The pitchers are the critical players in a baseball game who significantly influence the outcome of the game. Having excellent throwing velocity and accuracy for pitchers are important techniques to offend the batters. However, the movement pattern of overhead pitching would place substantial stress on the throwing arm, which increases the likelihood of pitchers experiencing physical trauma and injury (3), especially microtrauma from repetitive upper extremity overuse injuries (19,22). These microtrauma to the upper extremity occur in all age-level young players, especially seen in adolescent players (9–14 years) who have the highest incidence and prevalence of injury (15,18–20,22). These results indicate that accumulation of microtrauma and overuse injuries would affect their next performance. The U.S. Baseball Medical & Safety Advisory Committee also recommended that young players should not perform over 75 pitches in 1 game to protect pitchers' development.
Although the pitching number limits reduce the risk of injury for young players, however, variant development of physical condition and strength may be seen in those youth pitchers (11,17). Therefore, the same regulation-weight ball was used to practice for different age-level players. We suspected that the arms of these young players can load the same regulation-weight ball throwing, especially the arm strength of those young players that were only half when compared with the adults (17). For this reason, regulation-weight ball throwing training for young pitchers is doubtful. Previous studies have provided such evidences. Fleisig et al. (13) reported that among young players, torque on the shoulder and elbow joints was considerably higher with a regulation-weight baseball (5 oz, 145 g) than with a lightweight baseball (4 oz, 113 g). They contended that lightweight baseballs are substantially more appropriate for young baseball players because they reduce the risk of injury during pitching training and also concluded that lightweight ball throwing may be suitable for young players. In addition, throwing a lightweight baseball between 3.5 and 4.4 oz (100 and 125 g) can produce a higher arm swing velocity compared with throwing a regulation-weight baseball (2,10,13), which increases the recruitment of high-threshold fast-twitch motor units during the throwing process, enhancing the throwing velocity after long-term training. Furthermore, throwing with a lightweight baseball (3.5–4.4 oz) does not alter the pitching movements or timing (2).
An excellent pitcher should be capable of not only reducing the risk of injury but also improving their pitching performance. Both throwing accuracy and throwing velocity are critical for being a competitive and qualitative pitcher. Previous studies indicated that throwing velocity is related to the arm swing velocity of the throwing hand before the ball is released (16) and the maximum shoulder external rotation (MSER) (21,26). Thus, young pitchers can train with lightweight baseballs to reduce the risk of upper extremity injury without altering the pitching pattern. However, evidence that long-term training with a lightweight ball affects the throwing performances and kinematical parameters of adolescent pitchers is limited.
Therefore, this study investigates the effects of 10 weeks of training with an appropriate baseball weight on adolescent players' throwing accuracy, throwing velocity, arm swing velocity, and MSER. We hypothesized that pitching training with an appropriate lightweight baseball can increase players' throwing velocity and arm swing velocity because of greater recruitment of fast-twitch motor units.
Experimental Approach to the Problem
This study examined the effects of 10 weeks of pitching training with a lightweight baseball among adolescent players' throwing accuracy, throwing velocity, arm swing velocity, and MSER. All participants were recruited from 1 junior high school baseball team and were assigned to either a lightweight baseball group (group L) or a regulation-weight baseball group (group R) according to their pretraining throwing velocity. Both groups performed the same training protocol for 10 weeks but used either lightweight (4.4-oz) or regulation-weight (5-oz) baseballs. The independent variables in this study were intervention of pitching training with 4.4-oz (group L) and 5-oz (group R) baseballs. Repeated measure was adopted as the experimental design in this study. All dependent variables, including throwing accuracy, throwing velocity, arm swing velocity, and MSER, were measured simultaneously using the same procedure before and after the training period.
We recruited 24 adolescent participants from the Hsin-Ming Junior High School baseball team, one of the top 3 teams at the junior high school tournament level in Taiwan. Additionally, the Hsin-Ming Junior High School baseball team has represented Taiwan at the IBAF competition in recent years. During the regular training season, the team usually practices for 5 hours a day, 6 days per week. Based on their pretraining throwing velocity, the 24 players were evenly divided into a lightweight baseball group (group L, with a mean throwing velocity of 107.81 ± 6.66 kph, approximately 66.99 mph) and a regulation-weight baseball group (group R, with a mean throwing velocity of 107.75 ± 8.51 kph, approximately 66.95 mph). The physical characteristics of the 2 groups are shown in Table 1. The experimental procedures of this study were approved by the Institutional Review Board of the Taipei Physical Education College. All participants and their parents or guardians were informed of the experimental risks and signed an informed consent form before participating in this study.
