The Latissimus Dorsi; The Posterior Deltoid - CYBEX VR2 Owner's And Service Manual

The Latissimus Dorsi

• Extension - The latissimus dorsi is responsible
for extension as well as adduction of the shoul-
der joint. This machine is designed to resist
shoulder extension from the front. The lat is
also involved in internal rotation of the shoul-
der, however, this is a mechanically weak
motion and becomes the limiting factor in
strength when combined with other motions.
The teres major works alongside the upper
fibers of the lat in extension.
• Range of Motion - Row/extension begins with
the arm positioned forward (shoulder joint in
approximately 90 degrees of flexion) and ends
with the arm at the side in 0 degrees. Full con-
centric shortening of the lat can only occur
when the associated scapular motion is per-
formed with the shoulder motion. With motion
and resistance from the front, scapular
retraction is required. For the arm to return to the starting position, scapular motion is not
required. However, if protraction is allowed during the eccentric phase, then the scapula
must be reset in retraction at the beginning of the next repetition.
• Associated Muscles - The rhomboids and middle fibers of the trapezius are responsible for
scapular retraction. The posterior deltoid is an assistant mover for shoulder extension. The
long head of the triceps is also involved in shoulder extension, although change in its length
is limited when elbow flexion coincides with shoulder motion. The biceps, brachioradialis,
and brachialis are always involved in pulling movements as elbow flexion is required. The
degree of their individual involvement depends upon radioulnar joint position.

The Posterior Deltoid

• Horizontal Abduction - The posterior deltoid is responsible for horizontal abduction of the
shoulder joint. Due to the attachment of the rear deltoid on the scapula, the scapula must
remain stabilized during shoulder joint motion. If scapular movement occurs, the resistance
will move without change in the length of the rear delt, minimizing effectiveness. The teres
minor and infraspinatus are also prime movers for horizontal abduction.
• Range of Motion - Horizontal abduction is limited concentrically at approximately 10 - 20
degrees (posterior to the shoulder) and eccentrically at approximately 90 degrees of horizon-
tal adduction (arms to the front) when the scapula remains retracted. From the starting
position in front, the arms move outward then back at shoulder level as the concentric
action is performed.
Exercise
Page 3-42
CYBEX VR2 Owner's Manual
MUSCLES TRAINED