Physical activity in childhood improves cardiovascular health and physical fitness, increases bone mass and density, is associated with better mental health, improves body composition, reduces the risk of obesity (26), and may promote the development of a physically active lifestyle for lifelong health benefits (23,31). The 2008 Physical Activity Guidelines for Americans reviewed the scientific evidence of the health benefits of physical activity and concluded that youth should participate in at least 60 min of moderate-to-vigorous physical activity (MVPA) each day (26).
Despite the array of health benefits from physical activity, most children and adolescents around the world do not achieve recommendations (2,25,28,32,35). Surveys from numerous countries consistently report that less than half of children are sufficiently active and that physical activity declines with age through childhood and adolescence (2,25,28,35). In Mexico, the nationally representative 2006 Survey of Health and Nutrition reported that <40% of children and adolescents 10-19 yr old participate in recommended amounts of physical activity (25).
The physical and social environments of the school can influence the physical activity of students (36), and a school physical education (PE) class is an important setting for practicing physical activity and instilling the importance of an active lifestyle in youth (5,36). Systematic reviews of the effectiveness of interventions to increase physical activity in the United States and in Latin America found strong evidence that interventions targeting the PE curriculum are effective in increasing physical activity during PE (15,18). However, the extent to which PE-targeted and other school-based interventions affect physical activity during and outside of the school day is not clear. In addition, the review from Latin America included few studies because of a paucity of interventions evaluated with sufficient scientific rigor (15). There is, therefore, a need to evaluate physical activity interventions in Latin America.
We recently reported that students in public primary schools in Mexico City participate in very little physical activity, that students are not sufficiently active during PE class, and that physical activity is often prohibited during the school day outside of PE class (17). Therefore, there is an opportunity to increase physical activity during school and improve the activity of youth in Mexico. The objective of this investigation was to test the effect of a school-based environmental intervention on physical activity and physical fitness of students attending public primary schools in Mexico City. Because the intervention was environmental, the unit of randomization was the school.
Subjects and sample selection.
This intervention was one component of a larger initiative to improve the diet and physical activity of students in Mexico City through changes in the school environment. The intervention was conducted in 27 public primary schools meeting the following inclusion criteria: 1) located in the south of Mexico City, 2) classified by the Secretary of Public Education as low socioeconomic status, 3) received benefits from the Federal School Breakfast Program, 4) demonstrated the minimum facilities necessary for the execution of the intervention, 5) possessed the standard Secretary of Public Education-issued set of sports equipment, 6) enrolled at least 350 students, and 7) consisted of two or more classrooms per grade.
Using a statistical program to draw a random sample from the complete list of eligible schools, 27 schools were randomly chosen for inclusion (Fig. 1). Using the same program to draw three samples from the 27, the three intervention groups were randomly generated. The intervention groups were control group (no change), basic intervention, and plus intervention. Because the interventions targeted environment and policy, all students were exposed to the intervention (or control conditions) on the basis of the group to which their school was assigned. All students in fourth and fifth grades whose parents signed a written informed consent and who gave oral assent were eligible to participate in the physical activity and physical fitness evaluations.
Because the intraclass correlation coefficient for physical activity in schools in Mexico is unknown, a conservative estimate of 0.1 was used to calculate the necessary sample size. Because physical activity recommendations are based on time in MVPA and given that at the onset of the investigation, the method for measuring physical activity was not known, the sample size was based on the minimum number of participants necessary to detect a difference of 20 min of MVPA per day between intervention groups. Eight schools per intervention group with 30 participants per school (240 participants per intervention group) would have a power of 0.80 and α of 0.05 to detect such a difference if the design effect was not more than the conservative estimate of 3.9. To account for a potential 10% loss to follow-up, 33 participants per school were randomly selected from all eligible students for evaluation. Students were chosen using a random number generation table based on students' school identification numbers. To increase precision in the control group without drastically increasing implementation cost; the number of schools in the control group was increased to 11.
Project staff visited each school and held informational meetings with all potential participants, their parents, and the school staff. Before any measurements were performed, parents of all eligible students who were willing to have their children participate in the physical activity and physical fitness evaluations signed a written informed consent, and children gave oral assent. The study protocol was reviewed and approved by the Research, Ethics, and Biosecurity Commissions of the National Institute of Public Health. The analysis of these data was considered nonhuman subjects research by the Centers for Disease Control and Prevention.