Group L pitched with custom-made lightweight baseballs weighing approximately 4.4 oz (weight: 125.34 ± 0.52 g; Tayang Sporting, Corp., Kaohsiung, Taiwan), which was defined as an appropriate baseball weight for adolescent players because it reduced the torque on joints (13) without altering the pitching movement (2,13). Group R pitched with regulation-weight baseballs weighing approximately 5 oz (official game baseball; weight: 145.65 ± 0.71 g; model number: KY-500; Tayang Sporting, Corp.). The characteristics of the lightweight and regulation-weight baseballs are shown in Table 2.
The training protocol for the 2 groups was modified according to the study by DeRenne et al. (4), as shown in Table 3. Both groups executed the pitching training using the specified baseballs for 10 weeks, 3 times per week, performing 4 sets each time with 3 minutes of rest between sets and 7–21 pitches per set. The number of total pitches each week was between 42 and 66. The pitching training was conducted between the teams' routine warm-up exercises and regular practice, excluding any pitching-related drills. During the pitching training session, the coach and one of the authors of the study paired the participants for pitching practice and observed the training session at a distance of 20 m. For the pitching training, one of the participants would pitch a baseball with their maximum effort to the other participant, who would be in a squatting position; the participants would alternate between pitching and catching.
The same measurement procedure was conducted for all the participants in an indoor bullpen before and after the training period. In the bullpen, a throwing net placed in the center of the rectangular grid behind home base was set as the target; the throwing distance from the rectangular grid to the pitching mound was 18.44 m. A Jugs radar gun (JUGS Sports, Inc., Tualatin, OR, USA) and a Sony DCR-SR87 digital video camera (Sony, Corp., Tokyo, Japan) with 60 fps were placed 2 m behind the rectangular grid at a height of 0.9 m and was used to measure the throwing velocity of each players' 10 pitches and record the ball location on the rectangular grid. Moreover, a Casio Exilim Pro EX-F1 digital high-speed camera (Casio Computer, Corp., Ltd., Tokyo, Japan) with 600 fps was placed 2 m from the sagittal plane to record the complete pitching movement of the players' throwing arm. The experimental setting is shown in Figure 1.
All participants attached a distinct marker for postprocessing analysis on the ulnar styloid process and lateral epicondyle of their throwing arm. After performing a regular warm-up, the participants were allowed to practice several times before pitching 10 times using their maximum effort with a new official game baseball (weight: 145.24 ± 0.38 g; model number: KY-500; Tayang Sporting Corp.). The data of throwing accuracy, throwing velocity, arm swing velocity, and MSER for each of the 10 pitches were measured and collected simultaneously.
The accuracy was defined as the distance between the ball location and the target on the rectangular grid and calculated each players' 10 pitches by a Siliconcoach Pro 7 software (SiliconCOACH, Ltd., Dunedin, New Zealand). The unit was centimeter.
The velocity of each players' 10 pitches was obtained from Jugs radar gun. The unit was kilometer per hour.
Arm Swing Velocity
The displacement and duration of the mark on the ulnar styloid process between the 5 frames before the ball was released were calculated using the Siliconcoach Pro 7 software, and then the arm swing velocity was calculated as the displacement between the first frame and the fifth frame divided by the duration (4/600 seconds). The unit was meter per second.
Maximum Shoulder External Rotation
According to the 6 pitching movement phases identified by Dun et al. (8), the MSER angle was analyzed during the arm cocking phase of the pitching movement and was calculated using the Siliconcoach Pro 7 software based on a vector from the mark on the ulnar styloid process to the other one on the lateral epicondyle and a vector from the posterior to anterior parallel with the ground. The unit was degree. The averages of all variables were used for statistical analysis.
SPSS 17.0 for Windows (SPSS, Inc., Chicago, IL, USA) was used to conduct statistical analyses. The test-retest reliability of each dependent variable was determined using an intraclass correlation coefficient (ICC). An ICC >0.75 was considered excellent, 0.60–0.74 good, 0.40–0.59 fair, and <0.40 poor. The partial Eta square (partial η2) and observed power (OP) were also analyzed in this study. A paired t-test was used to examine the changes throughout the 10-week training period. The change percentage (CP) was calculated using the following formula: (CP = [posttraining − pretraining]/pretraining × 100%). An independent samples t-test was conducted to compare the CP between the 2 groups. The level of significance was set as p ≤ 0.05. Descriptive statistics are represented as mean ± SD.
