The Horizontal Jump (HJ) is a daily tool that could be used to categorize the level of muscle fitness performance of the lower limbs. The goal was to compare the muscle fitness with those of international studies and to propose percentiles to assess the HJ performance of children and adolescents. A cross-sectional study was conducted. A total number of 3023 children and adolescents between the ages of 6.0 to 17.9 were studied. Weight, height, waist circumference (WC), and lower limb muscle fitness were evaluated. The student HJ performance values in Chile were inferior when compared to HJ performance in Brazil, Poland and Europe. For the Greek study, differences occurred only from age 6 to 15 years old. In comparison to Colombia, students showed better muscle fitness performance. These differences appeared in childhood and lasted until the beginning of adolescence. Percentiles were created to assess the lower limb fitness being an easy tool to be used and applied to classify lower limb strength.

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Muscle fitness has several dimensions. These may be assessed in children and adolescents (for example, maximum isometric strength, muscle endurance, and explosive strength).1 In fact, horizontal jump (HJ) and the vertical jump are from the classical batteries of field tests commonly used to assess the physical fitness of students through explosive muscle strength of the lower part of the body.2,3 The HJ is a combination of movements that not only depend upon properties of the muscles, but also multiple joints used in the motor system. This involves taking off and landing with both feet to attain the maximum horizontal distance.1 Basically, this test is proposed as a general indicator of muscle fitness in children and adolescents.4 Muscle fitness is an important health indicator that is inversely and independently associated with muscle endurance, metabolic risk, inflammatory proteins, and body adiposity during childhood and adolescence.5-7 It is an essential component of performance in sports. Therefore, it plays an important role in the selection of school athletes.8 The HJ test is low cost, has simple equipment to use, it is easy to administer to a large number of individuals simultaneously,9 and has high validity and reliability in children and adolescents.4 As a result, due to these characteristics, it is necessary to include the HJ as an important test in the educational system for assessing health and determining sport performance in students. In this sense, researchers in a number of studies in South America,9-11 and throughout the world,12-14 have proposed references to assess HJ performance for children and adolescents. Thus, its use and application in Chile may reflect discrepancies, limiting its use due to geographical, social, and cultural differences between countries.7 In addition, muscle fitness may vary between individuals, especially during adolescence, to repeat the exercise might be important to detect changes produced in biological maturation.15 In the absence of studies that address muscle fitness and especially to assess the performance of horizontal jump in school children and adolescents, this study proposed two objectives. The first was to compare the muscle fitness, using the HJ, between students of Chile Maule Region and those of international studies. The second was to propose percentiles for assessing HJ of children and adolescents from the Maule Region (Chile).

This descriptive cross-sectional study was carried out in 12 schools in the Maule Region (Chile). Maule, located in the central valley, is the seventh region of Chile. Its capital city is Talca. Agriculture is the primary industry of the region.

The sample population was composed of 29,500 (17,410 males and 12,100 females) children and adolescents from the public education system. The research sample was selected probabilistically (CI 95%). The appropriate sample size was 3061 (10.3%) [1930 (6.5%) males and 1131 (3.8%) females]. Students of both sexes, ages 6.0 to 17.9 years old, were included in the study. Students with physical and/or motor problems that impeded performing or assessing the horizontal jump or did not complete the physical tests were excluded from participating (120 males and 170 females).

The study was carried out according to the Declaration of Helsinki World Medical Association for Human Subjects.16 The research was also approved by the Ethics Committee from the Universidad (grant number-2413). All sample subjects for this study were informed about its objectives. Parents and/or guardians and students all provided signed informed consent for students to participate in the research.

