Baseball players perform many tasks in the course of a game, including running, batting, throwing, and fielding. An array of basic anatomical and performance variables determine, to a large extent, the level of success of baseball players. To evaluate such basic components, it is important to investigate the relationship between these characteristics and actual baseball performance. In addition, for younger players, their coaches, parents, and trainers, developmentally related changes in performance and physical characteristics are important to be aware of.
There have been several studies on the relationship between physical fitness characteristics and baseball performance in both collegiate and professional players (6,8–10,13). Kohmura et al. (13) performed 6 physical fitness tests covering throwing distance, back strength, medicine ball throwing, standing long jump, T-test, and base running on 43 college baseball players. Their findings suggest that strength, power, and agility were significantly correlated with a subjective evaluation by 3 coaches of batting and fielding performances. Hoffman et al. (10) investigated the relationship between anthropometric measurements, which included height, weight, body composition, grip strength, vertical jump power, 10-yd sprint speed, and agility and baseball-specific performances. Home runs, total bases, slugging percentage, and stolen bases were used to assess the playing skills of 343 baseball players from the major league and their minor affiliates. In their study, mean vertical jump power, pro-agility, and 10-yd sprint time were significant predictors of total bases. Mean vertical jump power was the only significant predictor of home runs and slugging percentage, and the 10-yd sprint time was the only significant predictor of stolen bases. None of the anthropometric measures were found to be a significant predictor for any of the dependent variables. In addition, this study indicated that both anthropometric and performance variables differed between the players of different levels of competition in professional baseball. It was pointed out that quantification of the physique, speed, and agility of top-level players would provide a useful reference to indicate the relationship between sports performance and body structure (2).
To our knowledge, no study has examined the anthropometric and physical fitness characteristics of "youth baseball players," including elementary and junior high school students, despite the popularity of youth baseball. For other sports such as rugby and soccer, previous studies have investigated such relationships in elementary and junior high school student players (7,14).
The objective of the current study was to clarify how anthropometric and physical fitness characteristics and speed are related to actual performance of young baseball players attending elementary and junior high schools. To evaluate baseball performance, we recorded the velocity of pitched and hit balls. We used a multiple regression analysis to predict performance from data obtained in the physical fitness tests, which were done in accordance with previous studies (10, 19, 20). For ball games, especially team sports, it is difficult to express baseball performance with objective indexes (13), as compared with individual sports such as track and field, swimming, and cycling (18). However, a numerical evaluation of the performance of baseball players would help coaches and trainers to plan physical training more effectively.
The study was designed to proceed in 3 steps. First, we analyzed the overall trends for all subjects. According to Hoffman et al. (10) and Kohmura et al. (13), the strength of lower leg and back muscles should be important factors relating to the batting performance in collegiate and professional players. Therefore, we hypothesized that these factors would be significant predictors of hit ball speed even in youth players. Furthermore, whereas there have been no previous studies investigating the relationship between physical fitness characteristics and pitching performance, we assumed that the strength of the lower leg muscles would be a significant predictor in baseball pitching because it is likely that the lower extremities contribute to the generation of ball velocity and to dynamic control of the body in the different unilateral and/or bilateral loading conditions with different stages of the pitch (3). Second, we performed further analyses by dividing the sample into 3 subgroups based on months of age to clarify the characteristics of each subgroup. We inferred that in the youngest youth players, significant predictors of baseball performance would differ from those in oldest youth players because the development of strength in the muscles would likely be insufficient in the youngest group. Finally, we also analyzed the data by dividing the sample into 3 subgroups based on the different baseball weights. The 2 balls with the lowest weight were rubber and had masses of 0.128 and 0.135 kg. The heaviest was a hardball with a mass of 0.145 kg. We considered that the characteristics of significant predictors would differ among players depending on the weight of the baseball they used.
