Nunez-Gaunaurd, Annabel MSPT, PhD; Moore, James G. PT, PhD; Roach, Kathryn E. PT, PhD; Miller, Tracie L. MD; Kirk-Sanchez, Neva J. PT, PhD
INTRODUCTION AND PURPOSE
The global prevalence of childhood obesity is a complex public health issue with many plausible causes. These include poor diet and physical inactivity, both of which have been suggested as leading causes of preventable death in the United States.1 Possible secondary conditions of childhood obesity include type 2 diabetes mellitus,2 hypertension,3 and increased risk for metabolic syndrome.4 Musculoskeletal complications secondary to childhood obesity have also been documented, including increases in slipped capital femoral epiphyses, tibia varum, skeletal fractures, impaired lower extremity strength, poor dynamic balance, as well as reports of musculoskeletal pain and difficulties with mobility.5–8
Children from minority backgrounds are at a greater risk of becoming obese (OB). Between 2009 and 2010, 24.3% and 21.2% of children and adolescents of African American and Hispanic race/ethnicity, respectively, were OB compared with 14.0% of children and adolescents of white non-Hispanic race/ethnicity.9 Concomitantly, physical activity (PA) is reduced by the age of 13 in girls and 14 in boys.10 Currently, the Center for Disease Control and Prevention and the World Health Organization recommend that children participate in at least 60 minutes of recreational activity daily.11,12 Children who are overweight (OW) and OB may have difficulty performing recommended levels of PA to maintain a healthy weight (HW) because of early onset of health-related conditions, musculoskeletal impairments, and activity limitations brought on by a high body mass index (BMI) and adiposity.
Physical therapists (PTs) have the potential to contribute positively to the management of childhood obesity. As a human movement expert, a PT can design a safe exercise program that accounts for a child's present medical condition, impairments, functional limitations, home/school environment, family support, and personal goals. According to the American Physical Therapy Association's (APTA's) Vision Statement 2020, PTs will be recognized as health care professionals with direct access by consumers and leading experts for the diagnosis, intervention, and prevention of impairments, functional limitations, and disabilities related to movement, function, and health.13 The Guide to Physical Therapist Practice14 elucidates the role of the PT in prevention and in the promotion of health, wellness, and fitness in the context of the disablement model. Physical therapists have the training to identify risk factors and behaviors that may impede optimal functioning. However, in the area of childhood obesity, there is a paucity of physical therapy–related research.
Objective and standardized measures of impairments and PA levels among children who are OW and OB are not well described and often rely on self-report. Previous studies have indicated a negative correlation between greater BMI and motor proficiency, PA, and strength among children aged 8 to 12 years.15–19 However, this relationship has not been examined in middle school–aged children of different ethnic backgrounds. A better understanding of the relationship between obesity-related impairments and activity limitations may assist in the design and implementation of effective strategies to increase PA levels, especially among children of minority ethnicities. More culturally appropriate strategies will assist in reducing health disparities.
The purpose of this study was to compare physical impairments, activity limitations, and PA, using validated measurement tools among children of Hispanic ethnicity who are HW, OW, and OB. The objectives of this study were (1) to compare motor proficiency (BOTS), strength (push-ups, abdominal curls, timed Sit-to-Stand), endurance (6-Minute Walk Test [6MWT]), musculoskeletal pain, and Timed Up and Down Stairs (TUDS) among these 3 BMI groups; (2) to compare duration, intensity, and frequency of PA among the 3 BMI groups; and (3) to examine the correlation between BMI percentile and strength, endurance, motor proficiency, and PA in middle school children of Hispanic ethnicity.
This study used a cross-sectional design. A convenience sample was drawn from students from 2 middle schools in a public school system. These 2 schools were chosen because of the diversity in socioeconomic status within the school and the school's willingness to participate. The principals and teachers at these schools received an institutional review board–certified information letter that summarized the purpose of the study, the time requirements, and contact information. To assist with recruitment and return of research equipment, parents were given gift cards when the research equipment was returned.
