Influencing Effect of Physical Fitness Components on Football Playing Ability Among Male Players Under 14 Years

The main purpose of this study was to evaluate the influencing effect of physical fitness components on football playing ability among male players under 14 years. This study uses a cross-sectional method of survey design. A total of 208 football male players under 14 years were randomly selected from a school-based football programme in Malaysia. The data of this study were analyzed using multiple linear regression test. The findings indicate that there are nine out of 14 predictor tests of physical fitness components which are body mass index, body fat percentage, sit and reach, standing long jump, Yo-Yo intermittent recovery level 1 (VO 2max ), 5 meter sprint, 30 meter sprint, T-test (left) and T-test (right) have significant influencing effect on football playing ability among male players under 14 years. The combination of these nine physical fitness component tests contributed 79.6 percent ( R Square value = .796) the variance of the physical fitness component can be explained by the linear combination of scores in the football playing ability [ F (14, 193) = 53.649, p <.000]. In conclusion, nine physical fitness component predictor tests can be used as a physical fitness standard test battery for male football players under 14 years. The implication of study showed that the use of nine physical fitness component predictor tests can ensure the selected football male player talent under 14 years are those who really have a high level of physical fitness to compete at international level. Aerobic Capacity. Aerobic capacity was measured using Yo-Yo intermittent recovery level 1 test (YYIR1) performed in the field by wearing football shoes for 10 - 20 minutes according to the procedure by Krustrup et al., (2003). The Yo-Yo intermittent recovery level 1 test consists of repeated 2 x 20-m runs back and forth between the starting, turning, and finishing line at a progressively increased speed controlled by audio bleeps from a tape recorder. Between each running bout, the subjects have a 10-s active rest period, consisting of 2 x 5 m of jogging. When the subjects twice have failed to reach the finishing line in time, the distance covered is recorded and represents the test result. In the present study, we used the Yo-Yo intermittent recovery test, level 1, which consist of 4 running bouts at 10 – 13 km·h-¹ (0 – 160 m) and another 7 runs at 13.5 – 14 km·h-¹ (160 – 440 m), whereafter it continues with stepwise 0.5 km·h-¹ speed increments after every 8 running bouts (i.e., after 760, 1080, 1400, 1720 m, etc.) until exhaustion. The estimated value of maximum oxygen intake (VO 2max ) is calculated through a non-gender specific formula proposed by Bangsbo et al., (2008) which is VO 2max (mL / min-¹ / kg-¹) = distance YYIR1 (meters) x 0.0084 + 36.4 and the YYIR1 test protocol table (Castagna et al., 2006). longitudinal conducted by assessing the development of the same players from age of 13 to 15 years to ensure that only players with high levels of physical fitness will be maintained within a single talent group as recommended by the Developmental Sport Future changes in characteristics and behaviors as well as assess the reasons for those changes.