The control group experienced no change to the standard practices of the public schools in Mexico City related to PE (one time per week) and recess (nonexistent). The basic intervention consisted of environmental and policy changes at the school level meant to foster an environment conducive to increased physical activity (Table 1). These changes were complimented with an educational campaign to increase students' and school staff's awareness of the importance of physical activity for health. The plus intervention included all of the components of the basic intervention plus additional changes requiring more resources such as the addition of a daily exercise session held before classes began in which all students participated. All intervention components were based on extensive formative research that evaluated the school environment as it related to physical activity (17).
Measurement of physical activity.
The NL-1000 pedometer (NEW-LIFESTYLES, Lee's Summit, MO) was used to measure physical activity during school, out of school, and all day (24 h). This pedometer counts steps and stores information for 7 d. Because the scope of the intervention and thus the focus of the investigation were in the schools, participants wore the pedometers during the school week and not on the weekend. Recruitment was staggered during 9 wk with the inclusion of three schools per week. Baseline measurements were taken from October to December 2006 and follow-up measurements were taken from May to June 2007.
Field staff trained in the management of pedometers gave both oral and written instructions to the participants on how to wear the pedometers properly. The field staff attached the pedometers to belts made for the study and gave the belts with pedometers to participants on Monday morning of the week of evaluation. Participants wore the pedometers as instructed during all waking hours from Monday morning until the end of the school day on Friday except when they participated in aquatic activities and bathing. A plastic safety strap was placed around the pedometer and the belt to prevent participants from opening the pedometer or the pedometer accidentally falling from the belt. To quantify steps during school, pedometers were programmed to have a step count of zero at the beginning of the school day. Before distributing pedometers to the participants, the internal clock on each instrument was programmed to restart every day at 8:00 a.m., the hour the school grounds were opened and the school day began. Field staff examined the pedometers at the end of each school day as the students were leaving the school grounds and recorded the number of steps taken during school, which was the step count on the pedometer display. Field staff also recorded steps in memory, which corresponded to the all-day (24 h) steps for the previous day (8:00 a.m. of the previous day to 7:59 a.m. of the current day). Field staff reminded participants to wear the pedometer during the remainder of the day. The calibration of all pedometers was verified before the baseline and the follow-up evaluations.
Physical fitness was measured through tests of cardiorespiratory fitness, flexibility, and strength during a week in which physical activity was not being measured by pedometers. The 9-min distance run that has been shown to be a reliable field method for estimating cardiorespiratory fitness was conducted (30). Participants ran around a calibrated track for 9 min, and the distance traveled was recorded in meters. Flexibility was assessed with the sit-and-reach test, which measures the flexibility of the back and hamstrings, an indicator of overall flexibility (14). The distance participants could reach as they sat on the ground with legs extended was recorded in centimeters. Muscle strength and endurance was evaluated by quantifying the number of sit-ups participants performed in 60 s (14).
For the measure of physical fitness, field staff participated in a 2-wk training and standardization course that included approximately 6 h of field exercises in schools not included in the study. The staff reached virtual complete agreement with the instructor by the end of the training, and standardization was verified through comparison with the trainer at multiple times throughout the investigation. All tests were administered during PE class by the trained field staff. Participants were informed in advance of the testing date. They wore their standard PE uniforms consisting of shorts or sweat pants and T-shirts. Field staff provided participants with PE uniforms and shoes if they did not have the proper attire for the evaluation.
Anthropometry and demographic information.
Prior to anthropometric measures, the field staff was trained by an anthropometry expert and standardized using the method of Habicht (12). Restandardization took place before each round of measurement. Trained field staff measured weight and standing height of participants using standard procedures (20). Children were categorized as normal weight, overweight, or obese using the age- and gender-specific body mass index (BMI) cut points suggested by the International Obesity Task Force (3). At the time of the measurements, field staff interviewed participants to collect demographic information such as date of birth, gender, grade, and classroom teacher.
Data reduction and analysis.
