Effects of Bat Grip on Baseball Hitting Kinematics

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Journal of Applied Biomechanics, 2009, 25, 203-209© 2009 Human Kinetics, Inc.

A motion system collected 120-Hz data from 14 baseball adult hitters using normal and choke-up bat grips. Six swings were digitized for each hitter, and temporal and kinematic parameters were calculated. Compared with a normal grip, the choke-up grip resulted in 1) less time during stride phase and swing; 2) the upper torso more opened at lead foot contact; 3) the pelvis more closed and less bat linear velocity at bat-ball contact; 4) less range of motion of the upper torso and pelvis during swing; 5) greater elbow flexion at lead foot contact; and 6) greater peak right elbow exten-sion angular velocity. The decreased time during the stride phase when using a choke-up grip implies that hitters quicken their stride when they choke up. Less swing time duration and less upper torso and pelvis rotation range of motion using the choke-up grip supports the belief of many coaches and players that using a choke-up grip results in a “quicker” swing. However, the belief that using a choke-up grip leads to a faster moving bat was not supported by the results of this study.

Escamilla is with the Department of Physical Therapy, Cali-fornia State University, Sacramento, CA, and the Andrews-Paulos Research and Education Institute, Gulf Breeze, FL. Fleisig is with American Sports Medicine Institute, Birming-ham, AL. DeRenne is with the Department of Kinesiology and Rehabilitation Science, University of Hawaii, Manoa, Hono-lulu, HI. Taylor is with the Naval Aerospace Medical Research Laboratory, Pensacola, FL. Moorman is with the Division of Orthopaedic Surgery and Duke Sports Medicine, Duke Uni-versity Medical Center, Durham, NC. Imamura is with the Kinesiology and Health Science Department, California State University, Sacramento, CA. Barakatt is with the Department of Physical Therapy, California State University, Sacramento, CA. And Andrews is with the Andrews-Paulos Research and Education Institute, Gulf Breeze, FL, and the American Sports Medicine Institute, Birmingham, AL.

Effects of Bat Grip on Baseball Hitting Kinematics

Rafael F. Escamilla,1,2 Glenn S. Fleisig,3 Coop DeRenne,4 Marcus K.Taylor,5Claude T. Moorman, III,6 Rodney Imamura,1 Edward Barakatt,1 and James R. Andrews2,3

1California State University, Sacramento; 2Andrews-Paulos Research and Education Institute; 3American Sports Medicine Institute; 4University of Hawaii, Manoa;

5Naval Aerospace Medical Research Laboratory; 6Duke University Medical Center

Keywords: batting, swing, choke up, biomechanics

It is common for a baseball hitter to choke up on the bat in certain situations, such as when a batter has two strikes. It is commonly believed among baseball coaches and hitters that choking up on the bat provides both bio-mechanical (e.g., quicker bat and more compact swing) and psychological (e.g., enhances a hitter’s concentra-tion and they get “fooled” less) advantages (DeRenne & Blitzbau, 1990). In addition, many believe that choking up on the bat provides more bat control and bat velocity (the bat feels lighter), resulting in more accuracy at bat-ball contact (DeRenne & Blitzbau, 1990). While limited data in the literature describe hitting mechanics (McIn-tyre & Pfautsh, 1982; Messier & Owen, 1985, 1986; Welch et al., 1995), there are no known studies in peer-reviewed literature that have examined hitting biome-chanics between normal and choke-up grips. Limited pilot data have shown that while bat linear velocity decreased 5–10% when choking up compared with a normal swing, the total time to swing a bat is approxi-mately the same between a normal and choke-up grip (DeRenne & Blitzbau, 1990). Nevertheless, it is largely unknown how baseball hitting kinematics varies as a function of bat grip, such as comparing a normal grip to a choke-up grip. The purpose of the current study was to compare baseball hitting kinematics between a normal bat grip and a choke-up bat grip. It was hypothesized that compared with the normal grip swing, the choke-up swing would be completed in less time, generate greater elbow extension angular velocities, and generate less linear bat velocity.

Methods

Data Collection

Fourteen adult baseball players (eight college and six professional) served as subjects, and signed an informed consent form before participation. The subjects had an

204 Escamilla et al.

waist to chest high on the subject; 3) all swings digitized and used as trials had to be a line drive hit to left-center outfield that carried in flight beyond a 68.6-m (225-foot) marker positioned in left-center field.

