The directors and teachers at the educational centres were notified of the objectives of the study. Once consent had been obtained from these individuals, a date for giving the information sessions for the parents and legal guardians of possible participants was set. After these sessions, teachers at each centre gave the parents and legal guardians the questionnaires and the informed consent form. To participate in the study, these documents had to be returned to the centre, duly completed and signed by the parents or legal guardians.

Each participant’s age and sex were requested, and participant PC was measured using the ALPHA-Fitness Battery,17 validated in Spanish schoolchildren. This battery includes measures of morphological condition (weight, height and waist circumference), as well as musculoskeletal condition (lower body explosive strength (LBES) and upper body isometric strength [UBIS]) and cardiorespiratory condition (20-meter shuttle run test [20mSRT]), which are measured in the sequence mentioned. For the PC measures, the children wore sports clothing (t-shirt and shorts) and sports footwear.

To measure LBES, the test of “standing long jump” was used: The child, with both feet placed outside the starting line, had to bend his/her knees while swinging the arms from behind to in front; with a strong push, the child would then jump forwards as far as possible, using his/her arms to help, and would fall to the ground with the feet together without losing balance. Each child performed the test twice, with the best result obtained being the one counted. To assess UBIS, the manual strength test was carried out with a Takei TKK 5001 analogue handgrip dynamometer. The child had to press the dynamometer little by little, continuously, for at least 2s. The test was performed twice (alternately with the 2 hands) with the optimum adjustment based on hand measurement (calculated previously using the reference data table).

Cardiorespiratory condition was established using the 20-meter shuttle run test (20mSRT). This test was carried out on a track marked with 2 lines at a distance of 20m from each other, with a tape recorder and an audio tape indicating the rhythm of the race. The child would stand behind one of the lines, facing the other one. He/she would begin to run when the first whistle was heard, and had to do so in time with the rhythm set by the music. Each 20-meter length was considered a period. The initial test speed was 8.5km/h, and the speed was increased by 0.5km/h every minute. Each speed increase was considered a stage. When the child was unable to reach the line before the whistle blew, the last period completed was recorded. The cardiorespiratory capacity corresponded to the stage of the last period completed.

Morphological condition factors were measured following the "International Society for the Advancement of Kinanthropometry" (ISAK) provisions, recommendations and techniques.18 The child, barefoot, would take position in the standard position: standing, with his/her arms extended along the side of the body in a relaxed position. At least 2 measurements were taken, with a third being taken when the difference between the first 2 was more than 5%. The result recorded was the mean between the 2 or 3 measurements taken. Weight was established using a Seca 813 digital scale (precision 100g); the child would stand in the middle of the scale, without holding on to anything, with his/her weight uniformly distributed over both feet. Height was measured using a Seca 217 portable measuring rod (precision 1mm): the child would stand with both feet together and with his/her buttocks and upper back in contact with the measuring rod, and his/her head in the Frankfurt plane; the corresponding measurement was taken at the upper part of the skull. The BMI was calculated dividing the weight expressed in kg by the height expressed in meters squared (BMI=weight (Kg)/ height (m)2). The BMI values were then classified based on the Word Health Organisation criteria: a child’s weight was considered to be underweight for values less than −2 standard deviations (SDs); normal weight, for values between −2SD and 1SD; overweight, for values between 1SD and 2SD; and obese, for values above 2SD.19 Waist circumference (WC) was established using a non-extensible Lufkin W606PM steel measuring tape (7-mm wide; precision, 1mm); the circumference corresponded with the measurement at the umbilical level, taken at the end of a normal exhalation.

The evaluation of the associated variables of interest was performed with the family questionnaire from the ALADINO study; these variables were classified according to the criteria of that study.20

Parental educational level was classified based on the highest level of studies attained: primary school, secondary school or university studies. The gross annual family income was classified into 3 levels: less than €18,000, between €18,000 and €30,000, and more than €30,000.

The children’s lifestyle variables were classified according to the criteria of the Public Health Agency of Catalonia.21 The number of days a week that the child participated in extracurricular sports activities was established, categorising the variable as 2 or fewer days a week and 3 days or more a week. The fact that a child spent 2 or more hours a day in front of a screen, watching television or playing computer games for entertainment was considered sedentary free time; and as active free time, when the child spent 1 or more hours a day playing outdoors. Children were classified as having an active lifestyle if they participated in extracurricular sports activities 3 or more days a week, spent fewer than 2h a day in front of a screen for entertainment, and played outside for 1 or more hours a day.