The average steps during school, out of school, and all day were calculated for each participant. The number of steps taken out of school was the number of steps taken during school subtracted from the number of steps taken all day. Data were checked for unreasonable values such as all-day steps being less than steps during school, negative values, or steps being unreasonably low (indicating the pedometer was not worn). An unreasonably low value for steps during school, all day, and out of school was defined for each participant as a daily value less than half of the average of the values for the other days for that participant (i.e., the calculation was on an individual basis without regard to the steps of other participants). At baseline, approximately 6.5% of student days measured were defined as unreasonably low and were set to missing in the database. The students who had a value of steps defined as unreasonably low were compared with those who did not, and there were no significant differences between groups in gender, age, grade in school, classroom, or BMI category.
Because steps and physical fitness measures were anticipated to be skewed, the sample mean, 95% confidence interval (95% CI), median, and interquartile range (IQR 25 75) for steps during school, out of school, and all day at both baseline and follow-up were calculated. These values were also calculated for the physical fitness measures. The basic and plus intervention groups were compared with the control group at baseline using a nonparametric test of the difference in medians. The differences in step counts and physical fitness measures from baseline to follow-up were anticipated to be normally distributed; therefore, the difference from baseline to follow-up in individual average steps during school, out of school, and all day, as well as in physical fitness measures, was calculated. The effect of intervention on physical activity and fitness was tested using multivariate linear regression with the difference in steps or difference in fitness measure as the outcome variable and intervention as the main predictor variable. Although one regression model was generated for each outcome, separate statistical tests compared the plus intervention to control and the basic intervention to control. All models were tested for the significance of covariates including age, sex, grade, and BMI category and were controlled for baseline steps when physical activity was the outcome variable and baseline fitness when fitness was the outcome variable. The potential effect modification on intervention by sex and BMI category was explored. Covariates remained in the model at a significance of P ≤ 0.05, and interaction terms remained in the model at a significance of P ≤ 0.10. The participant was the unit of analysis, and because randomization was done at the school level, robust SE accounting for the design effect of school were calculated. Results are presented in the tables as the mean and 95% CI.
Adequate physical activity for the all-day step measurement was defined as 12,000 steps for girls and 15,000 steps for boys on the basis of standards for children suggested by Tudor-Locke et al. (29). At baseline, the amount of physical activity conducted during school was approximately 30% of the all-day physical activity. Therefore, we created a cutoff for steps during school as 30% of the all-day cutoff (3600 steps for girls and 4500 steps for boys) and a cutoff for steps out-of-school as 70% of the all-day cutoff (8400 steps for girls and 10,500 steps for boys). We calculated the percentage of participants who reached these cutoffs during school, out of school, and all day at both baseline and at follow-up. We compared baseline and follow-up and calculated the following proportions: 1) participants that improved from not reaching to reaching cutoffs, 2) participants that declined from reaching to not reaching cut offs, and 3) participants who did not improve or decline. We used logistic regression with reaching cutoff (1 = yes, 0 = no) as the outcome variable to test the significance of intervention on reaching cutoffs and calculated robust SE to account for the design effect of school. Although the nature of the environmental intervention precluded blinding of the participants or field staff, the database was generated using numeric codes to represent intervention groups and other variables that could identify the intervention such as school. Data analysts and researchers were blinded to the meaning of all numeric codes until data analyses were complete. All analyses were performed using Stata (Stata Statistical Software, Release 9.2; StataCorp, College Station, TX).
A total of 699 participants participated in physical activity and physical fitness evaluations at both baseline and follow-up (Fig. 1). Those lost to follow-up and those with complete data were compared on baseline characteristics, and no differences in demographics or physical activity were found (data not shown). Sensitivity analysis revealed little change in outcome measures if those lost to follow-up were included in the sample assuming no change from baseline in this group. The mean ± SD age of the participants was 10.2 ± 0.69 yr (Table 2). The age of participants in the plus group was significantly (P < 0.017) less than that of the basic and the control groups. The sample was fairly evenly divided between boys (n = 339, 48.5%) and girls and fourth (n = 344, 49.2%) and fifth graders. Of the 677 participants with complete anthropometric data, 57.3% (n = 388) were of normal weight, 28.4% (n = 192) were overweight, and 14.3% (n = 97) were obese.
Physical activity during school.
As expected, the steps during school were positively skewed. At baseline, the median (IQR 25 75) number of steps taken during school in all participants was 3513 (2646-4693) (Table 2). There were significantly (P < 0.01) more steps taken by the participants in the control group relative to the basic and plus groups. Over time, the median number of steps taken during school increased in the basic and plus groups and decreased in the control group (Fig. 2A).