Anthropometric variables and the horizontal jump were assessed at the schools. School administrators from each educational institution provided birth certificates to collect information for the assessment date. Data was collected from April to November 2017. Anthropometric variables for body weight, height, and waist circumference (WC) were collected according to the standard procedures described by Ross-Marfell-Jones.17 All variables were measured while the students were barefoot and dressed with minimum clothing. Body weight was collected using an electronic portable scale (Tanita Inner Scan BC 532, Tokyo, Japan) with an accuracy of close to 0.10 kg. Using the Frankfurt Plane, height was measured with a portable stadiometer (Seca 213, Hamburg, Germany) with a precision of 0.1 cm. WC was assessed midway from the lower ribs and the upper part of the iliac crest. Measurements were taken with an anthropometric metal tape, Seca brand, with an accuracy of 0.1 cm. Body Mass Index (BMI) was calculated using the formula: BMI = weight (kg)/height2 (m). The horizontal jump (cm) for the muscle fitness test of the lower limbs was evaluated after a 10 minute warm up period. Students were dressed in tennis shoes, shorts, and a T-shirt to perform the test. Assessments were carried out based on the recommendations of Castro-Piñero et al.9 A 3 m metal tape measure with an accuracy of 0.1 cm was used to measure the distance of the horizontal jump. With feet together, the student performed a forward movement with as much momentum as possible in order to go as far as possible from the original starting line. Students performed three attempts. Then, the best distance was recorded. Afterwards, the results were compared. The levels of muscle fitness from the horizontal jump of the Chilean students were compared with the references from Brazil,11 Columbia,9 Poland,12 Greece,18 and the European 30 country multi-centric study.14 All those studies reported normal distribution in their data.

Data normalization was carried out using Kolmoronov Smirnov method. Descriptive statistical analysis of the mean, standard deviation (SD), and ranges were performed. Comparisons between both sexes were carried out by using the t-test for independent samples. The fraction 100 log (reference percentile/centile calculated) was used to make comparisons between the studies. P50 was used for all cases. All calculations were performed with SPSS 18.0. For all comparisons, p<0.05 was adopted. The LMS method was used to create the percentiles. This method was based on three smoothed curves [L(t) Box-Cox transformation, M(t) median, and S(t) coefficient of variation].19 Percentiles P50, P90, P95, and P97 were calculated for absolute height for both sexes. LMS Chart Maker software version 2.320 generated the curves.

Mean±SD, anthropometric variables, and HJ performance values for the children and adolescents from Maule (Chile) are presented in Table 1. No significant differences occurred in weight and WC from age 6.0 to 14.9 years old. However, from 15.0 years old to 17.9, males presented higher values than the females (p<0.05). Height values were similar until 13 years old. From age 14.0 to 17.9 years, males were taller than the females (p<0.05). For the HJ, for all age ranges, males had significantly higher values than the females (p<0.05). With regard to BMI, at age 17 years old, males presented higher values than females (p<0.05). P50 was used to compare the differences in the HJ performance between the Maule students studied and the international references. Table 2 illustrates these differences. The Maule students presented lower values than those of students from Brazil,11 Poland,12 and the European multi-centric study in all age ranges and in both sexes.14 These lower values were from -2.1 to -8.2 cm for males and from 0.3 to 17.9cm for females. For the Greek study,20 differences occurred from age 6 to15 years old (-7.5 to -1.0cm for males and -8.6.1 to -0.3cm for females). Then, at the age of 16 and 17, the females of Maule showed better performance in the HJ (2.1 to 5.3cm). In relation to the Colombian study,9 the students from the Maule Region performed better (for male: 0.7 to 7.1 cm and for females: 2.5 to 10.4 cm). Comparisons between HJ from international studies (p50) are shown in Figure 1. Values increased as age advanced until ages 14 to 15 years old. During the later ages, minor differences occurred between the Chile students and students of the international studies, except for the Colombian study, which performed poorly in relation to the other studies.9

Table 3 illustrates the percentiles for HJ by age and sex (P3, P5, P10, P15, P25, P50, P75, P85, P90, P95, and P97). For both sexes, the values increased as age advanced.