To assess parental weight, their BMI values were calculated with their self-declared weight and height data. Parents’ tobacco use was classified into 3 groups: neither of the parents was a habitual smoker; one of the parents was a habitual smoker; and both parents were habitual smokers.

Results are expressed as frequencies and percentages (%) for the qualitative variables, and means and SD for the quantitative variables. Medians were compared using Student’s t-test; the analysis of variance (ANOVA) was based on the number of groups to compare; and the relationship between quantitative variables used the Pearson correlation coefficient. Statistical significance was set to P<.05 and the data were processed with the statistical package “IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp.”

Informed consent was obtained from the parents or the legal guardians of the participants. The study was approved by the Commission for Research and Ethics of the Blanquerna Faculty of Health Sciences/Universitat Ramon Llull (Barcelona, Spain).

In this study, 13 of the 15 educational centres in the area participated (86.7%), 12public schools and 1 semi-public school. Informed consent was obtained for 269 children (participation rate of 75.8%). Table 1 shows the participants’ characteristics. It can be seen that the boys obtain better PC results in the tests for musculoskeletal and cardiorespiratory condition and present significantly better WC values than the girls. As for weight, 35.2% of the children were classified as overweight (17.8% overweight and 17.4% obese); obesity is more prevalent in boys (22.7%) than in girls (11.1%). More mothers have university studies than fathers (44.3% and 35.1%, respectively), although the differences are not statistically significant (P=.096). With respect to lifestyle, the percentage of boys that participate in extracurricular sports activities 3 or more days a week is statistically higher than that of the girls (43.4% and 19.4%, respectively). In reference to the hours a day spent on screen time for entertainment and spent playing outdoors, there are no statistically significant differences by sex. In contrast, the percentage of boys that have an active lifestyle is significantly higher than that of the girls: 20.2% and 6.4%, respectively. The self-declared parental weight and height data shows that the mean BMI is 26.1 kg/m2 for the fathers, and 23kg/m2 for the mothers. Somewhat more than half the families indicate that neither of the parents is a smoker.

No relationship is observed between the hours that the children spend on screen time for entertainment and the days a week that they spend participating in sports activities (Table 2). However, even though the differences are not statistically significant, the children that spend more hours a day playing outdoors spend fewer hours in front of screens.

The analysis of PC and the family setting (Table 3) shows that a higher level of the fathers’ studies is linked to better results in the children’s cardiorespiratory condition; likewise, the higher the fathers’ educational level, the lower the children’s WC and BMI values. As for the mothers’ educational level, there is a statistically significant relationship with cardiorespiratory condition, but not with the rest of the PC components. A higher gross family income level is linked to greater LBES and lower UBIS values.

The children that participate in extracurricular sports activities 3 or more days a week and have an active lifestyle obtain better results in LBES and cardiorespiratory condition that those that participate 2 days or less (Table 4). No relationship with the rest of the PC components is seen; likewise, no differences are observed in any of the PC variables in relation to sedentary and active free time.

The children whose parents are both non-smokers have better results in the LBES tests and in cardiorespiratory condition, and lower values in the WC and BMI measures (Table 5). The analysis of the correlation between PC and parental BMI reveals than increased BMI, both for the father and for the mother, is linked to an increase in the children’s WC and BMI values; in addition, a negative correlation between maternal BMI and child LBES and cardiorespiratory condition results can be observed (Table 6).

In this study, the boys show better results in the musculoskeletal and cardiorespiratory condition tests than the girls, as well as higher PC values. Although the differences in BMI are not statistically significant, the percentage of boys with obesity is higher than that of the girls. The differences observed between boys and girls with respect to musculoskeletal and cardiorespiratory condition results (which are also seen in other studies)22,23 might be due to the anatomical and physiological differences between sexes.24 However, as has been observed in our study, boys spend more time participating in sports activities than girls; consequently, the differences observed could also be explained by the fact that boys are more active than girls.25

The levels of musculoskeletal condition, LBES and UBIS, along with the cardiorespiratory condition, of the children in Baix Montseny are much the same as the values published as the European standards of reference obtained in the framework of the “Identification and prevention of dietary- and lifestyle-induced health effects in children and infants” (IDEFICS) study.10,22 Comparing the weight of the study children with the data published by the Spanish government, it can be seen that the percentages of children classified as overweight and obese in Baix Montseny (17.8% and 17.4%, respectively) are lower than those observed for Spanish 8-year-old children (where 24% are overweight and 18.6%, obese) and among Spanish 9-year-olds (25% being overweight and 21.2% presenting obesity).26 In contrast, comparing the data obtained with those of the Catalan population reveals that the data are very similar: 16.3% and 17% of the Catalan children aged between 6 and 9 years were categorized as overweight and obese, respectively, in 2014.27 It should also be pointed out that, just as occurs in Spain and in Cataluña in general,28,29 in Baix Montseny obesity is more prevalent in boys (22.7%) than in girls (11.1%).

