Regular participation in physical education (PE) has the potential to develop physically literate individuals who have the knowledge, skills, and confidence to engage in physical activity as an ongoing lifestyle choice (40). With qualified instruction and deliberate practice, children can improve their motor skill performance and enhance their muscle strength, which are the building blocks for future participation in games, sports, and fitness activities (5,7). Consequently, the development and mastery of selected physical abilities during the growing years is a prerequisite for continued participation in moderate to vigorous physical activity (MVPA) later in life (3,41).
Although early school-based PE in the 19th century focused on calisthenics and gymnastic activities, the current focus on health-related fitness in most contemporary PE programs seems to undervalue the critical importance of developing skill-related fitness early in life (37). That is, PE seems to have evolved from a skill-centered model to a health-centered model with a focus on time spent in MVPA (20). Consequently, children may not be developing prerequisite motor skills that promote continued involvement in recreational activities and sports (31). The percentage of schools that offer daily PE has declined dramatically in the United States over the past decade, and trends for indicators of youth physical activity around the world are low/poor (20,43). Concomitant with a reduction in daily PE and regular participation in physical activities is an observable decrease in muscular fitness (i.e., muscular strength, muscular power, and local muscular endurance) and fundamental movement skills (i.e., locomotor, object control, and stability skills) in modern day youth (8,18). These findings highlight the importance of initiating interventions that are purposely designed to enhance muscular fitness and improve fundamental movement skills in primary school children to alter physical activity trajectories and improve health and fitness outcomes.
The need to improve the quality and quantity of PE to provide children of all abilities with an opportunity to participate in meaningful experiences with appropriate instruction is recognized as an effective and sustainable strategy to reduce the risk of activity-related injuries, promote continued involvement in fitness activities, and prepare youth for sports participation (20,30). Meta-analytical findings indicate that developmentally appropriate learning experiences can improve muscular strength and fundamental movement skill proficiency in youth (5,29). Moreover, the potential health-related benefits of muscular fitness for school-age youth, which include improvements in adiposity and cardiovascular disease risk factors, highlight the significance of muscle-strengthening activities for children and adolescents (23,39). Although the importance of integrating both health- and skill-related fitness components into youth programs has emerged in the literature (9,10), there is an urgent need to develop and evaluate interventions while addressing common barriers (e.g., insufficient time and inadequate resources) to implementing innovative school-based programs. New research priorities for youth physical activity include the study of PE as a means to bring about long-term and sustained change in health behaviors (15).
Fundamental integrative training (FIT) is a method of conditioning that is designed to integrate both health- and skill-related components of physical fitness while overcoming common barriers (6). Fundamental integrative training is designed to enhance muscular fitness and fundamental movement skill performance with meaningful instruction, deliberate practice, and progression based on technical proficiency. The concept of FIT was based on earlier reports on resistance training for school-age youth and was refined based on process evaluation from previous investigations (10,11,30). The aim of this study was to evaluate the effects of FIT on health- and skill-related fitness measures in primary school children during PE.
Experimental Approach to the Problem
This study was designed to evaluate the effects of 8 weeks of PE with or without FIT on health- and skill-related fitness measures in children. Two fourth grade PE classes were cluster randomized into either an FIT group or a control (CON) group and were tested before and after the training period by members of the research team. The FIT and CON groups participated in PE with the same teacher during the study period, but each group had PE at different times during the school day. Subjects in the CON group were not exposed to FIT during the study period. Subsequent analyses of pretraining and posttraining measures were used to quantify changes in fitness and performance after PE with or without FIT.
Forty-one children from 2 different fourth grade PE classes in an urban public school participated in this study. Classes of boys and girls were cluster randomized into either an intervention group (FIT, n = 20) or a control (CON, n = 21) group (Table 1). This study was approved by the College's Institutional Review Board, and written parental permission was obtained from all parents and child assent was obtained from the participants.
All children in this investigation had previous experience with fitness testing as part of required school-based PE. One week before the pretest, a PE teacher and trained researchers reviewed all testing procedures and participants practiced the fitness tests. Height and body mass were measured using standard techniques with a stadiometer and standard physician's scale. Body mass index (BMI) was calculated using the standardized equation (mass/height [in kilograms per square meter]). The same PE teacher and trained researchers administered all fitness tests and offered encouragement to all participants. Standardized protocols for fitness testing were followed according to methods previously described (35,36).