The results of this study showed differences in the HJ performance when compared with those of the international studies. In general, the students from the Maule displayed lower values during childhood and adolescence when compared to studies carried out in Brazil,11 Poland,12 and other 30 European countries, multi-centries study.14 However, in comparison to the Greek studies,18,20 the Maule students HJ performance was lower until age 14, but the values began to be more similar as age advanced. Furthermore, the present research determined that both sexes of the students from the Maule presented higher values when compared to the Colombian student values,9 especially during adolescence. This demonstrated that at advanced ages (17.0 – 17.9 years old), the Maule students approached the medians achieved by students of the international studies (200 cm for males and 160 cm for females). These results are consistent with various studies carried out at diverse elevations over the see level. Some researchers have reported that the differences in muscle fitness are primarily due to genetic4,21,22 and environmental factors. Within environmental factors, differences have been reported due to living areas (urban and rural,23 training levels,24 secular tendencies,25 among other factors such performing physical activity,26 and lifestyle.27 In fact, Chile in recent years has been decreasing muscle fitness performance in children and adolescents and at the same time overweight and obesity has been increasing,7 which could be determined by low levels of physical activity and sedentary lifestyles. Consequently, the differences found between under developed and developed countries in different parts of the world help to describe the important role of the geographic variability. Furthermore, it seems reasonable to suggest that body weight plays an even more relevant role in the execution of the HJ test. Thus, in general, students with lower levels of physical activity, not completing the 60 minute minimum daily requirement of moderate to vigorous physical exercises, 28 may have difficulty achieving acceptable muscle fitness values for the lower limbs.7

Under this point of view, despite not having controlled for the patterns of physical activity of the students studied, the researchers of the present work found that the performance level of the HJ when compared with student HJ of the international studies was acceptable. Actually the Maule students participated once a week to a physical education classes performing activities related to body training, games, and sports. Many of these activities are frequently utilized in epidemiological studies and educational contexts,5,29 as a testimony for improving health and sports performance. As a result, after discovering differences in the HJ performance among students from different parts of the world, authors of the present study developed percentiles to assess the lower limbs muscle fitness from childhood to adolescence. To rank the students with low, moderate, and high levels of the lower limbs muscle fitness might very important either in the educational setting or in the sport context. This information is relevant for professionals working in educational environments (schools), athletics (identification of talent), and health (sports and fitness clubs).30 Researchers from various international studies have suggested classifying in quintiles as a normative framework for categorizing general physical fitness performance.31,32 The latter ranks individuals below p20 to be very low, between p20 and p40 low, from p40 to p60 moderate, from p60 to p80 high, and more than >p80 good/very high. Other studies have reported lower values up to <p15 as low level warning signs while interpreting p15 to p80 as adequate, and above >p85 as a high level of fitness.11,33 The cut-off points selected for this study coincide with those proposed by researchers from previous studies (p<15, p15 to p85, and >p85). However, according to Dobosz et al.,12 regardless of the uses and applications, children and/or adolescents classified above p90 or p97 need to be considered as talented, especially for those sports where this component is relevant. Those classified below p15, need to be informed or included into physical fitness programs. Given that risk groups exist among children, adolescents, young, and adults, the World Health Organization encourages research groups to find new tools and more precise evaluations of health, encouraging children to actively participate in lifestyle education at very early ages.34,35 Thus, the percentiles proposed in this research study could be used as a daily tool to categorize the level of muscle performance and fitness of the lower limbs. For the future, researchers need to take into consideration developing longitudinal studies to verify changes in muscular fitness during growth and development. In addition, it is necessary to quantify the levels of physical activity and nutrition in order to diminish interpretation bias. However, in addition to the importance of these results for the Maule Region, these findings can also be generalized to other Chile contexts,because the HJ is a well-known and widely used worldwide muscular fitness test.

In conclusion, differences emerged in the muscle fitness performance between the students from the Maule Region and those of the international studies. These differences began during childhood until the beginning of adolescence. Later, the values at adulthood approached those of the multi-centric European studies. The proposed percentiles are an easy-to-use tool, and they may be used to classify the strength of the lower limbs of students in relation to health and sports performance. The Maule results on percentiles to evaluate muscular performance are worth to be extended to Chilean students at primary and secondary levels.