The Relationship Between Physical Activity, Physical Fitness and Body Composition in Preschool (3-6 Years)


 BackgroundPhysical Activity (PA), body composition and fitness in children has been associated with short and long-term health benefits. However, little research that analizes these variables focuses on the Preschool Education stage. For this reason, the aim of this research is to study the relationship between PA, fatness and fitness in the Preschool Education stage (3-6 years).MethodsThis study included 230 children (109 boys and 121 girls) aged 3 to 5 years old with a mean age of 4.92±0.84. Body composition and fitness were assessed using PREFIT battery and a sit and reach test. For the multiple linear regression models of this study, we only included a total of 151 (65.65%) children in which PA levels were measured using accelerometers for seven days.ResultsThere were differences in the fitness test between boys and girls. There were not significant differences in fitness tests between normal-weight and over-weight children, except in handgrip strength in which over-weight children had better results. There was no significant association between body composition and PA subcomponents. Higher PA levels were related with better physical fitness values.DiscussionThe few studies that have studied the relationship between fatness, physical fitness and PA in Preschool have had controversial results. These differences might be caused by different reasons: different tests, age of the participants, sample size, study design, etc. were used.ConclusionsPA is associated with better physical fitness performance in Preschool children, although fitness is also influenced by sex in these ages. Thus, generally, except in the case of flexibility, boys obtained better results in fitness tests than girls. However, body composition does not seem to be related to PA or sex in Preschool children.


Background
Physical Activity (PA) is currently widely studied. PA in children has been associated with short and long-term health bene ts [1][2]. Regular PA improves tness levels in children and teenagers [3]. PA also prevents obesity [4]. Nowadays, urbanization processes, environment pollution, security consideration, and changes in family structure [5] have decreased PA levels. Furthermore, Aranceta-Bartrina et al. [6] have shown that the prevalence of being overweight in Spanish children between 3 and 8 years old is 40%, while obesity is 16%. This fact is aggravated by the importance that this stage has for the creation of healthy habits that are maintained in adulthood [7].
Some research have shown higher intensity PA levels (moderate-to-vigorous PA (MVPA) and vigorous PA) are more related to better results in tness and fatness than light PA [8].
Most of the research has shown that tness is a powerful health indicator in children [2,[9][10][11]. In addition, a lot of studies have shown a direct relationship between PA, especially MVPA, and tness [5,8,12].
Moreover, the term body composition generates controversy between different researchers, whether it should be included within physical tness as an additional component or whether it should be treated individually as a health outcome itself [10]. For this research it will be treated as a separate element of physical tness. Over-weight and obesity in childhood are linked to the increase of cardiometabolic risk and to a higher risk of becoming obese adults.
In addition, it is also associated with a greater possibility of future diseases, such as type 2 diabetes mellitus, cardiovascular disease, and some types of cancer [6]. Studies have shown that body composition correlates inversely with PA levels [9].
The majority of the research that has studied fatness, tness and PA has been conducted in Primary and Secondary Education stages (6-18 years) [4,13], but there are few studies that have been developed in the Preschool Education stage (3-6 years) [10,14]. For this reason, the aim of this research is to study the relationship between PA, fatness and tness in the Preschool Education stage (3-5 years).

Participants
This cross-sectional research included 230 children (109 boys and 121 girls) aged 3 to 5 years old with a mean age of 4.92 ± 0.84 from three urban and public schools in Cuenca, Spain. The participants of the three schools included in the study possess similar socio-economic characteristics. The majority of them are residents of Cuenca, a small city with approximately 50,000 inhabitants. Their families maintain a low to middle economic level. However, in one of the schools, most families are upper-middle class, while in the others two schools there is a higher average of lower-middle to lower class families.
Of the 230 participants included in this study, a subsample of 202 children (87.82%) were a randomly selected to wear accelerometers, but only 151 participants (65,65%) who had data that met the PA inclusion criteria were included in the multiple linear regression models. The children included in this analysis did not differ in age or sex from the whole sample of children participating in the study.

