An After-School, high-intensity, interval physical activity programme improves health-related fitness in children

Sergio Reloba Martínez Luis Javier Chirosa Ríos Ignacio Martín Tamayo Laura Guerrero Almeida Miguel Angel López-Gomez Christian Campos Jara About the authors

Abstract

Health problems related to a low level of physical activity (PA) in children and adolescents have prompted research into extracurricular PA programs. This study was designed to determine the effects of two different levels of PA on the health-related fitness of school children. Ninety-four girls and boys (7-9 years) were randomly assigned to a control group (CG) or intervention group (IG). Over a 12 week study period, children in the CG participated in a similar PA program to that of a standard school physical education program while those in the IG completed a high intensity interval training (HIIT) program. Both programs involved two 40 minute extracurricular sessions per week. Our findings indicate that the HIIT intervention improved motor capacity (speed/agility), Vpeak, VO2 max and excess post-exercise oxygen consumption (EPOC) (p < 0.05) along with the musculoskeletal capacity of the lower trunk (mean propulsive velocity and standing long jump, p < 0.05). The PA program had no effect on anthropometric variables or hand-grip strength. The data indicate that a 12 week strength training program using workloads adapted to children may significantly improve several markers of health and physical fitness compared to a standard school PA program.

Keywords
children; physical condition; aerobic training; high intensity; health; Alpha-fitness

Introduction

Concern about growing sedentary behaviour, overweight and obesity(11 Janssen I. Physical activity guidelines for children and youth. APNM 2007; 32: 109-121. ,22 Ortega F, Ruiz J, Castillo M, Moreno L, Gonzalez-Gross M, Wärnberg J et al. Bajo nivel de forma física en los adolescentes españoles. Importancia para la salud cardiovascular futura (Estudio AVENA) . Rev Esp Cardiol 2005; 58(8): 898-909.) along with reduced physical activity (PA) among children(33 Reverter J, Plaza D, Jové C, Hernández V. Actividad físico-deportiva extraescolar en alumnos de primaria: el caso de Torrevieja (Alicante). Retos. 2014; 25: 48-52.,44 Troiano RP, Berrigan D, Dodd KW, Masse LC, Tilert T, McDowell M. Physical activity in the United States measured by accelerometer. Med Sci Sports Exerc 2008; 40(1): 181-188. ) has recently prompted a series of investigations designed to assess the benefits of extracurricular PA programs (55 Escalante Y, Saavedra J, García-Hermoso A, Domínguez A. Improvement of the lipid profile with exercise in obese children: A systematic review. PrevMed 2012; 54: 293-301.

6 García-Cantó E, Pérez JJ. Programa para la promoción de actividad física saludable en escolares murcianos. Retos. 2014; 25: 131-135
-77 González J, Portolés A. Actividad física extraescolar: relaciones con la motivación educativa, rendimiento académico y conductas asociadas a la salud. RIPED. 2014; 1 (9): 51-65.). Such studies have indicated beneficial effects of PA interventions on various health and fitness markers(88 Annesi J, Faigenbaum A, Westcott W, Smith A, Unruh J, Hamilton F. Effects of the Youth Fit For Life protocol on physiological, mood, self-appraisal, and voluntary physical activity changes in African American preadolescents: Contrasting after-school care and physical education formats. Int J Clin Hlth Psyc. 2007; 3: 641-659.

9 Cordova A, Villa G, Sureda A, Rodriguez-Marroyo JA, Sanchez-Collado P. Actividad física y factores de riesgo cardiovascular de niños españoles de 11-13 años. Rev Esp Cardiol 2012; 65 (7): 620-626.

10 Hasselstrøm H, Karlsson M, Hansen S, Grønfeldt V, Froberg K, Andersen L. A 3-Year Physical Activity Intervention Program Increases the Gain in Bone Mineral and Bone Width in Prepubertal Girls but not Boys: The Prospective Copenhagen School Child Interventions Study (CoSCIS). Calc Tiss Res. 2008; 83: 243-250.

11 Hogg J, Diaz A, Cid M, Mueller C., Grace E, Cheruvu S. et al An after-school dance and lifestyle education program reduces risk factors for heart disease and diabetes in elementary school children. J Pediatr Endocr Met 2012; 25(5-6): 509-516.
-1212 Resaland GK, Anderssen LB, Mamen A, Anderssen SA. Effects of a 2-year school-based daily physical activity intervention on cardiorespiratory fitness. The Sogndal school-intervention study. Scand J Med Sci Spor. 2011; 21: 302-309. ) as well as diminishing sedentary habits13, 14.

