© 2014 John Wiley & Sons A/S.
Scand J Med Sci Sports 2015: 25: 543–551 doi: 10.1111/sms.12267
Published by John Wiley & Sons Ltd
Construct validity and test–retest reliability of the International Fitness Scale (IFIS) in Spanish children aged 9–12 years M. Sánchez-López1,2, V. Martínez-Vizcaíno1, A. García-Hermoso3, D. Jiménez-Pavón4, F. B. Ortega5 Social and Health Care Research Centre, University of Castilla-La Mancha, Cuenca, Spain, 2School of Education, University of Castilla-La Mancha, Ciudad Real, Spain, 3Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Talca, Chile, 4 Department of Physical Education, School of Education, University of Cadiz, Puerto Real, Spain, 5PROFITH “PROmoting FITness and Health through physical activity” research group, Department of Physical Education and Sports, Faculty of Sport Sciences, University of Granada, Granada, Spain Corresponding author: M. Sánchez-López, Centro de Estudios Sociosanitarios, Universidad de Castilla-La Mancha, C/Santa Teresa Jornet s/n, 16071 Cuenca, Spain. Tel: +34 969 179179, Fax: +34 969 179100, E-mail: [email protected]
1
Accepted for publication 15 May 2014
We aimed to examine (a) the construct validity and reliability of the International Fitness Scale (IFIS) in children; and (b) the association of both self-reported and measured fitness with cardiometabolic risk. Crosssectional study in 1145 Spanish children (9–12 years). We measured body fat, waist circumference, blood pressure, lipids, insulin, and fitness level (reported and measured). A validated cardiometabolic syndrome index was used. An age- and sex-matched sample of 245 children originally not included in the study sample fulfilled IFIS twice for reliability purposes. IFIS was able to correctly classify children according to their measured fitness levels (analysis of covariance, adjusted for sex and age was used).
Test–retest reliability of IFIS items was also good, i.e., average weighted Kappa = 0.70. Our data also suggest that both measured and reported cardiorespiratory, and speed and agility fitness were associated with cardiometabolic risk factors, such as adiposity and a cardiometabolic syndrome risk score. The associations for muscular fitness (both reported and measured) differed depending on how it was expressed (i.e., absolute vs relative terms). Our findings suggest that self-reported fitness, as assessed by IFIS, is a valid, reliable, and healthrelated measure, and it can be a good alternative at population level when physical fitness cannot be measured.
Physical fitness has been shown to be an important marker of health in children (Ortega et al., 2008a). Furthermore, low levels of physical fitness in childhood are associated with an increased risk of cardiovascular disease (CVD) in adulthood (Ruiz et al., 2009). The assessment of physical fitness in children has clinical, educational, and public health relevance. However, fitness testing is not always feasible in large surveys and epidemiological studies in which time, equipment or qualified personnel are sometimes limited. In this context, the International Fitness Scale (IFIS), a short and simple scale, available in nine different languages, including Spanish, has shown good reliability and validity in adolescents from nine European countries (HELENA study) (Ortega et al., 2011), and recently also in Spanish young adults (Ortega et al., 2013). Moreover, self-reported fitness levels in adolescents and adults, using IFIS, has shown to be strongly associated with CVD risk factors (Ortega et al., 2011, 2013). Because of their cognitive development it is unknown to what extent 12-year-old children or younger are able to correctly perceive and report their fitness levels.
The aim of the present study was to examine: (a) the ability of IFIS to accurately classify Spanish children aged 9–12 years according their measured fitness levels (i.e., construct validity); (b) its test–retest reliability; and (c) to examine the associations of both self-report fitness (IFIS) and measured fitness with adiposity and CVD risk factors in children.
