Transcript Articular Cartilage Biomechanics and Osteoarthritis

STRIDE LENGTH COMPENSATIONS AND THEIR IMPACTS ON
BRACE-TRANSFER GROUND FORCES IN BASEBALL PITCHERS
Crotin RL1,2 and Ramsey DK1
1Department of Exercise and Nutrition Sciences, University at Buffalo, NY
2Baltimore Orioles, Baltimore, Maryland
Improper baseball throwing mechanics, repetitive stress, and
physical immaturity increase a pitchers’ vulnerability to orthopedic
injury. “Pitching-fatigue” is considered a primary mechanism for
throwing arm injuries and may impact lower body biomechanics and
power generation.
In order to maintain peak ball velocities, compensatory throwing
mechanics are adopted. The brace-transfer phase is initiated at stride
foot contact (SFC) and ends at maximal external shoulder rotation
(MER). Brace-transfer ground reaction forces have the potential to be
impacted by compensatory adaptations, possibly affecting the kinetic
chain.
We propose reduced stride length can affect brace-transfer forces
despite maintaining ball velocity. Consequently, in support of current
pitch count standards, the evaluation of ground reaction force profiles
can offer greater injury protection in monitoring “pitching fatigue” and
its association to stride length compensation.
METHODS - continued
RESULTS –
GAME-SIMULATED PITCHING VELOCITY
• Jugs Radar Gun Pro with LED Feedback Display (Jugs Sports)
recorded ball velocity for analysis of 3,040 pitches
HYPOTHESIZED STRIDE LENGTH COMPENSATION TO
MAINTAIN BALL VELOCITY
(REDUCED STRIDE = LOWER BODY EXERTION)
(INCREASED STRIDE = THROWING ARM EXERTION)
STRIDE LEG
To demonstrate the impact of stride length changes on bracetransfer ground reaction forces. Exertion can impact stride length
and affect typical bracing strategies in competitive baseball
pitchers. As a result of atypical bracing, the risk for throwing arm
injury may be exacerbated by stride length compensations.
BRACE-TRANSFER GROUND REACTION FORCES
• Ground reaction forces normalized to body mass and synched
with time normalized pitching trials for 80-game pitches.
• Stride foot contact (SFC) considered at 5%BW upon footstrike.
• Time normalized shoulder kinematics identified (MER).
OVERSTRIDE
UNDERSTRIDE
P value
GRFZ
0.20 ±0.142 N/kg
0.31 ±0.198 N/kg
P=0.056
GRFY
-0.011 ±0.142 N/kg
0.05 ±0.627 N/kg
P<0.001
IMPZ
70.8 ±0.857 Ns
66.2 ±0.857 Ns
P<0.001
 lower

EMG
i Ns
25.0
±0.857
20.0
±0.255
Ns
  higher EMG  lower EMGi  higher EMGi 
i  IC 
i

PKAM
P<0.001
FORCE/IMPULSE
OVERSTRIDE
UNDERSTRIDE
P value
GRFZ
0.95 ±0.384 N/kg
0.69 ±0.411 N/kg
P=0.056
GRFY
-0.57 ±0.245 N/kg
-0.34 ±0.198 N/kg
P=0.002
IMPZ
7.84 ±5.34 Ns
6.30 ±5.29 Ns
P=0.372
IMPY
-4.60 ±3.30 Ns
-3.11 ±0.267 Ns
P=0.123
Ground reaction forces; GRFZ (vertical), GRFY (anterior+/posterior- shear),
IMPZ (vertical impulse), IMPY (anterior+/posterior- impulse)
METHODS
PITCHING PROTOCOL
• Warm-up throws at desired stride length for normalizing stride
length.
• Cross-over design used to randomly assign subjects to ±25% of
their desired stride. This equated to an understride at 50%
body height and overstride at 75% body height for sim-games.
• Pitches thrown in a ratio of 3 fastballs to 1 change-up.
FORCE/IMPULSE
cocontractionIMPY
index 
PURPOSE
SUBJECTS
• 19 high level pitchers from high school and collegiate baseball
programs were recruited to throw two, 80-pitch games.
• Ball velocity, 3D kinematics, and ground reactions forces were
recorded throughout each inning (20 pitches thrown per
inning).
GROUND REACTION FORCE DATA
GAME-SIMULATED MOTION CAPTURE
• 8 camera VICON F20 (240 Hz), 2 Kistler force plates (960 Hz))
• Two highest velocity pitches in the first (pitches 1-20) and last
inning of simulated play (pitches 61-80) analyzed
• Joint angles & ground reaction profile derived using rigid body
analysis (Visual3D)
DRIVE LEG
BACKGROUND
SUMMARY and CONCLUSION
Stride length compensations maintained linear hand and ball
velocities despite impacting brace-transfer ground reaction forces.
RESULTS –
SIMULATED GAME VELOCITIES
Increased Stride
• Increased drive impulse (increased time and force application)
• Increased bracing ground reaction forces.
SUBJECT CHARACTERISTICS
Age: 18.74 ± 1.56 yrs
Height: 1.84 ± 0.05 m
Weight: 81.95 ± 8.10 kg
BMI: 24.35 ± 2.58 kg/m²
LINEAR HAND VELOCITY
FASTBALL VELOCITY
OVERSTRIDE:
20.58 ±1.56 m/s (46.04 mph)
OVERSTRIDE:
126.29 ±8.46 km/h (78.5 mph)
UNDERSTRIDE:
20.13 ±1.50 m/s (45.03 mph)
UNDERSTRIDE:
126.32 ±7.66 km/h (78.5 mph)
P= 0.367
Reduced Stride
• Reduced drive impulse (reduced time and force application)
• Reduced bracing ground reaction forces.
P= 0.984
BENEFITS
At present, pitch count measures are unable to delineate
discrete occurrences where stride length variations influence
ground reaction forces. Ground reaction force monitoring may be
an efficacious way to detect changes in exertion for competitive
pitchers. If unmonitored, injurious consequences can arise when
high effort pitches are thrown consistently with altered, or less then
optimal ground reaction force profiles.