Briefly, aerobic fitness was assessed with the progressive aerobic cardiovascular endurance run (PACER), which is a shuttle run test that requires participants to run back and forth across a 20-meter space at a specified pace that gets faster each minute. The running pace was set by audio signals from a prerecorded CD. The recorded score was the total number of laps completed (36). Muscular fitness was assessed with 5 different tests. The curl-up and push-up tests were used to assess abdominal and upper body strength/endurance, respectively. The cadence of the curl-up and push-up tests was set with a metronome (1 curl-up per 3 seconds), and the maximum number of repetitions performed with proper technique after 1 test was recorded. Lower body power was evaluated by the standing long jump and single-leg hop tests. Participants were required to hold the landing of each jump and maintain body control until the distance was measured. Each jump test was performed 3 times, and the best score was recorded to the nearest whole centimeters. Lower back and hamstring flexibility for the left and right legs were evaluated by the sit and reach test. The best score of 3 trials for each leg was recorded. Test-retest reliability of standard PE fitness tests has been previously reported (21,36). Test-retest reliability for the single-leg hop test in 9- to 10-year old children from our testing center is R = 0.97.
The FIT program used in this study was specifically designed for primary school children and was based on previous research (10,11). The intervention was performed twice per week on nonconsecutive days during the first ∼15 minutes of each regularly scheduled 45-minute PE class and was purposely designed to be time-efficient and developmentally appropriate for children. That is, the intervention was designed to be consistent with the needs, interests, and abilities of children to optimize learning, engagement, and enjoyment. At the start of every class, the regular PE teacher demonstrated proper technique on selected exercises and reviewed training procedures. An undergraduate college student teacher was available for assistance during the FIT segment of the PE class. The FIT program included a circuit of 6–7 exercise stations that focused on enhancing muscular fitness and fundamental movement skills (primarily jumping, balancing, throwing, and catching). Fundamental integrative training included a series of progressive exercises using body weight and medicine balls (1–2 kg), fitness ropes, equalizer bars, BOSU balance trainers, fitness spots, dome cones, punch balloons, and spooners (plastic boards that simulate skateboarding). Table 2 outlines the structure and content of the FIT program, which took place in a school gymnasium during regularly scheduled PE.
After a warm-up, which included dynamic movements (e.g., calisthenics and jumping jacks), participants exercised with a partner and progressed through 1 set of all exercises in the FIT circuit with the aid of music set to the desired work to rest interval. Participants performed 2 exercises at every station in the circuit. Each exercise was performed for 30 seconds during weeks 1–4 and for 45 seconds during weeks 5–8. Participants performed the second exercise at a given station or progressed to the next station after a 30-second recovery period that remained constant throughout the study period. Participants completed the FIT circuit in about 15 minutes. Although the order of the exercise stations in the FIT circuit was consistent throughout the study period, participants started the circuit at different stations each week to provide an opportunity for the participants to navigate their own learning experience. Descriptions of exercises used in the FIT program have been previously described (6,10).
Participants received instructional cues and constructive feedback on the quality of each movement during every FIT class through a direct instructional model (28). Effort was encouraged at every exercise station, and the learning process was reinforced throughout the 8-week program as participants' mastered proper form and technique on basic exercises before progressing to more challenging skills. Of note, the primary focus of FIT was not to complete as many repetitions as possible within a predetermined time interval but rather to perform each movement with proper technique and enthusiasm. To develop motoric competence, participants were able to display mastery of learned motor skills on basic exercises and gain new knowledge by performing novel movements on other exercises that required more complex movement capacities. During weeks 5–8, participants created their own exercises at a mix and match station using information learned during the first 4 weeks of the FIT program. That is, FIT participants created new exercises with medicine balls or spooners, which contributed to a mastery-oriented climate as they were able to control the type of task engagement and overcome challenges that were self-determined as they applied learned skills in novel situations. Although participants were encouraged to be creative and develop a new exercise that was not part of the FIT circuit, the PE teacher or student teacher was nearby to ensure safety. This type of motivational climate can enhance the learning experience and promote physical engagement during PE (44).
