The Motion Analysis Corp. pitching analysis application creates measurements of the critical biomechanical parameters during left handed and right handed baseball pitching. It supplies a complete kinematic and kinetic report of the upper extremity as well as measurements about the player’s technique. The information can be used to indicate a potential for injury, compare the biomechanics among players, or show comparisons of the same player over time. This guide will step though the procedures to properly acquire the pitching trials and then operate PitchTrak.
What you need
Motion Analysis Corp. Motion Capture system 38 Retroreflective Markers and configured as shown below:
| MARKER | REQUIRED OR OPTIONAL | COMMENTS | |
|---|---|---|---|
| 1 | R.Acromion | required | End of the Clavicle (collar bone) – top of shoulder |
| 2 | R.Clavicle | optional | Placed at the middle of the clavicle, used for asymmetry |
| 3 | L.Acromion | required | End of the Clavicle – top of shoulder |
| 4 | Back Head | optional | rear/center of head |
| 5 | Top.Head | optional | Top/center of head |
| 6 | Front Head | optional | Front/center of head |
| 7 | L.Wrist.Rad | required | Styloid Process of the Radius. Wrist on thumbside. |
| 8 | L.Wrist.Uln | required | Styloid Process of the Ulna. Wrist on fingerside. |
| 9 | L.Epi.Lat | required | Lateral epicondyle of the humerus. Outside of elbow. |
| 10 | L.Epi.Med | required | Medial epicondyle of the humerus. Inside of elbow. |
| 11 | L.Hand or | required | Base of the 5th MCP joint. Left handed pitcher only |
| 11 | R.Hand | required | Base of the 5th MCP joint. Right handed pitcher only |
| 12 | L.Scap.Inf | required | Root of scapular spine. Bottom of scapula. //en.wikipedia.org/wiki/Spine_of_scapula |
| 13 | L.Scap.Med | required | Inferior angle of the scapula. Upper/Inside corner of the scapula. |
| 14 | R.Scap.Med | required | Inferior angle of the scapula |
| 15 | R.Scap.Inf | required | Root of scapular spine |
| 16 | R.Epi.Lat | required | Lateral epicondyle of the humerus //act.downstate.edu/courseware/haonline/figs/L06/060200.htm |
| 17 | R.Epi.Med | required | Medial epicondyle of the humerus |
| 18 | R.Wrist.Rad | required | Styloid Process of the Radius (Thumbside) |
| 19 | R.Wrist.Uln | required | Styloid Process of the ulna |
| 20 | R.ASIS | required | Over the right front of the hip |
| 21 | V.Sacral | required | Over the base of the spine, L5-S1 joint |
| 22 | L.ASIS | required | Over the left front of the hip |
| 23 | R.Thigh | optional | about 1/3 the distance from hip joint to knee joint |
| 24 | R.Knee | optional | on the Lateral Condyle |
| 25 | R.Knee.Med | optional | on the Medial Condyle |
| 26 | R.Shank | optional | about 1/3 the distance from knee joint to ankle joint |
| 27 | R.Ankle | optional | on the Lateral Malleolus |
| 28 | R.Ankle.Med | optional | on the Medial Malleolus |
| 29 | R.Heel | optional | Centered on the heel |
| 30 | R.Toe | optional | Over the base of the second toe |
| 31 | L.Thigh | optional | about 2/3 the distance from hip joint to knee joint |
| 32 | L.Knee | optional | on the Lateral Condyle |
| 33 | L.Knee.Med | optional | on the Medial Condyle |
| 34 | L.Shank | optional | about 2/3 the distance from knee joint to ankle joint |
| 35 | L.Ankle | optional | on the Lateral Malleolus |
| 36 | L.Ankle.Med | optional | on the Medial Malleolus |
| 37 | L.Heel | optional | Centered on the heel |
| 38 | L.Toe | optional | Over the base of the second toe |
Determining Your Marker Set
The full-body marker set combines a 7 segment upper body set (head, 2 upper arms, 2 lower arms, 2 shoulder girdles) with an 8 segment marker set for the lower body (trunk, pelvis, 2 thighs, 2 lower legs, 2 feet). Fifteen markers are required in order for PitchTrak to output any data. The optional markers determine whether certain kinematic parameters are calculated. For example, if markers are placed on the head, then head rotations will be calculated. Additionally, if markers are placed on the Left and Right Anterior Superior Iliac Spines (ASIS) and Sacral joint, then pelvic rotations will be calculated and trunk rotations are calculated relative to the pelvis. Otherwise, trunk rotations will be calculated relative to the global coordinate system. All six markers on the feet (#26-28,32-34) are needed to compute stride parameters. If any additional markers are used (e.g. more asymmetry markers), PitchTrak will simply ignore them for its calculations. Markers placed on the scapula are purely used to predict the location of the glenohumeral (GH) center during the pitch. Although scapular motion is compromised by skin motion, errors in regression have been found to be no less than those found with the GH center estimated with trunk based markers, particularly when the shoulder elevation is less than 120˚.