Materials and methods Study design and main study sample (Cuenca) Data from the Cuenca Study were gathered from the baseline measurements (September–November 2010) of a clusterrandomized trial aimed to evaluate the effectiveness of leisuretime physical activity on the prevention of childhood obesity (MOVI-2) (Martínez-Vizcaíno et al., 2012). All the fourth- and fifth-grade Primary School children (n = 1592) belonging to 20 public schools from the province of Cuenca, Spain, were invited to participate, and 1158 (72.7% participation rate) accepted. No differences were found between age and sex of children that agree to participate and who did not. Finally, self-report valid data from 1145 of them (578 boys and 567 girls) were obtained. All children completed the questionnaire, but 13 of them did incorrectly fulfill
543
Sánchez-López et al. it (children marked several response options on the same item, or left some unmarked items), and were consequently excluded from the analyses. The study protocol was approved by the Clinical Research Ethics Committee of the Virgen de la Luz Hospital, in Cuenca. After obtaining the approval of the Director and the Board of Governors (Consejo Escolar) of each school, a letter was sent to all parents of children in fourth- and fifth-grade, inviting them to a meeting at which the study objectives were outlined and written authorization for their children’s participation was requested. Informative talks, in which the schoolchildren were asked to collaborate, were then held class-by-class.
Study design and sample of the reliability study and replication study (Córdoba) Because of practical reasons in the Cuenca Study, physical fitness testing took place immediately after IFIS was administered. Therefore, these participants could not be used for reliability analyses, as this could influence the perception on their fitness levels at the retest. Consequently, the test–retest study was conducted in a separate age-matched sample of Spanish children (9–12.5 years old), from Córdoba province, South of Spain. The data from the Córdoba study were gathered from “the Healthy lifestyle; physical activity, fitness and nutrition in school children cross-sectional study” (HAFICA, Spanish name; Hábitos Saludables de Actividad FIsica, Condición Física y Alimentación en Primaria) aiming to obtain reliable data from Spanish school children about healthy behaviors, fitness levels, and nutrition. A total of 564 children (296 girls) were included. Parents and children gave their written informed consent to participate in the research. The study was performed following the ethical guidelines of the Declaration of Helsinki 1961 (revision of Edinburgh 2000), the Good Clinical Practice, and the legislation about clinical research in humans in each of the participating countries. The protocol was approved by the Human Research Review Committees of the university center. A total of 245 participants from Córdoba province (46% boys) successfully completed IFIS on two occasions (2 weeks apart) and were included in the reliability study. In addition, after the retest of IFIS was done, physical fitness was measured in this sample from Córdoba, so we decided to compare self-reported and measured fitness also in this smaller sample from Córdoba, as a replication study of the main data from Cuenca. A total of 339 participants had valid data on IFIS and at least one measured fitness test and were included in the replication study. The same methods were used to assess IFIS and measured fitness in both studies. The results of this replication analysis are presented as additional Supporting Information. The sample size for both validation and reliability was enough according to estimations of several studies (DeVellis, 2003).
Self-reported fitness Self-reported fitness was assessed by IFIS, originally validated in European adolescents (Ortega et al., 2011). IFIS consists of a Likert-type scale (range 1–5) with five response options (very poor, poor, average, good, and very good) about perceived overall fitness, and its main components: cardiorespiratory fitness (CRF), muscular strength, speed and agility, and flexibility. IFIS is available in nine different languages at the HELENA study website (http://www.helenastudy.com/IFIS). The Spanish and English versions of the IFIS used in this study are found in the Supporting Information Appendices S1 and S2, respectively. IFIS showed “high” validity and “moderate” to “good” reliability in Spanish young adults (Ortega et al., 2013).
