BIOMECHANICAL ANALYSIS OF FOREARM PRONATION AND ITS RELATIONSHIP TO BALL MOVEMENT FOR THE TWO-SEAM AND FOUR-SEAM FASTBALL PITCHES DAVID W. KEELEY,1 JASON WICKE,2 KEN ALFORD,3
AND
GRETCHEN D. OLIVER4
1
Department of Health Science, Kinesiology, Recreation and Dance, University of Arkansas, Fayetteville, Arkansas; 2Human Motion Research Laboratory, Department of Health and Human Performance, Texas A&M University-Commerce, Commerce, Texas; 3Department of Health and Human Performance, Texas A&M University-Commerce, Commerce, Texas; and 4Graduate Athletic Training Education Program, University of Arkansas and Department of Health, Kinesiology, Recreation, and Dance, University of Arkansas, Fayetteville, Arkansas
ABSTRACT Keeley, DW, Wicke, J, Alford, K, and Oliver, GD. Biomechanical analysis of forearm pronation and its relationship to ball movement for the two-seam and four-seam fastball pitches. J Strength Cond Res 24(x): 000–000, 2010—This study examined forearm pronation in relation to both the vertical and horizontal ball movement measured for 2 variations of the fastball pitch. Ten healthy collegiate baseball pitchers participated in the study (age: 19.4 6 0.7 yr, height: 1.90 6 0.06 m, mass: 88.50 6 9.05 kg). Reflective markers were placed at the level of each joint center’s location, and standard high-speed video techniques were used to record the participants as they threw 10 maximal effort fastball pitches. Marker positions were digitized in each video frame from which forearm pronation data were calculated. Across all pitchers, magnitude of both the vertical and horizontal ball movement was observed to be greater for the 2-seam fastball than for the 4-seam fastball. Regardless of pitch type, positive relationships were observed between all forearm pronation parameters and both vertical and horizontal ball movement. A significant positive correlation (r = 0.583, p , 0.01) was identified between forearm pronation acceleration at ball release and the magnitude of vertical ball movement regardless of pitch type. These results suggest that pitchers may be able to manipulate the magnitude of vertical ball movement by altering pronation accelerations at ball release. In addition, it appears that pitchers should alter their current training techniques so as to increase the endurance capabilities of the primary pronator muscles of the forearm. In doing so, they may be able to limit the effects of fatigue on these Research was conducted at the Texas A&M University - Commerce Human Motion Research Laboratory, Commerce, Texas. Address correspondence to David W. Keeley, dwk0611@msn.com. 0(0)/1–6 Journal of Strength and Conditioning Research Ó 2010 National Strength and Conditioning Association
muscles during pitching, thus preventing a decrease in the magnitude of vertical ball movement that typically occurs late in a pitching performance.
KEY WORDS kinematics, throwing, baseball, pitching INTRODUCTION
B
aseball is a sport in which the success of a team is determined by its individual players’ combined ability in the skills of fielding, base running, batting, and throwing (7). Because the demonstration of base running and fielding are determined by the interaction between the batter and the pitcher, it is believed that pitchers may have the greatest ability to influence the outcome of a game (4). To positively impact the outcome of a game, a pitcher must consistently produce pitches with the most effective predetermined velocity, ball movement, and accuracy. These pitch characteristics, which are the result of the interaction between the body segments, may be manipulated as pitchers alter pitching motion kinematics. However, to what degree differing segmental actions contribute to a pitcher’s successful outcome is currently unknown. The fastball is considered to be most important in a pitcher’s arsenal (10) and is commonly thrown in either the 2-seam or the 4-seam variation. Although the ability to maximize fastball velocity by using optimal pitching mechanics is considered critical for pitchers (12), attempts at generating maximum velocity have not consistently produced an increase in overall pitch quality. As pitchers have attempted to increase velocity, they have sacrificed both ball movement and accuracy. In addition, the general idea has developed among coaches and pitchers that as a pitch count increases to a level at which fatigue sets in, the magnitude of vertical ball movement for the fastball may decrease. As a result of these factors, it may be that the optimal mechanics for generating maximum pitch velocity may not be the optimal mechanics for generating ball movement or accuracy. Also, the optimal mechanics for generating maximum pitch velocity may result VOLUME 0 | NUMBER 0 | MONTH 2010 |
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Forearm Kinematics During Baseball Pitching in pitchers altering pitching kinematics because of fatigue earlier during a performance, further decreasing the magnitude of ball movement. Although previous studies have provided a general description of fastball pitching mechanics (5,6,9,10), as well as investigating the factors related to fastball velocity (8,12), there is no known research that examines forearm pronation and its relationship to ball movement. Because the pitching motion is a sequential movement that progresses from one body segment to the next, alterations in the kinematics of any segment will likely result in changes in segmental contributions to the final product and ultimately be related to alterations in performance. Thus, the purpose of this study was to examine the relationship between forearm pronation up to ball release in relation to the horizontal and vertical ball movement measured for the 2-seam and 4-seam fastballs. It was hypothesized that a positive relationship would exist between all forearm pronation parameters and ball movement. This would indicate that pitchers may be able to alter the magnitude of ball movement by altering forearm kinematics before and at ball release.