The difference in the mean steps from baseline to follow-up, as anticipated, was normally distributed and was thus used as the outcome variable in the regression analysis. During school, steps decreased in the control group and increased in the basic and plus groups from baseline to follow-up (Table 3). The plus group significantly increased steps relative to control (P < 0.05). There was no effect modification of sex or BMI category on the intervention groups in steps during school.
During school, a significantly (P < 0.001) greater percentage of participants improved from not reaching the step cutoff at baseline to reaching the step cutoff at follow-up in the basic and plus groups relative to control (Table 4). Conversely, a significantly (P < 0.001) lower percentage of participants declined from reaching the cutoff at baseline to not reaching the cutoff at follow-up in the basic and plus groups relative to control.
Physical activity out of school and all day.
As anticipated, steps out of school were positively skewed. Over time, the median number of steps taken out of school increased in the control group, remained unchanged in the basic group, and decreased in the plus group (Fig. 2B). The difference in the mean steps out of school from baseline to follow-up was normally distributed and, thus, used in the regression analysis as the outcome variable. Steps taken out of school increased in the control, remained almost unchanged in the basic, and decreased in the plus group (Table 3). The change in out-of-school steps in the basic and plus groups was not significant relative to control, controlling for baseline out-of-school steps (P > 0.05).
All-day steps were positively skewed, and thus, the normally distributed difference was used as the outcome variable in the regression analysis. All-day steps decreased in the control, increased in the basic, and remained virtually equivalent in the plus group from baseline to follow-up. The basic group significantly increased steps relative to control (P < 0.05). There was no effect modification of sex or BMI category on the intervention groups in steps out of school or all day.
From baseline to follow-up, the percentage of participants who declined in steps out of school from reaching the cutoff to not reaching the cutoff was greater in the plus group relative to control (P = 0.02) (Table 4). There were no differences among intervention groups in percentage of students reaching the all-day cutoff.
From baseline to follow-up, there were no significant changes in the basic and plus groups in distance run or flexibility score relative to control (P > 0.05). The control and basic groups decreased the number of sit-ups completed in 60 s (change: control = −1.7, 95% CI = −2.5 to −0.8; basic = −0.6, 95% CI = −1.4 to 0.2), and the plus group increased sit-ups (0.3, 95% CI = −0.6 to 1.1). The increase in the plus group was statistically significant relative to control (P = 0.05).
The results of this investigation demonstrate that changes in school environment and policy coupled with raising the awareness of teachers, staff, and students to the importance of physical activity can effectively increase physical activity of students of public primary schools in Mexico City during school. The plus intervention significantly increased physical activity in students during school, and both interventions relative to control resulted in significantly more students improving from not reaching the step cutoff to reaching the step cutoff during the school day. Although sample size was based on MVPA, which cannot be measured by pedometers, and not on steps, the investigation was still sufficiently powered to detect some differences between groups. Moreover, differences between groups, which were not statistically significant, were in the expected direction, and any increase in power would either leave the results and conclusions unchanged or strengthen them by detecting a greater number of statistically significant differences between intervention and control groups. Only two other studies to date have tested the effect of school-based interventions to increase physical activity during the school day. A 3-yr intervention aimed at changing school environment, increasing knowledge, improving attitude, and modifying behavior during school in Native American elementary schools reported no significant effect of intervention on physical activity during the school day (10). However, authors reported a 10% increase in physical activity in the intervention schools that did not reach statistical significance because of the large variability in the physical activity of students. A 2-yr intervention with environmental change and individualized computer-tailored feedback in middle schools in Belgium reported an increase in self-reported physical activity during the school day (13). Similar to the latter study, the current investigation improved physical activity during the school day. Moreover, the improvements occurred with relatively simple and inexpensive environmental and policy changes without the computer-tailored feedback used in the Belgium study that would not be sustainable in the context of most developing countries. Other analyses should document the effectiveness of the basic and plus interventions on multiple health outcomes and investigate the cost effectiveness of both.