Experimental Approach to the Problem
A quantitative analysis of performance quality in actual baseball games and anthropometric measurements and measures of specific physical performance factors are necessary to properly evaluate training regimes. This analysis should be the same for both adult and youth players. In the present study, we performed a battery of physical fitness tests and measured the actual baseball performance of youth players. We intended to help improve the performance of youth players and beginners and to aid coaches and athletic trainers' efforts to facilitate the development of young players by providing our findings. The results should be effective when used for planning actual training programs both for daily practice and long-term training. The physical fitness tests used here were selected based on the guideline of sport tests recommended by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan (http://www.mext.go.jp/).
One hundred sixty-four male baseball players participated in this study (age: 6.4–15.7 years = 77–188 months; baseball experience: 3–123 months; height: 115.3–174.7 cm; weight: 19.1–80.0 kg). The data were recorded in January and July 2011. There were 131 players in the January session and 33 in the July session. All players belonged to the same baseball training club and were trained in baseball skills once a week in this school. The baseball training club performed physical fitness test every January. If new players joined after the test, their tests were performed in July. Unfortunately, because we could not control the date of the physical fitness test to reduce the gap between testing sessions, this was a limitation of the present study. All subjects were injury free at the time of data collection. All subjects and their guardians received a detailed explanation of the experimental procedures and risks of the research before recordings were taken. Written informed consent was obtained from all subjects and their families, and they also provided assent for the study. The study was approved by the Ethical Committee of Faculty of Sport Sciences, Waseda University.
Physical Fitness Test
The subjects participated in the experiment on 2 separate days, with a 1-week interval between the days. We recorded height, weight, standing long jump, side steps, sit-ups, 10-m sprint, and trunk flexion on one day and back strength, grip strengths of left and right hands, pitching velocity, and batting velocity on the other day. In addition to the tests, the players also filled out questionnaires where they reported their training background, months of baseball experience, and the birth date. The time spent for testing each subject was less than 1 hour on each day. The order of the test days was randomized across the subjects. All physical fitness tests were performed at an indoor training facility, and all procedures over the entire study period were monitored by the same researchers. The subjects were instructed to maintain their typical intake of food and water on the day of the experiment and 1 day before the experiment. In addition, they were told to abstain from strenuous exercise for 24 hours before the experiment and not to change sleep patterns the night before the experiment. Before starting the physical fitness tests, a standardized warm-up, including 5 minutes of jogging, a stretching exercise, and a 1-minute rest, was performed on each day. The exercises involved stretching the quadriceps, hamstrings, calves, shoulders, posterior portion of the upper arms, wrists, chest, trunk, and neck. The procedures in each test were as follows.
Height was measured to the nearest 0.1 cm using a portable stadiometer (YG-200; YAGAMI, Inc., Nagoya, Japan). Weight was measured using an electronic scale (Karada Scan 701; OMRON Co., Kyoto, Japan) and determined to the nearest 0.1 kg. Height and weight were measured with the subjects wearing light clothing, but no shoes or socks.
For the standing long jump, the subjects were instructed to stand with their feet shoulder-width apart behind the starting line and to jump forward as far as possible. A preparatory crouch was permitted. The distance from the starting line to the heel of the closest foot was recorded and determined to the nearest centimeter. The best of 2 attempts was retained for analysis (12) (Figure 1A).
Trunk flexibility was measured by a sit and reach test using a digital flexibility testing device (TKK 5112; Takei Scientific Instruments Co., Niigata, Japan). A preliminary stretching involving bending forward with the knees locked was performed before the test. This was a different type of stretching as compared with the standardized warm-up. The subjects were asked to sit on the floor with their buttocks and backs to a wall with no shoes on and extend their knees fully. They were then instructed to put both hands on the device with arms held straight and bend forward, slowly, as far forward as possible. The most distant point reached with the finger tips was recorded and determined to the nearest centimeter. Each player was allowed 2 attempts, with the best score being recorded (21) (Figure 1B).
For sit-ups, the subjects sat on an artificial turf with knees bent at 90° angle and hands crossed on the chest. The examiner held the subjects' feet firmly on the ground. The subjects were asked to touch their elbows to the knee with each sit-up and to return their scapulae to the grass after each sit-up. The number of sit-ups completed in 30 seconds was recorded (Figure 1C).