However, authors such as Leek(1515 Leek D, Carlson J, Cain K, Henrichon S, Rosenberg D, Patrick K. et al. Physical Activity During Youth Sports Practices. Arch Pediatr Adolesc Med. 2010; 4 (165): 294-299.) and Myer and Faigenbaum(1616 Myer GD, Faigenbaum AD. Exercise is sports medicine in youth: Integrative neuromuscular training to optimize motor development and reduce risk of sports related injury. Kronos 2010; 10 (1): 39-48.) have argued that these PA interventions currently do not guarantee that young people attain the levels of health and PA recommended by the different organizations and authors. This has sparked an exponential increase in research on the impact of extracurricular PA (99 Cordova A, Villa G, Sureda A, Rodriguez-Marroyo JA, Sanchez-Collado P. Actividad física y factores de riesgo cardiovascular de niños españoles de 11-13 años. Rev Esp Cardiol 2012; 65 (7): 620-626.,1616 Myer GD, Faigenbaum AD. Exercise is sports medicine in youth: Integrative neuromuscular training to optimize motor development and reduce risk of sports related injury. Kronos 2010; 10 (1): 39-48.,1717 Ben Ounis O, Elloumi M, Zouhal H, Makni E, Denguezli M, Amri M, Lac G, Tabka Z. Effect of individualized exercise training combined with diet restriction on inflammatory and igf-1/igfbp-3 in obese children. Ann Nutr Metab 2010; 56: 260-266.

18 Kriemler S, Zahner L, Schindler C, Meyer U, Hartmann T, Hebestreit H, Brunner-La Rocca H, Van Mechelen W, Puder J. Effect of school based physical activity programme (KISS) on fitness and adiposity in primary schoolchildren: cluster randomised controlled trial. BMJ 2010; 340: 1-8.

19 Sandercock G, Cohen D, Griffin M. Evaluation of a multicomponent intervention to improve weight status and fitness in children: Upstarts. Pediatr Int. 2012; 6 (54): 911-917.

20 Sigmund E, El Ansari W, Sigmundová D. Does school-based physical activity decrease overweight and obesity in children aged 6¿ 9 years? A two-year non-randomized longitudinal intervention study in the Czech Republic. BMC Public Health 2012; 1 (12): 570-583.

21 Faigenbaum A, Westcott W, LaRosa R, Long C. The Effects of Different Resistance Training Protocols on Muscular Strength and endurance development in children. Pediatrics 2005; 1 (104): 1-7.

22 Gamelin FX, Baquet G, Berthoin S, Thevenet D, Nourry C, Nottin S, Bosquet L. Effect of high intensity intermittent training on heart rate variability in prepubescent children. Eur J Appl Physiol 2009; 105: 731-738.

23 Nourry C, Deruelle F, Guinhouya C, Baquet G, Fabre C, Bart F, Berthoin S, Mucci P. High-intensity intermittent running training improves pulmonary function and alters exercise breathing pattern in children. Eur J Appl Physiol 2005; 94(4): 415-23.

24 Rosenkranz R, Welk G, Dzewaltowski D. Environmental correlates of objectively measured physical activity and sedentary behaviour in after-school recreation sessions. JPAH. 2011; 8: 214-221.

25 Yu C, Sung YT, So R, Lui KC, Lau W, Lam P, Lau E. Effects of Strength Training on Body Composition and Bone Mineral Content in Children Who Are Obese. J Strength Cond Res. 2005; 19(3): 667-672
-2626 Baquet G, Guinhouya C, Dupont G, Nourry C, Berthoin S. Effects of a short-term interval training program on physical fitness in prepubertal children. J Strength Cond Res. 2004; 18(4): 708-713).

As may be inferred from the vast amount of literature available on the topic, most PA interventions involve moderate-intensity aerobic PA, or so-called moderate-intensity training (MIT), and are based on working techniques similar to those of a traditional school physical education (PE) program (99 Cordova A, Villa G, Sureda A, Rodriguez-Marroyo JA, Sanchez-Collado P. Actividad física y factores de riesgo cardiovascular de niños españoles de 11-13 años. Rev Esp Cardiol 2012; 65 (7): 620-626.,1717 Ben Ounis O, Elloumi M, Zouhal H, Makni E, Denguezli M, Amri M, Lac G, Tabka Z. Effect of individualized exercise training combined with diet restriction on inflammatory and igf-1/igfbp-3 in obese children. Ann Nutr Metab 2010; 56: 260-266.

18 Kriemler S, Zahner L, Schindler C, Meyer U, Hartmann T, Hebestreit H, Brunner-La Rocca H, Van Mechelen W, Puder J. Effect of school based physical activity programme (KISS) on fitness and adiposity in primary schoolchildren: cluster randomised controlled trial. BMJ 2010; 340: 1-8.

19 Sandercock G, Cohen D, Griffin M. Evaluation of a multicomponent intervention to improve weight status and fitness in children: Upstarts. Pediatr Int. 2012; 6 (54): 911-917.
-2020 Sigmund E, El Ansari W, Sigmundová D. Does school-based physical activity decrease overweight and obesity in children aged 6¿ 9 years? A two-year non-randomized longitudinal intervention study in the Czech Republic. BMC Public Health 2012; 1 (12): 570-583.). However, over the past 10 years, several complementary studies have started to emerge that suggest that high-intensity intermittent aerobic exercise, otherwise known as high-intensity interval training (HIIT), adapted for children and preadolescents(2121 Faigenbaum A, Westcott W, LaRosa R, Long C. The Effects of Different Resistance Training Protocols on Muscular Strength and endurance development in children. Pediatrics 2005; 1 (104): 1-7.