Eighty-six middle school children participated in the screening between October 2010 and June 2011, during extracurricular hours. Informed consents were translated to Spanish and certified for this community. Investigators communicating with the children were bilingual, and the study was explained in the child's preferred language. Informed consent and assent forms were signed by both parents and children on-site, before screening activities. This study was approved by the institutional review boards at the university and the public school system.
Children between the ages of 10 and 15 years, regardless of weight and fitness level, who attended these schools and were available and willing to participate in the after-school screening activity were included in the study. Children were excluded from study participation if the parents reported physical disabilities, congenital cardiovascular pathologic conditions, or respiratory pathologic conditions. All other children were enrolled in the screening process. Screening sessions were implemented in the schools' libraries and nearby corridors for walking and stair-climbing measurements. Participating children and parents were given a summary report on the child's physical fitness, motor proficiency, and BMI-for-age percentile results. They were given the opportunity to discuss these findings with a licensed PT.
Height, weight, and waist and hip circumference were taken for all children. Height to the nearest 0.25 in was measured using a standing height scale. Weight to the nearest pound was measured in standing, using a portable digital weight scale. Height and weight were converted to meters and kilograms to calculate BMI (weight [kg]/height2 [cm]). Waist circumference was taken in the standing position at a level between the last rib and the iliac crest, and hip circumference was taken at the level of the greatest protrusion of the gluteal muscles.
Children's BMIs were calculated using standard procedures, and percentiles for age were obtained from tables from the Centers for Disease Control and Prevention. Children were categorized as HW if BMI for age was greater than 5% and less than 85%, OW if BMI for age was greater than or equal to 85% and less than 95%, and OB if BMI for age was greater than or equal to 95%.20 High levels of body fat are associated with increasing health risks. The sensitivity and specificity associated with using BMI for age greater than 85th percentile as a criterion for screening children with high levels of body fat are 0.82 and 0.96, respectively.21 In contrast to more precise measures of body fat (such as underwater weighing or dual-energy x-ray absorptiometry), health care providers can assess weight and height routinely and easily in a clinical or community setting, using BMI-for-age percentile charts.20
Blood Pressure and Heart Rate
As per National Institutes of Health guidelines,22 blood pressure in children was measured with a standard clinical sphygmomanometer, using a stethoscope placed over the brachial artery pulse, proximal and medial to the cubital fossa, and below the bottom edge of the cuff (about 2 cm above the cubital fossa). The child's back was supported, and the arm (cubital fossa) was supported at the heart level. Prehypertensive and hypertensive classifications are generated from standardized tables for children's blood pressures on the basis of sex, age, and height.22 Furthermore, the expert task force currently recommend that children and adolescents with a blood pressure reading of 120/80 mm Hg or more be considered as prehypertensive.22
The Bruininks-Oseretsky Test of Motor Proficiency, Second Edition, Short Form
The Bruininks-Oseretsky Test of Motor Proficiency Short Form (BOT-2 SF) is an individually administered performance assessment used to measure fine and gross motor skills in children 4 through 21 years of age and provides a standardized measurement of motor proficiency.23 Previous studies have yielded excellent interrater reliability (r = 0.97) and good test-retest reliability (r = 0.85).23 The BOT-2 SF consists of 14 items taken proportionally from the BOT-2, which includes fine motor precision, fine motor integration, manual dexterity, bilateral coordination, balance, running speed and agility, and upper limb coordination and strength.23 The child is given a raw score for each of the 14 test items, which is then converted to a point score, thus allowing each item to be evaluated on a graded scale. Point scores from each individual item are then added to obtain the total BOT2 SF point score. On the basis of this total point score, a standard score and a percentile rank are obtained from age- and sex-specific tables provided in the BOT-2 manual. BOT-2 SF percentile ranks were chosen for analysis in this study.
