Original article

Validation by specialists of a reactive-strength plyometric exercises group for U-14 Soccer players

Wilson Fernando Téquiz Rojas^{1  *} 
http://orcid.org/0000-0002-3456-6403

¹Universidad Central del Ecuador. Ecuador.

ABSTRACT

Plyometry is a training method designed to reproduce fast explosive and powerful movements, it improves strength and speed in different muscle planes, which is why it is usually very useful to improve certain physical skills in sports such as soccer. The objective of this research is to theoretically validate, through consultation with specialists, a group of plyometric strength-reactive exercises for U-14 soccer players. This is a qualitative and correlational descriptive-explanatory research. Twenty-one soccer specialists classified into two independent groups were surveyed, theoretically validating the scope and limitations of a plyometric exercises proposal for lower limbs adapted to U-14 soccer players. The averages that describe the scores achieved were higher in the post-test, with significant differences when evaluating each group studied (Group 1: "I" r=0.004, "A" r=0.005, "P" r=0.003, " V "r=0.003 and" EP "r=0.003; Group 2:" I "r=0.002," A"r=0.003," P "r=0.001," V "r=0.003 and" EP "r=0.002), there is not significant differences when comparing the results between each independent group as part of the pretest "I" (p = 0.973), "A" (p = 0.756), "P" (p = 0.426), "V" (p = 1.000) and "EP" (p = 0.468), and as part of the post-test "I" (p = 0.223), "A" (p = 0.973), "P" (p = 0.173), "V" (p = 0.918) and "EP" (p = 0.918). With this work, the intervention proposal is theoretically improved, concerning 25 plyometric exercises applied to lower limbs of U-14 soccer players, in addition, five analysis indicators are taken into account. It is recommended to carry out a practical validation that focuses future research, with a type of experimental or quasi-experimental research.

Keywords: Plyometry; Explosive strength; U-14 Soccer.

INTRODUCTION

Physical capacities are qualities directly related to motor movement, ^{(Márquez & Celis, 2016}; ^{Morales & González, 2014}; Morales & González, 2015) given that the skills acquired through sports training, denoted as technical gestures, are based on the proper foundation of physical qualities; therefore, the higher the level in physical qualities, the greater the results in a specific sport modality.

For the specific case of strength development, this is usually one of the most important for sports training, considered as the capacity to overcome the opposition of a endurance; ^{(Correa Bautista & Diego Ermith, 2009)} it is conditioned by several variables, among them the anatomical and physiological structures, as well as the kinesiological dimensions.

Strength as a physical capacity is normally subclassified in the international literature as maximum, explosive and endurance type; ^{(Raposo, 2012)} however, other literature evidences the existence of other types of strength, including reactive strength, classified as the muscular performance that generates an impulse within a stretching-shortening cycle, ^{(Martin, Carl, & Lehnertz, 2007}; ^{Rojas, Eras, Jácome, Enríquez, & Chicaiza, 2020}; ^{Gamble, 2013)} widely used to enhance the specific performance in numerous sports.

For the specific case of soccer, the study of reactive strength levels is usually an indicator of comparison with other modalities of soccer, such as futsal, ^{(Flórez, Osorio, & Cely, 2020)} or as an indicator to assess the performance of agility in high performance soccer players, ^{(Zouhal et al., 2019)} among others.

The strength-reactive evidences a high and relative importance in the process of sports training direction of the soccer player, for which different types of training have been developed for its enhancement, as is the case of the multidirectional sprint to improve the speed of change of direction and reactive agility in highly trained soccer players, as evidenced in ^{Born, Zinner, Düking, & Sperlich (2016)} or as would be the case of specific plyometric training that uses the strength-reactive index as an indicator for the study of strength, ^{(Ramírez-Campillo, et al. , 2018)} or simply as another element in integrated models of sports training for the soccer player ^{(Torres, Coca, Morales, García, & Cevallos, 2015)}.

For the specific case of plyometric training, the literature evidences its numerous positive effects on the potentiation of strength performance in different sports, ^{(Frometa, Aymara, & Rojas, 2020)} including soccer, ^{(Wang & Zhang, 2016}; ^{Negra, et al., 2017)} among them, the effects on lower body power in female soccer players, using the strength-reactive index, ^{(Garavito Betancourt & García Zúñiga, 2019)} or the incidence on other associated variables such as speed and speed-strength in female soccer players ^{(Yépez & Ramírez, 2019)}.