The results of this randomized controlled trial of a school-based environmental intervention in public schools in Mexico City add important information to the evidence of intervention effectiveness in Latin America. A recent systematic review of physical activity interventions in Latin America found few studies with sufficient scientific rigor for inclusion in the review (15). Of more than 900 studies on physical activity interventions, only 15, <2%, were from Latin America. A recent Cochrane Review on the effectiveness of school-based interventions to promote physical activity and physical fitness concluded that there is some evidence that school-based physical activity can be beneficial; however, it found only four studies with strong methodological quality and stressed the need for more research focusing on physical activity as an outcome to evaluate the effectiveness of such interventions (6). Because the effectiveness of community interventions relies on successful adaptation of interventions to the target audience (6,18), evaluation of interventions in varying cultural contexts is especially important. These results help to fill an important knowledge gap left by the paucity of data on interventions in Latin America.
This investigation did not allow for the separate evaluation of the individual components of the interventions; however, it is likely that each of the components aided in intervention effectiveness. One component of the intervention was the modification of the PE curriculum. Interventions modifying PE curriculum and policy regarding frequency and duration of PE classes have proven effective in increasing physical activity during PE classes (15,18). Another component of the intervention was increased access to physical activity through a daily exercise class and a daily recess period. Verstraete et al. (34) reported that interventions targeting recess and lunch can successfully increase physical activity during those periods in elementary schools. A final component of the intervention was the improvement of the esthetics and spaces to practice physical activity (e.g., the school courtyard) coupled with an awareness-raising campaign of the importance of physical activity. Although not previously tested in the school context, the Guide to Community Prevention Services reported that the creation or enhancement of spaces for participating in physical activity in community settings was an effective strategy to increase physical activity in communities (18). The results of this investigation suggest that similar interventions in schools, coupled with policy changes to improve PE class and increase access to physical activity, can successfully increase physical activity during school.
Although the focus of the current investigation was on physical activity during school, the findings demonstrate that school-based environmental interventions have the potential to increase all-day physical activity but do not always do so. Results of other studies testing the effect of school-based physical activity on all-day physical activity have been equivocal (6). Some studies in elementary, middle, and high schools have reported no change in all-day physical activity with school-based interventions (9-11,13). Other studies, all in elementary schools, have reported an increase in leisure time physical activity (22) and all-day vigorous physical activity (21,24) with school-based interventions. Interventions reporting significant effects were varied and were often very similar to those reporting nonsignificant effects. Nonetheless, one common component among studies positively affecting all-day physical activity was the incorporation of community or family into the school-based intervention (21,22,24). Contrary to these reports, the intervention of the current investigation did not have a community or family component possibly explaining why the improvement in physical activity detected was confined almost entirely to increases during the school day. As has been previously suggested (6), it is recognized that for long-term sustainable improvements in physical activity in the pediatric population, it may be necessary to include school, family, and community in public health interventions.
Students in the plus intervention group actually decreased out-of-school physical activity on school days. Although the decrease was nonsignificant, it negated the significant increase in physical activity during school. Donnelly et al. (7) reported compensation in out-of-school physical activity in third to fifth graders during a 2-yr school-based intervention. They reported a significant increase in physical activity during school and a decrease in out-of-school physical activity similar to what was detected in the plus group of the current investigation. Although this hypothesis could not be tested, possibly, students in the plus group perceived themselves to be more physically active during school because of their daily exercise class, whereas students in the basic group did not perceive themselves to be more physically active. Given the results of this investigation and those of Donnelly et al. (7), clearly demonstrating compensation, and the results of the multiple studies reporting no overall increase in daily physical activity despite school-based interventions, compensation may be an important barrier to successfully increasing the physical activity of children. Because this investigation tested a school-based intervention, physical activity was not measured during the weekend; however, further research of compensation and how to overcome this potential barrier would be enhanced by the additional investigation of physical activity during the weekend.
This intervention detected a significant improvement in strength measured by sit-ups relative to control. The change, however, was small, and the physiological importance is not clear. The few school-based interventions in the literature that measured strength reported similar improvements (1,22,27). The current intervention did not improve physical fitness as measured by cardiovascular endurance or flexibility in this sample of students. In the literature, more than 10 studies targeting PE have reported improved physical fitness measured by aerobic capacity (15,18) and field measures of endurance (1,4,7,8,19,27,33) and flexibility (16,19). However, some studies found improvements only in boys (4), and others found improvements only in girls (27), whereas others found only transient effects that could not be detected at further follow-up (4,7). In addition, several studies using field tests of physical fitness found no improvement in cardiovascular endurance (21,22) or flexibility (22,27). Distinct from the intervention of this investigation, which focused on fostering an environment conducive to increased physical activity, most interventions reporting positive effects on physical fitness included targeted training for the improvement of endurance, strength and, flexibility. Thus, if improvement in physical fitness is the outcome of interest, it may be necessary for the intervention to train for specific components of physical fitness to be successful.