After FIT, children participated in a variety of traditional PE activities (e.g., team sports and group games) as directed by the PE teacher for the remainder of the class. Participants in CON did not perform FIT but attended their regular PE class twice per week on the same days during the study period and performed group games and team sport activities with the same PE teacher during the entire class. Physical activity outside of school-based PE was not controlled in this investigation.
Descriptive data (mean ± SD) were calculated for all variables. A repeated measure analysis of variance (ANOVA) (2 × 2) was used to test for interactions and main effects for time (pretest vs. posttest) and group (FIT vs. CON) on the dependent fitness variables. Partial eta-squared (η2) effect sizes were determined within- and between-groups. When interactions and main effects were significant, Tukey's LSD post hoc t-tests were run to detect specific between-group differences. Pearson's product moment correlations were run between body mass and all outcome variables and body height and all outcome variables to establish whether the change in body mass and body height of this growing population would affect any outcome variables. No significant relationships were observed between body mass and height and any outcome variables. Additionally, there was no sex effect based on a repeated measures ANOVA using sex as a covariate. Statistical analyses were conducted in SPSS (Version 18.0; SPSS, Chicago, IL, USA). Statistical significance was established a priori at p ≤ 0.05.
All participants completed the study according to aforementioned procedures, and no injuries or untoward responses were reported during the study period. The FIT and CON groups had participation rates in regularly scheduled PE of 99 and 97%, respectively, during the study period. There were no differences between the FIT and CON groups for the demographic variables including age, body mass and height, and BMI. There were no significant differences between the FIT and CON groups at baseline for any of the variables including PACER, push-up, sit-up, single-leg hop, and sit and reach scores. A significant interaction of group and time was observed after the 8-week intervention for the PACER, push-up, single-leg hop and sit and reach tests, which indicate that training responses were different between FIT and CON (Table 3). There was no significant interaction of group by time indicated for the sit-up and the long jump tests. Percent improvements in fitness performance highlighting significant group interactions are presented in Figure 1. Pre-post percent changes after FIT were significantly greater for the PACER laps, push-up repetitions, single-leg hop, and right and left leg flexibility tests. Using η2, there was a medium between-groups effect size for the PACER test and small between-groups effect size for the long jump, single-leg hop, sit-up, push-up, and sit and reach tests (Table 3).
The primary aim of this study was to evaluate the efficacy of a novel, multifaceted school-based intervention on health- and skill-related fitness measures in primary school children. The FIT program was found to be a safe, effective, and worthwhile method of conditioning for children that provided opportunities for participants to improve cardiorespiratory and muscular fitness. Treatment effects were found for both health- and skill-related fitness measures, and no injuries occurred throughout the training period. Given that the FIT program was designed to keep participants active during PE while engaging in meaningful activities that enhanced muscle strength and movement proficiency, these data provide support for incorporating a time-efficient FIT intervention into primary school PE to enhance children's physical fitness.
A novel finding from the present investigation was that ∼15 minutes of FIT performed twice per week resulted in significantly greater gains in health- and skill-related fitness measures than normally achieved with standard PE in 9- to 10-year old children. The effects of FIT across multiple health and fitness domains were particularly encouraging. Since both groups participated in the same traditional PE lessons with the same PE teacher during the study period, such differences in performance are likely due to the specific training adaptations that resulted from FIT. Of note, the FIT intervention was instructed by a qualified PE teacher and was purposely designed to enhance muscular strength and refine fundamental movement skills while requiring mental engagement and decision making due to the design of the FIT circuit. Integrative training programs that are matched with the cognitive abilities of children can be particularly beneficial because the motor capabilities of youth are highly “plastic” and responsive to this type of training (31). Others reported that combining developmentally appropriate physical activities with instruction and interaction from a qualified teacher is likely to yield the most physical, cognitive, and affective benefits for children (42).