The ICC of each dependent variable is shown in Table 4. The high coefficients (0.657–0.964) indicate that the test-retest reliability is good to excellent for all variables measured in this study. The results showed that the players in the group L significantly increased their throwing velocity from 107.81 ± 6.66 kph to 111.18 ± 6.74 kph (p = 0.014, η2 = 0.434, OP = 0.753) and arm swing velocity from 22.43 ± 2.04 m·s−1 to 23.59 ± 2.05 m·s−1 (p = 0.005, η2 = 0.528, OP = 0.891) after the 10-week pitching training with a 4.4-oz baseball; however, they did not significantly improve their throwing accuracy (p = 0.359, η2 = 0.077, OP = 0.141) or MSER angle (p = 0.740, η2 = 0.010, OP = 0.061). For the players in group R, their throwing accuracy, throwing velocity, arm swing velocity, and MSER angle were not significantly altered after the 10-week pitching training with a 5-oz baseball (p > 0.05). Furthermore, for group L, the CP for throwing velocity was approximately 3.20% (p = 0.049, η2 = 0.165, OP = 0.513) and approximately 5.34% for arm swing velocity (p = 0.035, η2 = 0.186, OP = 0.574), which is significantly superior to that of group R; these results are shown in Table 5.
The results of this study indicate that the 10-week pitching training with a 4.4-oz lightweight baseball not only significantly enhanced the throwing velocity by approximately 3.20% and the arm swing velocity by approximately 5.34% for adolescent players but also did not alter the youth players' pitching patterns. Thus, the training effect of 4.4-oz lightweight baseballs is superior to that of 5-oz regulation-weight baseballs for adolescent players in the rapid physical growth and technique development stage. Because adolescent players have the highest incidence and prevalence of injury (19,20,22), among school-aged players, lightweight baseballs should be provided to young baseball players to reduce their risk of injury during pitching training (13). This study verified that pitching training with a lightweight baseball has a positive benefit on the throwing velocity and arm swing velocity of young players. These results also indicate that lightweight baseballs may be the most suitable for adolescent players to be used during pitching training or in competition.
The average throwing velocity of 107.78 kph achieved by the 13- to 15-year-old players in this study was rational compared with the average throwing velocities of approximately 82.8 and 118.8 kph for players aged 10–12 years and 15–20 years, reported by Fleisig et al. (11). The players' throwing velocity increased by approximately 3.20% after the 10-week pitching training with a 4.4-oz lightweight baseball. The results of this study are similar to that reported by previous studies (5,6,10). They found that training with overweight and lightweight baseballs increased players' throwing velocity when using regulation-weight baseballs. The overweight baseballs ranged from 5.25 to 17 oz, and the lightweight baseballs ranged from 4 to 4.75 oz (10). Furthermore, DeRenne et al. (5) found an increase of approximately 6.67% in the throwing velocity of high school players (aged 16–18 years), from the pretest 113.91 kph to the posttest 121.51 kph, after completing 10 weeks of pitching training using a baseball that decreased from 5 to 4 oz incrementally (a 20% weight reduction every 2 weeks). DeRenne and House (6) also found a 3.3% increase in throwing velocity among high school players after 10 weeks of pitching training with a mixture of 4-oz lightweight and 5-oz regulation-weight baseballs at a ratio of 2:1 for the number of pitches thrown. The findings of these studies suggest that adolescent players in the rapid physical growth and technique development stage can increase their throwing velocity of regulation-weight baseballs through pitching training with lightweight baseballs.