This investigation was subject to many limitations. First, the intervention was conducted in primary schools in south Mexico City, and therefore, the results may not be generalizable to other areas of the city or country. Second, all participating schools accepted the intervention, and therefore, the sample may be more motivated than the general school population, again limiting generalizability. Third, pedometers provide a proxy measure of amount of physical activity but cannot measure intensity, another important component of physical activity in youth. Fourth, effectiveness of individual components of the intervention could not be measured. Fifth, although the degree of implementation of some aspects of the intervention could be measured (100% adherence to painted courtyards, teacher awareness-raising meetings, and workshops with PE teachers), an overall dose and/or intensity of the intervention could not be quantified. Finally, all-day step-count cutoffs are not universally accepted, and those used for evaluating activity during and after school were based on the distribution of steps within this population at baseline and, therefore, may not be generalizable to other populations.
In conclusion, the school-based environmental intervention of this investigation that targeted environment and policy accompanied with raising awareness was successful in improving physical activity of students during school in public primary schools in Mexico City. In some cases, however, compensation was detected with decreased out-of-school physical activity. School-based interventions with an environmental and policy focus can be a successful tool in increasing physical activity; however, for long-term sustainable changes in overall physical activity of children, more comprehensive interventions including community and/or family components may be necessary.
This investigation was funded in part by the International Life Sciences Institute and the Pan American Health Organization as part of the Healthy People/Healthy Lifestyles Project.
The authors, N.J. Aburto, J.E. Fulton, M. Safdie, T. Duque, A. Bonvecchio, and J.A. Rivera, declare no conflict of interest.
The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. The findings and conclusions are those of the authors and do not represent an official position of either the International Life Sciences Institute or the Pan American Health Organization.
The results presented in this article do not constitute endorsement by the American College of Sports Medicine.
1. Bonhauser M, Fernandez G, Püschel K, et al. Improving physical fitness
and emotional well-being in adolescents of low socioeconomic status in Chile: results of a school-based controlled trial. Health Promot Int
2. Centers for Disease Control and Prevention. Promote lifelong physical activity
among young people, risk behavior surveillance-United States. Morb Mortal Wkly Rep
3. Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ
4. Coleman KJ, Tiller CL, Sanchez J, et al. Prevention of the epidemic increase in child risk of overweight in low-income schools
: the El Paso coordinated approach to child health. Arch Pediatr Adolesc Med
5. Council on Sports Medicine and Fitness, Council on School Health. Active healthy living: prevention of childhood obesity through increased physical activity
6. Dobbins M, De Corby K, Robeson P, Husson H, Tirilis D. School-based physical activity
programs for promoting physical activity
and fitness in children and adolescents aged 6-18. Cochrane Database Syst Rev
7. Donnelly JE, Jacobsen DJ, Whatley JE, et al. Nutrition and physical activity
program to attenuate obesity and promote physical and metabolic fitness in elementary school children. Obes Res
8. Ewart CK, Young DR, Hagberg JM. Effects of school-based aerobic exercise on blood pressure in adolescent girls at risk for hypertension. Am J Public Health
9. Fardy PS, White RE, Haltiwanger-Schmitz K, et al. Coronary disease risk factor reduction and behavior modification in minority adolescents: the PATH program. J Adolesc Health
10. Going S, Thompson J, Cano S, et al. The effects of the Pathways Obesity Prevention Program on physical activity
in American Indian children. Prev Med
11. Gortmaker SL, Peterson K, Wiecha J, et al. Reducing obesity via a school-based interdisciplinary intervention among youth: Planet Health. Arch Pediatr Adolesc Med
12. Habicht JP. Estandarización de métodos epidemiológicos cuantitativos sobre el terreno [Standardization of anthropometric methods in the field]. PAHO Bull
. 1974;76:375-84. Spanish.