Procedures
Firstly, written consent from the researchers' Castilla-La Mancha University Ethics Committee, the school's Board of Governors and the students' parents were obtained to conduct the study. The directors of the different schools were contacted to explain what the study consisted of. Researchers assured them of the anonymity and con dentiality of the data obtained and that no student would suffer any type of harm. Parents could refuse to allow their children to participate in the research or in part of it. In addition, teachers were interviewed to nd information about the health history of the participants, in order to know if any of them had medical problems that could affect the measures. Furthermore, all the researchers were speci cally trained to conduct the study. To collect the data, a cross-sectional study was carried out between February and June 2019. Each course was measured one day. An informative sheet was sent to the parents the day before data was taken to remind them that the next day children must wear sports clothes.

Anthropometry measures
The tests included were weight, height, fat mass percentage, triceps skinfold and waist circumference. weight and obese children. We grouped the participants into two groups to analyse the group differences between means. One group was normal-weight and included thinness and normal-weight subjects and the other group was over-weight and included over-weight and obese children. Waist circumference was measured two times at the midpoint between the last rib and the iliac crest using a exible tape. Triceps skinfold was measured three times at the triceps on the non-dominant side of the body halfway between the acromion process and the olecranon process using a Holtain Ltd. Caliber (0.2 mm accuracy and consistent 10 g/mm 2 pressure between valves).

Physical tness measures
A PREFIT (FITness testing in PREschool children) battery was used to measure physical tness that it is designed and validated for 3-5 years [10,16]. Moreover, the sit and reach test was used to measure exibility, a health-related tness component [5] that is not measured in PREFIT battery.
Handgrip strength and standing long jump tests were used to assess muscular strength. Handgrip strength was measured with a manual dynamometer (TKK 5001, Grip-A, Takei, Tokyo, Japan). For the standing long jump the child jumped horizontally to achieve maximum distance, the best of the three attempts were recorded in centimetres. Speed-agility was assessed with the 4 x 10 m shuttle-run test of speed-of-movement, agility, and coordination [16]. An evaluator drew two parallel lines 10 m apart on the oor. Two examinator were placed behind the lines. Participants ran 4 x 10 m (back and forth) as fast as possible crossing each line with both feet every time. Every time children crossed any of the lines, they would touch the examinator hand. The stopwatch was stopped when the children crossed the end line with one foot. The test was performed twice with at least ve minutes of rest between attempts and the best score was recorded in seconds: hundredths.
Finally, the PREFIT 20m shuttle run test was used to assess cardiorespiratory tness [16]. For this test, 10 lanes of 20 m were created. In addition, the warning zone where children should be when the beep sounded was marked at 3 m. The test was led by a recording that indicated with beeps the speed at which they should run. An examiner stood on one of the lanes and ran alongside the students during the test to help them adjust their speed to that of the recording. The initial speed of the signal was 6.5 Km / h and increased by 0.5 km / h / min. Children had to get to the 20 m line before changing direction whether they were inside or outside the warning zone, even if the signal sounded. If a child was not in the designated 3 m zone when the signal sounded, a warning was given and if this happened again for the second consecutive time, the test nished. The test also ended when the students could not continue due to exhaustion. The test was performed only once and the total number of laps in which each student had travelled the distance of 20 m was recorded.
In addition, Sit and reach test were used to assess exibility [17]. The children sat barefoot with their legs stretched out in front of them and the soles of their feet completely touching the drawer wall. They put one hand on top pf the other and without bending their knees, slowly and progressively, did a deep trunk exion in front. They made three attempts that we registered in cm and mm and then we documented the best attempt.

Measurement of physical activity
Children wore a triaxial accelerometer (Actigraph GT3X model) for seven consecutive days to measure PA. Accelerometers are worn on the right side of the waist attached with an elastic band. A sheet with information related to the accelerometers was sent to the parents to explain that these devices cannot get wet; so to bathe the children or to go to the pool, parents had to take it off and when the activity was over, the device had to be adjusted with the elastic band on the right side of the waist again. The information from each accelerometer was programmed in 100 Hz and exported in one-second epoch. Accelerometer data was processed by the software Actilife V. 6.13.4 to provide values for total daily and hourly cpm. The inclusion criteria were to wear the accelerometer a minimum of three days, including at least two weekdays and one weekend day for minimum 10 registered hours per day [19], excluding 20-min intervals of continuous 'zero' activity with allowance for 1-2 min of counts between 0 and 100 [20]. The sleep period was also ignored because the study only analyzed the performance level of PA during the day. Children who did not accomplish them were excluded for the analysis.