In this study, the father’s educational level (more than the mother's) is seen to be linked to a better level of PC in the children. Specifically, the higher the level of studies of the father, the better the cardiorespiratory condition and the lower the WC and BMI values for the children; however, in the case of the mother, only a positive relationship between the maternal educational level and the children’s LBES values is seen. These results partially contrast with those obtained in the AVENA study (carried out with Spanish adolescents), in which the educational level of the two parents is directly linked to better LBES and cardiorespiratory capacity (the latter factor only for the girls); and an inverse relationship is observed between the boys’ body fat content and the maternal educational level, although not in the case of the girls.8 Likewise, the results of the ALADINO study show that there are more children with obesity among the parents with primary or secondary studies, and that there are more children with an appropriate weight among parents having university studies.26

In general, parental educational level is linked to family income level in our study, and gives an idea of the family’s socioeconomic status. However, a link is observed only between the gross family income level and LBES and UBIS, but not with the rest of the components of PC; this could be explained by the homogeneity of the study population.

Better results in the tests of LBES and cardiorespiratory condition are obtained by children that participate in extracurricular sports activities 3 or more days a week, and by those that have an active lifestyle (the ones that participate in extracurricular sports activities 3 or more days a week, spend less than 2h a day on screen time for entertainment and play outdoors for an hour or more a day). In contrast, no link has been found with weight, WC and BMI. These results could be explained by what has been seen in other studies, where performing moderate-vigorous intensity PA is related to better cardiorespiratory and musculoskeletal condition.5,10,12 However, the role of PA in preventing excess weight is subject to debate. While some studies seem to indicate that performing moderate-vigorous or vigorous PA appears to be a factor that protects against overweight and obesity,11,28,29 others suggest that excess weight might be the cause of a low PA level among children.30 No relationship has been observed between sedentary free time and PC either; these results coincide with those of other studies, in which the relationship between physical inactivity and worse PC is not significant.14,31 In fact, the studies indicate that physical inactivity has a negative impact on PC solely when it replaces PA.13,14 In our study, an inverse relationship is seen between the time spent in front of a screen for entertainment and the time participating in outdoor activities, although no relationship is observed between screen time and participating in sports activities. Even though the relationship is not statistically significant, the results suggest that encouraging outdoor activities might reduce children’s screen time for entertainment, which could help to improve their PC.

Our results demonstrate that parental tobacco use is linked to a lower PC, more limited cardiorespiratory condition and LBES, and higher WC and BMI values. Results of studies indicate that passive exposure to tobacco smoke in children increases the risk of overweight and obesity.15,16,32 However, in spite of the well-known negative effect that tobacco use has on both the individuals that smoke and the people around them, we have found only 1 study that links children’s passive exposure to tobacco smoke to worse lung function and cardiorespiratory condition in the children.16

The BMIs calculated from the parents' self-declared height and weight reveal a negative correlation between the maternal BMI and child LBES and cardiorespiratory condition, and a positive correlation between the parents’ BMIs and the WC and BMI values of their children. These results are similar to those involving European children, in which there is also a negative relationship between maternal BMI and child LBES and cardiorespiratory condition, as well as to the ALADINO study results showing a positive link between parental and child weights.15,26

This study has a few limitations that should be considered. As the study design is cross-sectional, it is not possible to establish causal associations. In addition, the restricted geographical area in which the study took place makes it difficult to extrapolate the results. The PA levels have been determined on the basis of qualitative criteria, without taking quantitative measurements; the parental height and weight data are self-declared, which might lead to interpretation errors because people generally underestimate their weights.33 Study strengths are that the children’s PC has been evaluated using the ALPHA-Fitness Battery validated using a population of Spanish schoolchildren, and that the children’s morphological condition has been determined according to the ISAK criteria.

In conclusion, the PC levels of the children included in the study are similar to those of European children. Their PC is more closely linked to the father’s educational level than to the mother’s, and is related to participation in PA outside of school time and to parental BMI and tobacco use.