore the accelerometers for nearly 24 hours per day, compared with the usual minimum wear time of 6 hours, allowed the researchers to asses not only whether the preschoolers were achieving the recommended 60 minutes of daily MVPA but also what that activity looked like.
The researchers found that the children spent 14.5 percent of their awake time in MVPA, averaging more than 100 minutes per day, which Barkin said was not surprising. The surprising finding, she said, was that it took the children 11 hours to accumulate that much MVPA. Unlike adults, she remarked, children do not go to the gym and work out for 30 to 60 minutes; they are active throughout the majority of their day (see Figure 2-3).
Regarding what the preschoolers’ physical activity looked like, Barkin and her team identified four patterns. The first they called an “isolated spurt”—defined as a single spurt of MVPA that lasts less than 1 minute and is followed and preceded by periods of quiescence. Running to a parent is an example of an isolated spurt. The second type they called “isolated sustained activity”—defined as a period of MVPA that is both preceded and followed by a period of quiescence and that lasts for more than 1 minute. Running after a dog until one gets tired and stops is an example of an isolated sustained activity. The third pattern is what Barkin and her colleagues called a “cluster spurt”—defined as a brief burst of MVPA that lasts less than 1 minute, followed by a rest that lasts less than 1 minute, followed by another burst of activity that lasts less than 1 minute. An example is playing the game red light, green light. The last type of physical activity observed by Barkin and her team was what they called “clustered sustained activity”—defined as a sedentary period followed by MVPA lasting longer
FIGURE 2-3 Sample 24-hour activity recording of preschoolers from accelerometry readings.
NOTE: PA = physical activity.
SOURCE: Presented by Shari Barkin on April 14, 2015 (Ruiz, R. M., D. Tracy, E. C. Sommer, and S. L. Barkin. A novel approach to characterize physical activity patterns in preschool-aged children. Obesity 21:2197-2203. Copyright © 2013 John Wiley & Sons Ltd.).
than 1 minute, then a brief period of rest of less than 1 minute, and then another longer period of activity. An example is playing a chasing game, such as tag or kick the can.
Again, it took the preschoolers about 11 hours to accumulate their more than 100 minutes per day of MVPA. With respect to the different types of physical activity observed, both girls and boys participated in all types. Girls were active in isolated spurts more often than boys were (isolated spurts accounted for 16.9 percent of girls’ MVPA, compared with 13.8 percent for boys, p = 0.01), and boys engaged in more clustered sustained activity than girls did (clustered sustained activity accounted for 23.6 percent of boys’ MVPA, compared with 17.1 percent for girls, p = 0.01). The difference between girls and boys was not in whether they were physically active, Barkin said; both sexes achieved the recommended 60 minutes of daily MVPA. The difference was in how they achieved that activity. In terms of daily events, both boys and girls achieved their MVPA largely through isolated spurts, which averaged one-third of a minute, and clustered spurts, which averaged 3 minutes.
For Barkin, these findings suggest that providing structured time to play does not capitalize on preschoolers’ normal development, which entails moving in spurts and sporadically. This conclusion is important, Barkin said, and should shape preschool physical activity programs and policies.
Intervention Trials in the Classroom Setting
Barkin highlighted three intervention studies conducted in the school setting. The first, by Nyberg and colleagues (2015), examined the effectiveness of a universal parental support program in promoting healthy dietary and physical activity in 14 preschool classrooms in Sweden. Most participants (80 percent) were of normal weight, with a total of 243 children participating. The 14 classrooms were randomized into intervention and control groups, with the intervention classrooms receiving health information for parents and 10 teacher-led classroom activities—both didactic and physical—for 6-year-old children. At the end of the 6-month trial, the researchers found no significant effect of the intervention on either physical activity or BMI.
In another classroom-based physical activity intervention study, this involving kindergarteners and first-graders in two urban schools in New York, Reznik and colleagues (2015) tested the effects of an intervention in which an audio CD consisting of 10-minute aerobic activities (led by the teachers) was used three times per day. At the beginning of the study, 58 percent of the children were of normal weight, with a total of 988 children participating. At the end of the 8-week study, pedometer measures revealed that the intervention children had taken 300 more steps per day, on average, compared with the controls, and that the intervention had been equally effective across sex, grade, and BMI subgroups.
