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Biomechanical
Principles to be Investigated
The linkage between the axial and appendicular skeletons during execution
of upper extremity movement patterns
Purpose
The
two vital functions of the shoulder girdle are to (a) improve ROM of the
upper extremity and (b) to create a stable platform from which the gleno-humeral
joint is capable of performing both cardinal plane and diagonal plane
movement patterns.
Injury to either the sterno-clavicular (SC) joint or to the
acromio-clavicular (AC) joint will result in severely restricted gleno-humeral
(GH) joint motion.
Why? This lab will investigate normal scapulo-humeral rhythm during
execution of a chin-up and a wall push-up.
Rationale
Normal
scapulo-humeral rhythm is defined as a 2:1 ratio of humeral to scapular
motion.
The first 60°
of humeral motion in either the sagittal or frontal planes is typically
independent of any scapular motion.
The remaining 120°
of humeral motion(s) is typically accompanied by complimentary scapular
motions.
For example, forward-upward motion of the humerus that reaches out
in front of the face is accompanied by scapular elevation, upward
rotation, protraction and upward-lateral tilt.
Whereas, downward-backward motion of the humerus that reaches
behind the body is accompanied by scapular depression, downward rotation,
retraction and downward-medial tilt.
Physical educators, coaches, sports medicine specialists, etc. must
emphasize the need for balanced strength and conditioning programs.
All to often, individual or team strength training programs
over-emphasize anterior chest musculature and scapular elevators, upward
rotators and protractors.
References
Norkin,
C.C. and Levangie, P.K. (1992). Joint Structure and Function (2nd
ed.). Philadelphia: F.A. Davis Company.
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