22 Gamelin FX, Baquet G, Berthoin S, Thevenet D, Nourry C, Nottin S, Bosquet L. Effect of high intensity intermittent training on heart rate variability in prepubescent children. Eur J Appl Physiol 2009; 105: 731-738.

23 Nourry C, Deruelle F, Guinhouya C, Baquet G, Fabre C, Bart F, Berthoin S, Mucci P. High-intensity intermittent running training improves pulmonary function and alters exercise breathing pattern in children. Eur J Appl Physiol 2005; 94(4): 415-23.

24 Rosenkranz R, Welk G, Dzewaltowski D. Environmental correlates of objectively measured physical activity and sedentary behaviour in after-school recreation sessions. JPAH. 2011; 8: 214-221.
-2525 Yu C, Sung YT, So R, Lui KC, Lau W, Lam P, Lau E. Effects of Strength Training on Body Composition and Bone Mineral Content in Children Who Are Obese. J Strength Cond Res. 2005; 19(3): 667-672) shows a beneficial effect on cardiovascular health and fitness16, 26. This type of PA program has been proposed as an alternative to the conventional school PE syllabus.

For HIIT, Baquet, Van Praagh and Berthoin(2727 Baquet G, Van Praagh E, Berthoin S. Endurance Training and Aerobic Fitness in Young People. Sports Med 2003; 33(15): 1127-1143.) suggested a relative exercise intensity of ≥80% of the maximum heart rate to produce significant changes in the maximal oxygen consumption (VO2 max) of prepubertal children. Myer and Faigenbaum(1616 Myer GD, Faigenbaum AD. Exercise is sports medicine in youth: Integrative neuromuscular training to optimize motor development and reduce risk of sports related injury. Kronos 2010; 10 (1): 39-48.) targeted neuromuscular development and motor skills to improve the health of young children while Naclerio and Faigembaum(2828 Naclerio F, Faigenbaum A. Integrative neuromuscular training for youth. Kronos 2011; 10 (1): 49-56.) highlighted the efficacy of high-intensity exercise in improving the health and fitness of school children. Other authors have also described positive effects of HIIT programs on growth and development(2929 Behringer M, Vom Heede A, Yue Z, Mester J. et al. Effects of resistence training in children an adolescents: a metaanálisis. Pediatrics 2010; 126 (5): 199-210.

30 Faigenbaum A, Myer GD. Resistence training among young athletes: safety, efficacy an injury prevention effects. Br J Sports Med 2009; 44: 56-63
-3131 Slining M, Adair LS, Goldman BD, Borja JB, Bentley M. Infant overweight is associated with delayed motor development. J Pediatric 2010; 157: 20-25.), along with improved postural control and stability(3232 Mickle KJ, Munro BJ, Steele JR. Gender and age affect balance performance in primary school-aged children. J Sci Med Sport 2011; 14: 243-248.), a spontaneous increase in PA during the day(3333 Faigenbaum A, Myer GD. Resistance training and paediatric health. Kronos 2011; 10 (1): 31-38.), and a reduced risk of injury while playing sport(1616 Myer GD, Faigenbaum AD. Exercise is sports medicine in youth: Integrative neuromuscular training to optimize motor development and reduce risk of sports related injury. Kronos 2010; 10 (1): 39-48.).

Despite the well-established beneficial effects of MIT and in smaller measure, HIIT, to the best of our knowledge no study has compared the effects of both training strategies on the health-related fitness of children. In addition, the different variables and training protocols such as duration, frequency, volume and intensity assessed along with intervening factors such as nutrition education(1717 Ben Ounis O, Elloumi M, Zouhal H, Makni E, Denguezli M, Amri M, Lac G, Tabka Z. Effect of individualized exercise training combined with diet restriction on inflammatory and igf-1/igfbp-3 in obese children. Ann Nutr Metab 2010; 56: 260-266.,3434 Donnelly J, Jacobsen D, Whatley J, Hill J, Swift L, Cherrington A, Polk B, Tran Z, Reed G. Nutrition and physical activity program to attenuate obesity and promote physical and metabolic fitness in elementary school children. Obes Res. 2012; 3(4): 229-243.,3535 Gortmaker S, Lee R, Mozaffarian R, Sobol A, Nelson T, Roth B, Wiecha J. Effect of an After-School Intervention on Increases in Children's Physical Activity. Med Sci Sport Exer. 2012; 44(3): 450-457. ) and healthy habits13, 36 hinder indirect comparisons between the two PA intervention strategies.

This study was designed to determine the effects of a moderate-intensity PA and a high-intensity interval PA program on the health-related fitness of school children. As markers of health and fitness, we used the Alpha-fitness battery of tests designed for children and adolescents(3737 Cuenca-García M, Jiménez-Pavón D, España-Romero V, Artero E, Castro-Peñero JC, Ortega F, Ruiz JR, Castillo M. Condición física relacionada con la salud y hábitos de alimentación en niños y adolescentes: propuesta de addendum al informe de salud escolar. Rev Invest Ed. 2011; 9 (2): 35-50.