METHODS Experimental Approach to the Problem
A single-group, repeated-measures design was used to collect forearm pronation and ball movement data, with each pitcher throwing both the 2- and 4-seam fastball in a randomized order. Subsequent to data collection, pronation and ball movement data were analyzed using a series of descriptive statistics to identify outliers and determine the nature of the distribution before testing for the presence of relationships. Once the data were deemed to be normally distributed, testing for relationships was conducted by calculating the Pearson product moment correlation coefficients to examine the relationship between forearm pronation and ball movement. In the current design, kinematic parameters were the independent variables, whereas vertical and horizontal ball movements were the dependent variables. These variable assignments are consistent with the opinion that the characteristics of a pitch are dependent upon the pitching mechanics used to produce that pitch. Because the parameters associated with pronation and ball movement were analyzed at 3 independent intervals, the Bonferroni technique was used to adjust the alpha level to 0.01 to control the overall probability of committing a type I error. Data analysis for the current study was conducted using the statistical analysis package SPSS 11.5 for Windows (SPSS, Chicago, IL, USA). Subjects
Ten healthy male collegiate baseball pitchers (age: 19.4 6 0.7 yr, height: 1.90 6 0.06 m, mass: 88.50 6 9.05 kg), regardless of throwing arm dominance, volunteered to participate in the current study. All participants had recently completed their fall baseball competitive seasons, were deemed appropriately conditioned for competition by their respective coaches, and
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were selected based on the following characteristics: a) coaching staff recommendation; b) a minimum of 3 consecutive years of pitching experience; c) consistently throwing the 2-seam fastball and 4-seam fastballs for the past year during competition; and d) free from injury for the last 18 months. Data collection sessions were conducted indoors at the Texas A&M University-Commerce Human Motion Research Laboratory and were designed to simulate a competitive setting. All testing protocols used in the current study were approved by the Texas A&M University-Commerce Institutional Review Board. Before participation, the approved procedures, risks, and benefits were explained to all participants who then signed the appropriate paperwork to provide consent for testing. Procedures
Three synchronized high-speed digital video cameras set to record at a rate of 300 Hz (Basler Vision Technologies, Ahrensburg, Germany) were arranged to capture front, dominant-side footage of the participants. Before testing, a standard portable indoor pitching mound (Portolite Products, DeLano, MN, USA) was placed 18.4 m (regulation distance) away from the center of home plate. The global axes system used in this study was similar to that described in previous research (5) and was defined so that the x-axis extended from the center of the pitching rubber toward the center of home plate, the z-axis was orthogonal to the x-axis and extended vertically from the center of the pitching rubber, and the y-axis was orthogonal to both the x- and z-axes and directed laterally to the left. Also, a 0.56 m3 calibration cube consisting of 18 calibration points was suspended directly above the pitching mound and used to calibrate the 3-dimensional space in which the pitching motion was to be performed by way of direct linear transformation (1). Data collection sessions were conducted using established procedures (2) that were modified to include data regarding ball movement. Reflective markers were placed on the throwing arm at the lateral superior tip of the clavicle and bilaterally on the medial and lateral epicondyles of the throwing elbow and the styloid processes of the throwing wrist. Upon attachment of the markers, each participant was allowed to perform his own specified warm-up routine. After completing the warm-up, each participant threw 20 maximal effort fastballs (10 2-seam and 10 4-seam, in random order) with a 40 to 60 second rest period between each pitch. SIMI째 Motion (Simi, Unterschleissheim, Germany) was used to digitize the location of each reflective marker from maximum shoulder external rotation through maximum shoulder internal rotation. After digitization, the 3-dimensional location of each marker was determined and then filtered independently in the 3 primary axes using a second-order Butterworth filter set at a cut-off frequency of 16.7 Hz (2). At home plate, 2 digital video cameras (Panasonic Corporation of North America, Secaucus, NJ, USA) were
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pitches that crossed home plate within the regulation strike zone were analyzed. Statistical Analyses
Figure 1. Pronation angle for typical 2-seam (:) and 4-seam (n) fastball trials throughout recorded duration of pitch cycle for all participants. Time is represented along x-axis where negative values denote time before ball release and time zero depicts ball release. Values are mean 6SD.
