unhealthy lifestyle behaviors including physical inactivity during childhood might track to adulthood , and in addition to their short - term health hazards , they might be associated with chronic diseases later in life . sedentary lifestyle is a well - documented predisposing factor for obesity , metabolic syndrome , and non - alcoholic fatty liver disease in younger ages resulting in further chronic problems in adulthood , e.g. cardiovascular disease , diabetes mellitus , hyperlipidemia , hypertension , cancers and osteoporosis ( 13 ) . the data clearly indicated that girls engaged in significantly less physical activity than their counterparts ( 4 ) in both childhood and adolescence ( 57 ) . thus , there is a critical need to pay attention to girls physical activity patterns and influences . this is a major concern globally and in iran because it has been reported that iranian girls are less physically active than boys ( 8) . physical activity describes the actions or movements that one actually makes ( 9 ) and is influenced by a variety of factors ( 10 ) . lindquist , reynolds and goran ( 1999 ) provided a hierarchal framework that included factors that affect children s physical activity behavior at four levels - physiological factors such as motor skill competence ( msc ) , psychological factors such as perceived motor competence ( pmc ) , socio - cultural factors including parents and family structure , and ecological factors such as the physical environment ( 11 ) . motor skill competence is mastery of physical skills and movement patterns that enable enjoyable participation in physical activities ( 12 ) , and perceived motor competence is defined as an individual s awareness and belief of their capability to perform both gross and fine motor tasks ( 13 ) . in two separate models , both welk ( 14 ) and stodden et al . although considering both perceived motor competence and motor skill competence in their conceptual models , they purported different competence more influential on children s physical activity behavior . welk in his model proposed that although direct effects of motor skill competence on children s activity behavior are possible , indirect effects of perceived motor competence are perhaps more likely ( 14 ) . on the other hand , stodden et al . , in their conceptual model proposed that the motor skill competence is the primary underlying mechanism that increases children s engagement in physical activity and perceived motor competence mediates relationbetween motor skill competence and physical activity ( 15 ) . there is no consensus on the influence of perceived motor competence and motor skill competence on children s physical activity behavior . previous researchers have studied the relation between physical activity and msc and pmc in children separately . evidence revealed positive association between physical self perception ( 16 , 17 ) , perceived competence in physical education ( 18 ) , perceived athletic competence ( 19 ) , perceived sport competence ( 20 ) , and motor skill competence ( 2124 ) , and just one research was found which compared the influence of both pmc and msc on children s physical activity ( 25 ) . motor skill competence , but not perceived motor competence , influenced children s physical activity behavior significantly and explained 9% variance of 9 year - olds girl s physical activity level ( 25 ) . this research was carried out to bulk out limited evidence of influence of perceived motor competence and motor skill competence on children s physical activity behavior . therefore , this cross - sectional study aimed to investigate correlates of iranian girls physical activity and determine which variable best predicts third grade school girls physical activity : perceived motor competence or motor skill competence . third grade girls from a state primary school located in the urban southwestern part of tehran province ( shahr - e - qods ) , iran in 2012 , were invited to voluntarily participate in the study . informed parental consent was obtained for 352 girls ( mean age 8.7 , sd 0.3 yrs ) and the institutional review board of the corresponding author s university approved the present study . the sample included children in the low - moderate range of socio - economic background , with no reported history of learning difficulties or behavioral , physical , neurological or orthopedic diagnoses . accordingly , 352 girls constituted the final sample , who completed iranian version of test of gross motor development-2 ( tgmd-2 ; 26 ) , and physical activity questionnaire for older children ( paqoc ) ( 27 ) , physical ability sub - scale of self - description questionnaire ( 28 ) ( table 1 ) . the physical activity questionnaire for older children ( paq - c ) was used to determine the participants physical activity level ( 29 ) . paq - c requests participants to respond to the physical activity behaviours for the last 7 days by asking them to check a list of activities for frequency of participation on a scale from no , 1 - 2 times per week , 3 - 4 , 5 - 6 , to 7 times or more . questions are also asked about their physical activity behaviours during physical education ; recess , at lunch - time , right after school , and evenings , as well as the last weekend. the paq - c demonstrates high test - retest reliability in a sample of 84 children in grades 4  8 and demonstrate interclass correlation coefficients of r = 0.82 for girls and significantly correlates with other measures of physical activity in elementary - age students ( 29 ) . this questionnaire has been supported as a valid and reliable measure and cronbach s alpha of 0.894 was measured in iranian children ( 27 ) . motor skill competence was assessed using the test of gross motor development-2 edition ( 30 ) . the measure is made up of locomotor ( run , gallop , hop , horizontal jump , and slide ) and object control ( t - ball strike , stationary basketball dribble , catch , kick , over hand throw , and underhand roll ) subtests , each assessing six skills . the tgmd-2 assesses the process of skill performance ( skill components ) rather than the outcome or product of performance ( 30 ) , and has proved to be a valid and reliable method for studying iranian children ( 26 ) . before testing each skill , participants were given a visual demonstration of skill by the researcher using the correct technique , but were not told what components of the skill were being assessed . general encouragement but no verbal feedback on performance was given during or after the tests . all skills were video - recorded and later assessed by one trained assessor who also administered the test . after each performance the examiner recorded a score on her form corresponding to the evaluation of that particular skill component . subtest scores were then summed to calculate each child s gross motor quotient ( gmq ) ( 30 ) . the self - description questionnaire-1 ( sdq-1 ) was used to assess girls perceived motor competence . the physical ability subscale of sdq-1 includes 8 items and uses a five - point response scale , with higher scores indicating more positive perception . scores were summed to create a total perceived motor competence score ranging from 5 to 40 ( 31 ) . previous researches support the internal consistency and construct validity of sdq-1 scores in iranian children ( 28 ) . in this sample , prior to gathering data , participants and parents were given written information about the nature of the study . written permission was obtained from the participants , parents , and guardians prior to their child s involvement in the study . no child had any reported history of learning difficulties or any behavioral , neurological or orthopedic problems that would qualify as exclusionary criteria for the history . first , the tgmd-2 was executed in school yard within 4 weeks and inter - rater objectivity was measured 87% . the physical subscale of sdq-1 was completed in the classroom , by all children at the same time . latterly , physical activity questionnaire was completed by all children at the same time at the classroom . the children were tested by the examiner and assistant who had been trained in the test protocols . the initial analysis was descriptive in nature ( i.e. , means , standard deviations ) . this was followed by multiple linear regression models to investigate the best predictor of girls physical activity . third grade girls from a state primary school located in the urban southwestern part of tehran province ( shahr - e - qods ) , iran in 2012 , were invited to voluntarily participate in the study . informed parental consent was obtained for 352 girls ( mean age 8.7 , sd 0.3 yrs ) and the institutional review board of the corresponding author s university approved the present study . the sample included children in the low - moderate range of socio - economic background , with no reported history of learning difficulties or behavioral , physical , neurological or orthopedic diagnoses . accordingly , 352 girls constituted the final sample , who completed iranian version of test of gross motor development-2 ( tgmd-2 ; 26 ) , and physical activity questionnaire for older children ( paqoc ) ( 27 ) , physical ability sub - scale of self - description questionnaire ( 28 ) ( table 1 ) . the physical activity questionnaire for older children ( paq - c ) was used to determine the participants physical activity level ( 29 ) . paq - c requests participants to respond to the physical activity behaviours for the last 7 days by asking them to check a list of activities for frequency of participation on a scale from no , 1 - 2 times per week , 3 - 4 , 5 - 6 , to 7 times or more . questions are also asked about their physical activity behaviours during physical education ; recess , at lunch - time , right after school , and evenings , as well as the last weekend. the paq - c demonstrates high test - retest reliability in a sample of 84 children in grades 4  8 and demonstrate interclass correlation coefficients of r = 0.82 for girls and significantly correlates with other measures of physical activity in elementary - age students ( 29 ) . this questionnaire has been supported as a valid and reliable measure and cronbach s alpha of 0.894 was measured in iranian children ( 27 ) . motor skill competence was assessed using the test of gross motor development-2 edition ( 30 ) . the measure is made up of locomotor ( run , gallop , hop , horizontal jump , and slide ) and object control ( t - ball strike , stationary basketball dribble , catch , kick , over hand throw , and underhand roll ) subtests , each assessing six skills . the tgmd-2 assesses the process of skill performance ( skill components ) rather than the outcome or product of performance ( 30 ) , and has proved to be a valid and reliable method for studying iranian children ( 26 ) . before testing each skill , participants were given a visual demonstration of skill by the researcher using the correct technique , but were not told what components of the skill were being assessed . general encouragement but no verbal feedback on performance was given during or after the tests . all skills were video - recorded and later assessed by one trained assessor who also administered the test . after each performance the examiner recorded a score on her form corresponding to the evaluation of that particular skill component . subtest scores were then summed to calculate each child s gross motor quotient ( gmq ) ( 30 ) . the self - description questionnaire-1 ( sdq-1 ) was used to assess girls perceived motor competence . the physical ability subscale of sdq-1 includes 8 items and uses a five - point response scale , with higher scores indicating