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Research Article Open Access
Underserved Minority Children Are Not Meeting the US Public Health Recommendation for Moderate-Vigorous Physical Activity
1USDA/ARS Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Texas, USA
2City of Houston Parks and Recreation Department, Texas, USA
*Corresponding author: Dr. William W. Wong
Ph.D, USDA/ARS Children’s Nutrition Research Center
1100 Bates Street, Houston, TX 77030, USA
Tel: 713-798-7168
Fax: 713-798-7194
E-mail: wwong@bcm.edu
 
Received April 16, 2012; Accepted May 22, 2012; Published May 25, 2012
 
Citation: Wong WW, Ortiz CL, Lathan D, Moore LA, Konzelmann KL, et al. (2012) Underserved Minority Children Are Not Meeting the US Public Health Recommendation for Moderate-Vigorous Physical Activity. J Obes Wt Loss Ther 2:132. doi:10.4172/2165-7904.1000132
 
Copyright: © 2012 Wong WW, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
 
Abstract
 
Background: In the US childhood obesity is more prevalent among underserved minority children. It is recommended that children should spend a minimum of 60 min/d in moderate-vigorous physical activity (MVPA) in order to maintain a healthy body weight.
 
Methods: We measured the amount of MVPA based on a minimum of 5 consecutive days of Actical measurements in 483 underserved minority children (10.3 ± 1.0 y (range 9-12 y); 51.1% male; 31.1% Black/68.9% Hispanic; 66% overweight or obese) who took part in our community childhood obesity intervention program (Healthy Kids-Houston). The majority of children (93.2%) were from low-income families.
 
Results: The minority children spent only 45 minutes per day on MVPA and only 23% were meeting the MVPA recommendation. Time spent on MVPA decreased with age (-6.8 ± 1.1 min/d (mean ± SE), P<0.01) with boys spending more time (+12.5 ± 1.1min/d, P<0.001) in MVPA than girls. Obese children spent significantly less time (32.1 ± 1.1 min/d) on MVPA than normal weight children (42.2 ± 1.1 min/d, P<0.001) and overweight children (39.7 ± 1.1 min/d, P<0.01). The amount of time spent on MVPA was not significantly different between normal-weight and overweight children (P=0.43). Race (P=0.12) and SES (P=0.39) had no effect on MVPA. Children spent more time on MVPA (+14.5 ± 1.0 min/d, P<0.001) during weekdays than weekend days.
 
Conclusions: Underserved minority children living in a large metropolitan city are not meeting the MVPA recommendation regardless of weight status. To combat childhood obesity, public and private resources should be utilized and the environment improved to promote MVPA in underserved minority communities.
 
Keywords
 
Minority health; Children; Childhood obesity; Moderate Vigorous Physical Activity (MVPA); Urban environment; Accelerometry
 
Introduction
 
The latest National Health and Nutrition Examination Survey 2007-2008 showed that approximately 35.5% of children between 6 and 11 years of age were overweight and 19.6% were obese with higher prevalence among Hispanics (42.6% overweight, 25.1% obese) and black girls (38.9% overweight, 21.1% obese) [1]. Higher prevalence of childhood obesity also has been reported among underserved minority children living in a major metropolitan area [2]. To combat childhood obesity among underserved communities, major efforts have been devoted to eliminate “food deserts” by increasing access to fresh foods and produce to achieve a healthy diet. Since physical activity plays an important role in the energy balance equation, the Centers for Disease Control and Prevention, the U.S. Department of Health and Human Services, the United States Department of Agriculture, and an expert panel collectively recommended that children should engage in 60 minutes or more each day on MVPA [3-5].
 
In a National Institute of Child Health and Human Development Study of Early Child Care and Youth Development, MVPA of children and youth between 9 and 15 years of age, estimated by accelerometry, showed that the majority of the younger children (9-12 years of age) exceeded the MVPA recommendation [6]. However, the study population consisted primarily of white children with only 25% of them from low-income families. Little is known about MVPA among underserved minority children who are at increased risk of childhood obesity.
 
This study describes MVPA in a large sample of underserved minority children living in an urban environment using an accelerometer that has been calibrated in children against whole-room indirect calorimetry.
 