544
Physical fitness Physical fitness was assessed using tests that have previously shown high validity and reliability levels, following the outcomes of three systematic reviews and several methodological studies conducted as part of the Assessing Levels of Physical Activity and fitness (ALPHA) project (Ruiz et al., 2011). Cardiorespiratory fitness (CRF) was assessed by the 20-m shuttle run test (Leger et al., 1988). Participants are required to run between two lines 20 m apart, while keeping pace with audio signals emitted from a prerecorded compact disc. The initial speed is 8.5 km/h, which is increased by 0.5 km/h (1 min equals one stage). Children were encouraged to keep running as long as possible throughout the course of the test, and it was finished when the child failed to reach the end lines concurrent with the audio signals on two consecutive occasions. The last half stage completed was recorded as an indicator of his or her CRF. Muscular fitness (MF) was assessed using two tests: (a) handgrip test (maximum handgrip strength assessment) using a hand dynamometer with adjustable grip (TKK 5401 Grip D; Takei, Tokyo, Japan). The grip span of the dynamometer was adjusted to the children’s hand size, using the equations previously validated in Spanish children (España-Romero et al., 2008). The participant squeezes gradually and continuously for at least 2 s, performing the test with the right and left hands in turn (Ortega et al., 2008b). Children made two trials (alternately with both hands) with a short resting time between them. The maximum score in kilograms for each hand was recorded. The average (in kilograms) of both hands was used in the analysis. (b) The standing broad jump test (lowerlimb explosive strength assessment). From a starting position immediately behind a line, standing with feet approximately shoulder width apart, the schoolchildren jump horizontally to achieve maximum distance. The best of three attempts was recorded in centimeters (Ortega et al., 2008b). MF/strength can be expressed in absolute (activities like carrying a suitcase, moving a heavy object, handgrip strength test, etc.) or relative terms (activities in which the person has to lift, hold or carry on his/her own body weight, standing long jump). In our analyses, we divided the score in handgrip by weight, which implies a transformation from absolute strength to relative strength; and we multiplied the score in standing long jump test by weight, so that it was transformed from relative strength to absolute strength (Artero et al., 2011; Jimenez-Pavon et al., 2012; Ortega et al., 2013). The analysis of these four variables (2 original + 2 transformed) in relation to IFIS informs about what the participants report (absolute vs relative strength) when they are asked about their MF levels. Speed and agility were measured using the 4 × 10 shuttle run test in which the child runs as fast as possible from the starting line to the other line and returns to the starting line (10 m apart), crossing each line with both feet every time. This is performed twice, covering a distance of 40 m (4 m × 10 m). Every time the child crosses any of the lines, he/she picks up (the first time) or exchanges a sponge, which has been previously placed behind the lines. The time taken to complete the test was recorded to the nearest tenth of a second (Vicente-Rodriguez et al., 2011). Flexibility by sit and reach test. This test uses a standard box. Subject performs a backward flexion of the trunk, and the maximum distance reached (in cm) by the subject’s fingertips is measured. The better of two attempts was recorded.
Adiposity and anthropometric variables Height and weight was measured using standard procedures. Waist circumference was measured three times with a flexible tape at the midpoint between the last rib and the iliac crest at the end of a normal expiration. Body fat percentage was estimated with an eight-electrode BC-418 MA bioimpedance analysis system (Tanita
Validity of self-reported fitness in children Corp., Tokyo, Japan) (Pietrobelli et al., 2004) using the mean of two readings. Measurements were made in barefoot children, under fasting conditions, after urinating, and after a 15-min rest.
Other CVD risk factors Diastolic and systolic blood pressure were determined by the average of two measurements taken at an interval of 5 min, with the subject resting for at least 5 min before the first measurement. The participant was seated in a quiet and calm environment, with the right arm placed in a semiflexed position at heart level. Blood pressure was measured by an automated procedure using the OMRON M5-I monitor (Omron Healthcare Europe BV, Hoofddorp, the Netherlands) (El Assaad et al., 2003). The mean arterial pressure (MAP) was then calculated using the following formula: Diastolic blood pressure + [0.333 × (Systolic blood pressure − Diastolic blood pressure)]. Trained nurses measured the anthropometric variables and blood pressure. Blood samples were taken by puncturing the cubital vein, under standardized conditions, between 08:15 h and 09:00 h, with the participant having fasted at least 12 h beforehand. Blood samples, which would take more than 75 min to reach the laboratory were centrifuged in situ and transported refrigerated. The following variables were determined following biochemical parameters: triglycerides (TG) (glycerol phosphate oxidase, peroxidase enzymatic method) and c-direct plus high-density lipoprotein (HDL). Lipid profile determinations were made in a weekend, in a MODULAR DPP system from Roche Diagnostics Corporation (Indianapolis, Indiana, USA), and the insulin levels were assessed using an Immulite 2000 double system platform of Siemens. We calculated a metabolic syndrome (MetS) index as the sum of the age-sex standardized scores of waist circumference, log triglyceride-to-HDL-c ratio (TG-to-HDLc), MAP, and fasting insulin. The validity of this MetS index has been previously tested using confirmatory factor analysis (Martínez-Vizcaino et al., 2010, 2011).