Angle Definitions
This section describes the plotting conventions used to define upper body movements. Sagittal and frontal plane movements are rotations of the long axis of the segment as observed down its medial-lateral and anterior-posterior axes, respectively. Transverse plane motion is the rotation about the long axis of the segment.
Head: Measured relative to the trunk.
Motions: sagittal plane: forward flexion (+) – ext (-) frontal plane: head tilt left (+) – right (-) transverse plane: left (+) – right (-) rotation.
Trunk: Measured relative to the pelvis (if markers on pelvis).
Motions: sagittal plane: forward flexion (+) – ext (-) frontal plane: trunk tilt left (+) – right (-) transverse plane: left (+) – right (-) rotation.
Shoulder: Measured relative to the shoulder girdle (ipsilateral trunk half segment).
Motions: plane of elevation: hor add (+) – hor abd (-) elevation: elevation (+) – depression (-) transverse plane: internal (+) – external (-) rotation.
Comments: The clinical rotations of shoulder flexion and abduction are described as shoulder elevation due to the ambiguity of these clinical descriptors.
Elbow: Measured relative to the humerus
Motions: sagittal plane: flexion (+) – extension (-) frontal plane: varus (+) – valgus (-).
PitchTrak Files
There are a number of files specific to this application that will be used by Cortex to help you set up, acquire and process your trials:
- PitchTrak.mars – holds the marker and segment information.
- PitchTrak.cal – holds the event information.
Data Collection Setup
Setup for data collection for PitchTrak with Cortex is done much the same as with any collection. There are some settings for calibration and data collection that will help ease the process. Learn about the recommended data collections settings in Data Collection Setup.
Trial Collection
You should already be familiar with how to collect 3D data using Cortex. However, PitchTrak requires some specific collection procedures to ensure correct calculations. Trial Collection describes the recommended procedures to collect your trials.
Running the PitchTrak Application
The PitchTrak software is simple to operate, and there are only a few fields to enter and several buttons to click. A video tutorial and some instructions for using the PitchTrak software are in Running the PitchTrak Application.
Output Definitions
The PitchTrak Report provides a series of biomechanical measures relevant to the pitching motion. Here is a brief explanation of each of their meanings.
| MEASURE | DESCRIPTION | |
|---|---|---|
| 1 | Stride Length (% body height) | Distance between left and right feet at front-foot contact in the direction from rubber to home plate |
| 2 | Shoulder Abduction at FC (deg) | Abduction angle of the throwing shoulder (GH joint) at front foot contact |
| 3 | Shoulder Horizontal Abduction at FC (deg) | Horizontal abduction angle of the throwing shoulder (GH joint) at front foot contact |
| 4 | Shoulder External Rotation at FC (deg) | External rotation angle of the throwing shoulder (GH joint) at front foot contact |
| 5 | Max Trunk Rotation (deg) | Peak trunk rotation angle (with respect to the pelvis) during the pitching cycle |
| 6 | Max Shoulder External Rotation (deg) | Peak shoulder external rotation angle during pitching cycle |
| 7 | Elbow Flexion at BR (deg) | Elbow flexion angle at ball release |
| 8 | Trunk Forward Flexion at BR (deg) | Trunk forward flexion angle at ball release |
| 9 | Max Shoulder Distraction Force (% body weight)1 | Peak reaction force directed along the longitudinal axis of the shoulder girdle coordinate system (parent reference frame) |
| 10 | Max Shoulder Abduction Torque (% bw-h) 1,2 | Peak moment about the anterior-posterior axis of the shoulder girdle coordinate system (proximal reference frame) |
| 11 | Max Shoulder Horizontal Abduction Torque (% bw-h) 1,2 | Peak moment about the superior-inferior axis of the shoulder girdle coordinate system (proximal reference frame) |
| 12 | Max Shoulder ER Torque (% bw-h) 1,2 | Peak moment about the longitudinal axis of the shoulder girdle coordinate system (proximal reference frame) |
| 13 | Max Elbow Flexion Torque (% bw-h) 1,2 | Peak moment about the medial-lateral axis of the humeral coordinate system (proximal reference frame) |
| 14 | Max Elbow Valgus Torque (% bw-h) 1,2 | Peak moment about the anterior-posterior axis of the humeral coordinate system (proximal reference frame) |
1All forces and net joint moments are resolved in the proximal segmental coordinate system.2Moments are expressed in external convention. bw = body weight; h = height.
References
References provides relevant articles and publications about pitching analysis.