You've seen them. Every single person in the gym stands between the cable towers, crosses those metal handles, and starts flailing their arms like they’re trying to take flight. Most of them are doing it wrong. Honestly, if you’re just pulling weight from point A to point B without feeling that specific, deep burn in the back of your shoulder, you’re basically just wasting your time and wearing out your rotator cuffs for nothing.
The rear delt is a stubborn little muscle. It’s tiny. Because it’s so small, the big players like the traps and the lats love to take over the movement. Rear delt flys with cable are arguably the best way to isolate this area, but only if you understand the physics of the tension. Unlike dumbbells, where the resistance disappears at the bottom of the rep, cables keep the muscle screaming the entire time. That constant tension is the secret sauce for that "3D" shoulder look.
Most people treat this like a back exercise. It isn't. If your shoulder blades are pinching together aggressively, you've already lost. You’re hitting your rhomboids now.
Stop Pulling With Your Hands
Here is the thing about rear delt flys with cable: your hands are just hooks. If you grip the handles too hard, your forearms and biceps start to chip in. I actually prefer grabbing the rubber balls on the ends of the cables or using a suicide grip. It shifts the focus. You want to think about pushing your elbows out to the side walls, not pulling them back behind you.
Think of your arm as a long lever. The further away from your body you can keep that lever, the harder the rear deltoid has to work to move the weight. If you start bending your elbows significantly, you're turning it into a row. Rows are great for mass, sure, but they won't give you that specific posterior delt "pop" that separates the shoulder from the tricep.
The Height of the Pulley Matters
Where do you set the cable? Most guys set it at eye level. That’s fine, but it’s not always optimal.
Try setting the pulleys slightly above your head. By pulling at a slight downward angle—maybe 15 to 30 degrees—you align the cable's path perfectly with the fiber orientation of the posterior deltoid. Dr. Mike Israetel from Renaissance Periodization talks about this a lot; it’s about "line of pull." If the cable doesn't line up with the muscle fibers, another muscle will pick up the slack. Usually, that’s the upper traps. And let's be real, your traps are probably already doing too much work.
Common Mistakes That Kill Your Gains
- The Ego Lift. This is the biggest one. You don't need the whole stack. If you have to swing your torso to get the weight moving, the rear delt has left the building.
- The Scapular Retraction. As mentioned, stop squeezing your shoulder blades. You actually want your shoulder blades to stay relatively "pinned" or even slightly protracted (pushed forward) to keep the tension on the delt.
- The Short Rep. People tend to stop when their hands are in line with their chest. Go further. Stretch the muscle at the start by letting the cables cross over each other significantly.
Actually, let's talk about that crossover.
When you start the rep, your arms should be crossed in front of you. This puts the rear delt in a fully lengthened position. Muscles grow best when they are challenged in that stretched state. If you start with your hands already wide, you’re missing out on the most productive 30% of the movement.
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Cable vs. Dumbbell: The Reality
Dumbbells are great for a lot of things. Bench press? Yes. Curls? Obviously. But for rear delts? They're kinda mid. When you do a bent-over dumbbell fly, there is zero tension at the bottom. Gravity is pulling the weight straight down toward the floor while your muscle wants to pull it out to the side. You only get real tension at the very top of the move.
Rear delt flys with cable fix this. Because the weight stack is being pulled by a pulley, the resistance is horizontal. It's pulling your arms across your body, meaning the rear delt is under load from the second you start the move until the second you finish. It’s a more efficient way to train.
How to Program This Into Your Split
You shouldn't lead with this. It’s an isolation move. Save it for the end of your "Pull" day or your shoulder workout.
Since the rear delt is mostly slow-twitch fibers, it responds incredibly well to higher volume. We’re talking 12 to 20 reps. If you can only do 6 reps, the weight is too heavy and your form is likely trash. Focus on the mind-muscle connection. Close your eyes if you have to. Feel the blood rushing into that small pocket on the back of your shoulder.
I've found that doing "partials" at the end of a set—where you just do the first half of the rep from the stretched position—absolutely torches the muscle. It’s a technique used by pro bodybuilders like the late John Meadows to really push past a plateau.
Variations to Try
- Single Arm Version: Stand sideways to a single cable stack. This allows for a massive range of motion and lets you focus entirely on one side at a time. It’s great if you have an imbalance.
- Lying Cable Rear Delt Flys: Lay on a bench in the middle of the cable crossover. This eliminates all momentum. You can't cheat if your back is glued to a bench.
- The "W" Fly: Instead of keeping arms straight, keep a slight bend and pull back so your arms form a W shape. This hits a bit more of the lateral delt as well.
Anatomy of the Rear Deltoid
The posterior deltoid originates on the spine of the scapula. It inserts on the humerus (your upper arm bone). Its main jobs are transverse abduction, extension, and external rotation.
Basically, it moves your arm back and rotates it outward. If you want to maximize the "squeeze" at the end of a cable fly, try rotating your hands so your pinkies are pointing up and back. This slight external rotation can help cramp the muscle at the peak of the contraction. It hurts. In a good way.
Actionable Steps for Your Next Session
To get the most out of your training, don't just mindlessly pull. Follow this specific sequence to recalibrate your form.
- Set the pulleys high: Position them just above head height and remove the handles. Grip the actual cable ends to keep your wrists neutral and reduce forearm involvement.
- The "Cross-Body" Start: Reach across your body to grab the left cable with your right hand and the right cable with your left hand. Your arms should be completely crossed in front of your face.
- Maintain a Soft Elbow: Don't lock your joints, but don't turn it into a press. Keep a 10-degree bend throughout the entire arc.
- Lead with the Elbows: Focus on driving your elbows out toward the walls. Stop once your arms are in line with your torso; pulling further back just uses your mid-back muscles.
- Tempo Control: Take two seconds to pull the weight out, hold the squeeze for a split second, and take three full seconds to return to the starting position.
- High Volume: Aim for 3 sets of 15-20 reps. If you lose the "burn" and start feeling it in your neck, drop the weight immediately.
Consistently hitting the rear delts twice a week with this level of intention will do more for your physique than a year of sloppy heavy rowing. The cable provides the tension; you just have to provide the discipline to stay in the right lane.