Back — upper back and traps

#Function

The trapezius runs from the base of the skull to the middle of the back and has three functionally distinct regions. Upper traps elevate the scapula (shrugging). Middle traps retract the scapula (pulling the shoulder blades together). Lower traps depress and rotate the scapula — the least-trained region in most programs, and the one most responsible for healthy overhead shoulder mechanics.

Rhomboids, underneath the mid traps, also retract the scapula and work closely alongside it.

The rear (posterior) deltoid belongs functionally with this group rather than with the rest of the shoulder: it extends and horizontally abducts the shoulder — pulling a raised arm back and out.

#The length problem, and how it's different from every other lesson so far

Unlike the lats, the quads, or the hamstrings, the upper-back muscles and rear delt have almost no meaningfully long stretched position to train through. Scapular retraction and horizontal shoulder abduction simply do not have a large range where passive tension builds the way it does at a hip or a shoulder moving through full flexion-to-extension.

This means the stretch-mediated hypertrophy argument that drives exercise selection everywhere else in this course does not apply as strongly here. What matters more for this muscle group is constant tension across the available range — which is why cable and machine work (face pulls, reverse pec-deck, cable seated rows) generally outperforms free-weight equivalents here specifically, rather than being a lesser substitute.

#Exercise selection

Source tier: the functional regions of trapezius are established anatomy. The stretch-versus-constant-tension distinction follows from the general length-tension literature applied honestly to a muscle group where the premise (a long, trainable stretched position) does not hold as strongly as it does elsewhere.