The Number of Abdominal Curls performed is one of the items in the BOT-2 SF battery that was analyzed individually as a measurement of trunk strength. The examiner instructed the child to complete as many abdominal curls as possible in 30 seconds. The abdominal curls test has a high degree of test-retest reliability (r = 0.97) among college students.24 Among younger children (aged 6-10 years), the reliability is lower but acceptable (r = 0.70).25
The Number of Push-ups performed, another item in the BOT-2 battery, was analyzed separately as an upper body strength and endurance measure. The child was given 30 seconds to complete as many 90° push-ups with or without knees supported (child's choice). The start and end position is a plank position with or without knee support and elbows in extension. For the downward phase, the child lowers the body until the elbows reach a 90° angle. The test-retest reliability for the 90° push-up calculated by intraclass correlation coefficients ranged from 0.50 to 0.86 for 3 separate samples of elementary and high school students.25
Timed Sit-to-Stand Test
The timed Sit-to-Stand (STS), a functional performance measure, was used to evaluate lower extremity strength and endurance. Similar to walking, STS is a repeated activity done throughout the day. The STS has been measured as the number of repetitions performed over a given time (10 or 30 seconds).26 A 60-second STS test was chosen for our study. With the use of an adjustable chair, the starting position of each child was standardized with hip flexion at 90°, knee flexion at 90° (full extension was defined as 0°), feet parallel and flat on the floor, trunk erect, and hands on waist or crossing the chest. The child was asked to stand up to the defined standing position (which required the child's trunk and lower extremities be fully extended) and repeat as many cycles as possible of STS at a comfortable speed in 60 seconds. The reliability and validity for the 60-second STS has not been tested in children.
6-Minute Walk Test
The 6MWT is a functional performance measure used to evaluate endurance and can easily be administered on school grounds. The purpose of the 6MWT is to have the child walk as far as they can in 6 minutes.27 In addition, resting heart rate and blood pressure were recorded before and after the 6MWT, using standard procedures as described previously. Concurrent validity was examined among a group of children and adolescents between the ages of 12 and 16 years by demonstrating a fair correlation between the 6MWT and maximum oxygen uptake determined on an exercise treadmill (r = 0.44). Test-retest reliability within a subgroup found the intraclass correlation coefficient to be 0.94 (0.89–0.96).28
Timed Up and Down Stairs Test
The TUDS test is a functional mobility outcome measure that can also be administered on school grounds. Potentially, the test can be used to examine strength of the lower extremities and trunk, coordination for fast reciprocal movements, and anticipatory and reactive postural control.29 The TUDS can be used to assess how quickly a child ascends and descends a flight of stairs (12-14 steps), using a stopwatch recording in seconds. Adequate reliability and validity have been found with the TUDS test, and scores are correlated with functional mobility and balance in the pediatric population.29 Intrarater and interrater reliability is excellent (ICC(2,1) = 0.99). The test-retest reliability of the TUDS is excellent (r = 0.94). Since the number of steps per flight of stairs was different for each school, steps per second were calculated instead of the TUDS score.
StepWatch Step Activity Monitor
The StepWatch Step Activity Monitor (SAM) (Orthocare Innovations, Oklahoma City, Oklahoma) was used to obtain objective measurement of frequency, intensity, and duration of the children's PA.30–32 The SAM is a light-weight instrument worn around the ankle that uses a custom accelerometer linked to a microprocessor to detect and store step counts in user-definable time intervals. It can record data continuously at 1-minute intervals for up to 41 days.30 The subject was asked to attach the SAM with a Velcro strap to the appropriate ankle and wear it daily for 7 days and remove only for bathing and sleeping.30 The SAM was returned and data were uploaded into the computer to obtain activity counts, including total steps per day and total steps and minutes per day of PA at different intensities of step activity. Intensity levels were set on the basis of previous SAM data from adults and defined as zero step rate (0 steps per minute), low (1-15 steps per minute), medium (greater than 16 steps per minute), and high (greater than 40 steps per minute).32 Gait characteristics are comparable to adults by 7 years of age.33 Reliability of SAM step measurements compared with observer counted steps in walking has been documented at r = 0.91 to 0.99.30,31 The SAM has been reviewed and validated in children in previous studies, including the step ranges defined earlier.30,31 At least 2 to 5 complete days from the 7-consecutive-day sampling period were used to estimate average daily PA levels. Investigators also piloted a strategy to increase compliance with SAM wear and return, by sending a daily text message to participating children to remind them to wear their SAM.