Introduction
In the actual 90 minutes of a game, a football player will need to do various movements such as walking, jogging, running, and sprinting, and the speed intensity that require a high level of physical fitness (Salvo, Pigozzi, Gonzalez-Haro, Laughlin, & Witt, 2013). In the knockout stage, if both teams have the same number of goals in the original 90 minutes, an additional 30 minutes will be held to determine the winner (Tumilty, 1993). The average total distance traveled by a player (excluding goalkeepers) in a game is about 10 to 12 kilometers which includes more than 1,000 different activities which changes in the type or level of activity that occurs every 6 seconds (Reilly, 1997). Several previous studies have been conducted to determine specific physical fitness demands during matches and the level of physical fitness performance required to achieve success in competitive football (Keller, Raynor, Bruce, & Iredale, 2018;Marques et al., 2016;Trecroci, Milanovic, Frontini, Iaia, & Alberti, 2018).
Physical fitness is an individual's ability to perform optimal physical activities (Ortega, Ruiz, Castillo, & Sjostrom, 2008) and can be defined in terms of performance and health (Artero et al., 2011). According to Ortega, Ruiz, Castillo, and Sjostrom (2008), physical fitness is an integrated measure of body functions (skeletomuscular, cardiorespiratory, hematocirculatory, psychoneurological and endocrine-metabolic) which involved in daily physical work and/or physical exercise. Physical fitness components such as endurance, speed, agility, strength, power and flexibility are the factors that influence the overall level of performance in football game (Murr, Raabe, & Honer, 2017;Turner et al., 2011).
Football requires repeated powerful movements like kicking, sprinting, tackling, and jumping which largely depending on the ability to use the greatest force (maximum strength) (Peterson, Alvar, & Rhea, 2006;Turner et al., 2011). Football involves from low to high intensity intermittent activities that require players to have the ability of aerobic and anaerobic systems for energy transmission while playing Williams & Reilly, 2000). This is because a player will perform physical movements such as (1) standing; (2) walking; (3) low-intensity running, encompassing jogging, low-speed running and backward running; and (4) high-intensity running, consisting of moderate-speed running, high-speed running and sprinting for 90 minutes Saward, Morris, Nevill, Nevill, & Sunderland, 2015). Bangsbo, Norregaard, and Thorso (1991) have reported that 90 percent of physical activity is contributed from an aerobic energy system with high-intensity activity for seven minutes. Therefore, a high level of maximum oxygen intake (VO2max) is a necessity for a player in a competitive matches. It is clear that aerobic capacity (VO2max) is a relevant indicator to determine the maximum level of oxygen that can be taken and used by the body during a game.
Since 1988, one of the most widely used physical fitness test batteries across Europe for testing children and adolescents aged six to 18 years is Eurofit (Cvejic, Pejovic, & Ostojic, 2013;Tomkinson et al., 2017). Eurofit includes a range of health-and performance-related fitness tests, consisting of (1) field tests measuring balance, cardio-respiratory (aerobic) endurance, muscular endurance (abdominal and upper body), flexibility, power, speed, speed agility and strength; (2) anthropometric tests measuring height, mass and skinfold thicknesses at various sites, and (3) age and sex identification data (Tomkinson, Olds, & Borms, 2007). Eurofit test battery has high value of reliability and criterion validity for measuring an individual's physical fitness performance at the stage of childhood to adolescence (Artero et al., 2011;Castro-Pinero et al., 2010;Tomkinson et al., 2017Tomkinson et al., , 2007. According to Tomkinson et al., (2017), Eurofit is a very useful field test battery because it is convenient and economic, practical to be carried out on large groups of participants such as schools and clubs, requires minimal equipment and testers, and suitable for body mass testing. Some of the Eurofit test battery commonly used by previous researchers to measure the level of physical fitness of football players aged 12 to 16 years are body mass index and body fat percentage (body composition), sit and reach test (flexibility), flamingo balance test (dynamic balance), standing long jump test (explosive leg power) and handgrip strength test (maximum isometric strength) (Deprez et al., 2015;Fransen, Bennett, et al., 2017;Pion et al., 2014;Vaeyens et al., 2006).
In addition, the Bruininks-Oseretsky test of motor proficiency, second edition (BOT-2;Bruininks & Bruininks, 2005) is a standard norm test used by physical therapists and occupational therapists in school and clinical practice settings to measure fine and gross motor skills of children and adolescents aged four to 21 years (Deitz, Kartin, & Kopp, 2007). The Bruininks-Oseretsky test (BOT-2) of motor proficiency, second edition is used by practitioners (occupational therapists, physical therapists and adapted Physical Education teachers) and researchers to support the diagnosis of motor disability, screening children and adolescents who may have motor impairments, assist with program placement or adjustment and evaluation of motor interventions (Deitz et al., 2007). Several previous studies have reported that knee push-ups and sit-ups tests (upper body strength endurance) using test procedures (BOT-2; Bruininks & Bruininks, 2005) have been widely used for the purpose of identifying talent in sports (Opstoel et al., 2015;Pion et al., 2014;Vandorpe et al., 2012).

Methodology
Methodology of this study focuses on the research design, sample, instrument and data analysis procedures.

Research Design
This study uses a cross-sectional method of survey design (Ary, Jacobs, Sorensen, & Walker, 2014).

