Original scientific article received: 2016-12-06 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 UDC: 796.012.414.2-053.4(497.4) VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY IN 4- TO 6-YEAR-OLD CHILDREN Katja KOREN1, Rado PIŠOT1, Boštjan ŠIMUNIČ1 1 Science and Research Centre Koper, Institute for Kinesiology Research, Garibaldijeva 1, 6000 Koper, Slovenia Corresponding author: Boštjan ŠIMUNIČ Science and Research Centre Koper, Institute for Kinesiology Research, Garibaldijeva 1, 6000 Koper, Slovenia Tel.: +386 5 66 37 700 E-mail: bostjan.simunic@zrs-kp.si ABSTRACT Preschool children are intensively involved in the process of developing fundamental movement skills such as walking, running, jumping, climbing, crawling and other simple movements. We aimed to compare age- and gender- related trends in counter-movement vertical jump (CMJ) performance (jumping height) measured with a means of ground force plate during a longitudinal study of 4- to 6-year old children (N=79; 43% boys). Furthermore, we classified children CMJ arm-leg coordination into poor, average, or excellent on the grounds of high speed video footage. We found that CMJ height progresses significantly with age when arms are used (P<.001; rf=.632) and without the use of arms (P<.001; rf=.620). There were no sex effects. After classification of CMJ arm - leg coordination we found that children with excellent CMJ coordination progress more intensively than those with average coordination, whereas poorly coordinated jumpers do not progress at all. After extrapolating our data with the data of others we found logarithmic CMJ height trends until the age of 16 in both sexes, athlete boys jumping higher than the non-athletes after the ages of 14 or 15. It seems that the initial movement patterns level, in this case the observedjumping technic, develops and refines in 4- to 6-year old children at that age. We conclude that jumping coordination is a very important factor of CMJ performance in the studied age span. Keywords: countermovement jump; ground force plate; coordination, explosive power, pre-school children. 153 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 Katja KOREN, Rado PIŠOT, Boštjan ŠIMUNIČ: VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY ..., 153-170 RAZVOJ NAVPIČNEGA SKOKA OTROK - LONGITUDINALNA ŠTUDIJA 4- DO 6-LETNIH OTROK IZVLEČEK Predšolski otroci so intenzivno vključeni v proces razvoja elementarnih gibalnih vzorcev, kot so hoja, tek, skok, plezanje, plazenje in drugih enostavnih gibanj. Naš namen je longitudinalno primerjati uspešnost skoka z nasprotnim gibanjem - CMJ (višina skoka) merjeno s tenziometrijsko ploščo 4 do 6 let starih otrok (N=79; 43% dečkov) glede na starost in spol. Poleg tega smo otroke razvrstili glede na CMJ koordinacijo med rokami in nogami v slabše, povprečne ali odlične na podlagi visokofrekvenčnih video bočnih posnetkov. Ugotovili smo, da CMJ višina narašča z leti, pri skokih z uporabo rok (P<,001; n2=,632) in brez uporabe rok (P<,001; rf=,620). Med spoloma ni bilo razlik. Po klasifikaciji koordinacije CMJ smo ugotovili, da otroci z odlično koordinacijo CMJ napredujejo intenzivneje kot tisti s povprečno koordinacijo CMJ, medtem ko otroci s slabšo koordinacijo CMJ sploh niso napredovali. Po ekstrapolaciji naših podatkov z drugimi, smo ugotovili logaritemski trend višine CMJ do starosti 16 let pri obeh spolih, kjer po starosti 14-15 let fantje športniki skočijo višje kot fantje, ki niso športniki. Ugotavljamo intenziven trend razvoja CMJ v tem starostnem obdobju, kjer je koordinacija CMJ zelo pomemben dejavnik uspešnosti izvedbe CMJ. Ključne besede: skok z nasprotnim gibanjem, tenziometrijska plošča, koordinacija, eksplozivna moč, predšolski otroci INTRODUCTION The reported children sedentary behavior (Carson, LeBlanc, Moreau, & Tremblay, 2013; Colley et al. 2011; ParticipACTION 2015, 2016) and obesity (Gotay et al. 2013; Ng et al. 2014) are among the major health problems. The epidemic of physical inactivity and the associated epidemic of obesity are being driven by multiple factors: societal, technologic, industrial, commercial, financial (Council on Sports Medicine and Fitness and Council on School Health, 2006). Obesity among children in Slovenia is increasing. The data collected in the context of the European initiative show that the Slovenian children are among the most endangered of obesity among the EU countries (OECD/EU, 2016). This global trend of prolonged sitting and obesity is likely to continue due to the growing availability and popularity of computer, mobile phones, video games and television (Lepp, Barkley, Sanders, Rebold, and Gates, 2013; Public Health England, 2013) and due to less favorable food availability (Raychaudhuri & Sanyal 2012; Skidmore & Yarnell, 2004). Moreover, we must be aware that health behaviors and obesity is transferred into adulthood. 154 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 Katja KOREN, Rado PISOT, Bostjan SIMUNIC: VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY ..., 153-170 On the other hand, physical activity and exercise helps preventing chronic diseases such as cardiovascular disease (Kruk, 2007; Warburton, Nicol, & Bredin, 2006), diabetes (Kruk, 2007; Warburton, Nicol, & Bredin, 2006), cancer (Kruk, 2007; Warburton, Nicol, & Bredin, 2006), hypertension, obesity (Kruk, 2007; Warburton, Nicol, & Bredin, 2006), osteoporosis (Kruk, 2007; Warburton, Nicol, & Bredin, 2006), fall-related injuries (Kruk, 2007), depression (Kruk, 2007; Warburton, Nicol, & Bredin, 2006) and emotional stress (Kruk, 2007). Therefore, it is essential to encourage preschool children to engage healthy lifestyle as early as possible, to develop motor abilities satisfactory and develop fundamental movement skill (FMS) such as walking, running, jumping, crawling, climbing, hopping, catching, kicking, throwing and hitting a ball. If sufficiently developed, FMS plays an important role in establishing physical confidence and competence (Gallahue and Ozmun, 1998). FMS development has been classified into stages, progressing from a beginner level to a mature level (Hynes-Dusel, 2002). The beginner level generally depicts the minimal standard of children ages 4 to 7 (Gabbard, 1992). By the completed age of 8, with practice and maturity, most children will have achieved mature level (Gabbard, 1992). The experts believe that motor delays negatively influence future motor and cognitive development (Gallahue, 1996). Therefore, mastering FMS is linked also to cognitive development (Diamond, 2000; Krombholz, 1997). Most of the studies reports FMS data obtained in adult male subjects (Laffaye and Choukou, 2010; Harman, Rosenstein, Frykman, & Rosenstein,1990; Markovic, Dizdar, Jukic, & Cardinale, 2004; Markovic, 2007; Runge, Rittweger, Russo, Schiessl, & Felsenberg, 2004) and there are few longitudinal data about children development trends of both sexes where the most frequent FMSs observed are walking and the vertical jump (Focke et al., 2013). Different researchers defined the factors affecting vertical jump ability: a) composition of skeletal muscles (Kaneko, Fuchimoto, Toji, & Suei, 1983; Wilson, Newton, Murphy, & Humphries, 1993), b) well-developed alactic or anaerobic power capacity (in comparison with the athletes with high aerobic power capacity) (Shorten, 1987; Conlee, McGown, Fisher, Dalsky, & Robinson, 1982), c) neural adaptation (motor unit activation, motor unit synchronization and the specificity of the movement pattern (Wilson et al., 1993; Sale, 1988), d) initial levels of strength of the person and the ability to make use of a stretch shortening cycle (Adams, O'Shea, O'Shea, & Climstein, 1992; Duke & BenEliayhu, 1992; Wilson, Newton, Murphy, & Humphries, 1993), e) the use of elastic and contractile energy for producing dynamic muscle contractions (Adams et al., 1992; Duke & BenEliayhu, 1992), f) effective use of the arms for increased vertical velocity (Harman et al., 1990), g) trunk extension, head movements and utilization of a countermovement to initiate the stretch shortening cycle (Young, 1995; Van Soest, Ro-ebroeck, Bobbert, Huijing, & van Ingen Schenau, 1985; Harman et al., 1990), h) upper body