THE ROLE OF THE LOWER EXTREMITIES & TRUNK IN PITCHING

Gregory Jue, PT

OBJECTIVES

• Understand the typical phases of pitching and the goals of each phase

• Identify the common faults in each phase that influence the outcome of that phase

• Understand the lower body/trunk biomechanics and LE muscle activity that influence each phase

• Recognize that deficits in lower extremity ROM, muscle strength, and balance impact proper pitching biomechanics

BIOMECHANICAL ANALYSIS

PHASES OF PITCHING

Six phases:

  Windup

  Stride

  Arm cocking

  Arm acceleration

  Arm deceleration

  Follow-through

EMG ACTIVITY OF PITCHING

• Pitching motion was divided into 4distinct phases:• Phase 1: initiation of pitch to

maximum knee kick height• Phase 2: maximum stride leg

knee height to stride foot contact• Phase 3: stride foot contact to ball

release• Phase 4: follow-through

  Vastus Medialis (VM), Biceps Femoris(BF), Rectus Femoris (RF), GluteusMaximus (GM), and Gastrocnemius(GAST)

Campbell et al. JSCR 2010.

WINDUP PHASE

• The objective of the windup phase is to put the pitcher in agood starting position.

• Begins when the pitcher initiates the first motion and endswhen the front knee reaches its maximum height

• The body winds up so that all segments of the body from thelegs to the arms are able to contribute to the ball’s propulsion

• Concentric contraction of the hip flexors promotes hip flexionof the stride leg, while the hip extensors, knee extensors, andknee flexors dynamically stabilize the trail leg to promote thebalance point

• Stride foot should move behind the stance leg to generatemomentum and the stride leg should come into at least 90° ofknee and hip flexion

WINDUP PHASE

• Length of time for this phase is variable

• Common faults:• Moving too quickly through the phase• Prevents 1st balance position

• Over-rotating the pelvis backwards• Requires more angular velocity

• Decreased hip flexion of the leading leg and a more flexed trailing leg • Decreased ability to store gravitational potential energy to be

used later

WINDUP PHASE – LE EMG

Trail Leg Stride Leg

Campbell et al. JSCR 2010

STRIDE PHASE

• Production of initial linear momentum of the body and is the initial factor in the generation and transfer of momentum up through the kinetic chain. • Begins as the stride leg begins its descent and ends with

stride foot contact.

• Pitcher strides his front leg towards the target. At the time of front foot contact:• the stride length should be 83+/-4% of body height • the lead knee should be flexed 45 +/_-9 degrees. • the pelvis should be 33+/-10 degrees open to the target• the shoulder line should be about 15 degrees closed.

STRIDE PHASE

  Generally lasts between 0.5 and 0.75 seconds.

  Common faults:  Opening hips too early/too late  Altered positioning and timing of the rotation of

the pelvis may affect the kinetics at the shoulder and elbow

  Pushing off rubber vs. “controlled fall”  Can lead to higher humeral IR torque and elbow

valgus stress  Missed stride direction  Should be towards target and slightly closed

STRIDE PHASE – LE EMG

Trail Leg Stride Leg

Campbell et al. JSCR 2010

ARM COCKING PHASE

• Builds the potential energy that is used for the next phase

• Begins at lead foot contact and ends at maximum shoulder

external rotation

• The pelvis and then upper trunk rotate to face the target

while the throwing arm cocks back.

• Lag between pelvis rotation and upper trunk rotation is

critical for generating energy from the trunk

• Stride leg either maintains its degree of hip flexion or

begins to extend

• Trail leg foot begins to lose contact with the pitching

rubber

ARM COCKING PHASE

• Lasts between 0.10 and 0.15 seconds.

• Common faults:• Improper timing of pelvis and upper trunk rotation• Low ball speed and/or excessive loads in the

shoulder and elbow. • Uncontrolled fall• Altered positioning and timing of the trunk, pelvis,

and/or lower extremities may affect shoulder and elbow kinetics

ARM ACCELERATION PHASE

• Transfer of potential energy into kinetic energy

• Begins at maximal external rotation of the throwingshoulder and ends at ball release.

• Stride leg continues to dynamically stabilize the hip,knee, and ankle as the center of mass of the bodybegins to move forward over the stride leg.

• At the time of ball release:• Front knee is flexed 35 +/-12 degrees.• Trail leg is completely off the ground for most

pitchers.• Trunk is tilted 36+/-7 degrees forward and 23+/-10

degrees to the side.

ARM ACCELERATION PHASE

• Lasts only a few hundredths of a second (0.03-0.04 seconds)

• Common faults:• Increased knee flexion at foot contact and

decreased knee extension• Associated with slower ball speeds

• Improper timing of pelvis and upper trunkrotation• Low ball speed and/or excessive loads in the

shoulder and elbow.• Uncontrolled fall• Altered positioning and timing of the trunk,

pelvis, and/or lower extremities may affectshoulder and elbow kinetics

ARM COCKING & ARM ACCELERATION PHASES – LE EMG

Trail Leg Stride Leg

Campbell et al. JSCR 2010

ARM DECELERATION PHASE

• Decelerates the rapidly moving humerus and scapula

• Begins at ball release and ends when the shoulder has reached its maximum internal rotation

• Lasts a few hundredths of a second.