positioned to capture the vertical and horizontal position of the ball as it passed over home plate. To convert the vertical and horizontal ball location as it crossed the center of home plate from image pixel values to actual values, meter sticks cut in half (0.5 m) and placed orthogonally to each other were suspended above home plate. A single image of the meter sticks was captured and digitized to provide a known pixel to actual unit ratio. Once all test trials had been performed and captured, they were reduced to include the 10 frames leading up to ball release as well as the instant of ball release. Ball release was determined to be the first frame of video footage in which a distinct separation of the baseball and pitching hand was observed. To calculate forearm pronation kinematics from the joint displacement data, a program was written using MATLAB software (The MathWorks, Natick, MA, USA) using methods established by Barrentine et al. (2). Once the forearm pronation angles were calculated, corresponding accelerations were determined using the finite differences technique described by Winter (14). To determine the horizontal and vertical deviations of the ball, the 3dimensional location of the ball at release was compared with that as it crossed home plate. In the current study, only
For each participant, mean and SD for both pronation kinematics and ball movement were calculated. The number of trials analyzed was reduced to include the 6 trials (3 2seam and 3 4-seam) with the lowest average coefficient of variation for the calculated upper and lower arm segment lengths. Upon selection of the 6 trials to be analyzed, a series of descriptive statistics were conducted to identify the possible presence of outliers (z-scores) and to determine the nature of the distributions (i.e., skewness and kurtosis) before testing to identify relationships. Testing for the assumption of normality of the pronation data, as well as the ball movement data for each fastball variation, was performed by calculating both the skewness index and kurtosis index (3). After the data were deemed to be devoid of outliers and normally distributed, Pearson product moment correlation coefficients were then calculated to identify the possible relationships between 2-seam and 4-seam fastball pronation kinematics and 2-seam and 4-seam vertical and horizontal ball movement. Because Pearson product moment correlation coefficients were calculated for data derived from the same group of participants at 2 intervals, the level of significance was adjusted to reduce the risk of type I errors. With regard to both vertical and horizontal deviation of the ball, alpha was set at 0.05/2 = 0.025. This reduction of alpha in the current study resulted in a decrease in the observed correlation power; however, significance was indicated by an observed power $ 0.70.
RESULTS Angle of Pronation
Analysis of forearm kinematics revealed that the throwing arm remained pronated (u . 90°) throughout the duration of the movement and that, regardless of pitch type, the mean angle of pronation across all pitchers was observed to remain greater than 140°. Although the forearm remained in a pronated position throughout the movement for both pitch types, differences in the pattern of the movement were observed (Figure 1). For the 2-seam fastball, pitchers were supinating the forearm from a time of 0.30 seconds through TABLE 1. Mean and standard deviation forearm accelerations (°/s/s) at selected intervals, broken down by pitch type. a time of 0.06 seconds before ball release. In contrast, as 2-Seam 4-Seam pitchers threw the 4-seam fastball, they were pronating the Interval Mean 6SD Mean 6SD forearm throughout the duraInitial Acceleration (°/s/s) 22404 961 219 87 tion of the movement.
Minimum Acceleration (°/s/s) Peak Acceleration (°/s/s) Acceleration at Release (°/s/s)
235718 13784 222642
17145 6340 14994
235375 11726 231285
16626 4456 18428
Pronation Acceleration
Pronation accelerations observed at specific intervals throughout the movement for VOLUME 0 | NUMBER 0 | MONTH 2010 |
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Forearm Kinematics During Baseball Pitching forearm acceleration increased, obtaining a peak pronation acceleration of 11,726 6 4,456°/s2 at 0.012 seconds before ball release. After this peak acceleration, the throwing arm decelerated through ball release, reaching a minimum supination acceleration value of 230,828 6 7,426°/s2 at release. Ball Movement
Figure 2. Forearm accelerations for a typical 2-seam (- - - -) and 4-seam (–––––) fastball pitches for all participants. Time is represented along xaxis where negative values denote time before ball release and time zero depicts ball release. Values are mean 6SD.