38 Serra-Paya N, Ensenyat A, Real J, Castro-Viñuales I, Zapata A, Galindo G, Solé-Mir E, Bosch-Muñoz J, Mur JM, Teixido C. Evaluation of a family intervention programme for the treatment of overweight and obese children (Nereu Programme): a randomized clinical trial study protocol. BMC Public Health 2013; 13: 1-14.
-3939 Torrijos-niño C, Martínez-Vizcaino V, Pardo-Guijarro MJ, García-Prieto JC, Arias-Palencia NM, Sánchez-López M. Physical Fitness, Obesity, and Academic Achievement in Schoolchildren. J Pediatr. 2014; 1 (165): 104-109. ) along with several other frequently used markers. A further objective of this study was to assess the use of the Alpha-fitness test battery and of the indicators, VO2 max, excess post-exercise oxygen consumption (EPOC) and mean propulsive velocity of the lower trunk (MVprop) in school children.

Methods

Subjects

The study participants were 52 boys and 42 girls, aged 7-9 years (mean 8.2 ± 0.7 years) randomly assigned to a control group (CG, n = 56; 34 boys) that took part in an extracurricular moderate-intensity aerobic PA program or an intervention group (IG, n = 38; 18 boys) that participated in a similar duration high-intensity interval training (HIIT) PA program The age range selected was based on criteria that identify the onset of neuromuscular coordination in children(2828 Naclerio F, Faigenbaum A. Integrative neuromuscular training for youth. Kronos 2011; 10 (1): 49-56.). The sample selection criteria were: 1) belonging to the second cycle of primary school education (ages from 7 to 9); and 2) Having a higher attendance than 90% in the programs over 90% of program assistance The exclusion criteria were: 1) any illness suggesting possible difficulty in completing the study in the 3 months prior to its onset; and/or 2) any medical or orthopaedic problem that could impair completion of the exercise program. All the participants (and their parents or legal guardians) were informed of the procedures involved and possible risks and/or benefits. The study protocol was approved by the Bioethics Committee of the Universidad de Granada (Granada, Spain) and adhered to the tenets of the Declaration of Helsinki. All parents/legal guardians signed a written consent form.

Experimental design

The study consisted of a pre-posttest with natural groups that had similar characteristics. The extracurricular intervention was performed during the two hours per week of physical education (PE) on the primary school timetable. The groups did not engage in regular PE classes. Instead, they followed the two programs offered. Five groups were randomly assigned to either program.

The following indicators of fitness and health were used as dependent variables: maximum oxygen consumption (VO2 max); peak velocity (Vpeak); hand-grip; -grip; jumping ability; lower trunk mean propulsive velocity (MVprop); excess post-exercise oxygen consumption (EPOC); percentage of fat mass (% body fat); body mass index (BMI); and waist circumference. PA practised by the participants was employed as an independent variable.

Data acquisition and measurements

To compare the two interventions, the following tests were performed before and after each program. All the participants took part in several practice sessions before each set of tests.

Alpha-fitness. An explanation of the tests that were performed follows. a) Maximum oxygen consumption (VO2 max). As a measure of aerobic capacity, VO2 max was determined in the 20 m shuttle run test. For the test, subjects ran 20 m (there and back) in time with an acoustic signal. The signal sets a starting velocity of 8 km/h, which thereafter increases by 1 km·h−1 each minute. The test ends when the subject cannot keep up with the rhythm set. The authors of the Alpha-fitness test battery express the test results as the "stage' completed by the subject. However, we indirectly calculated VO2 max by entering the maximum velocity recorded for each subject in the equation described by Leger, Mercier, Gadoury and Lambert(4040 Leger LA, Mercier D, Gadoury C, Lambert J. The multistage 20 metres shuttle run test for aerobic fitness. J Sport Sci. 1988; 6: 93-101.) for children under 18 years of age. b) Peak velocity (Vpeak). As a further measure of aerobic capacity, we determined Vpeak as the maximum velocity recorded before the child abandoned the 20 m shuttle run test. c) Speed/agility. As a measure of motor capacity, speed/agility was determined in the 4x10 m shuttle run test. In this test, the subject runs 10 m, picks up a cone, returns to the starting line, switches the cone for another cone and continues the process until he/she covers 4 x 10 m. The result is expressed in seconds. d) Hand-grip. Hand strength (right and left) was measured by dynamometry in kilograms. e) Jumping ability. The distance jumped in a standing long jump was recorded in centimetres. Starting with the legs at shoulders' width, the subjects were instructed to jump as far as possible, landing with their feet together. f) Waist circumference. As a measure of central body fat, waist circumference was measured in centimetres.

Body composition analyser. Body composition was assessed through bioimpedance and measured using Tanita(r) Body Composition Monitor model BF-350. This instrument provides body fat and body mass index (BMI) when height is introduced.