Subjects and Methods
 
Study subjects
 
A total of 582 children living in the Greater Houston Metropolitan area were enrolled in the Healthy Kids-Houston Study between January 2009 and February 2011. To qualify for the study, the children must be between 9 and 12 years of age with no physical or medical limitations to physical activity. All children, regardless of race and body weight, meeting the above criteria were allowed to take part in the study. The children were recruited from neighborhoods surrounding the 14 community centers through promotions at the community centers and at nearby elementary and middle schools. The study protocol was approved by the Institutional Review Board for Human Subject Research for Baylor College of Medicine and Affiliated Hospitals. To enroll in the study, the parents completed the City of Houston Parks and Recreation Department enrollment form and the Baylor College of Medicine consent form. The program brochures, enrollment forms, and consent forms were available in both English and Spanish.
 
Anthropometric techniques
 
Body weight and height of each child were measured in duplicate with an electronic digital scale and with a digital stadiometer to the nearest 0.1 kg and 0.1 cm, respectively. The electronic scale and stadiometer were calibrated with a reference weight and rod, respectively, prior to the measurements. The average values were used to calculate BMI z-scores with adjustment for age.
 
Physical activity level
 
Actical (Philips Respironics, Bend, OR) accelerometer-based monitors were used to objectively measure Physical Activity Level (PAL). The monitors were affixed above the iliac crest of the right hip with an elastic belt and adjustable buckle. Children were instructed to wear the activity monitor for seven consecutive days, and to remove the monitor only for bathing or showering. A log recording the times and reasons for monitor removal, and sleep times was kept by the children and parents.
 
Actical contains an omni directional accelerometer built from a cantilevered rectangular piezo-electric bimorph plate and seismic mass, which is sensitive to movement in all directions. The piezo-electric sensor is oriented in the monitor such that maximum sensitivity is obtained when the center of body mass is moved against gravity. When positioned on the hip, the device is most sensitive to vertical movements of the torso. Actical is designed for measurement of whole body physical activity and is sensitive to movements in the 0.5 to 3 Hz range. The monitor sums all 32 values in a 1-second window, divides the sum by four, and then adds this result to the accumulated value for the epoch. In this study, 60 1-second values were summed together to generate one resultant raw activity datum for each 1-minute epoch. Using room respiration calorimetry, thresholds were established to represent sedentary, light, moderate and vigorous levels of physical activity [7]. Sedentary level was defined as activity energy expenditure (AEE) <0.01 kcal.kg-1.min-1 or physical activity ratio (PAR) <1.5, encompassing physical activities of minimal body movements in the sitting or reclined position. Light level was set at 0.01<AEE<0.04 kcal. kg-1.min-1 or 1.5<PAR<3.0, reflective of a low level of exertion in the standing position. Moderate level was set at 0.04<AEE<0.10 kcal.kg-1. min-1 or 3.0<PAR<6.0, and involved medium exertion in the standing position. Vigorous level was set at AEE>0.10 kcal.kg-1.min-1 or PAR>6.0, reflective of activities at a high level of exertion in the standing position.
 
Upon completion of the 7-day measurement period, monitors were collected and activity data downloaded into a computer. Data output included the time stamp and total counts. In the initial examination, data completeness was verified against the subject’s log. Times and reasons for removal of the monitor was coded in the file. Awake and sleep times were identified. If continuous zeros for more than 20 minutes during awake periods were not accounted for in the subject’s log, it was assumed that the monitor was removed. A 24-hour day was required to have 1,000 minutes or more out of 1,440 minutes per day to be valid and useable. After this initial data treatment, activity counts were summed for each 24-hour period. Awake time was categorized into sedentary, light, moderate and vigorous levels of physical activity according to thresholds defined in terms of AEE and PAR [7].
 
To achieve a reliability of 80% in activity measurements, the number of days required was calculated to be five days based on the between-participant variance and within-participant variance using the Spearman Brown prophecy equation [8].
 
Statistical analyses
 
Descriptive statistics were used to generate the means and standard deviations of all the outcome measures. Independent-samples t-test or Pearson Chi-Square test was used to evaluate potential differences between the race/ethnic groups. Since time spent on MVPA was not normally distributed, the data were normalized by natural logarithmic transformation prior to statistical analysis. Generalized linear models procedure including all 2- and 3-way interactions was used to test the effect of gender, age (9-10 y vs. 11-12 y), race/ethnicity (black vs. Hispanic) and obesity status (normal-weight, overweight, obese) and socio-economic status (SES) on MVPA. Non-significant 2- and 3-way interactions, starting with the most non-significant 3-way interaction, were removed from the model one at a time using the backward stepwise elimination procedure. Generalized estimating equations procedure for repeated measures was used to test the potential differences in activity outcomes between weekdays and weekend days. Statistical analyses were performed with SPSS software (SPSS Inc, Chicago, IL).
 