From pilot data, hitting kinematic and temporal parameters from multiple swings by a hitter that meet the above pitch and swing criteria were found to be remarkably similar between swings, typically varying less than 5–10% for each kinematic or temporal param-eter. Therefore, from the 10 hard, full-effort swings with a normal grip, the first three swings that met the above pitch and swing criteria were digitized for each hitter. Similarly, from the 10 hard, full-effort swings with a choke-up grip, the first three swings that meet the above pitch and swing criteria were digitized for each hitter. Digitizing began five frames before the front foot left the ground (first event) and ended five frames after bat-ball contact.

The swing was defined by four events and three phases. The first event was “lead foot off ground,” which represented the beginning of the stride phase and was defined as the first frame in which the lead foot was no longer in contact with the ground. The next event was “lead foot contact with ground,” which represented the end of the stride phase and was defined as the first frame when the lead foot made contact with the ground. “Lead foot off ground” to “lead foot contact with ground” rep-resented the time duration of the stride phase of the swing. The third event was “hands started to move for-ward,” which was defined as the first frame that both hands started to move forward toward the pitcher in the positive X direction as shown in Figure 1. “Lead foot contact with ground” to “hands started to move for-ward” represented the time duration of the transition phase of the swing (transition between the stride phase and acceleration phase). The last event was “bat-ball contact,” which was defined as the first frame immedi-ately before bat-ball contact. We chose this frame to represent bat-ball contact because not all trials involved a frame that captured the exact moment of bat-ball con-tact. For example, one video frame might capture imme-diately before bat-ball contact while in the subsequent frame the ball was just leaving the bat. We used this convention because after bat-ball contact bat velocity would be slower compared with just before bat-ball contact.

“Hands started to move forward” to “bat-ball con-tact” represented the time duration of the acceleration phase of the swing. Therefore, the “swing” was defined as from “lead foot off ground” to “bat-ball contact” and consisted of stride, transition, and acceleration phases.

A fourth-order, zero-lag Butterworth digital filter was used to smooth the raw data using the Jackson knee method of optimal data smoothing (Jackson, 1979), employing cutoff frequencies between 6 and 12 Hz depending on the marker that was being smoothed. To smooth data at bat-ball contact and beyond, data were cut at a frame just before bat-ball contact and a mathe-matical procedure was used to pad the data from that

average age, weight, and height of 22.2 ± 2.3 years, 84.8 ± 6.6 kg, and 180.6 ± 3.7 cm, respectively. Bats were self-selected, and average bat weight was 8.5 ± 0.3 N (30.6 ± 1.1 oz.) and average bat length was 84.8 ± 1.3 cm (33.4 ± 0.5 in.). The college and professional hitters were statistically equivalent to each other with respect to age, body mass, body height, bat characteristics, and temporal and kinematic parameters.

Two synchronized, genlocked 120-Hz video cam-eras (Peak Performance Technologies, Inc., Englewood, CO) were optimally positioned to view the hitter. Each camera’s optical axis formed approximately a 45° angle to the sagittal plane of the hitter. The cameras were posi-tioned approximately 12 m apart and faced perpendicu-lar to each other, with each camera approximately 8 m from the hitter. To minimize the effects of digitizing error, the cameras were positioned so that the hitter was as large as possible within the viewing area of the cam-eras. Each hitter completed 10 hard, full-effort swings with a normal grip (hands as far down as possible on the bat) and 10 hard, full-effort swings with a choke-up grip (hands 6.35 cm above the normal grip) as a pitching machine “pitched” balls to them during their normal batting practice. Whether a normal grip or choke-up grip was used first was randomly determined for each hitter. Ball velocity was recorded from a Jugs Tribar Sport radar gun (Jugs Pitching Machine Company, Tualatin, OR) as the ball left the pitching machine. The radar gun was calibrated before a testing session, and was accurate within ±0.22 m/s.

An event synchronization device (Peak Perfor-mance Technologies, Inc.) was employed to generate a time code directly onto the video signals, thereby allow-ing corresponding time-synchronized video frames between the two videotapes to be determined. Before and just after the subjects were videotaped, a 2- 1.5- 1-m three-dimensional (3-D) calibration frame (Peak Performance Technologies, Inc.), surveyed with a mea-surement tolerance of 0.5 cm, was positioned and video-taped in the same volume occupied by the hitter. The calibration frame was comprised of 24 spheres of known spatial coordinates.