For the side steps, 3 parallel 200-cm long lines 100 cm apart were marked on the floor. The subjects were instructed to initially straddle the middle line and then touch the right line with their right foot. Then, they were asked to change direction and touch the left line with their left foot, still facing the front. This pattern was then repeated as fast as possible. The number of side steps completed in 20 seconds was recorded. The subjects performed 2 trials with approximately 3 minutes of recovery between trials (Figure 1D).
For the 10-m sprint, the subjects were asked to set their right foot behind the start line in a base-running stance, which was similar to the stance they would use when taking a lead in a real-game situation. The time to run 10 m was monitored by the researcher using a handheld stopwatch. The elapsed time was measured to the nearest 0.01 seconds, and the fastest time of the 2 trials was selected for analysis (Figure 1E).
Back strength was recorded using a back dynamometer (TKK 5002, Takei Scientific Instruments Co.). The subjects were instructed to grasp a handle, with their knee extended, and to lean forward at 30° angle while keeping their back straight. The subject was then asked to pull on the handle as hard as they could by raising their upper body. Each subject performed the test twice; the best performance was recorded (Figure 1F).
Grip strength was measured using an electronic hand dynamometer (EH101; Hata Sporting Goods Industries, Ltd., Osaka, Japan). The dynamometer was first adjusted to best fit the subject's handgrip. Then, the subject was placed in a standing position and asked to squeeze the grip as hard as possible for 3 seconds without moving their arm. The subjects were requested to squeeze the left and right hands as hard as possible, twice alternately. The highest scores were recorded.
Water breaks and extra rest time were allowed if requested by the players. The subjects were encouraged to perform with maximum effort throughout the tests.
Ball Speed Test
To measure the velocity of balls pitched by the subjects, they threw a ball toward a 10-cm-diameter white circle attached to a net, which was 11 m away. Measurements were made using a speed gun (JUGS Speed Gun R1010; Decatur Electronics, Tualatin, OR, USA). The players were asked to throw as accurately as possible, but accuracy was not taken into account in the results. The researcher measured the velocity from behind the subjects with a speed gun pointing to the ball release point. The players had a 15-minute warm-up period before the measurements were made. They were instructed to throw balls to a net. Intertrial intervals were at least 1 minute. The best of 5 trials was retained for analysis.
Hit ball velocity was examined by using a batting tee (MIZUNO collapsible portable batting tee 2ZA-770; Mizuno, Osaka, Japan). First, the subjects were asked to place their feet in an optimal position to swing and choose the height of the tee. Second, they were instructed to take a full swing and hit the ball toward center field. The researcher sat diagonally behind and to the right of a right-handed batter and in a similar position on the left side for a left-handed batter. A speed gun set behind a batter was used to measure the speed of the ball as soon as possible after impact. The players were asked to take practice swings for 10 minutes as a warm-up before the measurements. The number of swings was not specified, and it depended on the player's choice. The best of 5 ball speeds was retained for analysis. The pitching and batting tests were all performed by one investigator.
Because of the use of different regulation baseballs based on players' age groups, the weight of the ball used for recording both pitching and batting differed. One hundred seven players from an elementary school used a rubber ball with a mass of 0.128 kg, and 11 from a junior high school used a rubber ball with a mass of 0.135 kg. A hardball with a mass of 0.145 kg was used by 10 players from an elementary school and 36 from a junior high school. The kinetic energies in pitching and batting were calculated with the following mathematical expression:
Measured and calculated values are presented as means with SDs. A hierarchical linear regression analysis was used to generate prediction equations for the kinetic energies of pitching and batting balls (4,5). We entered the data concerning months of age, months of baseball experience, height, weight, standing long jump, side steps, sit-ups, 10-m sprint, trunk flexion, back strength, and grip strengths of left and right hands into the first analysis. Age was specified in "months" rather than years because there can be a difference of almost a full year between the oldest and youngest participants within the same age category as specified by years (i.e., relative age effect) (15,16). Age was defined based on the player's birthday and the day of the physical fitness test. If the variance inflation factor (VIF) was greater than 10, we changed the independent variable and reanalyzed the data. The precision of the regression equations was evaluated using multiple coefficients of determination (R and R2). In addition, we performed a further analysis by dividing the entire sample into 3 subgroups by months of age grade. The mean age in months for each group was as follows—young group: 113.0; middle group: 137.9; oldest group: 163.2. We also performed an analysis by dividing the sample into 3 subgroups based on baseball weight: 107 players used the lighter rubber ball with a mass of 0.128 kg (mean age: 126.6 months, range 77–151 months); 11 players used the heavier rubber ball with a mass of 0.135 kg (mean age: 166.0 months, range 152–182 months); and 46 players used the hardball with a mass of 0.145 kg (mean age: 158.5 months, range 104–188 months). Because the sample size in the second group was too small, we could not perform a linear regression analysis. Therefore, we analyzed the data by comparing the first and third groups.