Participants in the FIT group made significantly greater gains in aerobic capacity as measured by the PACER test after the training period than CON. These findings suggest that primary school students respond to FIT by increasing their ability to perform endurance exercise. Performance gains on the PACER test after FIT were particularly notable because the training intervention did not include continuous aerobic training. In support of these findings, others reported that children improved their cardiorespiratory endurance after fitness training that included resistance exercise (26,27). Of potential relevance, Marta et al. (26) found that combined resistance and endurance training was more effective than resistance training alone for enhancing maximal oxygen uptake in 10- to 11-year old children. Youth programs that integrate different types of fitness training may be more effective than “stand alone” programs (e.g., jogging) for enhancing the health and fitness of children. Although training adaptations in adults tend to be specific to the metabolic demands of the program, current findings support the concept that children demonstrate a propensity to be “metabolic nonspecialists” (2). That is, children do not seem to exhibit specialized metabolic adaptations in response to specific training programs.
The FIT program alternated between relatively vigorous exercises (e.g., fitness rope slams) and less intense but challenging exercises (e.g., spooner board surfing), which provided a unique training stimulus. Although continuous activity is more established as a training mode to improve cardiorespiratory endurance, our findings indicate that intermittent activities which include low and high intensity bouts of strength and skill-based exercise can improve aerobic capacity in children. Since a strong and stable trunk will allow for optimal force production and postural control in a gravity-based environment (33), the observed gains in upper body strength and single-leg hop performance in our investigation may have influenced the positive adaptations in aerobic endurance. Previous studies support our findings and demonstrate that the aerobic fitness levels of children can improve relatively quickly after interventions that include engaging and enjoyable activities that enhance muscular strength and motor skill competence (10,11,27). For example, primary school children who participated in an 8-week plyometric program during PE made significant improvements in endurance performance after the intervention (11). Others found significant improvements in shuttle run performance after an 8-week circuit weight training program in 10- to 12-year old children in the PE setting (27). These findings demonstrate that higher intensity bouts of muscular fitness training that are mainly anaerobic in nature can induce favorable changes in aerobic fitness—especially when the program is delivered by a qualified PE teacher.
Our findings regarding muscular fitness are in line with a recent international consensus paper on youth resistance training, which states that children can enhance their muscular strength, muscular power, and local muscular endurance by regular participation in a resistance training program (23). Participation in the FIT program resulted in significantly greater gains in the push-up and single-leg hop tests than CON, which is consistent with others reports that noted significant gains in upper body strength and motor performance in children after structured resistance training (13,22). These positive findings indicate that muscular fitness can be safely enhanced when FIT is incorporated into PE within curricular time and are in support of recommendations to include strength development during school-based PE so all children can be targeted (24).
The lack of treatment effects for the long jump test and sit-up test may be attributed to the quality of PE lessons for the CON group, which involved traditional PE games and sport activities that required jumping, twisting, and sprinting. The FIT program did target muscular fitness—especially muscular power and torso (i.e., abdominal, hip, and lower back) strength; however, gains made by the CON group were observable after the study period. These observations indicate that the design of the intervention may be a critical factor for success. In the present investigation, children in the FIT group participated in about 240 minutes of training (∼15 min per class × 2 classes per week × 8 weeks) over the study period. Although the advantage of a short concentrated lesson in primary school PE is that children remain engaged and eagerly complete all activities before they lose interest, the disadvantage is that desired changes in some fitness measures may not be observed.
Subjects in the FIT group made significant improvements on the sit and reach test, although static stretching was not part of PE for the FIT or CON groups during the study period. Although these findings highlight the value of dynamic movements, they also question the necessity of supplemental flexibility exercises in FIT interventions because time is limited. Others noted improvements in flexibility after fitness training in children (12,38). The curricular time available for additional training is an important consideration when FIT is incorporated into PE.
An emerging body of evidence increasingly supports the need for school-age youth to improve their muscular strength and enhance their motor skill performance (1,19,34). The inclusion of muscle-strengthening activities as part of comprehensive school physical activity guidelines demonstrates the importance of this type of intervention for all youth (40). Most of the FIT exercises were challenging and tended to spark a natural desire to engage in high-energy “play” in children. Because primary school children are still learning how to manipulate their bodies through space, FIT that emphasizes the development of basic conditioning movements in a supportive environment can be an effective approach for improving the physical fitness of school-age youth. Of note, recent investigations have found that motor skill proficiency is a predictor of physical activity in children and adolescents (4,25,32). Furthermore, children with higher motor competence have been found to outperform children with lower motor competence on physical fitness tests, and these differences seem to remain stable over time (14,17). Given that physical activity declines rapidly after puberty (45), fitness programs that specifically target exercise deficits in school-age youth should begin early in life before children become resistant to targeted interventions.