• Common faults:• Abbreviated deceleration and follow-through

• May not be using his body to dissipate the energy produced in throwing

FOLLOW-THROUGH PHASE

• Continuation of decelerating the shoulder and the rest of the body

• Begins at maximum shoulder internal rotation and ends when the pitcher regains a balanced position.

• The trunk continues to tilt forward and the back leg steps forward.

• Common faults:• Abbreviated deceleration and follow-through • May not be using his body to dissipate the energy

produced in throwing

ARM DECELERATION & FOLLOW-THROUGH PHASES – LE EMG

Stride Leg

Campbell et al. JSCR 2010

KINEMATIC VARIABLES

KINEMATIC VARIABLES

• Foot Placement at SFC

• Stride Length

• Knee Flexion at SFC

• Trunk Forward Tilt

• Trunk Lateral Tilt

• Hip Rotation Mobility

• Pelvis/Trunk Angular Velocity and Timing

FOOT PLACEMENT AT SFC

• Stride foot should be closed at an angle of 15° ± 10° - Fleisig (1994)

• Open position – prematurely initiates the arm-cocking phase, which

results in the loss of kinetic energy:

• Places greater torque being generated at the shoulder, in order to

produce the desired ball velocity

• 2.1 N of increased anterior GHJ force per degree of being open

• Increases trail leg hip ER torque

• Closed position – pitcher is forced to pitch more across his body, which

limits the kinetic energy transfer to the arm

• Increases lead leg hip IR torque

• Posterior shoulder eccentric overload

Wilk et al. SMAR 2010

Fleisig

STRIDE LENGTH

• Average stride length to be ~87% of body height - Fleisig (1994)• This stride was directed toward the plate within 10cm in either

direction• 3.0 N of increased anterior GHJ force per cm open

• Increasing the stride length may increase in throwing velocity:• Reduces the duration spent in double support prior to the acceleration

phase

• Greater flexion of the hip and knee of the trailing leg at the balanceposition may reduce the excursion of sagittal-plane movement ofthe trailing leg’s hip.

Whiteley JSSM 2007, Crotin et al. HMS 2015, Kung et al. AJSM 2017

KNEE FLEXION AT SFC

• At the time of ball release, the front knee is flexed 35 +/-12 degrees.• Critical to allow force transfer up the kinetic chain• Altering knee flexion at ball release may impact pelvic, torso, and

shoulder rotational timing, which can translate into highershoulder and elbow torques

• The front knee is extending through ball release, which allows theathlete to stop the forward motion of his pelvis and transfer energyup his body to the ball.

• During Arm Acceleration, the rate of knee extension has beenshown to be associated with an increase in ball velocity - Matsuo etal. (2001)

Chalmers et al. SH 2017

FORWARD TRUNK TILT

• During the arm acceleration phase, the trunk is tilted 36+/-7 degrees forward

• Trunk forward tilt has been shown to correlate with fastball velocity - Stodden et al. (2005)• Variable trunk tilt may produce inconsistent ball velocity

• Variability in trunk tilt may also affect pitch location. • Change in trunk forward tilt at the time of ball release might

change the trajectory of the ball• Ball may cross the home plate at different heights

Whiteley JSSM 2007, Oyama et al. AJSM 2013, Fleisig et al. SB 2009

TRUNK LATERAL TILT

• Contralateral trunk tilt of 20-30° tends to create a shoulderabduction angle that minimizes the elbow varus torque• Early studies reported closer to 10° contralateral trunk tilt and

100° shoulder abduction

• Change in trunk lateral tilt might change the angle of the release• May affect the ball’s horizontal position as it crosses the plate.

• Greater contralateral trunk tilt (above 25°) resulted in increased ballvelocity (~3.3 mph)• Produced greater elbow proximal force, greater shoulder

proximal force, greater elbow varus moment, and greatershoulder internal rotation moment• Compensatory pattern due to weakness of the hip and abdominal

musculature

Whiteley JSSM 2007, Oyama et al. AJSM 2013

HIP ROTATION MOBILITY

• Optimal orientation of the pelvis at lead foot contact requiressufficient hip ROM:• Internal rotation ROM of the trail hip is necessary to prepare for

proper positioning of the lead leg• Insufficient internal rotation ROM may lead to throwing

across the body and place unnecessary stress on the shoulder

• Sufficient amount of external rotation ROM of the lead leg isrequired to position the lead foot• Excessive external rotation will result in decreased trunk

rotation and decreased energy production.

Laudner et al. AJSM 2010, Robb et al. AJSM 2010, Saito et al. OJSM 2014

TRUNK ROTATIONAL TIMING

• Improper trunk rotational timing correlates with higher peak elbow valgus load, higher shoulder proximal force, and shoulder external rotation angle

• Closed-shoulder position - “opening up too soon” • Increase hyperangulation of the shoulder• Hyperangulation – horizontal abduction of the humerus beyond

the plane of the scapula which can lead to injury in the throwing shoulder and elbow

• Desynchronization of trunk timing with stride and pelvic rotation may lead the peak of potential energy to pass through the shoulder and elbow • “flying open at the shoulders” or lacking “hip and shoulder

separation”Chalmers et al. SH 2017, Oliver et al. JSCR 2010

CONCLUSION

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