T-force System platform. Lower trunk mean propulsive velocity (MVprop) was measured using this force platform (T-Force System, Ergotech, Murcia, Spain) when subjects performed 5 half-squat repetitions using a lightweight wooden barbel with no added weights. The children were given instructions carefully and encouraged verbally to undertake the concentric phase of the athletic movement as quickly as possible. Feedback was provided by an observer, who informed the subject of the velocity reached in each repetition. Six practice sessions were performed before the test.

HR monitor equipped with the corresponding software (Bodyguard, Firstbeat SPORTS software, Jyväskylä, Finland). Excess post-exercise oxygen consumption (EPOC) was estimated after the 20 m shuttle run test from the variation produced in heart rate (HR).

All participants were assigned to stage I of Tanner's development stage(4141 Muñoz MT, Pozo J. Pubertad normal y sus variantes. Pediatr Integral 2011; 15 (6): 507-518.,4242 Tanner JM. The measurement of maturity. Trans Eur Orthod Soc 1975; 45-60.)

Training interventions

Intervention group (IG)

Subjects in the IG participated in an interval training program for 12 weeks, which consisted of 2 sessions of 40 minute duration per week. Each session involved 20 minutes of high-intensity intermittent exercises (around 10-20 s) and 20 minutes of sports activities as described in prior studies by Faigenbaum and Myer(3333 Faigenbaum A, Myer GD. Resistance training and paediatric health. Kronos 2011; 10 (1): 31-38.), Behringer, Vom Heede, Yue, Mester(2929 Behringer M, Vom Heede A, Yue Z, Mester J. et al. Effects of resistence training in children an adolescents: a metaanálisis. Pediatrics 2010; 126 (5): 199-210.), Baquet, Van Praagh, Berthoin(2727 Baquet G, Van Praagh E, Berthoin S. Endurance Training and Aerobic Fitness in Young People. Sports Med 2003; 33(15): 1127-1143.) and Baquet, Guinhouya, Dupont, Nourry, Berthoin(2626 Baquet G, Guinhouya C, Dupont G, Nourry C, Berthoin S. Effects of a short-term interval training program on physical fitness in prepubertal children. J Strength Cond Res. 2004; 18(4): 708-713) . Following a standard warm-up, sessions commenced with several sets of half-squats followed by sprints and a training circuit consisting of jumps, speed/agility tasks, carrying weights, pulling exercises, etc. Activities were performed as games or in a competitive manner and participants were constantly encouraged verbally to perform the high-intensity exercises with maximum effort. The details of the HIIT performed in each session are provided in Table 1. Workloads and stimuli in each session were carefully designed for maximum efficiency(1616 Myer GD, Faigenbaum AD. Exercise is sports medicine in youth: Integrative neuromuscular training to optimize motor development and reduce risk of sports related injury. Kronos 2010; 10 (1): 39-48.).

Control group (CG)

The CG subjects underwent the same 12 week extracurricular training program, but instead of completing 20 minutes of interval exercises they took part in 20 minutes of moderate-intensity aerobic exercises and games; this was also followed by 20 minutes of sport.

Table 1
Details of the first 20 minutes of each high-intensity interval training (HIIT) session

Statistical Analysis

Data are provided as means and their corresponding standard deviations (M ± SD). The homogeneity of the two study groups in terms of the anthropometric and health-related fitness variables recorded at baseline was confirmed by one-way ANOVA. Intervention effects were assessed through ANOVA of pre/post intervention data by examining PA intervention and measurement time point as the independent variables along with their interactions. Significant interactions were subjected to Bonferroni correction. All statistical tests were performed using the software package SPSS version 20.0 for Windows (Chicago, IL, USA). Significance was set at p<0.05.

Results

The means and standard deviations of the health-related fitness and anthropometric variables recorded before and after the intervention are provided in Tables 2 and 3. The effects of each intervention on the health-related fitness variables are illustrated in Figures 1 and 2, and Tables 4 and 5.

Table 2
Health-related fitness variables (M ± SD) recorded before and after a 12 week extracurricular, moderate-intensity training (MIT) or high-intensity interval training (HIIT) program.

Table 3
Anthropometric variables (M ± SD) recorded before and after a 12-week, extracurricular, moderate-intensity training (MIT) or high-intensity interval training (HIIT) program.

The HIIT intervention led to improved motor capacity (speed/agility), Vpeak, VO2 max and EPOC, along with improved musculoskeletal capacity of the lower trunk (MVprop and standing long jump). As may be observed in Tables 2 and 3, differences in means following the intervention were higher in the GI than in the CG. Both PA programs had no effect on anthropometric or hand strength measurements.

No significant differences were detected when Vpeak values between the two interventions were compared (F1,79=1.927; η2=0.024;1-β=0.279; p=0.169) though differences were observed between pre- and post-intervention values (F1,79=155.88; η2=0.664; 1-β=1.000; p=0.001) and for the interaction between time point and intervention (F1,79 =12.306; η2=0.135; 1-β=0.934; p=0.001). When Vpeak values between the CG and IG were compared, no significant differences were recorded before the intervention (p=0.627), but differences did emerge after the intervention (p=0.002). In addition, both groups showed significant effects of the intervention when pre- and post-intervention data were compared (IG p=0.001; CG p=0.001).

