Download Faulty Throwing Biomechanics

Faulty Throwing Biomechanics
Razif Ali, WM Ng, M. Zubair, Khalid Elnour.
University Malaya, Kuala Lumpur, Malaysia
Background: The vulnerability to injury stages of throwing in over use injuries of
the shoulder and elbow are in the stages of arm cocking, arm acceleration and
arm deceleration.
Methods: The popular sports of baseball and softball are the cases in point and
as a reference for this presentation.
Results: A significant proportion of the velocity in throwing is attributed to 2
main factors: (1) the timing of the shoulder rotation and the elbow extension (2)
The trunk / shoulder cocking and distance.
In the release and deceleration phase, there are high joint loads in the shoulder
and the elbow. There is distraction of the shoulder and elbow. There are large
proximal muscular forces stabilizing the shoulder and elbow: in the shoulder 125
% of the bodyweight and in the elbow 100% of the body weight. If these muscles
are overused which later result in fatigue, can result in distal tendon
degeneration. There are high eccentric contractions controlling throwing motion.
The long head of the biceps contracts eccentrically to stabilize the shoulder in
the magnitude of 1000 N of compressive forces. If wrongly executed throws, this
poses high stresses giving rise to eg the SLAP lesion or labral tears. Distally the
biceps contracts to decelerate rapid elbow extension in a force as high as 60
Nm. Faulty postures as follows: the lead foot becomes too open, the lead foot
points outward, the shoulder rotation is too early or occurs too late and leading
the elbow in acceleration phase leads to growing enormous stresses in the
shoulder and the elbow.
Conclusion: The 2 main factors in injury prevention are as follows: (1)
avoidance of shoulder and elbow muscle fatigue ( avoiding excessive sports
practice and usage of rest intervals ). (2) Good throwing techniques which
maximizes throwing power but reduce inherent excessive joint loads.