Sample
The participants involved in this study are male student-athletes under 14 years from a schoolbased football programme in Malaysia. Sample size selection for this study is based on Power Tables for Effect Size from Cohen (1988), with the sampling power value of .80, the effect of size (d) .30, the power of .80 and the significant level at α = .05. Based on the formula, the sample size should be 175 people. However, the researchers used a sample size of 208 after considering the absence or mortality factor (Tuckman & Waheed, 1981) that could possibly happen. All study samples were randomly selected.
Body Composition. Body composition is measured based on body mass index and body fat percentage. Height and weight values are used to calculate body mass index (BMI = weight / height²) (Malina, 2003). The body fat percentage (BF%) was obtained using the formula provided by Deurenberg, Weststrate, and Seidell (1991) BF% = 1.51 x BMI -0.70 x age -3.6 x gender + 1.4 (male = 1).
Flexibility. Flexibility is measured using sit and reach test according to guidelines (Council of Europe, 1988) (0.5 cm). Sit and reach test has adequate validity and reliability values between .60 to .73 and .70 to .98 respectively, measured in children and adolescents aged 4 to 18 years (Opstoel et al., 2015).
Dynamic Balance. Flamingo balance test (Council of Europe, 1988) is performed to measure the body's ability to balance in a static state. Players balancing on one foot for 60 seconds while standing at the preferred foot on the wood beam balance (length 50 cm, height 5 cm and width 3 cm). Scores are calculated based on the number of balance losses within 60 seconds.
Maximum Isometric Strength. Handgrip strength test are used to measure the maximum isometric strength of the hand and forearm muscles (Council of Europe, 1988). Handgrip strength test is measured using a handgrip dynamometer.
Upper Body Strength Endurance. Upper body strength endurance are measured using knee push-ups and sit-ups tests according to the procedure by Bruininks-Oseretsky test of motor proficiency, second edition (BOT-2;Bruininks & Bruininks, 2005) which requires players to perform as many repetitions as possible in 30 seconds (Pion et al., 2014).
Power. Standing long jump test was used to measure the explosive power of the legs. The subject attempts to jump as far as possible, landing on both feet without falling backwards. The longest distance jumped is counted as the test score.
Aerobic Capacity. Aerobic capacity was measured using Yo-Yo intermittent recovery level 1 test (YYIR1) performed in the field by wearing football shoes for 10 -20 minutes according to the procedure by Krustrup et al., (2003). The Yo-Yo intermittent recovery level 1 test consists of repeated 2 x 20-m runs back and forth between the starting, turning, and finishing line at a progressively increased speed controlled by audio bleeps from a tape recorder. Between each running bout, the subjects have a 10-s active rest period, consisting of 2 x 5 m of jogging. When the subjects twice have failed to reach the finishing line in time, the distance covered is recorded and represents the test result. In the present study, we used the Yo-Yo intermittent recovery test, level 1, which consist of 4 running bouts at 10-13 km·h-¹ (0-160 m) and another 7 runs at 13.5-14 km·h-¹ (160-440 m), whereafter it continues with stepwise 0.5 km·h-¹ speed increments after every 8 running bouts (i.e., after 760, 1080, 1400, 1720 m, etc.) until exhaustion. The estimated value of maximum oxygen intake (VO2max) is calculated through a non-gender specific formula proposed by Bangsbo et al., (2008) which is VO2max (mL / min-¹ / kg-¹) = distance YYIR1 (meters) x 0.0084 + 36.4 and the YYIR1 test protocol table (Castagna et al., 2006). Acceleration and Speed. Acceleration and speed performance are measured through 5 meter and 30 meter sprint test. Split times were recorded at 5 meter and 30 meter, enabling the assessment of starting speed, the capacity to accelerate, and running speed (Deprez et al., 2015;Pion et al., 2014).
Speed and Agility. To assess speed and agility, participants performed a T-test according to the procedure by Vandendriessche et al., (2012). The athletes ran 5 meter straight, turned 90° and ran 5 meter towards the next turn of 180°, ran 10 meter towards the third turn (180°), ran a further 5 meter towards the last turn of 90°, ultimately finishing at the initial starting point. The T-test was performed in both directions with the participants turning to the left at the first attempt.
Football Playing Ability. Football playing ability refers to a visual analog scale adapted from Lovell et al., (2017) and Sieghartsleitner et al., (2019). Visual analog scale have been used by coaches to assess football playing ability comprehensively which includes physical, technical, tactical and psychological aspects. The football playing ability score is calculated based on the average score obtained from two qualified coaches. Scores will be rated between 0 and 100. The highest score is 100 and the lowest score is 0.

