childhood obesity has reached epidemic proportions in the united states , with 32 percent of children and adolescents defined as either overweight or obese . among latino american children and adolescents , the prevalence and complications of obesity are even higher compared with children of other racial and ethnic identity . this issue has substantial public health relevance as hispanics are the largest and fastest growing ethnic minority in the united states , and data suggest that 85% of overweight youth will remain overweight as adults . potential explanations include : ( 1 ) biological differences in the susceptibility or resistance to weight gain ; ( 2 ) differences in metabolic / mechanical efficiency ; ( 3 ) sociocultural differences in lifestyle factors ( such as dietary composition or participation in physical activities ) ; or ( 4 ) environmental factors such as access to preventive or treatment programs [ 36 ] . obesity is commonly accompanied by insulin resistance , which precedes and plays a major role in the etiology of the metabolic syndrome , type 2 diabetes mellitus and subsequent cardiovascular disease [ 711 ] . among us adults and adolescents , latinos have the highest prevalence of the metabolic syndrome , and more recent reports indicate an increasing incidence of type 2 diabetes among obese latino american , african american , and native american adolescents .   sedentary behavior is associated with both the risk of obesity and of insulin resistance [ 1416 ] , and there are data to suggest that the prevalence of sedentary behaviors is higher among children from less - represented minority groups [ 3 , 4 , 1719 ] . in an effort to reduce physical inactivity in children , the united states public health service ( usphs ) 2008 physical activity guidelines for americans recommends a minimum of 60  minday of moderate - to - vigorous physical activity ( mvpa : e.g. , bicycle riding , skate boarding , soccer , jump roping ) . furthermore , there are now data in adults confirming the distinct contributions of physical activity and sedentary behavior to the development of obesity and metabolic impairments ; whether this remains so among children , however , is not clear . few studies have examined the associations among physical activity , sedentary behavior , body composition , and metabolic markers in defined samples of latino children . moreover , determining the interrelatedness of these factors is complicated by the fact that obesity lies in the biologic pathway between mvpa or sedentary behavior and metabolic risk , thereby minimizing the true magnitude of contribution from these lifestyle behaviors . we studied cross - sectionally a sample of obese latino children in order to determine the independent contributions of mvpa and sedentary behaviors on the odds of insulin resistance ( ir ) over and above that of obesity . we hypothesized that obese children reporting more mvpa will have a lower odds of ir compared with their less active counterparts ; however , the magnitude of this association would be mediated by obesity and other risk factors in the biological pathway between obesity and insulin resistance ( e.g. , sedentary behavior , glucose , and fasting insulin concentrations ) . participants were 113 latino youth ( 58 boys and 55 girls ) , ages of 715 years enrolled in a comprehensive community - based obesity intervention program . participants were recruited through advertisements placed at community facilities such as clinics , schools , and churches in washington , dc , usa . to avoid selection biases from large families , as well as correlated reporting biases within families , only one child from each family eligibility requirements included latino ethnicity ( as determined by the parent 's identifying themselves , their spouses , and both sets of grandparents within the hispanic or latino cultural group ) , a body mass index ( bmi )  95th percentile for age and sex , and otherwise good health . children who were chronically ill and/or with known medical conditions such as type 2 diabetes , pervasive development delay , cerebral palsy , severe asthma , cushing syndrome , obesity - associated genetic syndrome ( e.g. , prader - willi syndrome ) , or untreated hypothyroidism were excluded from study . all study procedures were approved by the institutional review board of children 's national medical center ( cnmc ) , and parents provided informed written consent , while the children provided signed assent prior to their participation . all data were collected at one baseline visit prior to participation in the comprehensive treatment program . on the day of testing , participants were admitted to the general clinical research center ( gcrc ) at cnmc at 07:00 following a 12 hr overnight fast . body weight was measured on a digital scale ( healthometer , bridgeview , il , usa ) with the participant in underwear and a hospital gown , while height was measured using a wall - mounted stadiometer ( seca 216 , hanover , md , usa ) . the body mass index ( bmi ) waist circumference was measured in triplicate at the umbilicus using a non - elastic tape measure to the nearest 0.1 centimeter . total body fat mass ( kg ; % ) and fat - free mass ( kg ) were determined by air displacement plethysmography ( life measurement inc . , pubertal stage was determined by a pediatrician separately for boys and girls , and children were classified as prepubertal ( tanner stage 1 ) ; mid prepubertal ( tanner stage 2 ) ; or late prepubertal ( tanner stage 3 ) . resting energy expenditure ( ree ) was measured using an open - circuit indirect computerized calorimeter equipped with a mask ( sensor medics , yorba linda , ca , and ultima cardio2 system , medical graphics corporation , st . all calibration procedures were performed to manufacturer specifications prior to testing each morning , including manual flow calibrations using a 3  l syringe and gas calibration with gases of known concentration . participants were measured at rest in a supine position for a total of 30 minutes including a 5-minute acclimation period . data collected during the initial five minutes of testing were excluded from the total 30-minute test period to allow for an adjustment period to the test conditions . measurements were recorded at 1 minute intervals and then averaged over the remainder of the test period to obtain a measure of ree that was adjusted for body weight ( kg ) . the respiratory exchange ratio ( rer = vco2/vo2 ) values of the rer closer to 0.70 indicate a greater reliance on fat ( relative to glucose ) oxidation , while values closer to 1.00 indicate greater glucose oxidation . a 2-hour oral glucose tolerance test was performed using the protocol described by the world health organization . fasting blood samples were collected from an antecubital vein for the determination of basal glucose , insulin , and free fatty acids ( ffas ) concentrations . participants were then given oral glucose drink ( 1.75  gmkg ( body weight ) of glucose with a maximum of 75  gm ) to consume within 2 - 3  min . serum insulin concentrations were determined by a solid - phase , 2-site chemiluminescent immunometric assay ( immulite 2000 analyzer , diagnostic products , los angeles , ca , usa ) . plasma glucose levels were determined using the hexokinase - glucose-6-phosphate dehydrogenase method ( dade behring inc , deerfield , il , usa ) . insulin sensitivity was calculated using the whole - body insulin sensitivity index ( wbisi = 10,000/ ( ( fasting glucose ( mgdl )  fasting insulin ( uml ) )  ( average glucose  average insulin ) ) ) , which has been validated in children and adolescents . the wbisi has demonstrated excellent correlation with clamp - derived insulin sensitivity estimates in children and adolescents and with intramyocellular lipid content , a tissue marker for insulin resistance . we also considered the 2 h postchallenge insulin concentration as an indicator of insulin action . postchallenge insulin concentrations correlated strongly with the wbisi ( r = 0.81 ; p < 0.0001 ) and is easier to interpret compared with the wbisi . there currently exist no evidence - based cut - points for defining insulin resistance in children . therefore , in order to determine the odds of insulin resistance ( ir ) associated with physical activity in these obese children , those with a 2 hr postchallenge insulin concentration > 57  uml were characterized as ir ; otherwise they were considered not insulin resistant . this postchallenge insulin concentration corresponds to a homeostatic model assessment ( homa - ir = ( fasting glucose  0.056 )  ( fasting insulin/22.1 ) )   value of > 2.5 , which is a clinical cut - point often used to characterize insulin resistance in children . children completed the activity and sedentary behavior questionnaire ( asbq ) , which comprised questions from the validated 2001 youth risk behavior survey and the world health organization study of health behavior of school children survey . the asbq queried both the frequency and duration of moderate - to - vigorous physical activity acquired through organized sport , informal recreational pursuits , and physical education class . in addition , the asbq contained questions about time per day watching television and at the computer . two indices were then calculated by multiplying the frequency score by the duration score for these activities : ( 1 ) moderate - vigorous physical activity ( mvpa ) index , with scores that ranged from 0 to 150 ; ( 2 ) sedentary index ( si)which was derived from questions pertaining to tv viewing and computer time  with scores ranging from 0 to 150 . physical education ( pe ) volume was derived by multiplying reported frequency by duration of weekly pe class resulting in scores ranging from 0 to 300  minwk . to address the aims of the 2008 physical activity guidelines , the mvpa index was then dichotomized based on a volume of mvpa that did or did not meet those guidelines for moderate - to - vigorous physical activity ( every day for 60  min or more ) . level of acculturation is an important confounder of the associations among physical activity , obesity and diabetes risk . to assess this important study variable , mothers answered questions ( administered in spanish by a fluently bilingual trained research assistant ) derived from the bicultural involvement questionnaire . acculturation was measured via 17 items assessing constructs of linguistic fluency and comfort level in spanish and in english ; language use at home , and with work and friends ; preferences in music , books , magazines and visual media . each of the items was scored on a scale with a maximum score of 4 for 14 items , of 3 for two items , and of 5 for one item . total scale scores ranged from 17 to 67 , with higher scores reflecting greater acculturation to american culture . in the current study , the acculturation scale demonstrated adequate internal consistency (  = .77 ) . descriptive statistics ( mean  sd ; frequencies ( % ) ) were generated on all study variables according to those who were and who were not ir . between - group differences in mean levels of the study variables were tested using t - tests for independent samples , while the chi - square statistic tested associations between categorical variable frequencies