(Pearson correlation). To estimate polyserial correlation coefficients, we used the Hetcor library of the R software.
Results The distribution of the answers of the IFIS for the five question responses were shifted to the right in both genders, with a low percentage of participants reporting to have a very poor or poor fitness level (Fig. 1). Because of the small number of participants at the bottom extreme, the categories were merged as very poor/poor for the rest of the analyses, except for reliability analyses in which the raw data were used. Participants reporting average, good, and very good CRF, MF, speed and agility, and flexibility had a better measured CRF, MF, speed and agility, and flexibility, respectively, compared with participants reporting very
Statistical analysis For all the analyses, we used IBM SPSS 19 (SPSS, Inc., Chicago, Illinois, USA). The ability of the IFIS to categorize children correctly into physical fitness levels was determined by means of analysis of covariance (ANCOVA) adjusted for sex and age. This analysis was considered an indicator of the validity of IFIS. Measured fitness variables were entered as dependent variables and self-reported fitness variables as fixed factors. Differences between boys and girls in self-reported fitness were analyzed using the Chi-squared tests. The test–retest reliability of the IFIS was examined by quadratic weighted Kappa coefficient, (Cohen, 1968). Cohen’s weighted Kappa is not available in the standard SPSS package, but command syntax is available from the “Knowledgebase” at http:// www.SPSS.com (SPSS, Inc.). Data for imputation into the syntax were generated from cross-tabulation. Finally, ANCOVA models were used to test differences in the mean scores of total body fat and MetS index by categories of self-reported and measured fitness, controlling for sex and age. Sex- and age-specific percentiles 10th, 30th, and 50th for physical fitness variables were calculated and used to class the participants into measured fitness groups: very poor/poor (P50th). These percentiles were selected a posteriori so that the distribution of participants falling into the measured fitness groups was equivalent to that observed in IFIS categories, i.e., very poor/poor, average, good, and very good. In order to analyze the intensity of the relationship between measured and self-reported fitness with total body fat and MetS index, we estimated correlation coefficients between these cardiometabolic indicators with IFIS’s items (polyserial correlation) and objectively measured fitness variables
Fig. 1. Distribution of the answers for the five questions of International Fitness Scale (IFIS) in male and female children of Cuenca Province (n = 1145, 578 boys and 567 girls). CRF, cardiorespiratory fitness; MF, muscular fitness; SP-AG, speed and agility; Flex, flexibility; Overall, overall physical fitness.