A limitation of this study is that it addressed only the initial phase of FIT in 9- to 10-year old children. Thus, the results from this investigation neither applicable to younger children or adolescents nor do the results provide insight into long-term training adaptations. It was not possible to include a no-PE control group in the school setting as PE is a compulsory subject in this school district. Also, the small effect sizes should be considered in light of the target group and the design of the school-based intervention.
Children in this study had an opportunity to learn proper movement mechanics on a variety of exercises while improving their physical fitness in a supportive environment that was fun and mentally engaging. Although this investigation did not compare performance between children with high and low motor competence, FIT may be particularly beneficial for children with low muscle strength or reduced motor skill development because they may be less likely to engage in physical activity and most likely to benefit from developmentally appropriate exercise training (14,16,17). Our findings indicate that the delivery of FIT with appropriate instruction and assessments has the potential to be a sustainable school-based intervention as it can be implemented within the existing PE curriculum.
The findings from the present investigation indicate that FIT instructed by a qualified PE teacher can result in significant improvements in health- and skill-related fitness components in children, and is a safe, enjoyable, and time-efficient method for children to learn meaningful context in PE. The salient findings from the present investigation indicate that ∼15 minutes of FIT performed twice weekly results in significantly greater gains in selected health- and skill-related fitness measures than gains normally achieved with traditional PE. Multifaceted interventions such as FIT may be an important component of youth strength and conditioning programs because the synergistic relationship between muscular fitness, motor skill performance, and physical activity may strengthen over time, and this may help to reinforce and maintain the desired trajectories in physical activity behaviors. The positive results from this study can be used to inform the design and implementation of future interventions which are needed to assess the long-term effects of FIT on health and fitness outcomes in school-age youth.
The authors thank the children for participating in this study and gratefully acknowledge Bud Kowal and the Ewing Township School District in New Jersey for supporting this study.
1. Artero E, España-Romero V, Jiménez-Pavón D, Martinez-Gómez D, Warnberg J, Gómez-Martínez S, González-Gross M, Vanhelst J, Kafatos A, Molnar D, De Henauw S, Moreno L, Marcos A, Castillo M; HELENA study group. Muscular fitness, fatness and inflammatory biomarkers in adolescents. Pediatr Obes 9: 391–400, 2014.
2. Bar-Or O. Sports Medicine for the Practitioner. New York, NY: Springer-Verlag, 1983.
3. Barnett L, Van Beurden E, Morgan P, Brooks L, Beard J. Does childhood motor skill proficiency predict adolescent fitness? Med Sci Sports Exerc 40: 2137–2144, 2008.
4. Barnett L, Van Beurden E, Morgan P, Brooks L, Beard J. Childhood motor skill proficiency as a predictor of adolescent physical activity. J Adolesc Health 44: 252–259, 2009.
5. Behringer M, Vom Heede A, Matthews M, Mester J. Effects of strength training
on motor performance skills in children
and adolescents: A meta-analysis. Pediatr Exerc Sci 23: 186–206, 2011.
6. Bukowsky M, Faigenbaum A, Myer G. Fundamental integrative training (FIT) for physical education. J Phys Educ Rec Dance 85: 23–30, 2014.
7. Clark J, Metcalfe J. The mountain of motor development: A metaphor. In: Motor Development: Research and Review. Clark E, Humphrey H, eds. Reston, VA: National Association for Sports and Physical Education, 2002. pp. 62–95.
8. Cohen D, Voss C, Taylor M, Delextrat A, Ogunleye A, Sandercock G. Ten-year secular changes in muscular fitness in English children
. Acta Paediatr 100: e175–e177, 2011.