Results
 
Of the 582 children enrolled in the study, 84 children wore the activity monitors for less than the 5-day requirement. These 84 children were excluded from the analysis. Since our objective is to evaluate the MVPA among black and Hispanic minority children, we also excluded 12 white and three Asian children from the database. Comparison of the 84 children with the remaining 483 children showed no differences in weight (P=0.38), height (P=0.78), BMI (P=0.29), BMI z-score (P=0.37), gender distribution (P=0.06) and SES (P≥0.63) between the two groups, thus assuring that the elimination of these 84 children from the database would not bias our findings.
 
Table 1 shows the demographic and physical characteristics of the 483 children. Age, gender distribution, and body weight did not differ by race/ethnicity (P≥0.35). The black children were taller (P=0.001) but the Hispanic children were heavier by BMI (P<0.001) and BMI z-score (<0.001). The majority of children (66.1%) were overweight and obese with more Hispanic children falling into this category (76.9% vs. 42.0%, P<0.001) than black. Approximately 93% of the children were from low-income families with more Hispanic children falling into the low SES category (P<0.006) than black.
 
Table 1: Demographic and physical characteristics of study subjects.
 
Table 2 summarizes the activity data that were collected from the children using the Acticals. As shown in the table, the majority of children (72.9%) wore the monitors for all seven days. The number of days worn and the total number of minutes recorded on the activity monitor were not different between the two race/ethnicity groups (P≥0.59). Overall, the children spent the majority of their awake time (95%) on sedentary-light physical activities and only 45 minutes per day (5%) on MVPA, well below the recommended level. Only 23% of the children attained the 60 minutes per day recommendation.
 
Table 2: Time spent on moderate-vigorous physical activity (MVPA) by gender (A), race/ethnicity (B), obesity status (C), socio-economic status (SES) (D), age range (E) and day type (F). The whisker above each column represents the standard error. Different letters (a, b) above the columns in each figure indicate significant difference.
 
Main effects of gender, age, and obesity status but not race/ethnicity or SES on time spent on MVPA were observed.
 
Figure 1 shows the expected means for MVPA by gender, race/ ethnicity, obesity status, SES and age range based on generalized linear models procedure. No significant 2- or 3-way interactions were detected.
 
Figure 1: Demographic and physical characteristics of study subjects.
 
Figure 1A shows that boys spent more time on MVPA (+13 minutes/day, P<0.001) than girls. Race/ethnicity (Figure 1B) was found to have no effect on MVPA (P=0.12).Reduced MVPA (Figure 1C) was observed among obese children when compared to overweight children (-8 minutes/day, P=0.003) and normal-weight children (-10 minutes/ day, P<0.001). Time spent on MVPA was not different between the normal-weight and overweight children (P=0.43). SES also was found to have no effect on MVPA (Figure 1D, P=0.39). However, age was found to be negatively related to time spent on MVPA. As shown in Figure 1E, children between 11 and 12 years of age were spending less time (-7 minutes/day, P=0.002) on MVPA than children between 9 and 10 years of age.
 
The above observations were confirmed based on total activity counts per day. Main effects of gender, age, and obesity status but not race/ethnicity or SES on total activity counts were observed. Boys registered 44,227 more counts or 32 counts per minute higher than the girls (P<0.001). Race/ethnicity had no effect on activity counts (P≥0.14). Normal-weight children registered higher activity counts than both overweight (+31,267 counts per day or +24 counts per minute, P≥0.03) and obese (+50,155 counts per day or +37 counts per minute, P<0.001) children. Activity counts expressed either in total counts per day or counts per minute were not different between the overweight and obese children (P≥0.13). Younger children (9-10 years of age) also registered higher activity counts (+27,447 counts per day or +16 counts per minute, P≤0.03) than the older children (11-12 years of age). SES had no effect on activity counts (P≥0.15).
 