Statistical analyses
Data analysis was made using the Statistical Package for Social Sciences (SPSS) version 25.0 for Windows (IBM SPSS Statistics, Armonk, NY).
Descriptive statistics were presented as mean ± standard deviations. Since each accelerometer recorded different time validation, descriptive data of the PA subcomponents were adjusted for the total PA per day recorded. A covariance analysis was used in order to calculate the mean of the PA subcomponents. Kolmogorov-Smirnov test was used to check for normality before the analysis. All variables presented normal distribution. Independent t-test was used to analyse group differences between means. Multiple linear regression models were used to examine the independent associations of body composition (BMI, % body fat, waist circumference and triceps skinfold) variables with tness indices (20 m shuttle run, 4x10 m shuttle run, standing long jump, sit and reach, handgrip strength) and PA subcomponents (Sedentary, Light, Moderate, Vigorous, MVPA, Total PA and Counts per minute). Standardised β coe cients were used. The variance in ation factors between variables were less than ve, suggesting that multicollinearity was not a problem in the models [21]. Two regression models were used: unadjusted model and model adjusted for age and sex of the child (Model 1).
Moreover, the associations between tness indices with PA subcomponents were further examined. Two regression models were also used: unadjusted model and model adjusted for age and sex (Model 1). Signi cance was set at 5%. So, all p-values less than 0.05 were treated as signi cant.

Results
Data of participants compared by sex are demonstrated in Table 1. Boys had a better signi cant performance (p < 0.05) in standing long jump, 4x10 m shuttle run, and 20 m shuttle run tests, while girls had better results in the sit and reach test. Moreover, fatness and PA subcomponent values were similar among both sexes. Values are means ± standard deviations; *better signi cant performance (p < 0.05); a adjusted for total PA recorded BMI -body mass index; PA -physical activity; MVPA -moderate-vigorous physical activity Descriptive data of the participants according to weight status are showed in Table 2. Over-weight children had higher signi cant values (p < 0.05) in height, weight, BMI, fat mass percentage, waist circumference, triceps skinfold and handgrip strength in comparison with normal-weight children.
Furthermore, tness tests performances and PA subcomponent values were similar between normal-weight and over-weight children. Values are means ± standard deviations; * signi cantly higher values (p < 0.05); a adjusted for total PA recorded BMI -body mass index; PA -physical activity; MVPA -moderate-vigorous physical activity The associations among the different variables of the body composition with each tness test and PA subcomponents are demonstrated in Table 3.
Higher BMI was positively associated with better results in handgrip strength in both models. Thus, increase in BMI by one unit (kg/m 2 ) was associated

