Biomechanics of Throwing

Joints involved are

PhalangesAny break down in any of this structures effects the throwing mechanism

While the baseball pitch is one continuous, fluid motion, it can be broken down into 4 distinct phases.

Wind up Phase (0.5 – 1.0sec)

It is a initial phase that puts the thrower in a good starting position.

KINEMATICS

Lead leg – concentric contraction hip flexors ( rectus femoris, iliopsoas, sartorius)
Stance leg – eccentric contraction of quads
Shoulder – partially flexed and abducted (deltoid, supraspinatus, pec major)
Elbow – flexion 45deg (biceps, brachioradialis)

KINETIC

Wind up and stride position the body to optimally generate the forces and power required to achieve top velocity The pitcher keeps COG over the back of leg allowed to generate max momentum once forward motion is initiated.

EARLY COCKING (0.50-0.75SEC)

Begin at the end of the wind up phase when the lead leg begins to fall and move towards the target.

KINEMATICS

HIP – eccentric contraction of hip flexors at lead leg, concentric contraction from the stance leg hip abductor helps to lengthen the stride.

Once the lead leg touched the ground and moves forward lead hip will begins to rotate externally (sartorius, 6 external rotators) stance hip extends due to concentric contraction of hip extensors) gluts mx and hams.

TRUNK – tilted sideways away from the target, stride length depends upon the type of throw.
KNEE – lead knee is flexed approximately 45- 55 deg with foot contact.
LEAD FOOT – placed directly in front of rear foot towards the direction of throw.
SHOULDER – B/L abduct, ER, horizontal abduction owing to concentric muscle action.
THROWING ARM – positioned slightly behind the trunk (horizontal abduction)(deltoid, Latissimus dorsi, infraspinatus, teres minor, trapezius and rhomboids)
ELBOW- 80-100deg flexion
FOREARM – rotated up approaching vertical position.
FINGERS – Extension
WRIST- Flexion.

KINETICS

Functions to increase distance over which linear and angular trunk motions occur allowing max energy production to transfer to UL. It initiate pelvic rotations and forward tilt followed by upper torso rotation Pelvis achieves maximum rotation velocity of 400- 700 deg per second at this phase.

LATE COCKING (0.10- 0.15SEC)

Begins at lead foot contact and ends at maximum shoulder ER.

KINEMATICS

Upper body is rotated to face the target. Quads of lead leg contracts eccentrically to decelerates knee flexion Ankle – stance leg plantar flexed and leaves the contact this motion occurs when pelvic rotation just after foot contact

Pelvis - continues the transverse motion , hip internally rotated occurs approximately 0.03-0.05 sec after baseball pitching max rotation 700 deg / sec
Upper trunk rotates in reverse direction to the rotation of the pelvis.
Upper torso angular velocity is maximum during this phase-900-1300deg/sec is achieved (Abdominals & oblique muscles is placed on stretch during trunk hyperextension).
Shoulder-This leads to maximum shoulder horizontal adduction velocity relative to the trunk is approximately 500-600 degrees/sec. (Pectoralis major deltoids)horizontal adductors initially contracts eccentrically then isometrically to stabilize to allow the arm to move with the trunk to provide dynamic horizontal adduction at the shoulder.

Shoulder girdle muscles (levator scapulae, s.anterior, trapezius ,rhomboids & pec minor) work. Serratus anterior is more active to provide both stabilization & protraction to the scapula. All muscles stabilize the scapula & provides position of the glenoid for the subsequent action of the humeral head. Elbow – 90 deg about 30ms before maximum shoulder external rotation ,triceps contract eccentrically then isometrically in resisting centripital elbow flexion then triceps contract concentrically to aid in elbow extension.

KINETICS

Pelvis reaches its maximum rotation & the upper torso continues to rotate & tilt forward and backward and laterally. Maximum shoulder internal rotation torque occurs just before maximum shoulder external rotation. at the end of this phase max valgus torque is experienced at elbow flexors and pronators muscles generates a counter varus torque. Increased amount of shoulder external rotation help to allow the accelerating forces to act over the longest distance , allowing greater pre stretch & elastic energy transfer to the ball during acceleration. The biceps muscle reaches peak activity as it flexes the elbow, limits anterior translation and provides a compressive force on the humeral head. Acceleration phase(0.03-0.05sec) Trunk flexes forward to neutral position from extended position. This is a very rapid phase.

KINEMATICS

Elbow – Extension begins prior to IR allowing to reduce rotational inertia therefore allowing greater velocity in pitching. Trunk- flexion from vertical position (25-40deg) Throwing shoulder- abduction 80-100deg throughout the phase( rotator cuff and scapular muscles demonstrate high activity to control humeral head and scapular stabilization) Ball release – elbow is fully extended and slightly anterior at release elbow flexed 20-30deg, horizontal adduction 5-20deg. Hand- hyperextension to neutral wrist position at ball release(wrist flexors and pronator teres are active at this phase)

KINETICS

The trunk continues to rotate and tilt to tranfer potential energy into UL

Scapula protracts to maintain a stable base as the humerus undergoes horizontal adduction to violent IR.
A rapid maximum IR and trunk tilt to release ball increase ball velocity.
Elbow extension results from combination of the centrifugal force by rotating torso and concentric contraction of the triceps. Followed by shoulder IR.
Concentric contraction of rectus femoris contributes to lead leg hip flexion and knee extension, providing a stable front side help to create increased angular moment of trunk.

DECELERATION (0.03-0.05)

From ball release to max IR trunk continues to flexion

KINEMATICS

Lead knee and throwing elbow extends
Pronation due to activation of pronator teres
Upward reaction of flexing trunk and hip
Biceps and supinator are eccentrically loaded
Elbow- extension terminate at 15-25deeg(triceps)
Shoulder - posterior muscles stops the shoulder distraction (infraspinatus, lattisimus dorsi, and post deltoid)
Wrist and fingers- flexors have very high eccentric activity.

KINETICS

It is the most violent phase of throwing cycle resulting in greatest amount of joint loading encountered during throwing. Excessive posterior (400n) and inferior shear force (300n) occurs as do elevate compressive force (>1000n) and adduction torques.