9. DiStefano L, Padua DA, Blackburn J, Garrett W, Guskiewicz KM, Marshall S. Integrated injury prevention program improves balance and vertical jump height in children
. J Strength Cond Res 24: 332–342, 2010.
10. Faigenbaum A, Farrell A, Fabiano M, Radler T, Naclerio F, Ratamess N, Kang J, Myer G. Effects of integrated neuromuscular training on fitness performance in children
. Pediatr Exerc Sci 23: 573–584, 2011.
11. Faigenbaum A, Farrell A, Radler T, Zbojovsky D, Chu D, Ratamess N, Kang J, Hoffman J. Plyo play: A novel program of short bouts of moderate and high intensity exercise improves physical fitness in elementary school children
. Phys Educator 69: 37–44, 2009.
12. Faigenbaum A, Mediate P. The effects of medicine ball training on physical fitness in high school physical education students. Phys Educator 63: 160–167, 2006.
13. Faigenbaum AD, Loud RL, O'Connell J, Glover S, Westcott WL. Effects of different resistance training protocols on upper-body strength and endurance development in children
. J Strength Cond Res 15: 459–465, 2001.
14. Fransen J, Deprez D, Pion J, Tallir I, D'Hondt E, Vaeyens R, Lenoir M, Philippaerts R. Changes in physical fitness and sports participation among children
with different levels of motor competence: A 2-year longitudinal study. Pediatr Exerc Sci 26: 1–21, 2014.
15. Gillis L, Tomkinson G, Olds T, Moreira C, Christie C, Nigg C, Cerin E, Van Sluijs E, Stratton G, Janssen I, Dorovolomo J, Reilly J, Mota J, Zayed K, Kawalski K, Andersen L, Carrizosa M, Tremblay M, Chia M, Hamlin M, Thomas N, Maddison R, Biddle S, Gorely T, Onywera V, Van Mechelen W. Research priorities for child and adolescent physical activity and sedentary behaviours: An international perspective using a twin-panel Delphi procedure. Int J Behav Nutr Phys Act 24: 112, 2013.
16. Haga M. Physical fitness in children
with high motor competence is different from that in children
with low motor competence. Phys Ther 89: 1089–1097, 2009.
17. Hands B. Changes in motor skill and fitness measures among children
with high an low motor competence: A five year longitudinal study. J Sci Med Sport 11: 155–162, 2008.
18. Hardy L, Barnett L, Espinel P, Okely A. Thirteen-year trends in child and adolescent fundamental movement skills
: 1997-2010. Med Sci Sports Exerc 45: 1965–1970, 2013.
19. Hardy L, Reinten-Reynolds T, Espinel P, Zask A, Okely A. Prevalence and correlates of low fundamental movement skill competency in children
. Pediatrics 130: e390–e398, 2012.
20. Institute of Medicine. Educating the Student Body: Taking Physical Activity and Physical Education to School. Washington, DC: The National Academies Press, 2013.
21. Larkin D, Revie G. Stay in Step: A Gross Motor Screening Test for Children
K-2. Perth, Australia: Authors, 1994.
22. Lillegard WA, Brown EW, Wilson DJ, Henderson R, Lewis E. Efficacy of strength training
in prepubescent to early postpubescent males and females: Effects of gender and maturity. Pediatr Rehabil 1: 147–157, 1997.
23. Lloyd R, Faigenbaum A, Stone M, Oliver J, Jeffreys I, Moody J, Brewer C, Pierce K, McCambridge T, Howard R, Herrington L, Hainline B, Micheli L, Jaques R, Kraemer W, McBride M, Best T, Chu D, Alvar B, Myer G. Position statement on youth resistance training: The 2014 international consensus. Br J Sports Med 48: 498–505, 2014.
24. Löfgren B, Daly R, Nilsson J, Dencker M, Karlsson M. An increase in school-based physical education increases muscle strength in children
. Med Sci Sports Exerc 45: 997–1003, 2013.
25. Lopes V, Rodriques L, Maia A, Malina R. Motor coordination as a predictor of physical activity in childhood. Scand J Med Sci Sport 21: 663–669, 2011.