and ir status . study variables demonstrating a statistically significant association with ir status in the bivariable analysis were then entered into a multivariable logistic regression model in order to determine their independent contribution to the odds of insulin resistance . the variables age , sex , pubertal status , and acculturation were forced into this model . the regression model was then run backward , with those variables demonstrating an alpha level of 0.10 or greater eliminated from the model . parameter estimates , as well as adjusted odds ratios ( ors ) and 95% confidence intervals ( ci ) are reported for the final regression model . because our primary study variables ( mvpa and sedentary behavior ) were ordinal indices , the or represents the increase ( or decrease ) in the odds of ir for each unit increase of the given index . the odds of ir among children meeting the 2008 mvpa guidelines were compared with the odds of children who did not ( the referent group ) . study characteristics according to ir status are presented in table 1 . as indicated , subjects with and without ir were similar with regard to age , bmi , fat mass , and percent body fat and tanner score . girls tended to have a slightly higher prevalence of ir ( 0.56 ) compared with boys ( 0.44 ) ( p = 0.13 ) , and those with ir also tended to have a higher z - score for waist circumference ( 0.33 ) . fasting rer was comparable between the groups ; however , it is worth noting that it was high in both groups , suggesting some degree of metabolic inflexibility among these obese children . weight - adjusted ree was significantly lower ( p < 0.01 ) and acculturation score was significantly higher ( p < 0.05 ) in those children with ir , compared with those without ir . fasting glucose and ffa concentrations were no different between study groups ; however , fasting insulin and 2 h glucose levels were significantly greater ( p < 0.01 ) in the children with ir compared with those without it ( table 2 ) . as expected , insulin sensitivity , based on the wbisi , was markedly lower ( p < 0.001 ) and 2 h insulin concentrations substantially higher ( p < 0.001 ) in those children who were defined as ir compared with those who were not . of note is the observation that both groups of children were able to maintain normal glucose tolerance based on a fasting glucose concentration criterion of < 100  mgdl .   reported sedentary behavior was similar between groups ( si = 10.5  6.2 versus 10.9  6.5 for those with and without ir , resp . ; in contrast , the reported mvpa index was significantly lower among those characterized as insulin resistant compared with who were not ( mvpa index = 14.8  18.4 versus 24.9  32.1 , resp . ; p < 0.05 ) . participation in physical education tended to be lower among those children with ir compared with those without it ( pe  volume = 73.7  74.3 versus 80.0  79.6  minwk , resp . ; only 18% of the participants met the uspha guidelines for 60  min or more of mvpa on most days of the week . those who met the guidelines had an mvpa index score of 58.6  31.7 , compared with a score of 8.3  6.9 among those who did not ( p < 0.001 ) . we observed a strong unadjusted association between meeting those guidelines and protection from insulin resistance ( or = 0.28 ; p < 0.01 ) . study variables that were statistically significant in the bivariable analysis were then entered in a stepwise multivariable logistic regression model to determine their independent contribution to the odds of ir . these variables were mvpa , as well as fasting insulin , 2 h glucose concentrations , ree , and acculturation score . the variables age , sex , pubertal status , and waist circumference were also included due to their reported association with ir in the literature . each unit increases in the mvpa index lowered the odds of ir by 3% ( or = 0.97 ; 95% ( ci : ( 0.951.00 ) ) . we then repeated the analysis and substituted the dichotomous mvpa variable for the mvpa index . parameter estimates from the final logistic regression model are presented in table 3 . in the presence of two very powerful correlates of insulin resistance : 2 hr postchallenge glucose ( p < 0.01 ) and fasting insulin ( p < 0.001 ) concentrations , mvpa maintained a significant association with ir as those obese children who reported enough mvpa to meet the 2008 guidelines experienced a substantially lower odds of ir , compared with the children who did not ( ( or = 0.29 ; 95% ci : ( 0.100.92 ) ) ) . age , sex , puberty status , ree , and acculturation score did not remain statistically significant in the multivariable model . since obesity lies along the biological pathway between mvpa and insulin resistance , it would seem as though the contribution of mvpa to ir would be diminished in the presence of obesity . similarly , the association among the weight - adjusted ree , the rer , the waist circumference , and ir appeared blunted in these obese children . that we observed mvpa to be associated with the odds of ir ( independent of fasting insulin and 2  h postchallenge glucose levels ) underscores the distinct relation of muscle contraction to insulin action ( via improvements in mitochondrial function , insulin signaling , and glucose transport ) from that of obesity , as well as the continued importance of mvpa in mitigating the risk of metabolic impairments with obesity . other research has described the benefits of vigorous activity or mvpa to ir among diverse samples of children , and these reported benefits were also independent of total or central adiposity [ 2931 ] . importantly , these studies relied on both self - report and objective measures