As a supplementary analysis, Pearson's product correlations were calculated between the independent variables (months of age, months of baseball experience, height, weight, standing long jump, side steps, sit-ups, 10-m sprint, trunk flexion, back strength, and grip strengths of left and right hands) and kinetic energies of pitching and batting balls. All analyses were done with SPSS Advanced Models 16.0 for Windows (SPSS Japan, Inc., Tokyo, Japan). The statistical significance level was set at p < 0.05.
The physical characteristics, the results of physical fitness tests, and the kinetic energies of pitching and batting for 2 groups are listed in Table 1. All scores improved with the players' age.
Table 2 shows the results of the multiple regression analysis for all samples. In the first analysis for predictors of pitched ball kinetic energy, because VIF in height was 13.911, body mass index (BMI) was calculated by dividing weight in kilograms by the square of height in meters (kg·m−2). We then calculated the "average grip strength" for the 2 hands and reanalyzed the data because VIFs in grip strengths of the left and right hands were 16.122 and 19.264, respectively (Table 1). Age, BMI, standing long jump, 10-m sprint, and grip strength were found to be significant predictors of pitched ball kinetic energy (R = 0.947, R2 = 0.897). In the first analysis for hit ball kinetic energy, VIF was 13.911 in height, 16.122 in left grip strength, and 19.264 in right grip strength. We deleted these factors and used BMI and average grip strength to reanalyze the data. Age, BMI, standing long jump, and back strength were significant predictors of hit ball kinetic energy (R = 0.941, R2 = 0.886).
Table 3 shows the results of the multiple regression analysis for the youngest group. Side steps, 10-m sprint, trunk flexion, and right grip strength were significant predictors of pitched ball kinetic energy (R = 0.878, R2 = 0.771), whereas there were no significant predictors of hit ball kinetic energy (R = 0.866, R2 = 0.751).
Table 4 lists the results of the multiple regression analysis for the middle group. Sit-ups and 10-m sprint were significant predictors of pitched ball kinetic energy (R = 0.817, R2 = 0.667), and weight was a significant predictor of hit ball kinetic energy (R = 0.881, R2 = 0.777).
Table 5 shows the results of the multiple regression analysis for the oldest group. In the initial analysis for predictors of pitched ball kinetic energy, VIF in grip strength of the right hand showed 11.676, so we calculated the average grip strength for the 2 hands and reanalyzed the data. The 10-m sprint was a significant predictor of pitched ball kinetic energy (R = 0.878, R2 = 0.771). For analyzing predictors of hit ball kinetic energy, because VIF in grip strength of the right hand was 11.676, we used the average grip strength to reanalyze the data again. Weight and standing long jump were significant predictors of hit ball kinetic energy (R = 0.869, R2 = 0.755).
Table 6 shows the results of the multiple regression analysis for 107 players using the lighter rubber ball. Age, weight, and 10-m sprint time were significant predictors of pitched ball kinetic energy (R = 0.890, R2 = 0.793), and age, weight, and back strength were significant predictors of hit ball kinetic energy (R = 0.927, R2 = 0.859).