and abdominal (trunk) strength has also shown to be a contributing factor to vertical jump performance (Shorten, 1987; Cisar & Corbelli, 1989; Bobbert & Van Soest, 1994), and i) development of a motor pattern for vertical jump - arm swing (Young, 1995). All the above-mentioned factors develop through childhood and, thus, this development must affect vertical jump development as well as other FMS. 155 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 Katja KOREN, Rado PIŠOT, Boštjan ŠIMUNIČ: VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY ..., 153-170 There have been numerous studies which have investigated jumping in adult athletes from various sports, and the most commonly reported parameter is jumping height. However, it is difficult to compare the results of various studies as they all vary greatly in the experimental design, in the duration of research, in the testing procedures utilized and in the application of training techniques. Although vertical jumping is often used in physical performance tests for both children and adults, normative data for children are lacking in the literature. Only few studies focused on jumping performance in primary and secondary school children (Klausen, Schibye, & Rasnussen, 1989; Temfe-mo, Hugues, Chardon, Mandengue, & Ahmaidi, 2009; Focke et al., 2013) and some in pre-school children (Neelly & Zebas, 2003; Harrison & Moroney, 2007; Focke et al., 2013). Neelly and Zebas (2003) where a research was performed on a 4.5 year-old children, while Focke et al. (2013) measured 1835 children aged from 4 to 17 years of age. They specified that boys jump higher than girls and reported cross-sectional developmental trends for both sexes. Therefore, we aimed to develop longitudinal CMJ height trends in 4- to 6 year-old children for both sexes. Additionally, our goal is to detect the jumping technique used by children. When comparing CMJ height in children classified with different jumping coordination score (1 - poor; 2 - average; 3 - excellent) we hypothesized that the percentage of excellent jumpers would increase and excellent jumpers would progress in CMJ height more intensively with their age. We also plan to extrapolate CMJ height age trends with the data of others. METHODS Participants Four-year-old children were recruited in 2009 from three randomly selected Slovenian kindergartens, all in the Coastal region: Koper, Škofije and Semedela. All tests and procedures were explained to the parents on organized meetings in kindergartens prior to the obtainment of their written consent. None of the children had any history of neuromuscular disorders or muscle diseases. In regard to the recruitment process, 160 children in total were selected (only those who had their 4th birthday in 2009), of which 79 children (34 boys, 45 girls) completed all three longitudinal jumping measurements and were selected for the analysis. Moreover, all procedures conformed to the 1964 Declaration of Helsinki and were approved by the National Medical Ethics Committee of the Republic of Slovenia. Procedures The organizational settings of the conducted longitudinal study were the same for all three assessments. The assessments were conducted in autumn of 2009, 2010, and 156 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 Katja KOREN, Rado PISOT, Bostjan SIMUNIC: VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY ..., 153-170 2011. A week before the assessment we notified the teachers to follow a specific protocol prior to the measurement, namely, that all major physical or sport activities were discouraged two days before the assessment. Daily, from 2 to 5 children arrived in the laboratory and performed a series of tests (body composition, muscle architecture, posture analysis, and five FMS analysis) from where only basic anthropometrical data and vertical jumping is presented in this report. Measurements of Anthropometrical Characteristics All children had their standing height and weight measured. Participants' body mass and height were measured by a means of standard tools. Their body mass was measured to an