545
Sánchez-López et al. Table 1. Means and standard error (SE) of measured physical fitness by self-reported physical fitness categories in children
n
Cardiorespiratory fitness 20-m shuttle run (stage) Muscular fitness handgrip (kg) Standing long jump (cm) Speed and agility shuttle run 4 × 10 m (s)† Flexibility sit and reach (cm)
Very poor/poor (1) Average (2)
Good (3)
Very good (4) P
Pairwaise comparisons*
Mean
Mean
Mean
1–2 2–3 2–4 3–4 1–3 1–4
SE
Mean
SE
SE
SE
1108
2.55
0.19
2.79 0.09
3.47 0.08
4.14 0.08 < 0.001 ns
Scand J Med Sci Sports 2015: 25: 543–551 doi: 10.1111/sms.12267
Published by John Wiley & Sons Ltd
Construct validity and test–retest reliability of the International Fitness Scale (IFIS) in Spanish children aged 9–12 years M. Sánchez-López1,2, V. Martínez-Vizcaíno1, A. García-Hermoso3, D. Jiménez-Pavón4, F. B. Ortega5 Social and Health Care Research Centre, University of Castilla-La Mancha, Cuenca, Spain, 2School of Education, University of Castilla-La Mancha, Ciudad Real, Spain, 3Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Talca, Chile, 4 Department of Physical Education, School of Education, University of Cadiz, Puerto Real, Spain, 5PROFITH “PROmoting FITness and Health through physical activity” research group, Department of Physical Education and Sports, Faculty of Sport Sciences, University of Granada, Granada, Spain Corresponding author: M. Sánchez-López, Centro de Estudios Sociosanitarios, Universidad de Castilla-La Mancha, C/Santa Teresa Jornet s/n, 16071 Cuenca, Spain. Tel: +34 969 179179, Fax: +34 969 179100, E-mail: [email protected]
1
Accepted for publication 15 May 2014
We aimed to examine (a) the construct validity and reliability of the International Fitness Scale (IFIS) in children; and (b) the association of both self-reported and measured fitness with cardiometabolic risk. Crosssectional study in 1145 Spanish children (9–12 years). We measured body fat, waist circumference, blood pressure, lipids, insulin, and fitness level (reported and measured). A validated cardiometabolic syndrome index was used. An age- and sex-matched sample of 245 children originally not included in the study sample fulfilled IFIS twice for reliability purposes. IFIS was able to correctly classify children according to their measured fitness levels (analysis of covariance, adjusted for sex and age was used).
Test–retest reliability of IFIS items was also good, i.e., average weighted Kappa = 0.70. Our data also suggest that both measured and reported cardiorespiratory, and speed and agility fitness were associated with cardiometabolic risk factors, such as adiposity and a cardiometabolic syndrome risk score. The associations for muscular fitness (both reported and measured) differed depending on how it was expressed (i.e., absolute vs relative terms). Our findings suggest that self-reported fitness, as assessed by IFIS, is a valid, reliable, and healthrelated measure, and it can be a good alternative at population level when physical fitness cannot be measured.
Physical fitness has been shown to be an important marker of health in children (Ortega et al., 2008a). Furthermore, low levels of physical fitness in childhood are associated with an increased risk of cardiovascular disease (CVD) in adulthood (Ruiz et al., 2009). The assessment of physical fitness in children has clinical, educational, and public health relevance. However, fitness testing is not always feasible in large surveys and epidemiological studies in which time, equipment or qualified personnel are sometimes limited. In this context, the International Fitness Scale (IFIS), a short and simple scale, available in nine different languages, including Spanish, has shown good reliability and validity in adolescents from nine European countries (HELENA study) (Ortega et al., 2011), and recently also in Spanish young adults (Ortega et al., 2013). Moreover, self-reported fitness levels in adolescents and adults, using IFIS, has shown to be strongly associated with CVD risk factors (Ortega et al., 2011, 2013). Because of their cognitive development it is unknown to what extent 12-year-old children or younger are able to correctly perceive and report their fitness levels.
The aim of the present study was to examine: (a) the ability of IFIS to accurately classify Spanish children aged 9–12 years according their measured fitness levels (i.e., construct validity); (b) its test–retest reliability; and (c) to examine the associations of both self-report fitness (IFIS) and measured fitness with adiposity and CVD risk factors in children.