Data Analysis

A 3-D system (Peak Performance Technologies, Inc.) was used to manually digitize data for all subjects. A spatial model was created that was comprised of the top of the head; centers of the left and right midtoes (at approximately the head of the third metatarsal); joint centers of the ankles, knees, hips, shoulders, and elbows; midpoint of hands (at approximately the head of the third metacarpal); and proximal and distal ends of bat. All points were seen in each camera view. Each of these points was digitized in every video field.

Pitches and swings were standardized according to the following criteria: 1) all pitches were between 32.6 and 33.5 m/s (73–75 mph); 2) for a trial to be used, the pitch had to be a strike on the inner half of the plate from

Bat Grip and Baseball Hitting Kinematics 205

the X-axis (Figure 1), positive values occurred with counterclockwise rotations (as illustrated in Figure 1), and negative values occurred with clockwise rotations, as viewed from above. As pelvis and upper torso angles became less positive or more negative, the pelvis and upper torso assumed a more “closed” position, and as pelvis and upper torso angles became more positive, the pelvis and upper torso assumed a more “open” position. Both the upper torso and pelvis assumed an “open” position at ball contact, as shown in Figure 1. Angular velocity of the pelvis was calculated as the cross prod-uct of the pelvis vector and the derivative of this vector, whereas angular velocity of the upper torso was calcu-lated as the cross product of the upper torso vector and the derivative of this vector (Feltner & Dapena, 1989).

Kinematic and temporal data were averaged for the three normal swings and for the three choke-up swings and used in statistical analyses. Dependent (paired) t tests were employed to test for differences in kinematic and temporal parameters between the normal grip and choke-up grip. To minimize the probability of making a type I error without increases the probability of making a type II error, the level of significance used was set at p < .01, resulting in an experimentwise error of 0.31.

Results

Temporal stride and swing parameters are shown in Table 1. Compared with using a normal grip, using a choke-up grip resulted in significantly less time during the stride phase (lead foot off ground to lead foot con-tact with ground) and during the swing (lead foot off ground to bat-ball contact).

Upper and lower extremity angular displacement parameters are shown in Table 2. Compared with using a normal grip, using a choke-up grip resulted in greater left elbow flexion at lead foot contact with ground and greater right elbow flexion at lead foot contact with ground.

Upper torso and pelvis angular displacement parameters are shown in Table 3. Compared with using a normal grip, using a choke-up grip resulted in a sig-nificantly smaller upper torso angle (more open posi-tion) at lead foot contact with ground and significantly smaller pelvis angle (more closed position) at bat-ball contact. The range of motion of the upper torso and pelvis during the swing (defined as the upper torso angle difference between bat-ball contact and lead foot off ground, and the pelvis angle difference between bat-ball contact and lead foot off ground) was significantly greater using the normal grip compared with using the chock-up grip. There were no significant differences in trunk twist angle (upper torso angle minus pelvis angle) throughout the swing.

Angular velocity parameters are shown in Table 4. Compared with using the normal grip, using the choke-up grip resulted in greater peak right elbow extension angular velocity.

point forward. Kinematic data were not analyzed after bat-ball contact. Using the direct linear transformation method (Shapiro, 1978), three-dimensional coordinate data were derived from the 2-D digitized images from each camera view. An average resultant mean square calibration error of 0.3 cm produced an average volume error of 0.1%. The origin of the global three-dimen-sional orthogonal axis system was centered at home plate with the positive X-axis pointing toward the pitch-ing machine, which was positioned on a line from the home plate to the pitching rubber. The positive Z-axis pointed up in the vertical direction, and the positive Y-axis pointed orthogonally to the X-axis and Z-axis.

Linear and angular displacements and velocities were calculated for both the left and right sides of the body, using appropriate kinematic equations (Peak Per-formance Technologies, Inc.). Stride length was deter-mined as the distance between the right and left ankles. Knee and elbow flexion angles were defined as 0° when full extension was achieved.