Since soccer is the sport with the greatest international projection in the country, it becomes a research priority in the area of sports training, from early ages. The knowledge of the specific aspects of strength is key for the development of a successful training process, aimed at increasing the result of the competition, in addition to sports performance. The present research will allow us to have exercises aimed at enhancing reactive strength in soccer players, based on the plyometric method, but these will only be analyzed by specialists as a preliminary part of the research, where through various quality indicators they will evaluate the scope and limitations of a proposal for future intervention, theoretically validating the present research.

In addition, the theoretical validation carried out by a group of specialists will have greater pertinence and viability, given that the practical implementation of a group of plyometric exercises to improve reactive strength in soccer players is not currently possible, given the pandemic process that Ecuador is going through. On the other hand, the consultation of national literature does not address many works related to the field of action studied, an aspect that would generate originality in solving a problem of the theory and methodology of sports training of U-14 soccer players.

The results to be obtained will be of direct benefit to the athletes of the mentioned selection (U-14), who, with the application of a validated system of exercises, based on the model of stretching and shortening (plyometrics), will manage to improve their reactive strength and, therefore, the capacity to dominate the ball and approach more effectively to the goal with the intention of placing it as a goal. The improvement in the results of the competition, in addition to having a direct impact on sports performance, has an influence on the mood of the players, team unity, among other psychological aspects, which are also recognized as important in the development of soccer as a team sport ^{(Reina & Hernández, 2012)}.

On the other hand, the research will indirectly benefit the soccer coaches of this team, at the Sociedad Deportiva la Merced del Valle Soccer School, who will have a methodological tool that will allow them to optimize the sports training process, especially oriented to reactive strength. All this will allow the selection of the mentioned school to raise the results in competition and to ascend in the level of local and regional recognition among the schools of similar category. In this sense, the purpose of the research is to theoretically validate, through consultation with specialists, a group of plyometric exercises of reactive strength for U-14 soccer players.

MATERIAL AND METHODS

Descriptive-explanatory, qualitative and correlational research. Twenty-one soccer specialists in the category of interest were surveyed, divided into two independent groups (group 1: national specialists-11 subjects; group 2: international specialists-10 subjects), theoretically validating the scope and limitations of a proposal of plyometric exercises for lower limbs, adapted to U-14 soccer players.

The inclusion assumptions for the selection of the specialists were:

1. Demonstrable experience of at least ten years as soccer coaches in the category of study.

2. Third level degree in Physical Activity and Sport Sciences or related field.

Five indicators were studied to validate in two moments the proposal of intervention with plyometric exercises that enhance the reactive strength in the lower limbs, in soccer players of the U-14 category. The analysis indicators were:

1. Comprehensiveness (I): that the exercises include various training elements in an integrated manner, allowing to respond to the principle of multilateralism.

2. Affordability (A): that the exercises are designed to effectively meet the training objectives according to the age range studied, responding to the principle of affordability.

3. Progression (P): that the exercises can be classified by groups of increasing complexity, allowing to comply with the principle of progression in sports training.

4. Variety (V): that the exercises are varied, allowing to adapt them to the needs and individualities of each soccer player and to respond to the principle of general multilateralism.

5. Progressive Specialization (EP): that the exercises have a consecutive complexity that allows, in stages, to adapt to the principle of sport specialization during the whole macrocycle of training.

The evaluation indicators of the intervention proposal, mentioned above, were studied through a questionnaire applied to the specialists mentioned in two moments of the proposed design; the first, when the author proposed 13 exercises, recording the shortcomings detected by the specialists and the recommendations issued by them and, in a second moment, to 25 refined exercises that made up the final intervention proposal.

A five-level Likert-type scale was used to evaluate the above-mentioned indicators, described as follows:

• Level 1: (1 point) insufficient.

• Level 2: (2 points) poor.

• Level 3: (3 points) fair.

• Level 4: (4 points) good.

• Level 5: (5 points) excellent.

