PEDIATRIC ORIGINAL ARTICLE Relationship of physical activity with motor skills, aerobic fitness and body fat in preschool children: a cross-sectional and longitudinal study (Ballabeina) F Burgi1, �� U Meyer1, U Granacher2, C Schindler3, P Marques-Vidal4, S Kriemler3 and JJ Puder5 1Institute of Exercise and Health Science, University of Basel, Basel, Switzerland 2Institute of Sport Science, Friederich- Schiller-University Jena, Jena, Germany 3Swiss Tropical and Public Health Institute, University of Basel, Basel, Switzerland 4Institute of Social and Preventive Medicine, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland and 5Service of Endocrinology, Diabetes and Metabolism, Centre Hospitalier Universitaire Vaudois and University of Lausanne, Lausanne, Switzerland Background: Adiposity, low aerobic fitness and low levels of activity are all associated with clustered cardiovascular disease risk in children and their high prevalence represents a major public health concern. Objective: The aim of this study is to investigate the relationship of objectively measured physical activity (PA) with motor skills (agility and balance), aerobic fitness and %body fat in young children. Design: This study is a cross-sectional and longitudinal analyses using mixed linear models. Longitudinal data were adjusted for baseline outcome parameters. Subjects: In all, 217 healthy preschool children (age 4���6 years, 48% boys) participated in this study. Measurements: PA (accelerometers), agility (obstacle course), dynamic balance (balance beam), aerobic fitness (20-m shuttle run) and %body fat (bioelectric impedance) at baseline and 9 months later. Results: PA was positively associated with both motor skills and aerobic fitness at baseline as well as with their longitudinal changes. Specifically, only vigorous, but not total or moderate PA, was related to changes in aerobic fitness. Higher PA was associated with less %body fat at baseline, but not with its change. Conversely, baseline motor skills, aerobic fitness or %body fat were not related to changes in PA. Conclusion: In young children, baseline PA was associated with improvements in motor skills and in aerobic fitness, an important determinant of cardiovascular risk. International Journal of Obesity (2011) 35, 937���944 doi:10.1038/ijo.2011.54 published online 29 March 2011 Keywords: young children accelerometers physical fitness adiposity Introduction Adiposity, low aerobic fitness and low levels of physical activity (PA) are all associated with clustered cardiovascular disease risk in children1 and their prevalence, especially when combined, represents a major public health concern.2���4 Well-developed motor skills are possible determinants of fitness and PA in adolescents and young adults.5,6 In children, a new model suggest a reciprocal and developmen- tally dynamic relationship between motor skill competence and PA mediated by factors such as physical fitness and obesity.7 As PA is a potentially modifiable lifestyle behavior, it is of interest to known the nature of the relationship of PA with motor skills, aerobic fitness and body fat. Several studies described that PA is positively, although weakly, related to different motor skills in school8 and preschool children.9,10 As those studies represent cross- sectional data, it is difficult to draw conclusions about the direction of causality. Therefore, prospective data are needed that may help to establish recommendations for strategies in health promotion, especially in younger children. Other cross-sectional studies revealed weak to moderate positive associations between PA and aerobic fitness in children.11,12 In addition, a study in school children showed that the decrease in habitual PA between 1975 and 2005 was accompanied by a decrease in aerobic fitness.13 Similarly, Received 17 September 2010 revised 27 January 2011 accepted 31 January 2011 published online 29 March 2011 Correspondence: F Burgi, �� Institute of Exercise and Health Sciences, University of Basel, St Jakob-Turm, Birsstrasse 320B, Basel CH-4052, Switzerland. E-mail: flavia.buergi@unibas.ch International Journal of Obesity (2011) 35, 937���944 & 2011 Macmillan Publishers Limited All rights reserved 0307-0565/11 www.nature.com/ijo

high levels of PA in school children were associated with a better aerobic fitness 4 years later.14 However, there is a lack of longitudinal data looking at the influence of PA on aerobic fitness, particularly in preschool children. The relationship of PA with body fat has been studied in several longitudinal designs, but their results are controver- sial. Indeed many,15���17 but not all18 studies in prepubertal children could demonstrate a negative association between PA and increases in body fat. To our knowledge, previous studies have not investigated the strength of the relationship of PA with motor skills, aerobic fitness and body fat together in one single study. Furthermore, there is a need for longitudinal studies in young children. Therefore, we investigated the cross- sectional and