However, 2 issues related to using lightweight baseballs in pitching training must be considered seriously. The first is whether pitching lightweight baseballs increases the risk of injury, and the other is whether throwing lightweight baseballs alters the players' pitching movements (10). Fleisig et al. (13) compared the kinematic and kinetic parameters between pitches with standard (5 oz, 142 g) baseballs and pitches with lightweight (4 oz, 113 g) baseballs of 34 young players (11.1 ± 0.7 years). The results showed that although pitching with lightweight baseballs produced no difference in arm position, greater shoulder, elbow, and ball velocities were generated. Young players pitching with lightweight baseballs experienced significantly less elbow varus torque and internal shoulder rotation torque. This finding suggests that pitching with a 4-oz baseball can reduce loads on the elbows and shoulders of young pitchers, thereby minimizing the risk of injury. Another benefit of lightweight baseballs is that they enable young pitchers to develop arm speed while maintaining good arm mechanics (13). For pitching movement changes, in one of our sequence studies (2), we investigated the effects throwing 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, and 300 g baseballs had on pitching velocity, shoulder abduction, external rotation, flexion angle, and elbow flexion angle. The results indicated that throwing a baseball weighing between 100 and 175 g (3.5 and 6.2 oz) does not change players' pitching posture and temporal position. A 100–125 g (3.5 and 4.4 oz) baseball is the appropriate weight for training to increase pitching velocity, and a 175 g (6.2 oz) baseball is the appropriate weight for improving muscular strength in ballistic training (2). The weight of the baseball used in this study was approximately 4.4 oz (125.34 ± 0.52 g), which potentially reduced the players' risk of injury without altering their pitching pattern.
The pitching arm movement is considered a ballistic movement that involves a momentum delivery sequence from the lower extremities to the upper extremities. According to previous studies, the throwing velocity contribution from the lower extremities and trunk is 46.9%, and is 53.1% from the throwing hand (21); thus, the kinematic parameters of the throwing arm are related to the throwing velocity (9). A higher arm swing velocity before ball release and a greater MSER of the throwing arm during the cocking phase are believed to increase the throwing velocity (9,21,26). We speculated that a greater arm swing velocity may increase players' throwing velocity. Fleisig et al. (13) found that pitching with lightweight baseballs (4 oz) produced greater shoulder, elbow, and ball velocities. A potential benefit of the lightweight baseball is enabling young pitchers to develop arm speed while maintaining good arm mechanics (13). High-velocity arm swing movements increase the recruitment of high-threshold motor units, which increase the involvement of fast-twitch muscles (7,14,23,24), thereby enhancing explosive force production. Therefore, arm swing velocity is one of the crucial mechanisms enhanced by throwing velocity, which is improved by training with a lightweight baseball.
The MSER of the throwing arm during the cocking phase also has an important influence on pitching performance (9,21,26). The pitching movement should be adjusted to avoid generating high torque on the shoulder joint because the ball weight is too heavy to increase the MSER during the arm cocking phase (12). In contrast to throwing an overweight baseball, throwing a lightweight baseball may require greater MSER to increase the acceleration distance. However, Fleisig et al. (13) showed that the arm position of young pitchers when throwing a lightweight and a regulation-weight baseball did not differ during the cocking phase. In this study, the players' MSER during the arm cocking phase did not change substantially after the 10-week pitching training with a lightweight baseball, which may not have altered their pitching pattern. Regarding throwing accuracy, a number of studies have investigated the benefits of pitching training with an overweight baseball (7–17 oz) and found no significant improvements after 6–12 weeks of training (1,10,25). Additionally, although previous studies found that training with lightweight baseballs increases throwing velocity by approximately 6.67 (5) and 3.3% (6), they did not measure the players' throwing accuracy. The findings of this study indicate that the throwing accuracy of both the lightweight and regulation-weight baseball groups did not improve significantly after 10 weeks of pitching training. Because throwing accuracy involves complicated and precise mechanisms, it is associated with the coordination between each segment and is affected by numerous factors. According to these results, pitching training with overweight, regulation-weight, and lightweight baseballs may not increase players' throwing accuracy.
In conclusion, 10 weeks of pitching training with lightweight baseballs, which may reduce the risk of injury without altering pitching patterns, can substantially improve the arm swing velocity and throwing velocity of adolescent baseball players, who are in a stage of rapid physical growth and technical development.
Lightweight ball throwing training may be suitable than regulation-weight ball throwing for adolescent players. According to our results, 10-week lightweight ball throwing training, 3 times per week, substantially enhanced the throwing velocity and the arm swing velocity of adolescent players. This finding indicates that lightweight baseballs provide positive training benefit for players who are in a stage of rapid physical growth and technical development.
This study was financially supported by the National Science Council, Taiwan, under the grant number NSC 100-2627-B-154-001. The authors thank the Tayang Sporting Corporation in Taiwan for producing the lightweight baseballs used in this study.
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Keywords:Copyright © 2013 by the National Strength & Conditioning Association.
underweight; throwing; pitcher; youth player