Data Analysis Procedures
Data obtained from physical fitness tests were analyzed using SPSS 20.0 (Statiscal Package for Social Science 20.0) software. Multiple linear regression was used to identify the extent of influencing effects of the significant components of physical fitness on the football playing ability among male players under 14 years. Temporarily, assumptions test of multivariate data analysis (MVA) were tested encompasses normality, linearity and multicollinearity (Pallant, 2010). These assumptions need to be met to ensure that least square measures are unbiased.
In multiple linear regression, the independent variable (X) is named as the predictor variable, while the dependent variable (Y) is named as the criterion variable. In multiple linear regression, all independent variables or predictors are included simultaneously in one equation. The multiple linear regression equation of physical fitness components is shown as below: In the above equation, Y is the value of the criterion variable predicted by the predictor variable value X1, X2, X3, X4, X5, X6, X7, X8, X9, X10, X11, X12, X13, and X14. b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, and b14 is a regression coefficient for each predictor variable, while a is a regression constant.

Results
The results of multiple linear regression analysis were used to identify the significant influencing effect of physical fitness components on the football playing ability among 14-year-old male players. Fourteen independent variables were the score of the body mass index, body fat percentage, sit and reach, handgrip strength (right), handgrip (left), standing long jump, knee push-ups (BOT-2), sit-ups (BOT-2), flamingo balance, Yo-Yo intermittent recovery level 1 (VO2max), 5 meter sprint, 30 meter sprint, T-test (left) and T-test (right). The dependent variable is the football playing ability.

Discussion
The physical fitness component is a factor influencing the overall level of performance in the game of football (Murr et al., 2017). Most of previous studies evaluated the similar physical fitness performance such as body composition, flexibility, balance, power, speed, agility, cardiovascular endurance, muscle endurance and muscle strength for children and adolescents aged six to 18 years (Bianco et al., 2015;Cattuzzo et al., 2016;Kolimechkov, 2017).
The results of this study indicate that body composition, flexibility, power, speed and agility, aerobic capacity, acceleration and speed are significant predictors on the football playing  T-test (left) and T-test (right) have a significant influencing effect on the football playing ability. These findings are supported by the evidences of previous studies where these physical fitness tests have been proven as valid and reliable tool for evaluating the performance of young male football players (Deprez et al., 2015;Pion et al., 2014;Vaeyens et al., 2006;Vandendriessche et al., 2012).
This finding is consistent with football expertise prediction model by Williams and Reilly (2000) which states that the physical fitness is an important indicator of physical and physiological demands during competitive games. There is evidence that the rate of work in modern football games requires young players to have high physical fitness capabilities (Bangsbo, 2014;Dodd & Newans, 2018). Therefore, physical fitness tests are considered crucial by coaches (97%), fitness coaches (94%) and players (83%) to monitor performance progress and analyze the training effects (Hulse et al., 2013).

Conclusion and Recommendations
It is important for a young players to have physical fitness to play at international level. To achieve optimal performance in competitive matches, a young players needs to have a combination of physical fitness components such as body composition, flexibility, power, speed and agility, aerobic capacity, acceleration and speed. Furthermore, the components of physical fitness are interrelated with the motor competence capabilies of a young players . This study has shown that body mass index, body fat percentage, sit and reach, standing long jump, Yo-Yo intermittent recovery level 1 (VO2max), 5 meter sprint, 30 meter sprint, T-test (left) and T-test (right) has the significant influencing effect on the football playing ability among male players under 14 years.
As the finding of this study is obtained through a cross-sectional approach, the researchers suggest that further longitudinal studies be conducted by assessing the development of the same players from age of 13 to 15 years to ensure that only players with high levels of physical fitness will be maintained within a single talent group as recommended by the Developmental Model of Sport Participation (Cote, Baker, & Abernethy, 2007). Future researchers may identify changes in characteristics and behaviors as well as assess the reasons for those changes.