Shoulder anatomy

Rear-delt anatomy and training.

The rear delt is the posterior region of the deltoid. It contributes to shoulder extension, horizontal abduction, and external rotation while sharing work with the upper back and rotator cuff.

Published and last reviewed September 14, 2026 · 7-minute read

Anatomical regionPosterior deltoid

Main jointShoulder

Main patternsExtension and abduction

Training contextReverse flies plus rows

Short anatomy: the posterior deltoid begins along the spine of the scapula and attaches to the humerus with the other deltoid regions. It helps move the upper arm backward and away from the chest, but it does not retract the shoulder blade by itself.

Parts and roles

Posterior region

Its fibers run from the scapular spine toward the humerus and contribute to extension, horizontal abduction, and external rotation.

Scapular muscles

Trapezius and rhomboid activity can accompany rear-delt exercises by moving or stabilizing the scapula.

Rotator cuff

Several cuff muscles stabilize or rotate the shoulder during reverse flies and rows. They are not parts of the deltoid.

Exercise map

Reverse pec deckA supported horizontal-abduction task that reduces the need to hold the torso position.

Cable reverse fliesCable height, arm path, and body position change the direction of resistance.

Dumbbell reverse fliesChest-supported and hip-hinged versions create similar movement goals with different stability demands.

RowsElbows-out rows can involve the posterior deltoid alongside scapular retractors, lats, and elbow flexors.

What activity studies add

A study of 19 resistance-trained men found that a neutral hand position during reverse flyes increased measured posterior-deltoid and infraspinatus activity compared with a pronated position. Another study of 12 trained men measured higher posterior-deltoid activity during the reverse pec deck than in the tested seated row and inclined lat pulldown.

Evidence boundary

These were small acute EMG studies, not long-term hypertrophy trials. They describe activity in specific protocols and do not establish that one grip, machine, or movement will produce the most rear-delt growth for every person.

Weekly sets and recovery

Track reverse flies as direct work and rows as supporting work whose contribution depends on arm path and execution. Record load, repetitions, range, and optional RIR so changes remain comparable. Use the weekly-sets guide for adjustment principles and the recovery library for general session context.

Frequently asked questions

What is the rear delt?

The rear delt is the posterior or spinal region of the deltoid muscle. It begins along the spine of the scapula and joins the anterior and lateral regions at the deltoid attachment on the humerus.

What movements train the rear delts?

The posterior deltoid contributes to shoulder extension, horizontal abduction, and external rotation. Reverse flies create direct horizontal-abduction work, while several rowing patterns provide supporting work.

Are reverse flies better than rows for rear delts?

Small acute EMG studies have measured greater posterior-deltoid activity in reverse-fly or reverse-pec-deck conditions than in some tested rows. That does not prove greater long-term growth or universal superiority.

How many weekly sets do rear delts need?

There is no universal rear-delt set target. Track direct reverse-fly work and supporting rows separately, then adjust using performance, recovery, execution, and the rest of the program.

Sources

Deltoid anatomy and function.

NCBI Bookshelf, StatPearls. Updated 2023.

Hand position during the reverse fly.

Journal of Strength and Conditioning Research, 2013. PMID: 23302754.

Posterior-deltoid activity across three pulling exercises.

Journal of Strength and Conditioning Research, 2014. PMID: 24947920.

Explore other muscles

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Separate direct rear-delt work from shared pulling.

Forma connects exercises, muscle roles, load, repetitions, optional RIR, weekly volume, and estimated recovery without exposing its proprietary mappings.

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