For all participants, both horizontal and vertical ball movement measured for both fastball variations are shown in Table 2. Regardless of participant, both ball movements were observed to be greater for 2-seam trials. Across all participants, vertical ball movement averaged 1.1 6 0.06 m for 2-seam trials and 0.9 6 0.02 m for 4-seam trials. Horizontal ball movement averaged 0.09 6 0.02 m for 2-seam trials and 0.05 6 0.01 m for 4-seam trials. Correlation
both pitch types are displayed in Table 1. For the 2-seam fastball, initial forearm acceleration was 22,404 6 961°/s2 (a negative value indicates supination). As the movement progressed, forearm acceleration increased, becoming positive (pronation) 0.02 seconds before ball release (Figure 2). Peak pronation acceleration for 2-seam trials occurred 0.017 seconds before ball release and was 13,784 6 6,340°/s2. After peak pronation acceleration, the forearm slowed as forearm acceleration once again became negative 0.006 seconds before release. Acceleration of the forearm then remained negative through release. Initial acceleration for the 4-seam fastball was 219 6 87°/s2. Unlike the 2-seam trials, 4-seam trials demonstrated a decrease in the supination acceleration through the first 0.003 seconds of the movement and remained negative longer than 2-seam accelerations (Figure 2). As the movement continued,
Correlation coefficients were computed to see whether a possible relationship between pronation kinematics at specific points in the pitch and ball movement existed, regardless of pitch type. Pearson product moment correlation coefficients are shown in Table 3 (angle) and Table 4 (acceleration). Correlation coefficients indicated that, although all values between forearm pronation angles and ball movement were positive (Table 3), none were significant. In contrast, correlation analyses between selected forearm accelerations and ball movement did identify a significant positive correlation (r = 0.58, p , 0.01) between forearm acceleration at ball release and vertical ball. This correlation value indicates that 33.9% of the variance in vertical deviation (ball movement) of the baseball is associated with pronation acceleration at ball release. In addition to these findings, the interclass correlation coefficient (r) was calculated between
TABLE 2. Mean vertical and horizontal ball movement and standard deviation in meters (m)for the 60 selected trials (10 participants 3 2 pitch types 3 3 pitches), broken down by pitch type and participant. Vertical Movement Participant 1 2 3 4 5 6 7 8 9 10
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Standard Deviation
Horizontal Movement
Standard Deviation
2-seam
4-seam
2-seam
4-seam
2-seam
4-seam
2-seam
4-seam
1.2 1.1 1.1 1.1 1.1 1.1 1.1 1.0 1.2 1.1
1.1 0.9 0.9 0.9 1.0 1.0 0.9 1.0 0.9 0.9
0.09 0.04 0.08 0.09 0.05 0.07 0.07 0.10 0.08 0.08
0.12 0.09 0.15 0.04 0.03 0.06 0.01 0.12 0.11 0.02
0.09 0.08 0.10 0.08 0.10 0.10 0.08 0.08 0.10 0.09
0.04 0.05 0.06 0.04 0.04 0.06 0.05 0.06 0.05 0.04
0.02 0.01 0.02 0.05 0.02 0.02 0.03 0.05 0.01 0.02
0.02 0.02 0.03 0.01 0.01 0.02 0.01 0.01 0.03 0.01
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TABLE 3. Calculated pearson product moment correlation coefficients (r) between selected forearm angles and horizontal/vertical ball movement, regardless of pitch type. Variable
Maximum pronation angle
Minimum pronation angle
Pronation angle at release
horizontal ballmovement vertical ball movement
0.30 0.21
0.19 0.13
0.24 0.36
Note - No forearm angles were found to significantly correlate to increased ball movement.
TABLE 4. Calculated pearson product moment correlation coefficients (r) between selected forearm acceleration parameters and horizontal/vertical ball movement, regardless of pitch type. Variable
Maximum acceleration.
Minimum acceleration
Acceleration at release
horizontal ball movement vertical ball movement
0.30 0.28
0.34 0.36
0.33 0.58*
*p , 0.01.
the 2 dependent variables to determine the relationship between ball movement in the horizontal and vertical planes. This value (r = 0.28; r2 = 0.078) indicated that only 8% of the variance in vertical ball movement could be explained by horizontal ball movement.