Discussion
This research aimed to study the relationship between PA, fatness, and tness in the Preschool Education stage. The major ndings were: 1) There were differences in tness test between boys and girls; 2) There were not signi cant differences in tness tests between normal-weight and over-weight children, except in handgrip strength in which over-weight children had better results; 3) There were no signi cant associations between body composition and PA subcomponents; 4) Higher PA levels were related with better physical tness values.
Differences in physical tness tests were more related to sex than fatness. Boys had signi cant better results in standing long jump, 4x10 m shuttle run and 20 m shuttle run tests, but their performance in the sit and reach test was worse. This nding is in concordance with Cadenas-Sánchez et al. [22] study that found signi cant better results in the standing long jump test in boys than girls. Latorre et al. [23] found that boys had better performance in speed and lower body strength tests and girls had higher values in the cardiorespiratory tness test. This last difference could be because a different test was used to measure cardiorespiratory tness.
However, signi cant differences were not found in tness tests means between normal-weight and over-weight children, except in handgrip strength, in which over-weight children had higher results. Thus, higher BMI was associated with better results in handgrip strength. These results agree with Cadenas-Sánchez et al. [22] study that found this result in both sex and Riso et al. [8] research that found that the mean in handgrip strength of normalweight children was 10.5 kg, while the mean of over-weight participants was 12.2 kg. In addition, higher BMI was associated with worse performance in 4x10 m shuttle run. This nding does not agree with Henriksson et al. [14] and Riso et al. [8], that both did not nd signi cant association (p < 0.05) between BMI and 4x10 m shuttle run. This discrepancy in the results could be due to the different age of the participants in these studies. However, no signi cant association with standing long jump, sit and reach and 20 m shuttle run test was found. Henriksson et al. [2] aimed that BMI could not detect the associations between body composition and physical tness in Preschool children. This could be because Preschool children are so young [14] due to the fact that different research with older participants (6-7-year-old) observed signi cant associations between higher BMI, greater standing long jump and lower cardiorespiratory tness [8]. Thus, for example, Carson et al. [12] found some research with mixed or null ndings because of their infants and toddlers' samples.
Furthermore, fat mass percentage was related with lower results in 4x10 m shuttle run. This concordats with Henriksson et al. [14] study that found a signi cant negatively association (p < 0.001) among both variables, but not with Riso et al. [8] research that did not nd a signi cant association (p > 0.05). This difference could be because of the different age of the participants in each study. Moreover, our results showed that waist circumference was associated with better performance in handgrip strength and triceps skinfold was related with worse results in 4x10 m shuttle run test. As far as we know, no study has analysed the relationship of these two components of body composition with these tness tests in Preschool children, so we cannot compare these ndings with others. So, there are some studies that have studied the relationship between body composition and physical tness in Preschool children [14] and their results have been controversial [5,21,23]. These differences might be caused by different reasons: different tests, age of the participants, sample size, study design, etc. were used [5,23].
Body composition values were not signi cantly related to PA levels, although waist circumference was associated positively with sedentary time. These results coincide with those found by Carson et al. [12] review that observed a lot of null, unfavorable and mixed associations between PA and adiposity.
Previous studies have shown BMI was not related to PA in some studies [25]. For this reason, Leppänen et al. [25]  Nevertheless, this research has some limitations. Firstly, sample size was not too big, especially the over-weight population (n = 36). So, we could not separate over-weight and obese children into different groups. This could in uence the signi cant differences that were found as Niederer et al. [24] found associations between normal-weight and obese children which were not found in over-weight participants. In addition, 79 children did not accomplish the inclusion criteria. Therefore, PA associations could be in uenced by the relatively small nal sample (n = 151). Another limitation was that a cross-sectional design was used, so we could not conclude causality and direction of associations found. Moreover, the research did not analyse some variables that could be in uential like socioeconomic status or participation in sports clubs. Regarding the body composition, fat free mass was not studied, which Riso et al. [8] found was associated with all physical tness and PA levels. For this reason, considering that it is an important value, it should have been analysed. However, we used waist circumference and triceps skinfold that few research has studied, so our study revealed new information about the relationship of these body composition variables with tness and PA levels.
The strength of this study is that the measurements used were objective. PA was measured by accelerometer and physical tness was measured by PREFIT battery, which is validated for 3-5-year-old children [10]. In addition, we analysed some variables that only some research studied such as: exibility, waist circumference and cpm. Moreover, we used a model that was adjusted for age and sex of the participants to analyse data. Differences among the variables in unadjusted model usually disappeared in the adjusted model because these variables are in uenced by age and sex. So, our results showed the real relationship between fatness, tness, and PA regardless of age or sex. Finally, our sample included 3-year-old children, who were not included in the research that has studied Preschool children health.

Conclusions
PA is associated with a better physical tness in Preschool children. However, tness is also in uenced by sex at this stage. Thus, except in sit and reach test, boys had better performance in tness tests than girls. Nevertheless, body composition is not related to PA or sex in children so young. All the same, some experts have aimed that the relationship between PA, tness and body composition increases with the age of the participants [14].
The discrepancy between the results of the different research makes it necessary to carry out more studies that analyze the relationship between these three variables separately in each year of age (3, 4 and 5 years) because it has been demonstrated that there are differences in the results with respect to the studies whose sample only includes children from the last year of Preschool. Therefore, it would be interesting to analyze the evolution of the relationship between these three variables from year to year to see if age explains the discrepancies found. Likewise, it would be interesting to analyze the relationship of these three variables with other sociocultural ones (urban or rural environment, socio-economic level, level of education of the parents, type of family, etc.) to check if they also affect the relationship. Availability of data and material The data that support the ndings of this study are available from Natalia María Arias-Palencia but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the authors upon reasonable request and with permission of Natalia María Arias-Palencia.

Funding
Not applicable.
Authors' contributions GSG, VGL and NMAP collected the data. GSG and MSM analyzed and interpreted the data. GSG, NMAP and SGV were major contributors in writing the manuscript. All authors read and approved the nal manuscript.