Statistical analysis was conducted using SAS software, Version 9. Descriptive statistics were computed to determine the mean, median, and standard deviation for child age, height, weight, grade level, BMI, and BMI-for-age percentile. For comparison, subjects were initially assigned into 1 of 3 groups as defined by BMI-for-age percentile, HW, OW, and OB. Analysis of variance was used to compare differences in motor proficiency (BOT-2), strength (push-ups, abdominal curls, STS), endurance (6MWT), and activity limitations (TUDS) among children who were HW, OW, and OB. Analysis of variance was completed to compare differences in moderate to vigorous PA levels, which included minutes in moderate to high activity, high activity only, moderate- and high-level step counts, total step counts, and sedentary time arising from SAM data, among BMI-for-age percentile groups. Because of smaller samples of children who were OW and OB, BMI-for-age percentile groups were further collapsed into 2 groups, HW versus a combined overweight and obese group (OWB). Pearson product-moment correlations were computed to examine relationships between children's BMI-for-age percentile and motor proficiency, strength, endurance, and PA levels in children who were HW and children who were OWB.
Of the 86 children who participated in the study, 47 (55%) were male and 39 (45%) female. Children were an average of 12.2 years old, with a standard deviation of ±1.0. Fifty-four percent, 27%, and 19% were in the 6th, 7th, and 8th grades, respectively. Seventy-eight children (92%) reported to be of Hispanic ethnicity/race. Of the remaining 8% of children who reported to be of non-Hispanic ethnicity/race, 5, 2, and 1 reported to be of White non-Hispanic, African American, and Asian race, respectively. The BMI percentile ranged from 7% to 99.3%. Fifty-five percent of the children were classified as HW, 23% OW, and 22% OB. No statistical difference in age was found among the 3 BMI percentile categories. Resting and postexercise vital signs were not statistically different among children in the 3 BMI categories except for resting systolic blood pressure, which was significantly higher among children who were OB (109 vs 112 vs 118, P = .019). See Table 1. A further analysis using χ2 statistics identified 53% of children who were OB as prehypertensive, compared with 22% and 20% of children who were HW and OW, respectively (P = .032).
For all impairment and activity measures except the TUDS and push-ups, a significant difference was found among the 3 groups (Table 2). Post hoc testing indicated statistically significant differences between the children who were OB and HW in all cases, except for the STS test where differences were seen among all 3 BMI groups. Overall, children of HW performed better than children who were OW or OB, and children who were OW performed better than children who were OB. Compared with children with HW, children who were OW and OB had significantly lower BOT-2 SF standard scores (45 [HW] vs 43 [OW] vs 39 [OB]; P = 0.003). Post hoc testing demonstrated statistically significant differences between children who were OB and children with HW. Furthermore, most children who were categorized as OB (68.4%) scored less than 17% in the BOT-2, which is interpreted as below-average motor proficiency ability,23 as compared with 40% of children who were OW and 27% of children with HW.
Differences among BMI groups in average daily PA were analyzed in 2 ways. First, a 3-way comparison was done among BMI groups of HW, OW, and OB participants. Second, a 2-way comparison was carried out between children who were grouped as HW versus the combined group of children who were OWB. Figure 1 illustrates the average daily minutes spent in low, moderate, and high activity and minutes sedentary among the 3 BMI groups. Figure 2 illustrates the daily average for total steps and steps taken at moderate and high activity levels. No statistically significant differences were found among the 3 BMI groups, but a trend was observed for children who were OB to be the least active and most sedentary and children of HW were most active and least sedentary. Analysis of weekend-only PA was omitted since the number of weekend days with proper SAM wear varied considerably, ranging from 0 to 2 days.
Statistical significant differences were demonstrated, however, when comparing weekday-only PA levels between children who were OWB versus children of HW (Table 3). Weekday-only data for total daily step count means (12 848 OWB vs 14 214 HW, P = .043) and high step rate means (4520 OWB vs 5378 HW, P = .050) were lower and minutes sedentary (1016.3 OWB vs 986.18 HWB, P = 0.038) were higher for children classified as OWB.