DISCUSSION The purpose of this study was to quantify forearm pronation up to, and through, ball release as well as the magnitude of horizontal and vertical ball movement for the 2 primary fastball variations. Specifically, this study analyzed forearm pronation and ball movement in an attempt to identify the relationship between these 2 variables. Although a number of studies have investigated the biomechanical similarities or differences between the various pitch types (i.e., fastball, curveball, change-up, and slider) commonly thrown in baseball (4,5,10,11), no known kinematic comparisons of the 2 predominant fastball variations have been conducted. The importance of identifying this relationship has direct applicability to pitchers of all levels. Pitching coaches commonly emphasize the production of similar pitching kinematics across a variety of pitch types, which may or may not be the most effective technique. In the current study, the forearm remained in a pronated position throughout the movement, at an angle near 140째 for both variations of the fastball. In fact, the patterns observed for pronation angles (Figure 1) and its acceleration (Figure 2) leading up to ball release were remarkably similar for both fastball variations. This finding indicates that pitchers do indeed produce similar mechanics across the 2 variations of
the fastball. The similarity observed for forearm kinematics between the 2 fastball variations may be attributed to the pitching techniques currently taught by coaches who stress the production of similar mechanics across all pitches (4,5). In addition to the production of similar mechanics across the 2 fastball pitches, it is thought that kinematic alterations of the pitching motion should occur late in the pitch cycle so as to allow pitchers to disguise the pitch being thrown and reduce the amount of time a batter has to react (10). This is only applicable if the kinematic alterations made late in the movement are indeed related to the magnitude of ball movement. The current study identified a significant positive correlation (r = 0.58, p , 0.01) between pronation acceleration at release and the magnitude of vertical ball movement regardless of pitch type. Both this relationship at release, which indicates that 34% of the variance in the vertical deviation of the fastball can be explained by the rate of pronation acceleration at release (r2 = 0.34), and the lack of a significant relationship between forearm kinematics and ball movement before the instant of ball release support the opinion that alterations in forearm kinematics should be made late in the pitch cycle. These alterations, if produced at release, may allow pitchers to effectively prevent the batter from identifying the pitch before release and may provide them with a tactical advantage.
PRACTICAL APPLICATIONS This study demonstrated a relationship that is indicative of greater pronation acceleration being associated with nearly 35% of the variance in vertical ball movement. This is VOLUME 0 | NUMBER 0 | MONTH 2010 |
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Forearm Kinematics During Baseball Pitching important because one common problem associated with fatiguing pitchers is a decrease in ball movement. Typically, as a pitch count increases, the vertical movement of the fastball decreases, leading to what is commonly known to pitching coaches as a ‘‘flattening out’’ of the pitch. One major characteristic of successful pitchers is their ability to produces pitches with appropriate ball movement, and differences of a few centimeters in ball location as the ball passes through the hitting zone can greatly influence the results of an at-bat when contact is made by the batter. In fact, it has been shown that that the location at which the bat impacts the baseball can influence the ball’s flight speed and distance (13). When contact occurs 10 cm closer to the hands, there is a 5% decrease in a baseball’s flight speed. This change in flight speed translates to a 10% decrease in flight distance and may be the difference between a ball being hit to the outfield being caught or being a homerun. On the basis of these findings, it is speculated that if the rate of forearm pronation acceleration at ball release is addressed from a training perspective, prevention of the decrease in vertical movement as the pitch counts rise may be possible. Commonly, exercises designed to work on the endurance capabilities of the flexor pronator mass in the forearm are not implemented into a pitcher’s everyday strength and conditioning regimen. This lack of endurance training of the forearm should be greatly scrutinized based on the results of this study. On the basis of the findings of this study, coaches, trainers, or athletic trainers should focus on having pitchers perform pronation exercises on a regular basis. More importantly, it is possible that coaches and trainers alike should address both the specific musculature exercised during a workout as well as the point during the workout regimen that the pitchers are conditioning this musculature. Unlike the shoulder musculature, which is strengthened on a consistent basis, strengthening of the 2 primary pronator muscles (pronator teres and pronator quadrates) is often only implemented into a strength program as a second thought. Essentially, the positive relationship found between pronation acceleration and vertical ball movement in this study, coupled with the ball movement problems commonly observed in fatiguing pitchers, indicates that pitchers need to focus on improving both the strength and endurance of these specific pronator muscles. In doing so, pitchers may experiences less fatigue in both the pronator teres and pronator quadrates as pitch counts increase and thus remain capable of producing the pronation accelerations at ball release that are necessary to retain the desired vertical ball movement on the fastball.
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ACKNOWLEDGMENTS The authors thank Crystal Burton of the Texas A&M University-Commerce Human Performance Lab, Dr. Laurene Fausett her assistance with the mathematics and programming used during data processing, Dr. John Slovak, Dr. Ben Cranor, and Dr. Serge von Duvillard for their involvement in this project, and the players and coaches who consented to participate. No authors received financial support for this study.
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