of physical activity . pubertal status is often implicated as an effect modifier in the pathway toward pediatric diabetes . previous studies consistently report that puberty is associated with about a 2530% reduction in insulin sensitivity , with peak reduction occurring at tanner stage 3 ; whether this functional impairment operates independent of accelerated fat deposition during puberty is not clear . an ample body of evidence also supports the complicated relation that acculturation has with physical activity , obesity , and diabetes risk . in general , a high level of acculturation is associated with greater amounts of reported physical activity and exercise ; however , acculturation also increases the risk of obesity and diabetes risk , presumably through dietary changes . we did not observe an association between acculturation and mvpa , but those with ir had a significantly higher acculturation score compared with those without ir . this later association did not maintain statistical significance in the presence of fasting insulin and 2 hr glucose concentrations , however . adolescents watching greater than two hours of television per day engage in significantly less vigorous physical activity than those who spend less time in front of the screen ; however , very few studies report a strong correlation between television viewing and total physical activity , indicating that time engaging in one behavior does not necessarily displace time in the other . moreover , the small positive correlation often reported between television viewing per se and obesity in children has been attributed to higher caloric intake with television viewing , rather than to lower energy expenditure [ 33 , 34 ] . we observed that reported sedentary behavior ( tv viewing and computer use time ) was similar between those with and without ir in our obese pediatric sample , and similar to other studies [ 3335 ] , our measure of sedentary behavior demonstrated no association with the mvpa index ( r = 0.02 ; p = 0.83 ) , to bmi ( r = 0.13 ; p = 0.16 ) , or to body fat% ( r = 0.17 ; p = 0.11 ) . this assumes that sedentary behavior is not sufficiently biologically relevant to ir in the face of pediatric obesity , or that sedentary behavior was not measured accurately . studies that used objective measures of sedentary time in children [ 30 , 35 , 36 ] report associations with metabolic outcomes that are distinct from those using measures of mvpa  thereby supporting the notion that sedentary time and mvpa are two separate behavioral and physiologic constructs .   among the strengths of this study was the reliance on several clinical measures of metabolic control under both fasting and postprandial conditions . in addition , we believe the 2-h insulin response to an actual physiologic challenge ( the ogtt ) to be a more valid indicator of insulin resistance than a simple fasting value or the homa . we note , however , the limitations inherent to a cross - sectional analysis in that the temporal sequencing between physical activity , attained obesity , and insulin resistance could not be established . indeed , there is now evidence that children with the greatest impairments in insulin sensitivity have the greatest susceptibility to weight gain over time [ 16 , 37 , 38 ] and the greatest resistance to weight loss interventions [ 39 , 40 ] . second , we relied on a valid and widely used self - reported measure of physical activity and sedentary behavior ; yet the information bias associated with any self - reported measure is well known . we assume , however , that the tendency to over- or underreport mvpa was nondifferential between those with and without ir , since participants were not aware of their 2 hr postchallenge insulin values when answering the physical activity questions . therefore , we are confident that no systematic reporting bias occurred which would have falsely inflated the independent contribution of mvpa to ir risk . these findings support the notion that even in the presence of frank pediatric obesity , moderate - to - vigorous physical activity conveys important benefits to insulin sensitivity  although further longitudinal evidence is necessary to infer a causal relation with confidence . nonetheless , home- , school- , and community - based programs for promoting mvpa through physical education , sports , and/or culturally appropriate physical activities should be of primary public health importance in order to protect the health of children at risk for obesity and insulin resistance .
we examined the independent association between moderate - to - vigorous physical activity ( mvpa ) and insulin resistance ( ir ) among obese latino children ( n = 113 ; 715 years ) who were enrolled in a community - based obesity intervention . 
 baseline information on physical activity was gathered by self - report . 
 clinical assessments of body composition , resting energy expenditure ( ree ) , as well as glucose and insulin responses to an oral glucose tolerance test ( ogtt ) were performed after an overnight fast . 
 insulin resistance was defined as a 2 h insulin concentration > 57  uml1 . 
 we observed that those obese children who met the 2008 guidelines for mvpa ( 60  min / day ) experienced a significantly lower odds of ir compared with those not meeting the guidelines ( or = 0.29 ; 95%  ci : ( 0.100.92 ) ) and these findings were independent of age , sex , pubertal stage , acculturation , fasting insulin , and 2 h glucose concentrations . efforts to promote 60 min or more of daily mvpa among children from ethnic minority and high - risk communities should assume primary public health importance .