Barkin suggested, however, that 8 weeks is a short period of time. In a longer study involving 342 Arab-Israeli kindergarteners aged 4 to 6 years, 71 percent of whom were of normal weight, Nemet and colleagues (2011) tested the effects of training teachers to incorporate both nutrition and physical activity into the existing curriculum. The physical activity program was conducted 45 minutes per day, divided into three 15-minute sessions, six times per week. Eighty percent of the physical activity involved running games and 20 percent endurance activities. Barkin noted that the segmented nature of the physical activity sessions was consistent with what she and others have learned about how preschoolers move. The researchers found, at the end of the school year, a significant difference in reduction in BMI percentile in the intervention group compared with the control group. They also observed a significant difference in change in fitness levels, based on a shuttle run lap test: fitness increased in the intervention group (11.6 more shuttle run laps at the end of the year than at the beginning), compared with a decrease in fitness in the control group (10.2 fewer shuttle run laps).
In Barkin’s opinion, more important than the significant difference observed in changes in BMI percentile and fitness between the intervention and control groups was what Nemet and colleagues found when they reevaluated the preschoolers 1 year later to see whether the effects of the
intervention had been sustained (Nemet et al., 2013). The effect on fitness had indeed been sustained, with fitness in the intervention group having actually increased slightly; moreover, the changes in BMI percentile had also been sustained.
Interventions in the Community Setting
When Barkin arrived in Nashville, in 2006, the city’s then mayor, Bill Purcell, had helped the city double the number of parks and recreation centers, many of them in dense urban areas where residents previously had lacked access to a built environment supportive of physical activity. Barkin and colleagues wanted to take advantage of this “natural experiment” by examining how people were using the newly built parks and recreation centers for physical activity and how use of these facilities could be promoted for routine physical activity in early childhood.
With funding from the state of Tennessee and the Vanderbilt Institute of Clinical and Translational Research, the Salud con la Familia (Health with the Family) study examined a family-based, community-centered intervention designed to prevent and treat obesity in Latino parent–schoolchild pairs. Barkin and colleagues enrolled 106 Latino families with preschool-age children in a 12-week session on dyadic skill building. The researchers determined that almost all participating parents knew they should be physically active, should not be feeding their children high-fat, high-sugar foods, and so on. In other words, they did not need knowledge; they needed skills. Finding a way to feed one’s children with only $10 in one’s pocket is a skill, Barkin explained, as is using a recreation center in the community. The goal of the intervention was to improve outcomes not only in children but also in participating parents. The focus in the control group was on promoting school readiness, with control group participants being provided a library tour and membership. Intervention group participants received a tour of and membership in a recreation center as 1 of 12 skill-building sessions.
At the start of the study (Barkin et al., 2012), 41 percent of children were already overweight or obese. Based on accelerometry measurements—surprisingly, in Barkin’s opinion—70 percent of awake time (when they were wearing accelerometers) for the preschool-age children, who, she said, “are built to move,” was sedentary (Ruiz et al., 2011). Parents had a mean BMI of 30 and a mean waist circumference of 100 cm, the latter indicating visceral adiposity, and 80 percent of their awake wear time was sedentary behavior.
The 12-week intervention made a big difference, Barkin said. By the end of the study and compared with children in the control group, children in the intervention group were twice as likely to have changed their weight category from obese to overweight or from overweight to normal
weight (Barkin et al., 2012). In fact, children in the control group actually increased their BMI over time.
Barkin emphasized that it was not just the children but their parents as well who were using their new built environment for physical activity. She and her research team found that when families were taught how to use their built environment for physical activity, that skill was sustainable: parents from the intervention group were still visiting their community recreation center with their child 1 year later (Barkin and Poe, 2012).
In other formative research work, Barkin and colleagues found that the reason many Nashville parents were not sending their children outside to play was not just because of crime, traffic, or any of a number of other seemingly likely factors, but also because of stray dogs.
Barkin’s conclusions were fourfold. First, physical activity patterns are spurt-like and sporadic in preschool children. Programs and policies should consider how to align with this developmental stage to reinforce early MVPA patterns. Second, families with young children benefit from being taught the skills needed to use the existing built environment to support regular physical activity. “You don’t just build it and they come,” Barkin said. “You build it and then you teach them how to use it and then they will come.” Third, the use of the existing built environment for regular physical activity is influenced by perception. Even if there are no stray dogs outside, parents who perceive that stray dogs are a problem will not send their children outside to play. Finally, children’s routine physical activity is influenced by the activity of their parents. “Don’t think about this as one child at a time,” Barkin said. “Think of this as one family at a time.”