With the children spending majority of their awake time on sedentary-light physical activities, we found no effect of gender (P=0.20), race/ethnicity (P>0.06), SES (P=0.18) and age (P=0.27) on sedentary-light activity minutes. Only the obese children were found to spend significantly more time (+23 minutes/day, P<0.001) on sedentary-light physical activities than the normal-weight children. No difference was detected in sedentary-light physical activity minutes between the normal-weight and overweight children (P=0.07) and between the overweight and obese children (P=0.16).
 
Generalized estimating equations analysis showed that during the week days, the children registered higher activity counts (+23,668 units, P<0.001), spent more time on MVPA (Figure 1F,+1.4%, P<0.001) and less time on sedentary-light physical activities (-0.6%, P<0.002) than during the weekend days.
 
Discussion
 
This study provides an objective assessment of physical activity levels of a large sample of underserved minority children who are overweight or obese, or at risk of obesity and living in an urban environment. Prior to enrollment into an obesity prevention program, children wore a minimum of 5 days of an accelerometer that has been calibrated in children against whole-room indirect calorimetry. Thus, our study provides an accurate assessment of physical activity patterns, particularly MVPA, of contemporary, minority children from lowincome families living in a large metropolitan area. Our major findings indicate that black and Hispanic children did not differ, boys were physically more active than girls and that underserved minority children were more physically active during weekdays than during weekend days. Both age and obesity were found to be negatively associated with MVPA. Most disturbing, our results showed that underserved minority children, regardless of their weight status, were not even close to meeting the 60 minutes per day MVPA recommendation. Only 23% of these children spent ≥60 minutes per day on MVPA.
 
Based on a minimal of 4-day of activity data collected between 2000 and 2006 in a National Institute of Child Health and Human Development Study of Early Child Care and Youth Development using the ActiGraph accelerometer, children in this longitudinal cohort were reported to spend 181 minutes/day on MVPA at age 9, 122 minutes/day at age 10, and 90 minutes/day at age 12 [6]. However, approximately 77% of the study participants were white and only 25% of the study participants were from low-income families. Therefore, the MVPA results from this national survey do not reflect underserved minority children. In our study, the children spent on average 45 minutes per day on MVPA. The national study also documented that time spent on MVPA was significantly higher during weekdays than weekend days and that activity counts per minute were higher among boys than girls, both similar to our observations.
 
ActiGraph also was used to collect cross-sectional activity data in a National Health and Nutrition Examination Survey between 2003 and 2004 [9]. Based on activity data collected from 587 children between 6 and 11 years of age, approximately 42% of the children were meeting the 60-minute MVPA recommendation with boys spending more time on MVPA (95.4 minutes per day) than girls (75.2 minutes per day). These children consisted of 60.2% white, 14.6% black, and 15.4% Hispanic with 36% of them being overweight and obese. The study, however, did not look at the effect of SES on MVPA. A followup analysis of the National Health and Nutrition Examination Survey taken between 2003 and 2006 based on a minimal of 4-day of activity measurements again confirmed that activity counts were lower among girls and decreased with age [10]. Normal-weight participants also had higher activity counts than the obese. The study reported 88 minutes per day of MVPA among the 6-11 years old and 33 minutes among the 12-15 years old. BMI percentile was negatively associated with MVPA in all race/ethnic groups for both genders. The study population consisted of 36.3% black and 36.5% Hispanic. Among the black children, 26.8% were overweight and obese whereas among the Hispanic children, 38.6% were overweight and obese. The prevalence of overweight and obesity (66.1%) was significantly higher among the children in our study. Our study population also consisted primarily (93.2%) of children from underserved low-income families. Although the National study adjusted for the poverty-to-income ratio, the results were not segregated by SES. Therefore, it is possible that our study population is a more representative sample of underserved minority children living in a major metropolitan area. The national study also reported that among the 6-11 years old, white children were spending approximately 87 minutes per day on MVPA as compared to 97 minutes per day among the black children and 85 minutes per day among the Hispanic children. Our results showed that both the black and Hispanic children were spending only 45 minutes per day on MVPA. Therefore, it is also possible that time spent on MVPA among underserved minority children might have deteriorated further since 2006. However, the lack of effect of SES on MVPA observed in our study might be due to the homogeneous nature of our study population with the majority of our children coming from underserved families.
 
