The primary purpose was to investigate the influence of scapular dyskinesis (SD)
on pitching biomechanics and shoulder function in high school baseball pitchers.
The secondary purpose was to identify possible factors associated with shoulder
function in pitchers with SD. Thirty-eight pitchers were classified into the SD
group (n=26) or the non-SD group (n=12). They were evaluated
with the Kerlan-Jobe Orthopaedic Clinic shoulder and elbow (KJOC) scale and
clinical measurements of shoulder characteristics, and with measurements of
scapular kinematics, muscle activation, and ball speed during fastball pitching.
Compared to the controls, the pitchers with SD had less scapular external
rotation (difference=11.3 degrees, ES=0.92, p=0.012)
during overall pitching and less upper trapezius (UT) activation during the late
cocking (difference=7.1%, ES=0.79, p=0.019) and
acceleration phases (difference=12.5%, ES=0.75,
p=0.035). Higher UT activation during the late cocking phase was
significantly associated with higher KJOC scores (standardized
β=0.415, p=0.039). In conclusion, deficits in scapular
external rotation and decreased UT activation during pitching were found in
pitchers with SD. Higher UT activation may be important for shoulder function in
pitchers with SD.
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