Table 4 describes the correlation between BMI-for-age percentile and performance variables in HW and OWB groups. In OWB, BMI-for-age percentile showed a moderate negative correlation to the BOT-2 SF standard scores (r = −0.47, P = .002) and a fair negative correlation to STS (r = −0.36, P = .024) and total abdominal curls (r = −0.33, P = .041). No correlations were found between BMI percentile and performance measurements in the HW group.
Similar to previous cross-sectional studies that include BMI-for-age percentile assessment in US children of Hispanic ethnicity,34,35 our sample of predominately children of Hispanic ethnicity revealed that 45% were either OW or OB. An alarming finding from this study was that more than half of the children who were OB were considered to be at least prehypertensive by current pediatric guidelines of BP readings of 120/80 mm Hg or more.22 Childhood hypertension has been shown to persist in adulthood.36 It is optimal that trained health care professionals such as PTs assist OB children in designing an effective and safe exercise program. Furthermore, a parent of one participant was contacted by a PT to communicate the child's resting BP of 142/88 and to recommend a referral to the pediatrician for follow-up.
The results related to motor proficiency and BMI support previous finding by Graf and Koch,37 where negative associations between childhood obesity and motor proficiency were identified. Wrotniak et al,17 also found a negative association between BMI and motor proficiency in children who were not OB. It is plausible that the relationship between level of obesity and motor proficiency may be an indication that difficulty with motor tasks increases the likelihood of children being more OW or OB. A child who is OB with low motor proficiency may have more difficulty participating in recreational PA than peers of HW and average motor proficiency.
Our results related to abdominal strength support previous findings that abdominal strength and stamina were found to be compromised among children who were OB.38 The findings related to lower extremity strength are supported by previous research by Almuzaini,39 where an inverse relationship was found between knee extensor endurance and BMI among children. Deficiencies in trunk and lower extremity strength in this population may further contribute to musculoskeletal fatigue and increase risk of injury during both functional activities and recreational physical activities.40 Strength deficiencies in trunk and lower extremity may place children who are OB at a biomechanical disadvantage when performing activities of daily living, particularly when learning new tasks, and perpetuate musculoskeletal injuries. Differences in number of push-ups performed were not statistically significant in children who were either OW or OB when compared with children who were HW. This finding was expected since strength deficiencies in children who are OB are mostly observed in weight-bearing musculature.19
In this study, children who were OB walked an average of 45.25 m less than children who were HW in the 6MWT, reflecting a slower walking speed and decreased endurance. Similar observations were reported in a study by Geiger et al,27 where the 6MWT distance was significantly less among children who were OW before a weight loss intervention than among children who were not OW. This decrease in walking speed and endurance may contribute to increased fatigue during PA because of greater metabolic demands. The 6MWT distance not only revealed impaired endurance by children who were OB, but this finding can also be reflective of limitations in activities of daily living. No significant correlations between BMI-for-age percentile and 6MWT distance were observed in children who were OW or of HW.
The trend of declining PA as BMI-for-age percentile increased suggests the possibility of a dosage response to PA. Importantly, the average steps taken per day by children in this sample was not enough to meet BMI-referenced standard cut-point recommendations for maintaining a HW range for 6- to 12-year-old girls and boys (recommended levels of 12000 and 15000 steps,41 respectively, versus our 10688 and 13969 steps, respectively, observed in this study). Specifically, only 24% of children who were OB met these recommendations compared with 32% of children who were of HW. These results are consistent with another study investigating PA and obesity among children of Hispanic ethnicity.42 Current Centers for Disease Control and Prevention recommendation for PA among all children is 60 minutes of moderate-to-vigorous PA daily.11 Children in this sample averaged well over the recommended duration, 151 and 147 minutes, P = .09, for HW and OWB groups, respectively. However, durations spent in vigorous activity was 44 and 39 minutes, respectively, P = .07. These results illustrate the need to consider the intensity as well as duration of PA and sedentary periods.