Materials and methods Study design and main study sample (Cuenca) Data from the Cuenca Study were gathered from the baseline measurements (September–November 2010) of a clusterrandomized trial aimed to evaluate the effectiveness of leisuretime physical activity on the prevention of childhood obesity (MOVI-2) (Martínez-Vizcaíno et al., 2012). All the fourth- and fifth-grade Primary School children (n = 1592) belonging to 20 public schools from the province of Cuenca, Spain, were invited to participate, and 1158 (72.7% participation rate) accepted. No differences were found between age and sex of children that agree to participate and who did not. Finally, self-report valid data from 1145 of them (578 boys and 567 girls) were obtained. All children completed the questionnaire, but 13 of them did incorrectly fulfill
543
Sánchez-López et al. it (children marked several response options on the same item, or left some unmarked items), and were consequently excluded from the analyses. The study protocol was approved by the Clinical Research Ethics Committee of the Virgen de la Luz Hospital, in Cuenca. After obtaining the approval of the Director and the Board of Governors (Consejo Escolar) of each school, a letter was sent to all parents of children in fourth- and fifth-grade, inviting them to a meeting at which the study objectives were outlined and written authorization for their children’s participation was requested. Informative talks, in which the schoolchildren were asked to collaborate, were then held class-by-class.
Study design and sample of the reliability study and replication study (Córdoba) Because of practical reasons in the Cuenca Study, physical fitness testing took place immediately after IFIS was administered. Therefore, these participants could not be used for reliability analyses, as this could influence the perception on their fitness levels at the retest. Consequently, the test–retest study was conducted in a separate age-matched sample of Spanish children (9–12.5 years old), from Córdoba province, South of Spain. The data from the Córdoba study were gathered from “the Healthy lifestyle; physical activity, fitness and nutrition in school children cross-sectional study” (HAFICA, Spanish name; Hábitos Saludables de Actividad FIsica, Condición Física y Alimentación en Primaria) aiming to obtain reliable data from Spanish school children about healthy behaviors, fitness levels, and nutrition. A total of 564 children (296 girls) were included. Parents and children gave their written informed consent to participate in the research. The study was performed following the ethical guidelines of the Declaration of Helsinki 1961 (revision of Edinburgh 2000), the Good Clinical Practice, and the legislation about clinical research in humans in each of the participating countries. The protocol was approved by the Human Research Review Committees of the university center. A total of 245 participants from Córdoba province (46% boys) successfully completed IFIS on two occasions (2 weeks apart) and were included in the reliability study. In addition, after the retest of IFIS was done, physical fitness was measured in this sample from Córdoba, so we decided to compare self-reported and measured fitness also in this smaller sample from Córdoba, as a replication study of the main data from Cuenca. A total of 339 participants had valid data on IFIS and at least one measured fitness test and were included in the replication study. The same methods were used to assess IFIS and measured fitness in both studies. The results of this replication analysis are presented as additional Supporting Information. The sample size for both validation and reliability was enough according to estimations of several studies (DeVellis, 2003).
Self-reported fitness Self-reported fitness was assessed by IFIS, originally validated in European adolescents (Ortega et al., 2011). IFIS consists of a Likert-type scale (range 1–5) with five response options (very poor, poor, average, good, and very good) about perceived overall fitness, and its main components: cardiorespiratory fitness (CRF), muscular strength, speed and agility, and flexibility. IFIS is available in nine different languages at the HELENA study website (http://www.helenastudy.com/IFIS). The Spanish and English versions of the IFIS used in this study are found in the Supporting Information Appendices S1 and S2, respectively. IFIS showed “high” validity and “moderate” to “good” reliability in Spanish young adults (Ortega et al., 2013).