VO2 max values differed significantly, both according to the measurement time point (F1,79 =129.697; η2=0.621;1-β =0.9999; p=0.001) and its interaction with the intervention (F1,79 =15.370; η2=0.163; 1-β=0.972; p=0.001). No differences in VO2 max were recorded according to the type of intervention (F1,79 =0.757; η2=0.009; 1-β=0.138; p=0.387). Paired comparisons revealed an effect of the time point (pre- vs post-intervention) in both groups (IG p=0.001; CG p=0.001) along with differences between groups in post-intervention VO2 max values (p=0.044), but not pre-intervention values (p=0.207).

Figure 1
Vpeak and VO2 max values recorded in the 20 m shuttle sprint test before and after the control and high-intensity interval training programs (** p<.01; *p<.05).

EPOC values varied according to the measurement time point and the interaction time point x intervention. No effects were observed of the intervention type (see Table 4). Pre-intervention EPOC values failed to vary between the groups (p=0.560), but post-intervention values varied (p=0.050). No differences in pre- and post-intervention EPOC values were recorded in the CG (p=0.534), but differences were detected in the IG (p=0.001).

Table 4
Statistics obtained for excess post-exercise oxygen consumption

Similarly, when we compared the results of the 4x10 m speed/agility test, significant effects were observed of the measurement time point (F1,85 =11.398; η2=0.018;1-β =0.916; p=0.001) and of the interaction time point x intervention (F1,85 =17.483; η2=0.171; 1-β=0.985; p=0.001). No effects of the intervention were noted (F1,85=0.291; η2=0,003;1-β =0.083; p=0.591). In the Bonferroni test comparisons, speed/agility showed no inter-group differences before the intervention (p=0.219), but did differ after the intervention (p=0.027). Differences between the two time points were not observed in the CG (p=0.533), yet were detected in the IG (p=0.001).

Figure 2
Speed/agility and standing long jump values recorded in the Alpha fitness test battery before and after the control and high-intensity interval training programs (** p<.01; *p<.05)

Standing long jump results differed significantly according to both the measurement time point (F1,90 =8.019; η2=0.082; 1-β =0.800; p=0.006) and the interaction time point x intervention (F1,90 =6.095; η2=0.063; 1-β =0.685; p=0.015). No effects of the intervention were detected (F1,90 =2.237; η2=0.024;1-β =0.316; p=0.138). Bonferroni test comparisons revealed no differences between the CG and IG in pre-intervention long jump results (p=0.768), yet differences in post-intervention results were observed (p=0.036). No differences in before/after long jump distances were detected in the CG (p=0.772), but these emerged in the IG (p=0.001) (see Figure 2). MVprop varied according to the intervention and the interaction time point x intervention. After the intervention, this variable decreased in the CG to provide before/after differences (p=0.001) whereas MVprop showed a slight increase in the IG (see Tables 2 and 5).

Table 5
Statistics obtained for lower trunk musculoskeletal capacity

No significant effects were produced on the dynamometer results of the measurement time point (left hand F1,90=0.927, η2=0.010;1-β =0.159, p=0.338; right hand F1,89=0.012, η2=0.0001, 1-β=0.051, p=0.912), intervention (left hand F1,90=0.728, η2=0.008;1-β=0.135, p=0.396; right hand F1,89=0.257, η2=0.003, 1-β=0.079, p=0.613) or interaction time point x intervention (left hand F1,90=0.953, η2=0.010, 1-β=0.162, p=0.332; right hand (F1,89=0.486, η2=0.005, 1-β=0.106, p=0.488).

The anthropometric variables examined increased both in the IG and CG (see Table 3). Significant differences in BMI values were observed for the different measurement time points (F1,83=22.550; η2=0.214; 1-β=0.997; p=0.001), yet no changes were observed according to intervention type (F1,83=0.021; η2=0.0001;1-β=0.052; p=0.885) or the interaction between time point and intervention (F1,83=0.101; η2=0.001;1-β=0.061; p=0.752). The percentage of body fat varied similarly according to the time point (F1,83=55.488; η2=0.401;1-β=0.9999; p=0.001), but not according to the intervention (F1,83=0.002; η2=0.0001;1-β=0.050; p=0.965) or the interaction time point x intervention (F1,83=0.060; η2=0.001;1-β=0.057; p=0.807). Waist circumference failed to vary significantly according to the time point (F1,83=3.720; η2=0.043;1-β=0.479; p=0.057), intervention (F1,83=0.001; η2=0.0001;1-β=0.050; p=0.970), or interaction time point x interaction (F1,83=2.447; η2=0.029;1-β=0.340; p=0.122).

Discussion

The main findings of this study were that a 12 week extracurricular strength training program consisting of controlled workloads adapted for children was more able to improve several health-related fitness variables than the effects of a more conventional lower intensity PA program. The high-intensity interval activities undertaken in the training intervention led to significant improvements in Vpeak, VO2 max, EPOC and lower trunk MVprop as well as in the performance of speed/agility tests and long jump.