The pelvis was defined as a vector pointing from the right hip to the left hip, whereas the upper torso was defined as a vector pointing from the right shoulder to the left shoulder (Figure 1). Pelvis rotation was defined as the angle between the X-axis and the projection of the pelvis vector in the X-Y plane, whereas upper torso rota-tion was defined as the angle between the X-axis and the projection of the upper torso vector in the X-Y plane. The pelvis and upper torso rotated about a trunk axis defined from the midpoint of the left and right hips to the midpoint of the left and right shoulders. Pelvis and upper torso angles were defined as 0° when the pelvis and upper torso vectors were pointing in the direction of

Figure 1 — Upper torso and pelvis angle conventions (see text for explanation).


results are expected as the result of chance, whereas the remaining 96% are likely to be due to nonchance factors. The decrease in stride phase time using a choke-up grip compared with using a normal grip implies that batters quicken their stride when they choke-up, but maintain the same stride length compared with the normal grip. Choking up on the bat allowed the hitter to reduce the moment of inertia of the bat about the hands. That is, more of the bat mass was closer to the hands, so the summation of mass times distance squared, (m · r2), was reduced. While the smaller moment of inertia in the choke-up group may lead to faster movements (such as

Linear displacement and velocity parameters are shown in Table 5. There were no significant differences between using normal and choke-up grips in stride length. Bat linear velocity at bat-ball contact was sig-nificantly greater using a normal grip compared with using a choke-up grip.

DiscussionUsing the percent error rate as explained by Ottenbacher (1998), the 10 significant differences observed in the current study indicates that approximately 4% of our

Table 1 Temporal parameters during the swing

Normal Grip (n = 14) Choke-up Grip (n = 14)

Stride Phase: Time from Lead Foot Off Ground to Lead Foot Contact with Ground (s)

0.375 ± 0.075* 0.336 ± 0.072*

Percentage of Swing 64.0 ± 10.5 62.8 ± 10.2Transition Phase: Time from Lead Foot Contact with

Ground to Hands Started to Move Forward (s)0.071 ± 0.036 0.067 ± 0.035

Percentage of Swing 12.1 ± 9.6 12.5 ± 8.2Acceleration Phase: Time from Hands Started to Move

Forward to Bat-Ball Contact (s)0.140 ± 0.021 0.132 ± 0.027

Percentage of Stride/Swing Cycle 23.9 ± 4.9 24.7 ± 5.0Swing: Time from Lead Foot Off Ground to Bat-Ball

Contact (s) 0.586 ± 0.078* 0.535 ± 0.083*

*Significant difference (p < 0.01) between normal grip and choke-up grip.

Table 2 Upper and lower extremity angular displacementa parameters


Left Elbow Flexion Angle (°) Lead foot off ground 77 ± 13 78 ± 14 Lead foot contact with ground 57 ± 9* 62 ± 10* Hands started to move forward 66 ± 11 70 ± 12 Bat-ball contact 18 ± 7 16 ± 9

Right Elbow Flexion Angle (°) Lead foot off ground 126 ± 17 127 ± 14 Lead foot contact with ground 129 ± 8* 133 ± 8* Hands started to move forward 131 ± 19 132 ± 15 Bat-ball contact 54 ± 15 54 ± 15

Left Knee Flexion Angle (°) Lead foot off ground 46 ± 12 47 ± 13 Lead foot contact with ground 38 ± 10 39 ± 11 Hands started to move forward 65 ± 25 64 ± 24 Bat-ball contact 11 ± 5 11 ± 5

Right Knee Flexion Angle (°) Lead foot off ground 49 ± 15 49 ± 16 Lead foot contact with ground 44 ± 17 43 ± 15 Hands started to move forward 44 ± 15 45 ± 16 Bat-ball contact 64 ± 10 62 ± 9

*Significant difference (p < 0.01) between normal grip and choke-up grip.a 0° = full elbow or knee extension.


helping to explain why bat linear velocity at bat-ball contact was less using a choke-up grip compared with a normal grip. It also may be that when choking up the bat is shorter and so the distal end point of the bat is closer to the axis of rotation and thus is traveling slower

the greater peak right elbow extension angular velocity using the choke-up grip compared with the normal grip), it may also lead to a diminished force production in accordance with the force-velocity relationship for muscle contraction. This may be an important factor in

Table 3 Upper torso and pelvis angular displacement parameters


Upper Torso Angle (°) Lead foot off ground −16 ± 9 −13 ± 9 Lead foot contact with ground −25 ± 7* −22 ± 8* Hands started to move forward −20 ± 18 −19 ± 7 Bat-ball contact 51 ± 8 48 ± 8 Difference between bat-ball contact and Lead foot off ground 67 ± 8* 61 ± 9*