more positive perception . scores were summed to create a total perceived motor competence score ranging from 5 to 40 ( 31 ) . previous researches support the internal consistency and construct validity of sdq-1 scores in iranian children ( 28 ) . in this sample , prior to gathering data , participants and parents were given written information about the nature of the study . written permission was obtained from the participants , parents , and guardians prior to their child s involvement in the study . no child had any reported history of learning difficulties or any behavioral , neurological or orthopedic problems that would qualify as exclusionary criteria for the history . first , the tgmd-2 was executed in school yard within 4 weeks and inter - rater objectivity was measured 87% . the physical subscale of sdq-1 was completed in the classroom , by all children at the same time . latterly , physical activity questionnaire was completed by all children at the same time at the classroom . the children were tested by the examiner and assistant who had been trained in the test protocols . the initial analysis was descriptive in nature ( i.e. , means , standard deviations ) . this was followed by multiple linear regression models to investigate the best predictor of girls physical activity . table 1 provides an overview of descriptive statistics . sample characteristics and descriptive statistics ( n=352 ) pearson correlations showed significant relationships among correlates ( table 2 ) . a stepwise regression analysis indicates that gmq and pmc accounted for significant amounts of variance for moderate to vigorous physical activity ( r=0.21 , f=48.9 , p=0.001 ) . and , gmq ( r=0.15 , p= 0.001 ) resulted in more influence on pa in comparison with pmc ( r=0.06 , p=0.001 ( table 3 ) . pearson s bivariate correlations among measures ( n=352 ) predictors of girls moderate to vigorous physical activity ( n=352 ) a stepwise regression analysis indicates that gmq and pmc accounted for significant amounts of variance for moderate to vigorous physical activity ( r=0.21 , f=48.9 , p=0.001 ) . and , gmq ( r=0.15 , p= 0.001 ) resulted in more influence on pa in comparison with pmc ( r=0.06 , p=0.001 ( table 3 ) . pearson s bivariate correlations among measures ( n=352 ) predictors of girls moderate to vigorous physical activity ( n=352 ) this study describes the influential role of both pmc and msc on physical activity level of third grade school girls . the multiple regression models showed that both pmc and msc are significant predictors of girls physical activity , and of particular interest was that msc had more influence in comparison with pmc on physical activity level . our results suggest that having mastery of motor skills ( which includes locomotor and object control skills ) and high and positive perception of motor competence promote girls physical activity participation and as a result might reduce physical inactivity behavior . this findings support stodden s conceptual model which shows that msc , not pmc , is a more influential factor on physical activity level in young children ( 15 ) . the model showed that msc is underlying mechanism which influence children s physical activity participation ; and in middle and later childhood ( 6 - 10 year - olds ) , also higher levels of msc will offer a greater motor repertoire to engage in various physical activities , sports , and games ; in fact , msc drives physical activity levels ( 15 ) . the theoretical basis explaining the mechanism of the more influential role of msc on physical activity , as we found among girls in the current study , suggests that proficiency in movement skills provides the behavioral competency required for participation in a variety of physical activity ( 32 ) , and may influence other determinants of behavior , such as perceptions of competence ( 20 ) . without the prerequisite movement competence , children may opt out of opportunities for physical activity or may have preference for more sedentary pursuits ( 14 , 15 ) . the results , also , support mcintyre s longitudinal study which msc was better predictor of children s physical activity than pmc(25 ) . pmc was not a significant contributor to 9-year - olds girls physical activity levels ( 25 ) . however , our results along with previous studies revealed both msc ( 2023 ) and pmc ( 1620 ) are significant correlates of youth s physical activity . mcintyre s study is the first longitudinal research which investigated influential roles of msc and pmc on physical activity level jointly ( 25 ) . moreover , although pmc made significant contribution to our sample s physical activity , the variance just was 6% . the video assessments of msc using a validated , process - oriented measure , was a method that reduced measurement bias in the current study . however , physical activity assessment in this study may have been limited by the use of paqoc . this questionnaire does not provide an estimate of caloric expenditure or specific frequency , time , and intensity information and does not discriminate between specific activity intensities ( 29 ) . also , the findings of this research should be interpreted cautiously , since physical activity was assessed during autumn / winter and the data may also have been confounded by seasonal and weather - related variations . high competent girls in motor skill have motor repertoire to engage in various physical activities , sports , and games . this study highlights a need for intervention programs based on influential factors in order to promote children s physical activity behavior and healthy lifestyle in the future . ethical issues including plagiarism , informed consent , misconduct , data fabrication and/or falsification , double publication and/or submission , redundancy , etc . have been taken into consideration by authors .