544
Physical fitness Physical fitness was assessed using tests that have previously shown high validity and reliability levels, following the outcomes of three systematic reviews and several methodological studies conducted as part of the Assessing Levels of Physical Activity and fitness (ALPHA) project (Ruiz et al., 2011). Cardiorespiratory fitness (CRF) was assessed by the 20-m shuttle run test (Leger et al., 1988). Participants are required to run between two lines 20 m apart, while keeping pace with audio signals emitted from a prerecorded compact disc. The initial speed is 8.5 km/h, which is increased by 0.5 km/h (1 min equals one stage). Children were encouraged to keep running as long as possible throughout the course of the test, and it was finished when the child failed to reach the end lines concurrent with the audio signals on two consecutive occasions. The last half stage completed was recorded as an indicator of his or her CRF. Muscular fitness (MF) was assessed using two tests: (a) handgrip test (maximum handgrip strength assessment) using a hand dynamometer with adjustable grip (TKK 5401 Grip D; Takei, Tokyo, Japan). The grip span of the dynamometer was adjusted to the children’s hand size, using the equations previously validated in Spanish children (España-Romero et al., 2008). The participant squeezes gradually and continuously for at least 2 s, performing the test with the right and left hands in turn (Ortega et al., 2008b). Children made two trials (alternately with both hands) with a short resting time between them. The maximum score in kilograms for each hand was recorded. The average (in kilograms) of both hands was used in the analysis. (b) The standing broad jump test (lowerlimb explosive strength assessment). From a starting position immediately behind a line, standing with feet approximately shoulder width apart, the schoolchildren jump horizontally to achieve maximum distance. The best of three attempts was recorded in centimeters (Ortega et al., 2008b). MF/strength can be expressed in absolute (activities like carrying a suitcase, moving a heavy object, handgrip strength test, etc.) or relative terms (activities in which the person has to lift, hold or carry on his/her own body weight, standing long jump). In our analyses, we divided the score in handgrip by weight, which implies a transformation from absolute strength to relative strength; and we multiplied the score in standing long jump test by weight, so that it was transformed from relative strength to absolute strength (Artero et al., 2011; Jimenez-Pavon et al., 2012; Ortega et al., 2013). The analysis of these four variables (2 original + 2 transformed) in relation to IFIS informs about what the participants report (absolute vs relative strength) when they are asked about their MF levels. Speed and agility were measured using the 4 × 10 shuttle run test in which the child runs as fast as possible from the starting line to the other line and returns to the starting line (10 m apart), crossing each line with both feet every time. This is performed twice, covering a distance of 40 m (4 m × 10 m). Every time the child crosses any of the lines, he/she picks up (the first time) or exchanges a sponge, which has been previously placed behind the lines. The time taken to complete the test was recorded to the nearest tenth of a second (Vicente-Rodriguez et al., 2011). Flexibility by sit and reach test. This test uses a standard box. Subject performs a backward flexion of the trunk, and the maximum distance reached (in cm) by the subject’s fingertips is measured. The better of two attempts was recorded.
Adiposity and anthropometric variables Height and weight was measured using standard procedures. Waist circumference was measured three times with a flexible tape at the midpoint between the last rib and the iliac crest at the end of a normal expiration. Body fat percentage was estimated with an eight-electrode BC-418 MA bioimpedance analysis system (Tanita
Validity of self-reported fitness in children Corp., Tokyo, Japan) (Pietrobelli et al., 2004) using the mean of two readings. Measurements were made in barefoot children, under fasting conditions, after urinating, and after a 15-min rest.
Other CVD risk factors Diastolic and systolic blood pressure were determined by the average of two measurements taken at an interval of 5 min, with the subject resting for at least 5 min before the first measurement. The participant was seated in a quiet and calm environment, with the right arm placed in a semiflexed position at heart level. Blood pressure was measured by an automated procedure using the OMRON M5-I monitor (Omron Healthcare Europe BV, Hoofddorp, the Netherlands) (El Assaad et al., 2003). The mean arterial pressure (MAP) was then calculated using the following formula: Diastolic blood pressure + [0.333 × (Systolic blood pressure − Diastolic blood pressure)]. Trained nurses measured the anthropometric variables and blood pressure. Blood samples were taken by puncturing the cubital vein, under standardized conditions, between 08:15 h and 09:00 h, with the participant having fasted at least 12 h beforehand. Blood samples, which would take more than 75 min to reach the laboratory were centrifuged in situ and transported refrigerated. The following variables were determined following biochemical parameters: triglycerides (TG) (glycerol phosphate oxidase, peroxidase enzymatic method) and c-direct plus high-density lipoprotein (HDL). Lipid profile determinations were made in a weekend, in a MODULAR DPP system from Roche Diagnostics Corporation (Indianapolis, Indiana, USA), and the insulin levels were assessed using an Immulite 2000 double system platform of Siemens. We calculated a metabolic syndrome (MetS) index as the sum of the age-sex standardized scores of waist circumference, log triglyceride-to-HDL-c ratio (TG-to-HDLc), MAP, and fasting insulin. The validity of this MetS index has been previously tested using confirmatory factor analysis (Martínez-Vizcaino et al., 2010, 2011).
