CYBEX VR2 Owner's And Service Manual page 89

The Chest
• Horizontal Adduction While Externally Rotated -
The pectoralis major is primarily responsible for
horizontal adduction of the shoulder joint. The pec
is also involved in flexion and extension of the
shoulder joint, although the anterior deltoid and
latissimus dorsi muscles, respectively, are mechani-
cally more effective at performing these motions
respectively. The pec is also involved in internal
rotation of the shoulder, however, this is a mechan-
ically weak motion and becomes the limiting factor
in strength when combined with other shoulder
motions. Maintaining the shoulder in an externally
rotated position during the performance of horizon-
tal adduction allows strengthening of the muscle
from a slightly lengthened state when compared to
a neutrally rotated (chest press) position. It should
also be noted that this position will result in less
tension development within the muscle due to the length-tension ratio as well as limiting the
final amount of concentric shortening.
• Scapular Retraction - The position of full scapular retraction, when maintained, creates
the greatest possible force angles of the pectoralis major throughout the range of motion.
• Range of Motion - With scapular retraction maintained, horizontal adduction is limited to
approximately 90 degrees (humerus straight to the foot). While maintaining 90 degrees of
external rotation, horizontal abduction (achieved through the eccentric "lowering of the
weight" or return to the starting position) is limited by mechanical disadvantage at approxi-
mately 0 degrees (upper arm straight out from the shoulder) and, much more importantly, by
achieving the closed packed position for the shoulder at this point. Here the ligaments reach
their maximum length and if horizontally abducted further, while maintaining external rota-
tion, will under go undue stress.
• Associated Muscles - The anterior deltoid and caracobrachialis are also prime movers for
the motion of horizontal adduction. However, by maintaining motion in the horizontal plane,
scapular retraction, and limited horizontal abduction (limited stretch) the pectoralis major
will be emphasized over the anterior deltoid. Mechanical analysis indicates that the effec-
tiveness of the anterior deltoid in horizontal adduction may be slightly reduced in the
externally rotated position.
Exercise
Page 3-58
CYBEX VR2 Owner's Manual
MUSCLES TRAINED