13. Haerens L, Deforche B, Maes L, Cardon G, Stevens V, De Bourdeaudhuij I. Evaluation of a 2-year physical activity
and healthy eating intervention in middle school children. Health Educ Res
14. Haskell WL, Kiernan M. Methodologic issues in measuring physical activity
and physical fitness
when evaluating the role of dietary supplements for physically active people. Am J Clin Nutr
15. Hoehner CM, Soares J, Parra Perez D, et al. Physical activity
interventions in Latin America: a systematic review. Am J Prev Med
16. Hopper CA, Gruber MB, Munoz KD, Herb RA. Effect of including parents in a school-based exercise and nutrition program for children. Res Q Exerc Sport
17. Jennings-Aburto N, Nava F, Bonvecchio A, et al. Physical activity
during the school day in public primary schools
City. Salud Publica Mex
18. Kahn EB, Ramsey LT, Brownson RC, et al. The effectiveness of interventions to increase physical activity
: a systematic review. Am J Prev Med
19. Kain J, Uauy R, Albala, Vio F, Cerda R, Leyton B. School-based obesity prevention in Chilean primary school children: methodology and evaluation of a controlled study. Int J Obes Relat Metab Disord
20. Lohman T, Roche A, Martorell R. Anthropometric Standardization Reference Manual
. Champaign (IL): Human Kinetics Books; 1988. 184 p.
21. Luepker RV, Perry CL, McKinlay SM, et al. Outcomes of a field trial to improve children's dietary patterns and physical activity
. The Child and Adolescent Trial for Cardiovascular Health. JAMA
22. Manios Y, Moschandreas J, Hatzis C, Kafatos A. Evaluation of a health and nutrition education program in primary school children of Crete over a three-year period. Prev Med
23. Matton L, Thomis M, Wijndaele K, et al. Tracking of physical fitness
and physical activity
from youth to adulthood in females. Med Sci Sports Exerc
24. McKenzie TL, Nader PR, Strikmiller PK, et al. School physical education: effect of the Child and Adolescent Trial for Cardiovascular Health. Prev Med
25. Morales-Ruán Mdel C, Hernández-Prado B, Gómez-Acosta LM, Shamah-Levy T, Cuevas-Nasu L. Obesity, overweight, screen time and physical activity
in Mexican adolescents. Salud Publica Mex
. 2009;51(4 suppl):613S-20S.
26. Physical Activity
Guidelines Advisory and Committee. Physical activity
guidelines advisory committee report. Washington (DC): US Department of Health and Human Services; 2008. 683 p.
27. Sallis JF, McKenzie TL, Alcaraz JE, Kolody B, Faucette N, Hovell MF. The effects of a 2-year physical education program (SPARK) on physical activity
and fitness in elementary school students. Sports, Play and Active Recreation for Kids. Am J Public Health
28. Troiano RP, Berrigan B, Dodd KW, Mâsse LC, Tilert T, McDowell M. Physical activity
in the United States measured by accelerometer. Med Sci Sports Exerc
29. Tudor-Locke C, Pangrazi RP, Corbin CB, et al. BMI-referenced standards for recommended pedometer-determined steps/day in children. Prev Med
30. Turley K, Wilmore J, Simons-Morton B, Willison J, Epping JN, Dahlstrom G. The reliability and validity of the nine-minute run in third grade children. Pediatr Exerc Sci
31. Twisk JW, Kemper HC, van Mechelen W. Tracking of activity and fitness and the relationship with cardiovascular disease risk factors. Med Sci Sports Exerc
32. US Department of Health and Human Services. Healthy People 2010: Understanding and Improving Health
. 2nd ed. Washington (DC): US Government Printing Office; 2000. 76 p.
33. Vandongen R, Jenner DA, Thompson C, et al. A controlled evaluation of a fitness and nutrition intervention program on cardiovascular health in 10- to 12-year-old children. Prev Med
34. Verstraete SJ, Cardon GM, De Clercq DL, De Bourdeaudhuij IM. Increasing children's physical activity
levels during recess periods in elementary schools
: the effects of providing game equipment. Eur J Public Health
35. World Health Organization. Young People's Health in Context. Health Behaviour in School-Aged Children (HBSC) Study: International Report from the 2001/2002 Survey
. Copenhagen (Denmark): World Health Organization Press; 2004. 250 p.
36. World Health Organization. Global Strategy on Diet, Physical Activity and Health
. Geneva (Switzerland): World Health Organization Press; 2006. 18 p.