The data obtained at the two moments of study of the intervention proposal were subjected to a normality test (Shapiro Wilk test), the non-existence of a normal distribution of the data was determined, for which the Mann-Whitney U test (p≤0.05) will be applied as a correlational statistic. For two independent samples and for two related samples, the Wilcoxon test (r≤0.05), making a correction for missing data in subject 11 of Group 1.

RESULTS AND DISCUSSION

The evaluations issued by each specialist are shown, according to the level at which the indicators described in the material and methods section were classified (Table 1).

Table 1 - Data from the evaluation carried out by the specialists. Pretest 

No	I		A		P		V		EP
	Group 1	Group 2	Group 1	Group 2	Group 1	Group 2	Group 1	Group 2	Group 1	Group 2
1	2	2	3	3	1	1	1	1	1	1
2	2	2	3	3	2	1	1	1	2	1
3	2	3	4	3	1	1	1	1	1	1
4	3	3	3	4	2	1	1	1	1	1
5	2	2	3	4	2	1	1	1	1	1
6	1	2	3	5	2	2	1	1	2	1
7	2	2	4	3	1	2	1	1	1	1
8	2	2	3	3	1	1	1	1	1	1
9	3	2	3	3	1	1	1	1	1	1
10	2	2	3	3	1	1	1	1	1	1
11		1		3		1		1		1
	2,1	2,1	3,2	3,4	1,4	1,2	1,0	1,0	1,2	1,0

As part of the data collected in the first moment or pretest, Table 1 shows the scores obtained in the five indicators that evaluate the intervention proposal from the theoretical point of view, obtaining in all cases an average score between insufficient and poor, with the exception of the affordability indicator (A), which obtained an average score of Good (≈3). The scores obtained as part of the second moment of the proposal evaluation or post-test (Table 2).

Table 2 - Data from the evaluation carried out by the specialists. Posttest 

No	I		A		P		V		EP
	Group1	Group 2	Group 1	Group 2	Group 1	Group 2	Group 1	Group 2	Group 1	Group 2
1	4	3	5	4	3	3	3	3	2	3
2	3	3	4	4	3	3	4	4	3	3
3	3	4	4	4	4	3	4	5	3	3
4	4	4	4	4	4	3	4	4	3	3
5	4	4	4	5	4	3	3	3	2	2
6	3	3	5	5	4	4	3	3	3	2
7	4	3	4	4	4	5	3	3	3	3
8	4	3	4	4	4	3	4	4	2	2
9	3	3	4	4	3	3	5	4	3	3
10	4	3	4	4	3	3	4	4	3	3
11		3		4		3		4		3
	3,6	3,3	4,2	4,2	3,6	3,3	3,7	3,7	2,7	2,7

In the case of the evaluation carried out by the specialists at a second stage, after correcting the shortcomings detected and incorporating the most important recommendations pointed out, the average scores increased in all the theoretical indicators studied, obtaining an average qualitative score between fair and good (≥3), the highest score was reached in the "Affordability" indicator (A: ≈4 points).

On the other hand, the comparison of the scores for related groups (Wilcoxon), which were evaluated in their two moments, showed positive results for the two independent groups studied. In the case of the Ecuadorian national specialists (group 1), the data obtained in the two moments of the evaluation of the proposal of plyometric exercises to enhance the reactive strength in the lower limbs of U-14 soccer players showed significant differences in favor of the posttest in the indicator "Comprehensiveness" (r=0. 004), as well as the "Affordability" indicator (r=0.005), the "Progression" indicator (r=0.003), the "Variety" indicator (r=0.003) and the "Progressive Specialization" indicator (r=0.003), with notable theoretical improvements in all cases in the second design of the intervention proposal mentioned above.

In the case of the correlations established in the group of international specialists (group 2), in the two moments of evaluation of the proposal, improvements were noted in favor of the post-test in the means of the scores recorded and are, for all cases, significant in the second moment of evaluation of the intervention proposal in the indicator "Comprehensiveness" (r=0. 002), the "Affordability" indicator (r=0.003), the "Progression" indicator (r=0.001), the "Variety" indicator (r=0.003) and the "Progressive Specialization" indicator (r=0.002), which shows that the international specialists consulted evaluated the final intervention proposal notably and positively.