Following Shari Barkin’s presentation, Barkin and Janz participated in a panel discussion with the audience. To begin the discussion, Howell Wechsler asked both speakers to identify one public policy change inspired by their research conclusions that they think could have the greatest impact on increasing physical activity in children. Barkin stressed the importance of starting early, given that physical activity patterns are established early. “You don’t want to wait until children are school aged,” she said. Additionally, she stressed the importance of aligning programs and policies with normal development rather than, for example, imposing 30 minutes of structured play. Janz said she would like to see a rediscovery of outdoor education and exploration.
The Role of Light as Opposed to MVPA
An audience member commented on how much of the research described by Janz and Barkin focused on MVPA versus sedentary behavior. She asked about the role of light activity, which in her opinion is what is displaced by sitting, and whether either speaker had explored “that very gray area.”
In Janz’s opinion, at least in children and based on her research team’s data, MVPA matters more than light activity with respect to reducing adiposity and affecting other metabolic outcomes. “We need to see real movement,” she said. She is unsure whether the same is true of adults.
Barkin observed that the science has focused on MVPA, and much less is known about the health benefits of shifting from sedentary behavior to light physical activity. Based on her observations both in the clinic and in parks and recreation facilities, in her opinion, the latter shift is more achievable than increasing MVPA for many families. “The question is,” she said, “will it make a difference in terms of health?” That question has not been answered in the literature, either because the impacts of light activity on metabolic health outcomes have as yet not been fully explored, perhaps because of a publication bias, or because there simply is less interest in examining this question.
Pate agreed that this is an important and interesting question. He observed that the issue of physical activity and obesity is often approached from what he described as an algebraic standpoint—that is, energy in plus energy out—yet in their presentations, both Janz and Barkin had emphasized the importance of MVPA. If MVPA is particularly important in the prevention of excessive weight gain and obesity, he asked, is that because of its higher rate of energy expenditure? Or does it have a unique impact on the regulation of weight status?
Janz replied that, again based on her data with children, even at the same level of energy expenditure, MVPA appears to be more important than light activity. She suspects that this form of activity has a unique regulatory effect.
Barkin added that MVPA at a young age sets up many systems with long-term effects. For example, it helps establish bone density and muscle mass and, depending on how one interprets the literature, metabolism as well. She said, “There is no doubt that MVPA has really important effects for health, not just short term, but long term too.” Those effects do not mean that light physical activity does not have a benefit as well. “We just haven’t yet answered that question,” Barkin said. On a practical level, however, especially given that 40 percent of preschoolers in some communities are already overweight or obese, getting sedentary people to engage in routine MVPA is, she said, “not going to happen like a light switch.” In
her opinion, moving people in the right direction along that gradient (i.e., from sedentary to light activity initially, then to increasingly more vigorous-intensity physical activity) has benefits regardless of whether those benefits are reflected in the measure of BMI.
An audience member commented on the association between density of physical activity opportunities in a community and decreased obesity and the importance of educating families about physical activity opportunities. He asked, first, whether a reasonable policy direction would be to increase the density of physical activity opportunities in areas where there is a low density of such opportunities and, second, whether teaching families how to use available facilities could help move them in the right direction along the physical activity gradient.
In response to the first of these questions, Barkin suggested that policies should focus on after-school programs that involve family-based use of parks and recreation facilities. In response to the second question, Barkin said, “Absolutely. It is not really about education. It is about skills.” She and her research team, as part of Salud America!, found it took only one time getting a family through the door of a recreation center and teaching them what they needed to wear, which classes their children could attend, and other practical information to get that family to become regular users. She reiterated, “Just building it is not enough. Teaching people how to use these environments is critical.”
Physical Activity During Pregnancy
A question was asked about evidence on whether physical activity during pregnancy affects developmental programming in offspring such that some children may actually become addicted to physical activity. Barkin replied that many different areas of science have begun to explore the effects of physical activity during pregnancy. For example, what is the appropriate amount of physical activity during pregnancy, and when should pregnant women exercise (first, second, and/or third trimester)? Timing and intensity are really important questions, Barkin said, with no clear answers. She mentioned interesting work being done in epigenetics research with respect to how food and the physical environment are impacting placental and fetal function and whether and how fetal function can predict later adiposity (e.g., at the age of 3 years). At least in rodent models, evidence suggests that physical activity during pregnancy is a powerful mechanism for improving health in both mothers and offspring.
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