longitudinal relationship of objectively mea- sured PA with motor skills, aerobic fitness and %body fat in a large sample of preschool children. Subject and methods Study design and participants We analyzed data from a randomized controlled trial (Ballabeina-Study, clinicaltrials.gov NCT0067454),19 in which preschool classes from two separate regions in Switzerland were randomly selected. Children were assessed both at baseline (summer 2008) and 9 months later. Children from the 20 classes of the control group, who did not receive any intervention, were used for these analyses. The study was approved by the respective regional ethics committees, and written informed consent from the parents or legal representatives was obtained for 312 children. This analysis focuses on those 217 children with valid data for all PA and physical fitness measures at both time points (69% of the participating children). Children with and without valid data did not differ in baseline values of PA, physical fitness and anthropometry (all P �� not significant). Physical activity PA was measured over 6 consecutive days with an accel- erometer (GT1M, Actigraph, Florida, USA), which was programmed to save data in 15-s intervals (epochs). The Actigraph/computer science and applications is the most commonly used motion sensor in children and has a good reproducibility, validity and feasibility.20 This particular type of PA assessment has been shown to be valid across different activities in 3- to 5-year old children, with a Pearson cor- relation coefficient of r �� 0.82 between VO2 (ml kg 1 min 1) and Actigraph counts/epoch.21 The accelerometers were worn around the hip. To consider data as valid, at least 3 days of recording (2 weekdays and 1 weekend day)22 with a minimum of 6 h registration per day were needed. The 6-h validity was highly correlated with 10-h validity (N �� 502, r �� 0.92, Po0.001). Data from monitored days were extrapolated by weighing weekdays and weekends (5:2). Sequences of at least 10min of consecutive zero values were removed and interpreted as ���accelerometer not worn���.23 Total PA, moderate PA (MPA) and vigorous PA (VPA) were chosen as markers of PA. Total PA was expressed as counts per minute (total counts recorded divided by daily wearing time). MPA and VPA were based on cutoffs published by Pate et al.:21 420���841 counts per 15 s for MPA and X842 counts per 15 s for VPA. Each 15-s interval over the specific cutoff was summarized in the corresponding intensity level group and data are presented as the amount of 15-s intervals per day. As differences in daily wearing time between the groups were negligible and non-significant, we did not adjust for this variable (mean wearing time 10.8 h per day). Physical fitness Physical fitness in childhood is a powerful marker of health24 and can be grouped into two broad categories: health-related aspects (aerobic fitness, muscular strength, muscular endur- ance and flexibility) and skill-related aspects (agility, balance, coordination, power, reaction time and speed).25 In this study, aerobic fitness was chosen because it represents health-related aspects and agility and balance were selected because they represent some aspects of the skill-related physical fitness. Agility. Agility26 was assessed by an obstacle course specifi- cally designed for 3- to 6-year old children and described by Vogt27 and Kunz.28 It includes running 1 m from a marking cone to a transversally positioned bench, jumping over the bench (36 cm high, 28 cm wide), crawling under the bench and running back to the marking cone three times in a row as fast as possible. The test was assessed by the time needed to complete the obstacle course and was measured in seconds. Each child had two attempts and the faster one was used for further data analysis. The interobserver correla- tion and the test-retest reliability in our pilot study (n �� 14) were r �� 0.99 (Po0.01) and r �� 0.82 (Po0.01), respectively. Balance. Dynamic balance was tested by balancing forward barefoot on a balance beam (3 m long and 3 cm wide).29 As an outcome measure, the consecutive successful steps on the beam were counted until the foot of the child touched the floor. Children could reach a maximum of eight steps. They performed three trials and the mean of the best two trials was calculated and used for further analyses. The interobserver correlation and the test-retest reliability between the two better attempts in our pilot study (n �� 15) were r �� 0.97 (Po0.01) and r �� 0.84 (Po0.01), respectively. Aerobic fitness. Aerobic fitness was assessed by the multi- stage 20-m shuttle run test.30 The test measures aerobic capacity by running back and forth for 20 m with an initial running speed of 8.0 km h 1. The progressive 0.5 km h 1 increase in running speed every minute was indicated by a sound. The maximal performance was determined when the child could no longer follow the pace or the child decided A cross-sectional and longitudinal study (Ballabeina) F Burgi �� et al 938 International Journal of Obesity