Pelvis Angle (°) Lead foot off ground −10 ± 5 −9 ± 6 Lead foot contact with ground −10 ± 5 −10 ± 6 Hands started to move forward −10 ± 6 −9 ± 6 Bat-ball contact 72 ± 13* 65 ± 11* Difference between bat-ball contact and Lead foot off ground 82 ± 10* 75 ± 11*

Trunk Twist (°) (Upper torso angle minus pelvis angle) Lead foot off ground −6 ± 7 −4 ± 6 Lead foot contact with ground −15 ± 10 −12 ± 9 Hands started to move forward −9 ± 9 −9 ± 8 Bat-ball contact 21 ± 16 16 ± 14

*Significant differences (p < 0.01) were observed between normal and choke-up grips.

Table 4 Angular velocity parameters


Peak Pelvis Angular Velocity (°/s) 681 ± 94 669 ± 119 Timing—Percentage of Swing 60 ± 12 64 ± 13

Peak Upper Torso Angular Velocity (°/s) 850 ± 50 884 ± 67 Timing—Percentage of Swing 65 ± 7 67 ± 11

Peak Left Knee Extension Angular Velocity (°/s) 378 ± 65 350 ± 60 Timing—Percentage of Swing 66 ± 11 68 ± 10

Peak Left Elbow Extension Angular Velocity (°/s) 722 ± 131 732 ± 102 Timing—Percentage of Swing 73 ± 12 77 ± 11

Peak Right Elbow Extension Angular Velocity (°/s) 928 ± 120* 997 ± 110* Timing—Percentage of Swing 79 ± 12 82 ± 11


Table 5 Linear displacement and velocity parameters


Stride Length at Lead Foot Contact with Ground (Distance between ankles, cm)

86 ± 9 87 ± 8

Percentage of Body Height 48 ± 4 48 ± 4Bat (Distal end) Linear Velocity at Bat-Ball Contact (m/s) 31 ± 4* 28 ± 5*



The biomechanical findings in the current study are similar to hitting biomechanics data presented in previ-ous work (Welch et al., 1995). It has been previously demonstrated that a hitter tends to keep the left elbow straighter and bend the right elbow more (Welch et al., 1995). This observation was also observed in the current study, in which throughout the stride and swing phases of hitting the right elbow flexed approximately twice as much as the left elbow.

Knee flexion between left and right knees exhibited a different pattern compared with elbow flexion. From the beginning of the stride until the end of the swing, the right knee increased in flexion while the left knee decreased in flexion and became nearly fully extended. This is a similar pattern described in previous work (Welch et al., 1995), in which it was reported that hitters went from a left knee flexion of 70° when the hands started to move forward to 11° at bat-ball contact, which is nearly 60° of left knee extension. This emphasizes the importance of lead leg straightening (and strengthening) during the swing to help brace the body as the arms and trunk rotates. The rapid lead knee extension angular velocity generated during both the normal and choke-up grips during the swing illustrates the importance of lower extremity strength.

The sequencing of pelvis and upper torso rotation was the same sequencing reported in previous work (Welch et al., 1995). The upper torso remained in a more closed position compared with the pelvis and achieved a greater peak angular velocity of the upper torso com-pared with the peak angular velocity of the pelvis. Moreover, the peak angular velocity of the upper torso occurred later in the swing compared with the peak angular velocity of the pelvis. This sequencing occurred both in normal and choke-up grips, and is important because kinetic energy is transferred up the body from larger slower moving segments earlier in the swing to smaller faster moving segments later in the swing. The similar timing of peak angular velocities (Table 4) implies that using different bat grips does not affect the sequential timing that occurs throughout the swing.

In the current study all hitters use hard, full-effort swings for both the normal and choke-up grips. The rationale is that hitters take the same full-effort swing in games whether they choke up or not, because choking up does not result in the batter swinging “easier” com-pared with when using a normal grip. During a baseball game, a choke-up grip swing is usually performed with the same full range of motion and effort as is the normal grip swing. If a hitter is facing a 40 m/s (90 mph) fast-ball while choking up, swinging easier than normal would result in the batter not being able to get the bat around in time to make contact with the ball. Therefore, when a batter makes the decision to choke up on the bat, the intent is not to swing easier compared with using a normal grip, but rather to generate a quicker and better controlled bat, resulting in a more compact swing.