26. Marta C, Marinho D, Barbosa T, Izquierdo M, Marques M. Effects of concurrent training on explosive strength and VO(2max) in prepubescent children
. Int J Sports Med 34: 888–896, 2013.
27. Mayorga-Vega D, Viciana J, Cocca A. Effects of a circuit training program on muscular and cardiovascular endurance and their maintenance in school children
. J Hum Kinet 37: 153–160, 2013.
28. Metzler M. Instructional Models for Physical Education. Scottsdale, AZ: Holcomb Hathaway, 2005.
29. Morgan P, Barnett L, Cliff D, Okely A, Scott H, Cohen K, Lubans D. Fundamental movement skill interventions in youth: A systematic review and meta-analysis. Pediatrics 132: e1361–e1683, 2013.
30. Myer G, Faigenbaum A, Ford K, Best T, Bergeron M, Hewett T. When to initiate integrative neuromuscular training to reduce sports-related injuries and enhance health in youth?. Curr Sports Med Rep 10: 155–166, 2011.
31. Myer G, Kushner A, Faigenbaum A, Kiefer A, Kashikar-Zuck S, Clark J. Training the developing brain, part I: Cognitive developmental considerations for training youth. Curr Sports Med Rep 12: 304–310, 2013.
32. Okely A, Booth M, Patterson J. Relationship of physical activity to fundamental movement skills
among adolescents. Med Sci Sports Exerc 33: 1899–1904, 2001.
33. Oliver G, Adams-Blair H. Improving core strength to prevent injury. J Phys Educ Rec Dance, 81: 15–19, 2010.
34. Ortega F, Silventoinen K, Tynelius P, Rasmussen F. Muscular strength in male adolescents and premature death: Cohort study of one million participants. BMJ 345: e7279, 2012.
35. Presidential Youth Fitness Program. Presidential Youth Fitness Program Physical Educator Resource Guide (Internet Resource). Silver Springs, MD: National Foundation on Fitness, Sports and Nutrition, 2013.
36. Safrit M. Complete Guide to Youth Fitness Testing. Champaign, IL: Human Kinetics, 1995.
37. Siedentop D. Inroduction to Physical Education, Fitness and Sport. New York, NY: McGraw-Hill, 2004.
38. Siegal J, Camaione D, Manfredi T. The effects of upper body resistance training in prepubescent children
. Pediatr Exerc Sci 1: 145–154, 1989.
39. Smith J, Eather N, Morgan P, Plotnikoff R, Faigenbaum A, Lubans D. The health benefits of muscular fitness for children
and adolescents: A systematic review and meta-analysis. Sports Med, 44: 1209–1223, 2014.
40. Society of Health and Physical Educators. National Standards & Grade Level Outcomes for K-12 Physical Education. Champaign, IL: Human Kinetics Publishers, 2014.
41. Souza M, Chaves R, Lopes V, Malina R, Garganta R, Seabra A, Maia J. Motor coordination, activity and fitness at 6 years relative to activity and fitness at 10 years of age. J Phys Activity Health, 11: 1239–1247, 2013.
42. Tomporowski P, McCullick B, Horvat M. The role of contextual interference and mental engagement on learning. In: Education Games: Design, Learning and Application. Edvardsen F, Kulle H, eds. Hauppauge, NY: Nova Science Publishers, Inc., 2011, pp: 127–155.
43. Tremblay M, Gray C, Akinroye K, Harrington D, Katzmarzyk P, Lambert E, Liukkonen J, Maddison R, Ocansey R, Onywera V, Prista A, Reilly J, del Pilar Rodríguez Martínez M, Sarmiento Duenas O, Standage M, Tomkinson G. Physical activity of children
: A global matrix of grades comparing 15 countries. J Phys Act Health 11: S113–S125, 2014.
44. Wadsworth D, Robinson L, Rudisill M, Gell N. The effect of physical education climates on elementary students' physical activity behaviors. J Sch Health 83: 306–313, 2013.
45. Whitt-Glover M, Taylor W, Floyd M, Yore M, Yancey A, Matthews C. Disparities in physical activity and sedentary behaviors among US children
and adolescents: Prevalence, correlates, and intervention implications. J Public Health Policy 30 suppl 1: S309–S334, 2009.