Research Design
This was an experimental design that was randomized and within-subject study. The research investigates the kinematic differences and performance results between the throwing motions. The independent variables were the three throwing motions: throwing from the knees (K), the traditional throw down (TD), and the pitch-out (PO). The dependent variables will include joint angles (shoulder: abduction, extension, internal rotation, and external rotation;
elbow: flexion and extension; trunk: forward and lateral tilt), joint angular velocity (shoulder internal rotation, elbow extension, and trunk rotation), ball velocity, pop time, time to second base, and stride length for TD and PO. The study used a counterbalance design to account for ordering effects in which the order of the throwing conditions were randomly assigned to each subject.
Participants and Selection Criteria
Eleven healthy, male, right-handed, professional catchers were recruited from Taiwan’s professional baseball league to partake in the study. The data collected from the study were used in the statistical analysis. Participants were excluded if they have sustained an injury to the shoulder, elbow, and/or upper torso in the six months prior to recruitment. The participants partaking in the study completed an Informed Consent form prior to testing procedures. Upon completion of the Informed Consent form, the test participants completed baseball history questionnaires to confirm that an injury to the shoulder, elbow, and/or torso did not occur in the past six months.
Outcome Measurements and Instrumentation
Each participant completed the testing in one session, which lasted approximately an hour and a half. All testing sessions were performed in the National Taiwan Normal University (NTNU) Athletics building’s first floor indoor track. The testing session consisted of a period of instruction, walk-thru, demonstration, and practice of the throwing motions for familiarization.
All participants will have an assigned subject identification number, which was used to identify the data recorded on pre-made data collection documentation and Vicon’s motion capture system.
Anthropometric Data Collection
Anthropometric data was collected for each participant, with self-reported figures for height and weight. A Vernier scale was used to measure the: shoulder radius and offset, elbow width, wrist width, hand thickness and width, knee width, ankle width, and anterior superior iliac spine (ASIS) width. Furthermore, a tape measure was used to measure the length of the leg.
Anthropometric data was collected for both left and right extremities.
Equipment
- Vicon T-Series Motion Capture System (T-20s Vicon Motion Systems Ltd., Oxford, UK) infrared cameras recorded at 250 Hz to capture and record the reflective markers that were affixed to the joints on the test participants. The changes in the position of the reflective markers with respect to the lab coordinate system were recorded by the Vicon Nexus 1.8.1 software system in order to conduct kinematic analysis following the testing sessions.
- Visual3D (C-motion, Inc., Maryland, USA) was used to calculate kinematic data recorded by the Vicon system.
- Baseball – brand new, regulation size ball (5 oz.) - Baseball catcher’s mitt and shin guards
- Vernier scale, tape measurer
- Double sided tape, kinesiology tape, other supplies (scissors)
Research protocol
Data collection occurred inside the NTNU Athletics building’s indoor track. Prior to the arrival of the test participants, the order of throw motions was randomly assigned for each participant. The participants were scheduled for two-hour sessions for data collection with the researcher and were blinded to their testing order assignment until arrival to the facility. All participants had the purpose of the study explained to them and completed a baseball and medical history questionnaire upon reporting to the testing session. Following the completion of the questionnaire, an informed consent was read and signed before proceeding with the study.
Via a walkthrough, the researcher informed the participant of the testing confines and demonstrated the three throwing motions to be tested. The eight cameras created a capture zone surrounding home plate, both batter’s boxes, and the catcher’s area. The distance from home plate to second base measured 38.8 meters with a pitcher’s area ten meters away from home
Figure 3-1. Experimental setup.
plate.
At the conclusion of the instructional period, reflective markers were affixed to the C7 and T10 vertebrae, acromion, lateral and medial epicondyle of the elbow, distal ulna and radius bony landmarks, dorsum of hand at head of second metacarpal, left and right ASIS, and left and right PSIS. Additional markers for tracking purposes were affixed to the right scapula, upper arms, and forearms. A headband with four reflective markers was secured on the participant’s head. Lower extremity markers were fixed to the thighs, shin guards, and shoes of the participants. Kinesiology tape secured the reflective markers onto the test participant. The model of reflective markers can be seen below.
Table 3.1
C-7 Left Forearm Left/Right Thigh
T-10 Right Forearm 1 Left/Right Lateral Epicondyle of Femur
Right Scapula Right Forearm 2 Left/Right Medial Epicondyle of Femur
Left/Right
Acromion Right Forearm 3 Left/Right Tibia
Left Upper Arm Left/Right Radial Styloid Process Left/Right Lateral Malleolus Right Upper Arm
1 Left/Right Ulna Styloid Process Left/Right Medial Malleolus Right Upper Arm
2 Left/Right 3rd Metacarpal Left/Right Heel
Right Upper Arm
3 Right 2nd phalanx Left/Right 3rd Metatarsal
Right 3rd phalanx
After the placement of all reflective markers, the participants were allowed to warm up using their preferred routine. Once warm up was completed, the participants were asked to perform three successful trials for each throwing motion (throws from the knee, traditional throw down, and the pitch out). Prior to formal testing, the participants were given practice trials with regulation baseballs affixed with reflective tape to become familiar with the motions, ball, and pitcher throwing the ball. The test participants were reminded to simulate in-game scenarios when performing each trial i.e. quickly transfer and throw the ball as fast as possible to second base. When the researcher began the start of each trial, the pitcher proceeded to deliver the ball to the catcher. The ball thrown to the catcher would have to be in a catchable range for the catcher. A trial was deemed unsuccessful if the delivery of the ball to the catcher was too low (below the knees of the catcher) or too high (above the head of the catcher). While a trial was deemed successful if the participant catches the ball, smoothly transferred the ball to the throwing hand, takes one step, and throws the ball to second base within a catchable range. If the Figure 3-2. Reflective marker model.