In conclusion, the decreased time during the stride phase using the choke-up grip compared with using the

compared with when using a normal grip. Therefore, the slower bat linear velocity at bat-ball contact when using the choke-up grip compared with the normal grip could be related to either or both of these factors.

In the current study, bat linear velocity was approx-imately 10% less using a choke-up grip compared using a normal grip, which is similar to bat velocity pilot data of normal and choke-up grips reported by DeRenne & Blitzbau (1990). Moreover, the current study showed reduced stride phase time and swing time when using a choke-up grip. This supports the belief of many coaches and players that using a choke-up grip results in a “quicker” bat during the swing (DeRenne & Blitzbau, 1990). When choking up, the batter adjusted his swing mechanics to be quicker but sacrificed potential gains in bat velocity. The batter made his swing quicker through less contribution from the trunk (i.e., less pelvis and upper torso rotations) and more contribution from the arms (i.e., more left and right elbow flexion at lead foot contact and more right elbow extension angular veloc-ity). Further studies involving swing kinetics are needed to further examine these issues.

The slightly greater right and left elbow flexion that occurred during the swing while using the choke-up grip compared with using the normal grip may help keep the hands closer to the body, making it easier for the hitter to rotate the trunk, arms, and bat. Moreover, compared with using the normal grip, at the beginning of the swing the upper torso was in a more open position using the choke-up grip, and during the swing both the upper torso and pelvis rotated through a smaller range of motion in less time using the choke-up grip. There-fore, compared with the normal grip, using the choke-up grip may help the hitter rotate the upper torso, pelvis, arms, and bat around quicker and make ball contact ear-lier in the swing. Using the choke-up grip may give the hitter more time to decide whether to swing at a pitch, may help the hitter see the ball better due to the trunk being in a more open position, and may help the hitter better control the bat due to the smaller moment of iner-tia that choking up on the bat creates (Fleisig et al., 2002). However, based on the trunk twist angle, the trunk’s contribution to the swing does not appear to be dependent on grip type.

The greater bat linear velocity at bat-ball contact using the normal grip compared with the choke-up grip may appear surprising to many baseball coaches and players who believe that a “quicker” bat during the choke-up grip equates to greater bat speed. Although linear bat velocity was less in the choke-up grip com-pared with the normal grip, and although the mass of the bat is the same between normal and choke-up grips, there are data that imply that choking up on a bat may affect the “effective mass” of the bat, resulting in less momentum (mass velocity) with the choke-up grip (Fleisig et al., 2002). Therefore, using a choke-up grip may result in decreased ball distance after bat-ball impact, which should be the focus of subsequent hitting studies.


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normal grip implies that hitters may quicken their stride when they choke up. Although time was not signifi-cantly different in the acceleration phase between normal and choke-up grips, the total time of the swing (stride phase + transition phase + acceleration phase) was significantly less with the choke-up grip, which supports the belief of many coaches and players that using a choke-up grip results in a “quicker” overall swing. During the swing, the upper torso and pelvis rotated through a smaller range of motion and in less time using the choke-up grip compared with using the normal grip, which implies that with the choke-up grip a batter may have more time to decide whether to swing at a pitch. The similarity in most kinematic parameters between normal and choke-up grips implies that there are more similarities in hitting mechanics between normal and choke-up grips than there are differences. Because bat linear velocity was less in the choke-up grip compared with the normal grip, there may be less momentum with the choke-up grip because of the dif-ferences in mass distribution of the bat with choking up, which may result in decreased ball distance after impact. This can serve as a hypothesis to be tested in subsequent hitting biomechanical studies.

Acknowledgments

The authors would like to acknowledge Kevin Chen, Melissa Lewis, Shanaal Smothers, and Lazard ZaWaunyka for all their assistance in manually digitizing the data.

ReferencesDeRenne, C., & Blitzbau, A. (1990). Why your hitters should

choke up. Scholastic Coach, Jan., 106–107.Feltner, M.E., & Dapena, J. (1989). Three-dimensional inter-

actions in a two-segment kinetic chain. Part I: general model. International Journal of Sport Biomechanics, 5, 403–419.

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Effects of Bat Grip on Baseball Hitting Kinematics