(Pearson correlation). To estimate polyserial correlation coefficients, we used the Hetcor library of the R software.
Results The distribution of the answers of the IFIS for the five question responses were shifted to the right in both genders, with a low percentage of participants reporting to have a very poor or poor fitness level (Fig. 1). Because of the small number of participants at the bottom extreme, the categories were merged as very poor/poor for the rest of the analyses, except for reliability analyses in which the raw data were used. Participants reporting average, good, and very good CRF, MF, speed and agility, and flexibility had a better measured CRF, MF, speed and agility, and flexibility, respectively, compared with participants reporting very
Statistical analysis For all the analyses, we used IBM SPSS 19 (SPSS, Inc., Chicago, Illinois, USA). The ability of the IFIS to categorize children correctly into physical fitness levels was determined by means of analysis of covariance (ANCOVA) adjusted for sex and age. This analysis was considered an indicator of the validity of IFIS. Measured fitness variables were entered as dependent variables and self-reported fitness variables as fixed factors. Differences between boys and girls in self-reported fitness were analyzed using the Chi-squared tests. The test–retest reliability of the IFIS was examined by quadratic weighted Kappa coefficient, (Cohen, 1968). Cohen’s weighted Kappa is not available in the standard SPSS package, but command syntax is available from the “Knowledgebase” at http:// www.SPSS.com (SPSS, Inc.). Data for imputation into the syntax were generated from cross-tabulation. Finally, ANCOVA models were used to test differences in the mean scores of total body fat and MetS index by categories of self-reported and measured fitness, controlling for sex and age. Sex- and age-specific percentiles 10th, 30th, and 50th for physical fitness variables were calculated and used to class the participants into measured fitness groups: very poor/poor (P50th). These percentiles were selected a posteriori so that the distribution of participants falling into the measured fitness groups was equivalent to that observed in IFIS categories, i.e., very poor/poor, average, good, and very good. In order to analyze the intensity of the relationship between measured and self-reported fitness with total body fat and MetS index, we estimated correlation coefficients between these cardiometabolic indicators with IFIS’s items (polyserial correlation) and objectively measured fitness variables
Fig. 1. Distribution of the answers for the five questions of International Fitness Scale (IFIS) in male and female children of Cuenca Province (n = 1145, 578 boys and 567 girls). CRF, cardiorespiratory fitness; MF, muscular fitness; SP-AG, speed and agility; Flex, flexibility; Overall, overall physical fitness.
545
Sánchez-López et al. Table 1. Means and standard error (SE) of measured physical fitness by self-reported physical fitness categories in children
n
Cardiorespiratory fitness 20-m shuttle run (stage) Muscular fitness handgrip (kg) Standing long jump (cm) Speed and agility shuttle run 4 × 10 m (s)† Flexibility sit and reach (cm)
Very poor/poor (1) Average (2)
Good (3)
Very good (4) P
Pairwaise comparisons*
Mean
Mean
Mean
1–2 2–3 2–4 3–4 1–3 1–4
SE
Mean
SE
SE
SE
1108
2.55
0.19
2.79 0.09
3.47 0.08
4.14 0.08 < 0.001 ns