In an earlier study conducted in Houston, Texas, the Actiwatch accelerometer was used to assess the activity of 897 low-income Hispanic children and adolescents aged 4-19 years who participated in a major genetic study involving measurements of body composition, energy expenditure, and blood chemistries [11]. Among these 897 participants, 52.7% were obese. Based on 3 days of continuous measurements, 62% of the participants were determined to be meeting the MVPA recommendation. Among the children aged 8-12 years, 73% were meeting the MVPA recommendation as compared to 23% reported in the current study. The study also showed that boys were more physically active than girls; normal-weight participants were more active than the obese participants; and physical activity level decreased with age. On average, these Hispanic participants spent between 74 and 96 min/d on MVPA. The difference in time spent on MVPA between this earlier study and the present study might be attributed to the use of different accelerometers and PAL thresholds, since the SES status and BMI distribution were similar. However, we doubt the difference is due to the use of Actiwatch vs. Actical, since these accelerometers were calibrated using the same MVPA level threshold. Therefore, it is very possible that the MVPA levels of Hispanic children in Houston might have declined over the past decade.
 
In the Growing Up Today Study, 12,812 boys and girls between 10 and 18 years of age from Boston, Massachusetts self reported their physical activity level [12]. The results showed that among this largely white study population, the study participants were meeting the 60-minute MVPA recommendation. The results also showed that physical activity declined with age.
 
In a 5-year longitudinal study of students aged 11-12 year from 36 London schools and based on self-reported physical activity questionnaire, a reduction in physical activity was observed with age; boys were more active than girls; and levels of sedentary behavior were greater among lower SES students [13].
 
The low MVPA reported in our study among underserved minority children living in Houston, Texas has also been reported among 132 Hispanic children between 10 and 11 years of age [14]. The same accelerometer, Actical, was used to assess the MVPA of these Hispanic children attending five predominantly urban, Latino elementary schools in the economically distressed east end neighborhood of Houston, Texas. Based on an average of 5.8 days of measurements, these Hispanic children were found to spend approximately 49 minutes per day on MVPA, in agreement with our finding.
 
In a recent study to evaluate MVPA in youth sports in middleincome cities, ActiGraph was used to monitor the MVPA among 200 youth between 7 and 14 years of age during soccer, basketball or softball practices [15]. Participants in soccer teams spent an average 17 more minutes in vigorous physical activity during practices than participants in basketball or softball. Very interestingly, regardless of the youth sports, only 24% of the participants were meeting the 60-minute MVPA recommendation during practice suggesting that much of the time during sports practices were spent standing around. If youth sports are to be part of the strategy to promote active lifestyle among children, the programs need to be designed to encourage MVPA among all participants.
 
MVPA should be promoted to improve both short- and long-term health outcomes among US youth. In a Danish study of 589 children aged 9.6 ± 0.4 years of age, metabolic syndrome including blood pressure, adiposity, and blood levels of insulin, glucose, triglyceride, and high-density lipoprotein cholesterol was found to be inversely related to physical activity assessed using ActiGraph [16]. It also has been shown in a 21-year tracking study that a high level of physical activity at ages 9 to 18 was found to be significantly related to a high level of physical activity in adulthood [17].
 
Both the national studies [6,9,10] and our study, using objective measure of physical activity, clearly documented that MVPA is much lower during the weekends and among the girls. Therefore, more effort is needed to promote active lifestyle over the weekends at the family level. In the most recent report on the prevalence of obesity and trends in body mass index among U.S. children and adolescents [18], high prevalence of obesity was reported among the Hispanic and black girls aged 6-11 years. In order to combat the childhood obesity epidemic, more effort also is needed to promote an active lifestyle among girls in all interventions.
 
Conclusions
 
Our study showed that underserved minority children living in a large metropolitan city are not meeting the US public health recommendation for MVPA. Since physical activity is an important factor to achieve energy balance and a healthy weight, increased effort is urgently needed to eliminate “active play deserts” in underserved communities across the country.
 
Acknowledgements
 
None of the authors had any conflicts of interest to declare. All authors contributed to the study design, study supervision, data acquisition, drafting of the manuscript, and critical revision of the manuscript. Statistical analyses were performed by Wong, Smith, Adolph and Butte.
 
Supported by the National Research Initiative of the USDA National Institute of Food and Agriculture grant #2008-55215-18875 and USDA/ARS grant #6250- 51000-053, Clinical trials gov. NCT00994084
 
References
 


















 
 
 
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