accuracy of .1 kilograms, while the body height was measured to an accuracy of .5 centimeters. All participants were barefoot and wearing their sportswear during the measurements. The body composition was measured with bioimpedance (BioScan 916s, Maltron, UK), where children lied on a bed for 30 minutes before the assessment. Countermovement Jumping Height Assessment Each child performed a 15 minutes of standardized warm-up before the FMS assessment. After the walking and running analysis we analysed jumping performance. The instruction was to jump as high as possible, using their arms and countermovement jumping (CMJ) technique. Each child performed between 3 and 5 trial jumps followed by three maximal CMJs with the use of their arms and three maximal jumps without the use of their arms on a ground force plate system (AMTI sampling at 1000 Hz.). They were also simultaneously videotaped with high-frequency camera (Fujifilm Fi-nepix HS10) for qualitative analysis of arm-leg coordination and synchronization of movement. During each jump, there was at least one minute of rest. CMJ height was calculated based on the flight time. The highest jumps from both techniques (with and without the use of the arms) were taken for further analysis. We used several motivational methods to achieve a maximal performance (wall stickers), similarly as in some previous studies where they used balloons (Clark, Phillips, & Petersen, 1989; Jensen, Phillips, & Clark, 1994). Countermovement Jumping Coordination Assessment For the jumping coordination assessment, we used a scale developed by Plevnik (2014) adapted from the technique for the evaluation of the implementation of motor tasks (Vies, Kroes & Feron, 2004), where jumping coordination was qualitatively (based on high-speed video footage, see Figure 1) classified as: 157 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 Katja KOREN, Rado PIŠOT, Boštjan ŠIMUNIČ: VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY ..., 153-170 POOR (score 1): Hands do not follow the body movement. They move backwards, or not at all. AVERAGE (score 2): Hands are somewhat included in jumping performance, but less intensively or with less amplitude. EXCELLENT (score 3): Hands follow the vertical jump in all phases, correct timing, intensity and amplitude. Figure 1: Coordinated vertical jump classified as excellent (left) and non-coordinated vertical jump classified as poor (right). Data Analysis The data were analyzed using SPSS (version 22, IBM, USA) and Microsoft Excel (version 2013, Microsoft, USA) programs. Data are presented as means with standard deviation. There was no major deviation from normal distribution. Sex and age effects were tested with two-way Analysis of variance (ANOVA) with sex (2) as between factor and age (3) as within factor. Longitudinal changes were analyzed with repeated measures ANOVA, where improvement in jump performance of coordinated and non-coordinated jumpers was analyzed with repeated measures ANOVA and one fixed factor (jump coordination). The pooled longitudinal trends (our data and the data of others) were fitted by mathematical modelling using logarithmic curve to establish best fit. The Pearson correlation was used to analyze the correlation between fat mass and CMJ height. The level of significance for all tests was set at P<.05. If significance was confirmed, we reported also the n2 effect size. 158 ANNALES KINESIOLOGIAE • 7 • 2016 • 2 Katja KOREN, Rado PISOT, Bostjan SIMUNIC: VERTICAL JUMP HEIGHT IN YOUNG CHILDREN - A LONGITUDINAL STUDY ..., 153-170 RESULTS In all three-measurement points in total, 79 participants being included; their average body height, body mass, fat mass, muscle mass, CMJ height without arms, CMJ height with arms and percent of coordinated jumpers is shown in Table 1. to to o ,g ta sj S a g $ S a u 'is S 0 1 S5 a "a S5 O £ 2 ®jj PM" .339 .364 .701 .194 2 .0 .095 PM" <.001 (.943) §1 < (. <.001 (.293) <.001 (.881) <.001 (.620) 01 2) o rn H \o < (. <.001 (.881) jbr 1 Cl .073 .494 .001 (.133) .002 (.116) .337 .140 6 years 121±5.6 123±5.8 23.6±3.7 24.0±4.2 .7 4. -H