All the variables recorded after a 20 m shuttle run test was significantly improved in the intervention group. The effects produced on both Vpeak and VO2 max resemble those described in a large number of studies22, 26, 43, 44. Despite improvements in post-intervention VO2 max values recorded in both our intervention and control groups, the greatest effects were produced in the IG to the extent that significant post-intervention differences were observed with respect to the CG despite even lower pre-intervention values (see Figure 1). These findings are consistent with the conclusions arrived at by Baquet, Baquet, Van Praagh, Berthoin.(2727 Baquet G, Van Praagh E, Berthoin S. Endurance Training and Aerobic Fitness in Young People. Sports Med 2003; 33(15): 1127-1143.), who reported that the VO2 max improvement produced in response to the aerobic PA generally undertaken by children in this age group is reduced in comparison to the effects of high-intensity short-duration activities on the cardiovascular health of children. In effect, intermittent exercises performed at maximum intensity may be observed in a child's spontaneous activity(4545 Ratel S, Lazaar N, Dore E, Baquet G, Williams C, Berthoin S et al. High-intensity intermittent activities at school: controversies and facts. J Sport Med Phys Fit. 2004; 44: 272-280.). In a study by Bailey et al.(4646 Bailey R, Olson J, Pepper S, Porszasz J, Barstow T, Cooper D. The level and tempo of children´s physical activities: an observational study. Med Sci Sport Exer. 1995; 7 (27):1033-1041. ), it was found that the mean duration of the physical activities of children between the ages of 6 and 10 years was no more than 3 seconds (under 15 seconds in 95% of cases) and that intensities were high. Many authors have attributed the lower anaerobic performance of children to a non fully-developed glucose metabolism pathway(4747 Falgairette G, Bedu M, Fellman N, Van Praagh E, Coudert J. Bioenergetic profile in 144 boys aged from 6 to 15 years with special reference to sexual maturation. Eur J Appl Physiol 1991; 62: 151-156.,4848 Van Praag E, Doré E. Short-term muscle power during growth and maturation. Sports Med 2002; 32: 701-708.) thus, contraindicating high-intensity PA. However, the results of several studies seem to challenge this idea(4949 Armstrong N, Welsman JR, Kirby BJ. Performance on the Wingate anaerobic test and maturation. Pediatr Exerc Sci 1997; 9: 253-261.

50 Petersen SR, Gaul CA, Stanton MM., Hanstock CC. Skeletal muscle metabolism during short-term, high-intensity exercise in prepuberal and pubertal girls. J Appl Physiol 1999; 21 (87): 51-56.
-5151 Van Praagh E, Bedu M, Falgairette G, Fellmann N, Coudert J. Oxygen uptake during a 30-s supramaximal exercise in 7 to 15-year-old boys. In: R Frenkl, 1 editor. Children and exercise XV. Budapest: Natl Inst for health promotion 1991; 281-287.). Accordingly, Van Praagh and Doré(5151 Van Praagh E, Bedu M, Falgairette G, Fellmann N, Coudert J. Oxygen uptake during a 30-s supramaximal exercise in 7 to 15-year-old boys. In: R Frenkl, 1 editor. Children and exercise XV. Budapest: Natl Inst for health promotion 1991; 281-287.) argued that lower blood and muscle lactate concentrations in children may be explained by the lower muscle mass involved in physical exercise. According to Ratel et al.(4545 Ratel S, Lazaar N, Dore E, Baquet G, Williams C, Berthoin S et al. High-intensity intermittent activities at school: controversies and facts. J Sport Med Phys Fit. 2004; 44: 272-280.) , there is no sound physiological evidence to indicate that high-intensity exercise could be harmful for children and these authors endorsed this type of program based on their observation of appreciable effects on both the aerobic and anaerobic capacity of prepubertal children. These findings are in line with the present results.

The Vpeak and VO2 max improvements observed are related to the EPOC values attained by our subjects. During the stage of recovery following exercise, calorie intake increases and this increase is maintained until all metabolic processes return to their baseline state. In our study, EPOC were recorded during the rapid stage of oxygen consumption within the initial hour of recovery52, 53. The highest post-intervention EPOC levels recorded in the IG may be related to a greater metabolic disruption(5454 Earnest CP, Scott CB. Resistance Exercise Energy Expenditure is Greater with Fatigue as Compared to Non-Fatigue. JEPonline 2011; 14 (1): 1-10.) as a consequence of the increased oxygen consumption or VO2 max, during the 20m sprint. Descriptive studies in adults such as those of Bahr, Grønnerød, Sejersted(5555 Bahr R, Grønnerød O, Sejersted OM. Effect of supramaximal exercise on excess postexercise O2 consumption. Med Sci Sport Exercise. 1992; 1 (24): 66-71.) and Laforgia, Withers, Shipp, Gore(5656 Laforgia J, Withers T, Shipp J, Gore J. Comparison of energy expenditure elevations after submaximal and supramaximal running. J. Appl. Physiol 1997; 2 (82): 661-666.) have shown that the intensity at which an exercise is executed (3 x 2 min on a cycle ergometer at 108% VO2 max; 20 x 1 minute sprints at 105% VO2 max, respectively) will affect excess post-exercise oxygen consumption significantly. In a review of the effects of the exercise intensity, duration and modality on excess post-exercise oxygen consumption, Borsheim and Bahr(5252 Børsheim E, Bahr R. Effect of Exercise Intensity, Duration and Mode on Post-Exercise Oxygen Consumption. Sports 2003; 14 (33): 1037-1060.) reported that high-intensity activities significantly increase EPOC values, thus, supporting the results of our intervention. Despite the frequent use of this variable in adults, as far as we know no such data are available for children precluding any comparisons.