Table 7 illustrates the results of the multiple regression analysis for 46 players using the hardball. In the first analysis for pitched ball kinetic energy, because VIF was 12.902 in height, 10.954 in left grip strength, and 17.214 in right grip strength, we eliminated these factors and used BMI and average grip strength to reanalyze the data. After reanalyzing the data, standing long jump was a significant predictor of pitched ball kinetic energy (R = 0.929, R2 = 0.863). For analyzing hit ball kinetic energy, VIF was also 12.902 in height, 10.954 in left grip strength, and 17.214 in right grip strength. We used BMI and average grip strength to reanalyze the data. Body mass index, standing long jump, and 10-m sprint time were significant predictors of hit ball kinetic energy (R = 0.927, R2 = 0.859).
Results of the multiple regression analysis for all samples and each group are depicted in Figure 2.
Table 8 presents the Pearson's correlation matrix. Correlations between pitched ball and hit ball kinetic energies and all independent variables were statistically significant (p < 0.01), indicating that each independent variable was related to the kinetic energies imparted to pitched and hit balls by youth baseball players. For pitching, the correlations were strong for grip strengths in the right (R = 0.906) and left (R = 0.894) hands, age (R = 0.880), height (R = 0.870), back strength (R = 0.866), and standing long jump (R = 0.850). Correlations between batting and the tests were robust for grip strengths of the right (R = 0.898) and left (R = 0.877) hands, height (R = 0.877), weight (R = 0.865), back strength (R = 0.865), and standing long jump (R = 0.850).
This is the first study to investigate the relationship between anthropometric and discrete performance characteristics and actual baseball performance by youth players. This was accomplished by conducting a battery of physical fitness tests and measuring pitched and hit ball kinetic energies. Assessment of the physical characteristics of athletes is one of the most important topics in modern sports, and many tests are used for selection procedures, screening candidates, and monitoring the efficacy of training regimes (1). Developmental considerations are also very important, and our observations documented a progressive improvement in speed, muscular power of upper and lower limbs, agility, and velocities of pitched and hit balls with increasing age. Our findings will provide normative developmental data and performance standards (Table 1), and this profile will make possible an overall evaluation of the discrete measurable factors and actual baseball performance of players in relation to those of a similar age.
Although all independent variables significantly correlated with the kinetic energies of pitched and hit balls (Table 8), the multiple regression analysis showed that only some variables were predictors for baseball performance. For pitching, these were age, BMI, standing long jump, 10-m sprint, and grip strength. For batting, the predictive variables were age, BMI, standing long jump, and back strength (Table 2). These results indicated that the score of a standing long jump is a good predictor of baseball performance in both pitching and batting for youth players. As mentioned in the Introduction, strength of the lower leg muscles plays an important role in the batting performance in both adult and youth players. Additionally, this strength would also be associated with pitching performance because lower extremity movements contribute to the generation of ball velocity and are involved in the dynamic control of the body in movements, which require various types of unilateral and/or bilateral support during pitching (3). Sprint ability is an important indicator for predicting the kinetic energy of pitched balls. Interestingly, these abilities, which involve quick and short lunging and shuffling movements, seem to be a common factor that correlates highly with actual performance in many sports (17). The fact that back strength played an important role in batting is in agreement with a previous study (13), confirming that successful batting is strongly associated with muscle strength and muscle power of the back. Two recent studies have found that strength, power, and agility are related to batting and fielding performances in professional and college baseball players (10,13). The current study reinforces the conclusions of these studies and extends the findings to youth baseball players.