When comparing the scores made by the two independent groups consulted (Table 2), assessing the significant existence or not in the criteria expressed theoretically by each type of specialists, the Mann-Whitney U Test obtains, as part of the pretest, non-significant differences, "Comprehensiveness" (p=0.973), "Affordability" (p=0. 756), "Progression" (p=0.426), "Variety" (p=1.000) and "Progressive Specialization" (p=0.468) and, as part of the post-test, also non-significant differences, "Comprehensiveness" (p=0.223), "Affordability" (p=0.973), "Progression" (p=0.173), "Variety" (p=0.918) and "Progressive Specialization" (p=0.918).).

The above analyzed evidences that there is concordance among the independent groups of specialists, regardless of the characteristics and pedagogical approaches that could exist among them on the theoretical improvements achieved in the final design of the intervention proposal, an aspect that establishes reliability in the analysis of the data. Therefore, it will be possible to improve in praxis the reactive strength in the lower limbs of U-14 soccer players, a variable of notable importance in the soccer player's training, as indicated by authors such as ^{Rojas, Eras, Jácome, Enríquez, & Chicaiza, 2020}; ^{Gamble, (2013)}, in ^{Zouhal, et al., (2019)}, in ^{Born, Zinner, Düking, & Sperlich, (2016)}, in ^{Ramirez-Campillo et al., (2018)} and in ^{Torres, Coca, Morales, García, & Cevallos, (2015)}, among others.

CONCLUSSIONS

In conclusion, it is stated that: based on the results issued by the specialists, it has been possible to theoretically improve the intervention proposal concerning 25 plyometric exercises, applied to lower limbs of soccer players of the U-14 category, in addition, 5 indicators of analysis are present. It is recommended to carry out a complete validation of the present research, with emphasis on the practical aspect, focusing it in the future, with a type of experimental or quasi-experimental research.

Acknowledgements

To the Master's Degree Program in Sports Training of the Universidad Central del Ecuador.

REFERENCIAS BIBLIOGRÁFICAS

Bautista, J. E. C. (2009). Principios y metodos para el entrenamiento de la fuerza muscular. Universidad del Rosario. https://books.google.com.cu/books?id=NgMQxz4EHW8C

Born, D.-P., Zinner, C., Düking, P., & Sperlich, B. (2016). Multi-Directional Sprint Training Improves Change-Of-Direction Speed and Reactive Agility in Young Highly Trained Soccer Players. Journal of Sports Science & Medicine, 15(2), 314-319. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4879446/

Calero Morales, S., & Catalá, S. A. (2014). Teoría y Metodología de la Educación Física. https://www.researchgate.net/publication/319761738_Teoria_y_Metodologia_de_la_Educacion_Fisica

Flórez, J. F., Osorio, R. D. M., Osorio, R. D. M., Cely, W. F. C., & Cely, W. F. C. (2020). NIVELES DE FUERZA REACTIVA EN JUGADORES DE FÚTBOL DE CAMPO Y FUTBOL SALA. ACTIVIDAD FÍSICA Y DESARROLLO HUMANO, 10(0). https://doi.org/10.24054/16927427.v0.n0.2019.3953

Gamble, P. (2013). Strength and Conditioning for Team Sports: Sport-specific Physical Preparation for High Performance. Routledge. https://books.google.com.cu/books/about/Strength_and_Conditioning_for_Team_Sport.html?id=-T-eqNtc3igC&redir_esc=y

Garavito Betancourt, E. A., & García Zúñiga, S. (2019). Efectos del entrenamiento pliométrico sobre la potencia de tren inferior en jugadoras de fútbol utilizando el índice de fuerza reactiva Tesis de Grado, Universidad Pedagógica Nacional, Facultad de Educación Física. Bogotá, Colombia. http://repository.pedagogica.edu.co/handle/20.500.12209/10195

Gómez, A. R., & Mendo, A. H. (2012). Revisión de indicadores de rendimiento en fútbol. riccafd: Revista Iberoamericana de Ciencias de la Actividad Física y el Deporte, 1(1), 1-14. https://dialnet.unirioja.es/servlet/articulo?codigo=4221250

Márquez, J. M. C., & Celis, C. C. (2016). Capacidades Físicas Básicas: Su desarrollo en la edad escolar. Wanceulen S.L. https://books.google.com.cu/books/about/Capacidades_F%C3%ADsicas_B%C3%A1sicas.html?id=4Gx0DQAAQBAJ&printsec=frontcover&source=kp_read_button&redir_esc=y#v=onepage&q&f=false