Besides the beneficial cardiovascular effects observed, our HIIT program also led to better agility/velocity levels (see Figure 2). Other authors have also described a link between cardiovascular status and other fitness-related factors including agility/velocity(2626 Baquet G, Guinhouya C, Dupont G, Nourry C, Berthoin S. Effects of a short-term interval training program on physical fitness in prepubertal children. J Strength Cond Res. 2004; 18(4): 708-713,5757 Ara I, Rodriguez V, Perez-Gomez J, Jimenez-Ramirez J, Serrano-Sanchez JA, Dorado C, Calbet J. Influence of extracurricular sport activities on body composition and physical fitness in boys: a 3-year longitudinal study. Int J Obesity. 2006; 30: 1062-1071.

58 Ortega F, Ruiz JR, Castillo MJ, Moreno LA, González-Gross M, Wärnberg J, Gutiérrez À. Bajo nivel de forma física en los adolescentes españoles. Importancia para la salud cardiovascular futura (Estudio AVENA). Rev Esp Cardiol. 2005; 58(8): 898-909.
-5959 Secchi JD, García C, España-Romero V, Castro-Piñero J. Condición física y riesgo cardiovascular futuro en niños y adolescentes argentinos: una introducción de la batería ALPHA. Arch Argent Pediatr 2014; 112 (2): 132-140). In contrast, Ardoy(6060 Ardoy D, Fernández-Rodríguez JM, Ruiz JR, Chillón P, España-Romero V, Castillo M, Ortega F. Mejora de la condición física en adolescentes a través de un programa de intervención educativa: Estudio EDUFIT. Rev Esp Cardiol 2011; 64 (6): 484-491.) observed no such improvement in pairwise comparisons in two experimental groups despite high-intensity exercise in one of the groups reflected by a high mean heart rate.

Among the factors related to muscular-skeletal capacity, we detected significant improvements in the explosive force generated in the legs, both in the standing long jump test and in the variable MVprop. Thus, following the intervention, subjects in the IG covered a significantly longer distance in the long jump compared to those in the CG (see Figure 2). These data are consistent with those reported by Baquet, Guinhouya, Dupont, Nourry, Berthoin.(2626 Baquet G, Guinhouya C, Dupont G, Nourry C, Berthoin S. Effects of a short-term interval training program on physical fitness in prepubertal children. J Strength Cond Res. 2004; 18(4): 708-713), Secchi, García, España-Romero, Castro-Piñero.(5959 Secchi JD, García C, España-Romero V, Castro-Piñero J. Condición física y riesgo cardiovascular futuro en niños y adolescentes argentinos: una introducción de la batería ALPHA. Arch Argent Pediatr 2014; 112 (2): 132-140) and Cuenca-García.(3737 Cuenca-García M, Jiménez-Pavón D, España-Romero V, Artero E, Castro-Peñero JC, Ortega F, Ruiz JR, Castillo M. Condición física relacionada con la salud y hábitos de alimentación en niños y adolescentes: propuesta de addendum al informe de salud escolar. Rev Invest Ed. 2011; 9 (2): 35-50.), which the beneficial effects of a HIIT program on lower trunk strength. The mean propulsive velocity, MVprop, was unaffected by the intervention, most likely because of the instability experienced doing squat exercises at this age.

Our study has several limitations. For the post-intervention tests, our CG subjects had less practice at the half-squats than their peers in the IG. In addition, the HIIT intervention should have included exercises designed to improve upper limb strength. Finally, owing to the time available for the PA sessions, HR data could not be obtained during the strength training exercises such that the work intensity during the proposed strength training program could not be determined accurately.

In conclusion, the findings of our study indicate that short-duration high-intensity neuromuscular exercises are an effective option to improve the health-related physical fitness of school children. To date, this kind of program has only been implemented in sports' clubs and teams in which population bias exists due to the level of motor competence. Hence, this type of training program in an education setting, whether curricular or extracurricular, would be a powerful tool to improve the physical fitness of children, regardless of their unwillingness to participate in sport. More work in the field is needed with special emphasis on aspects such as motivation levels during longer-duration programs and levels of adherence to such programs.

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Publication Dates

  • Publication in this collection
    Dec 2016

History

  • Received
    12 Oct 2014
  • Accepted
    20 June 2016
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