test participant took any additional steps the trial was deemed unsuccessful. Furthermore, if the ball thrown to second base was out of catchable range at second base, the trial was deemed unsuccessful. The test participant would then be asked to redo the trial. Resting periods of two minutes were given in between each trial and five minutes between each throwing motions in order to avoid fatigue.
Throwing from the knees
In order to perform this throwing motion successfully, the test participant began in a crouched/squatted position – the ready position. The subject awaited the delivery of the ball from the pitcher during this time. Once the ball was pitched, the catcher first must catch the ball and proceed to transfer the ball to the throwing hand. During the transfer, the catcher began to kneel on both knees to prepare to throw the ball to second base.
Figure 3-3. Throwing from the knees’ throwing motion.
The traditional throw down
The traditional throw down required the test participant to begin in the ready position.
Once the ball was delivered to the catcher, the catcher received the ball and began to transfer the ball to the throwing hand. During this transfer phase, the catcher simultaneously hops up and turns their body perpendicular to second base with their left foot pointing towards second base.
Once the body was turned, the catcher proceeded to take only one step with the left foot and throws the ball to the target.
Figure 3-4. The traditional throw down’s throwing motion.
Pitch out
Performing the pitch out requires the catcher to begin in the ready position. However, unlike the previous two motions, the pitch out would have the catcher take a few steps towards the left-hand batter’s box to catch the ball from the pitcher. Once the ball was caught, it was transferred to the throwing hand; the catcher takes one step and throws to the target.
Figure 3-5. The pitch out’s throwing motion.
Research protocol flow chart
Data processing
Statistical Package for the Social Sciences (SPSS for Windows, 20.0, IBM, New York, USA) was used to perform the statistical analysis for this study. Descriptive statistics (mean ± SD) for the test participants’ age, height, weight, and baseball experience was calculated. A
one-way repeated measures analysis of variance (ANOVA) test was used to assess the differences between the three motion’s joint kinematics and performance results, α = .05. Regression analysis provided the means to determine the relationships between joint kinematic measurements and performance results.
Kinematic analysis was performed with C-Motion’s Visual3D software. Reflective markers affixed to the bony landmarks allowed for calculations of the shoulder and elbow joint angles as well as the trunk rotation angles relative to the local coordinate system: x-axis is in the direction towards second base, y-axis is to the left and right of home plate, while the z-axis is in the vertical direction above home plate. The rotation angle sequence (Euler Angles) to be used for shoulder calculations was Z-Y-Z with the x-direction portraying the flexion and extension, y-direction representing abduction and adduction, and the z-y-direction characterizing internal and external rotations. Elbow rotation sequences utilized Cardan angles of X-Y-Z to calculate the flexion and extension motions that occurred in the x-direction. Cardan angles (Y-X-Z) were also used to calculate the forward tilt (y-direction) and lateral tilt angles (x-direction) of the trunk.
Furthermore, angular velocities for shoulder internal rotation, elbow extension, and trunk rotation were calculated with the Visual3D software. Performance factors were calculated with the Vicon Nexus 1.8.1 software, tracking the reflective markers of the subject’s foot and the ball relative to the local coordinate system.
The throwing motion of a catcher throwing to second base was defined into five phases:
1) Ready position, 2) Catching and transfer, 3) Stride and arm cock, 4) Arm acceleration, and 5) Ball release phases. Joint kinematic and performance analysis initiated the moment the ball entered the glove of the catcher in the second phase. In this phase, pop time performance data recording began. As the catcher continued through the throwing motion into the stride and arm cock, kinematic data for maximum shoulder external rotation angle, shoulder extension, shoulder abduction, elbow flexion, and trunk lateral tilt angles were analyzed. As the arm progressed through the acceleration phase, maximum trunk extension angles, shoulder internal rotation, elbow extension, and trunk rotation velocities examined. The last phase investigated the shoulder internal rotation, elbow extension, and trunk forward tilting angles when the ball was released.
The instant the baseball left the fingers of the catcher’s throwing hand, the pop time’s time recording ceased. Ball velocity was calculated as soon as the ball was released. The total elapsed time for the throw to second base was calculated with the addition of pop time and the time required for the ball to travel 38.795 meters to second base.
Figure 3-6. Throwing phases.
Table 3.2
Figure 3-7. Maximum shoulder external rotation.
Joint Kinematics Analysis Parameters
Shoulder Max Extension Elbow Extension Velocity Shoulder Max Abduction Trunk Forward Tilt Shoulder Max External Rotation Trunk Lateral Tilt [Left]
Shoulder Max Internal Rotation Trunk Extension
Elbow Max Flexion Trunk Rotation Velocity
Elbow Max Extension Shoulder Internal Rotation Velocity