Martin, D., Carl, K., & Lehnertz, K. (2007). MANUAL DE METODOLOGÍA DEL ENTRENAMIENTO DEPORTIVO. Editorial Paidotribo. https://books.google.com.cu/books/about/MANUAL_DE_METODOLOG%C3%8DA_DEL_ENTRENAMIENTO.html?id=_ehXzkJzpQIC&redir_esc=y

Morales, S. C., & González, S. A. (2015). Preparación física y deportiva. Quito, Ecuador: Editorial de la Universidad de las Fuerzas Armadas ESPE.

Negra, Y., Chaabene, H., Sammoud, S., Bouguezzi, R., Abbes, M. A., Hachana, Y., & Granacher, U. (2017). Effects of Plyometric Training on Physical Fitness in Prepuberal Soccer Athletes. International Journal of Sports Medicine, 38(5), 370-377. https://doi.org/10.1055/s-0042-122337

Ramírez-Campillo, R., Álvarez, C., García-Pinillos, F., Sánchez-Sánchez, J., Yanci, J., Castillo, D., Izquierdo, M. (2018). Optimal Reactive Strength Index: Is It an Accurate Variable to Optimize Plyometric Training Effects on Measures of Physical Fitness in Young Soccer Players? Journal of Strength and Conditioning Research, 32(4), 885-893. https://doi.org/10.1519/JSC.0000000000002467

Raposo, A. V. (2005). FUERZA, LA. Entrenamiento para jóvenes. Editorial Paidotribo. https://books.google.com.cu/books/about/FUERZA_LA_Entrenamiento_para_j%C3%B3venes.html?id=phwi-kin-NMC&redir_esc=y

Rojas, W., Eras, N., Jácome, C., Enríquez, S., Torre, L., & Chicaiza, J. (2020). Ejercicios pliométricos para potenciar la fuerza reactiva en futbolistas de la categoría sub-14. Lecturas: Educación Física y Deportes, 25, 60-72. https://doi.org/10.46642/efd.v25i263.2095

Romero Frómeta, E., Aymara Cevallos, V. D., Rojas Portero, J. M., Romero Frómeta, E., Aymara Cevallos, V. D., & Rojas Portero, J. M. (2020). Efectos de la pliometría en la fuerza explosiva de miembros inferiores en la lucha libre senior. Revista Cubana de Investigaciones Biomédicas, 39(1). http://scielo.sld.cu/scielo.php?script=sci_abstract&pid=S0864-03002020000100018&lng=es&nrm=iso&tlng=es

Torres, H., Coca, O. R., Calero Morales, S., Vaca García, M., & Cevallos, M. (2015). Incidencia de un programa integrado en el desarrollo de las capacidades físicas en la etapa preparatoria. Club de Fútbol Independiente del Valle, categoría reserva 2014-2015. Lecturas Educación Física y Deportes, 20, 1-22. https://www.researchgate.net/publication/318020142_Incidencia_de_un_programa_integrado_en_el_desarrollo_de_las_capacidades_fisicas_en_la_etapa_preparatoria_Club_de_Futbol_Independiente_del_Valle_categoria_reserva_2014 -2015

Wang, Y.-C., & Zhang, N. (2016). Effects of plyometric training on soccer players. Experimental and Therapeutic Medicine, 12(2), 550-554. https://doi.org/10.3892/etm.2016.3419

Yépez, E. P. H., & Ramírez, J. C. C. (2019). La pliometría y su incidencia en la velocidad y velocidad-fuerza en jugadoras de fútbol. Revista Cubana de Investigaciones Biomédicas , 38(2). http://www.revibiomedica.sld.cu/index.php/ibi/article/view/288

Zouhal, H., Abderrahman, A. B., Dupont, G., Truptin, P., Le Bris, R., Le Postec, E., Bideau, B. (2019). Effects of Neuromuscular Training on Agility Performance in Elite Soccer Players. Frontiers in Physiology, 10. https://doi.org/10.3389/fphys.2019.00947

Received: December 24, 2020; Accepted: January 08, 2021