Finally, results of this study provide evidence to support the role of PTs as experts in assessing mobility and function impaired by either obesity or other medical conditions. Either by administering consultative services in the extracurricular setting or implementing assessment programs aimed at helping children who are OB attain optimal health, PTs may play an integral role in the management, reversal, and prevention of childhood obesity. These findings also lend support to APTA's Vision 2020 as PTs become practitioners of choice by consumers for health and wellness needs. Furthermore, PTs can be part of the multidisciplinary team working toward Healthy People 2020 (see http://www.healthypeople.gov/2020/about/default.aspx) and the World Health Organization's Global Strategies on Diet, Physical Activity and Health objectives, as pediatric obesity continues to be an important public health priority.
Several limitations of this study must be considered. Behavioral characteristics of parents and children who choose to participate in this type of screening may not be representative of average children who are OW and their parents. Children who were not as active may have chosen not to participate in the screening. Most children in this cohort were also in after-school care, and programs varied from homework assistance to music instruction to outdoor play activities. Further work in school-based screening should take into consideration the types of programs that children are involved in after-school. Finally, results from this study and previous correlational studies stem from cross-sectional study designs that indicate an interrelationship between PA, motor proficiency, and BMI. One must also consider that being less physically active may make you more OW and an increase in weight may make you less proficient in your motor abilities. Future study recommendations would include a longitudinal examination to best explain the direction of causality for these variables.
Measurement strategies employed in this study, including those for BMI, have some limitations. The BMI-for-age percentile is not a direct measurement of body composition (fat mass vs fat-free mass). The relationship between body composition and BMI-for-age percentile improves at higher BMI-for-age percentile levels. The OW group likely included some children with a healthy level of fat but with higher lean muscle mass, thus confounding the results. Freedman et al,43 found that levels of body fatness among children who had a BMI for age between the 85th and 94th percentiles were more variable, as 50% of these children had a moderate level of body fatness, 30% had a normal body fatness, and 20% had an elevated body fatness, as determined by dual-energy x-ray absorptiometry. Furthermore, a study by Wang44 revealed a positive association between early sexual maturation and obesity among girls and a negative association among boys. Future studies with this age group may benefit from analyzing boys and girls separately and including measures of sexual maturation.
The lack of statistical association between children's PA levels or sedentary time and BMI percentiles in this study may have been because of insufficient power. A prestudy power analysis indicated that a sample of size of at least 30 subjects per BMI-for-age percentile category was necessary to achieve high statistical power (87%-97%) when calculating analysis of variance. Although overall SAM compliance was anticipated to be a problem for this sample, our study had a similar compliance rate as Mcdonald et al,30 86% and 87%. Future studies with the SAM should employ greater incentives to improve children's compliance, with emphasis on weekend days when most children forget or choose not to wear the SAM.
Children who are OB have greater impairments in motor proficiency, strength, and endurance than children of HW. Among children who are OW and OB, higher BMI-for-age percentile is negatively correlated with motor proficiency, trunk strength, and lower extremity strength. Children presenting more than the 85th BMI-for-age percentile are likely to take fewer steps per day, engage in less vigorous PA, and spend more minutes sedentary than children of HW. Body impairments and activity limitations may be constraining the ability of a child who is OW or OB to participate at recommended levels of PA. The findings of this study have important clinical relevance for PTs, who are uniquely qualified to assess existing medical conditions, body impairments, and activity limitations that impede PA participation in children who are OW or OB. Most importantly, this study elucidates potential modifiable factors in childhood obesity to assist in reducing health disparities in children from minority backgrounds.
The authors thank the administrative staff (Dr Siblesz, Mr Abreu, Dr Del Terzo, Mr Diaz, and Mr Gonzalez) and students from the participating Miami-Dade County Public Schools. They also thank recent University of Miami Physical Therapy graduates (Jessica, Julio, Lory, Maria, and Natalie) for their assistance in data collection.
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adolescent; body mass index; child; Hispanic Americans; ideal body weight; motor activity; motor skill; muscle strength; overweight; obesity
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