However, our results showed that the predictors for pitching and batting were not consistent through the 3 age-related groups. For the youngest group, side steps, 10-m sprint, trunk flexion, and right grip strength were significant predictors of pitching strength, whereas there were no significant predictors of batting (Table 3). It may be that for these youngest players, flexibility is a critical variable. Trunk flexion represents low back and hamstring flexibility. Huang and Malina (11) investigated the relationship between physical activity and health-related physical fitness in 282 Taiwanese, including 138 boys and 144 girls at 12–14 years of age, and showed that physical activity was significantly correlated with high values of trunk flexion and shorter time in 1-mile run. Their data indicated that the more active children had higher low back and hamstring flexibility and endurance. Although the mean age of the youngest group, 112 months (9.3 years), in the present study was considerably lower than the children in the study of Huang and Malina (11), our data did suggest the importance of flexibility in youth players belonging to the lower grades of elementary school. In addition, for the youngest players, our findings recommend that training should be focused on improving agility and sprint performances, rather than working on the development of strength in the lower leg and back muscles. In the middle group (mean age: 137 months = 11.4 years), sit-ups and the 10-m sprint were significant predictors of pitched ball kinetic energy, whereas weight was a significant predictor of hit ball kinetic energy (Table 4). These results indicate that trunk training, including sit-ups, is needed for players of the higher grades of elementary school to throw fastballs of high velocity. It is also important to work on sprint speed for this age group. In the oldest group (mean age: 163 months = 13.6 years), 10-m sprint time was a significant predictor of pitched ball kinetic energy and weight and standing long jump were significant predictors of hit ball kinetic energy (Table 5). Again, sprint training can be effective to improve pitching, and the strength of lower leg muscles was related to ball speed of hit balls for this group. Two previous studies, using collegiate and professional players, demonstrated that back strength and vertical jump performance were good predictors of batting performance (Figure 1) (10,13). For our combined data, back strength and standing long jump were significant predictors for batting, which was in accordance with the studies on adult players.
In addition, we reanalyzed the data by categorizing the sample based on the different baseball weights. In the group of 107 players using the lighter rubber ball, age, weight, and 10-m sprint time were significant predictors of pitched ball kinetic energy, and age, weight, and back strength were significant predictors of hit ball kinetic energy (Table 6). In the group of 46 players using the hardball, standing long jump was a significant predictor of pitched ball kinetic energy, whereas BMI, standing long jump, and 10-m sprint time were significant predictors of hit ball kinetic energy (Table 7). Taking these results into consideration, it is likely that using baseballs of different weights affects the significant predictors of pitched and hit ball kinetic energies. Especially for players using a hardball, standing long jump can be a key predictor contributing to ball speed for pitched and hit balls. However, we have to interpret this result carefully because the sample size is obviously different between 2 groups (i.e., 107 players using a rubber ball vs. 46 players using a hardball) and the mean age and age range also clearly differ between them (mean age: 126.6 vs. 158.5 months; range 77–151 vs. 104–188 months). This discrepancy is a limitation of the present study.
Overall, our results indicated that daily training programs should be carefully tailored for the age group and that batting success is best improved by strengthening the back and lower limbs.
The relationship between the results of physical fitness tests and sporting performance has been used to find talented athletes, to select players, to set goals, to evaluate muscle training, and to prevent injuries (13). To this end, an optimal performance evaluation should be expressed numerically using an objective index. This holds for both adult and youth players. However, although numerous studies have examined the relationship between indices and actual performance in adult players, there have been few such studies in youth players. Hence, our findings should help beginning and competing youth baseball players and coaches, parents, and strength and conditioning professionals to reach their desired goals. Coaches and athletic trainers need to provide players with a collective and strong sense of purpose in training and to use the appropriate muscular training programs to aid both pitching and batting. For example, because the standing long jump, 10-m sprint, and grip strength were significant predictors for pitched ball kinetic energy, the training programs should emphasize improvement in these areas. Coaches and trainers must always be aware of the importance of performance in the standing long jump and 10-m sprint. Such performances reflect both strength and endurance of the muscles of the lower body. Campbell et al. (3) also provide evidence for the importance of lower extremity muscular strength and endurance in the training of adult pitchers. To improve performance in the 10-m sprint, various running drills are recommended. In addition, both standing long jump performance and back strength were significant predictors for batting. Indeed, back strength can be easily trained by using a heavy barbell, but for youth players, other training methods without a barbell should be used, such as a back extension and rope pulling exercise. Of course, the exercise should be focused on training powerful movements not only for lower limb muscles such as those involved in the long jump but also for muscles strengthened by upper body exercise like bench throws or clap push-ups.
Finally, coaches, sport scientists, and team strategists will all find our results useful for the detection, identification, and development of talented players.
The authors thank Dr. Larry Crawshaw for English editing. This study was supported by the grant-in-aid for the Global COE, Waseda University "Sport Sciences for the Promotion of Active Life," from the MEXT of Japan. The authors declare no conflicts of interest.