How to Use the Rear Delt Fly Machine (Form and Benefits)

The rear delt fly machine is a staple in every gym. Fly machines are almost always built to support a pec fly and a delt fly. A machine-based rear delt fly, also known as a reverse pec fly, is an alternative to free weight lateral raise exercises with dumbbells, which can be limiting if you’re ready to increase your weight. 

The dumbbell rear delt fly is a great exercise, but heavier weights will severely limit your range of motion.

The fly machine is not a replacement for free weight deltoid exercises, but it does provide an excellent opportunity to engage the delts and pecs while utilizing the machine’s support to help you lift heavier loads.

Pec Deck

The rear delt fly machine/pec fly machine is commonly known as a “pec deck.” It may also be referred to as a seated lever fly. The pec deck isn’t just for pec exercises, however. Any pec dec can be adjusted to turn into a rear delt fly machine. Most of the time, the instructions will be found on the seated lever fly machine. This article will primarily discuss how to use this machine specifically for the rear delt fly.

Benefits of The Rear Delt Flyes

The rear delt fly is an effective and versatile upper back exercise that can be accomplished with dumbbells or a pec fly/delt fly machine. The rear delt fly with a fly machine specifically targets muscle groups in the upper back.

The rear delt fly effectively targets not only the rear deltoid, but also the traps, lats, and rhomboids as well. 

This exercise is commonly done with dumbbells, usually with an arched back, hinging at the hips. Using the fly machine gives you an advantage in that you can make your delt flyes into even more of an isolation exercise.

Using free weights is an excellent option for those who feel comfortable with performing a delt fly with good form or those who are training with high repetitions and light weights. 

If you want to increase the load without sacrificing your form, then the fly machine is going to be a hack that allows you to lift heavier while maintaining a substantial range of motion.

Range of motion is everything in the delt fly, especially when you cables and free weights. The fly machine gives you some flexibility in this area, and can even allow you to gain a benefit from partial range of motion exercises.

How to Use the Rear Delt Fly Machine

The rear delt fly machine can be intimidating to beginners, but it doesn’t have to be. When you walk up to a pec fly machine at a gym, it may or may not already be set for a rear delt fly. If not, don’t fret. You can adjust it. 

To adjust the rear delt fly machine specifically for the delt fly, make sure that it’s set to 0.  This is your delt setting. The handles should be directly behind the seat. Now that the machine is set from pec fly to rear delt fly, it’s time to perform the rear delt fly.

Here's how you perform the rear delt fly on a machine:

1. After adjusting the seat to 0 and making sure the handles are behind the seat, sit down on the seat with your stomach/chest touching the back of the seat. It should look like you’re sitting backward on the chair.
2. Make sure your seat is set so that your feet are flat on the floor. Sitting upright with good posture, your hands should be about shoulder height. If it isn’t, adjust the seat so that they are.
3. Pick a weight on the machine. Start low and work your way up. 50-150 lbs is common.
4. In the starting position, lean your torso against the seat but with an upright posture, grab the top part of the handles with a pronated grip (knuckles up).
5. Spread the levers apart, as far as you can, engaging and squeezing your back muscles.
6. Bring the levers back to the starting position slowly.
7. Repeat for 8-20 repetitions, depending on the load and training style.

This exercise should be felt primarily in the shoulders, specifically the posterior deltoids.

You should also feel this in your traps, lats, and rhomboids. Keep in mind that excessive use of the fly machine could cause an imbalance between the upper traps and lower traps.

Much of the benefit of a rear delt fly with dumbbells is that it effectively engages the lower traps when you hinge at the hips. There aren’t a lot of isolation exercises for the lower traps, so it is best not to consider the fly machine to be a complete replacement unless it is absolutely necessary for your situation.

A pec fly machine is a form of an upper body exercise hack. You will most likely be able to lift heavier weight with the fly machine than with dumbbells. If your range of motion is limited with the pec fly machine, you may want to consider reducing the weight.

If you insist on staying with a certain weight but are still having range of motion issues, then try doing partial reps.

To do a partial rep on the delt fly machine:

1. Do the first rep with a complete range of motion, but pause at the “top,” or apex of the lift.
2. Bring the levers back down slowly, but only come back down halfway.
3. It will be difficult to slow down and start another rep at the halfway point, but if you can do it, it’s a great way increase the resistance and still get a solid number of repetitions in.

Alternatives for the Rear Delt Fly Machine

The rear delt fly on the fly machine isn't the only effective upper back exercise. If accessibility to a fly machine is an issue with your gym, we've got you covered!

Whether you’re at home or you just can’t seem to find a fly machine that isn’t in use during the time that you need it, then there are plenty of alternative exercises to hit the back and shoulders.

Dumbbell Bent Over Raise

As mentioned earlier in the article, the rear delt fly with the fly machine is an alternative to the common dumbbell fly. Just because you learned how to properly use the rear delt fly machine doesn’t mean you need to forsake this classic shoulder muscle exercise. 

The rear delt fly can be done as a dumbbell bent-over raise, and it is a great exercise for everyone from beginners to bodybuilding experts. 

How to perform a bent-over raise with dumbbells:

1. Grab two lightweight dumbbells. 10-30 lbs is common. A full range of motion is necessary for this exercise, so make sure that the weights are light enough for you to do at least 10 solid reps.
2. In the starting position, with the two dumbbells in your hands, bend over, hinging at the hips. Bend your knees just slightly.
3. Holding the weights, extend your arms out with a slight bend at your elbows.
4. Rotate your arms so that your knuckles are pointed up and both sides of the dumbbell are parallel with the floor, and shoulder height. This is your up position. This is the top of the lift.
5. Bring the weights down slowly back down to your waist.
6. Bring your arms up and down, as if you were a large bird flapping your wings. Each repetition should have you going from to the side of your hips to the top of your shoulders.

Cable option:

If you have access to a cable machine, then the rear delt fly can be an insanely effective  time under tension exercise to help you get bigger, fast.

1. Set the weights low. The cable is going to make this exercise feel about 3x as heavy as dumbbells. 5-25 lbs is common.
2. Set the attachments to the cables. Consider taking the handless off. Handles will cause unnecessary tension on the wrists and mess with your form. Whenever you use a cable machine without handles or attachments, consider the risk and be careful not to pinch your fingers on the way back up.
3. Once your cables are set, in the starting position, grab the left cable with your right arm and grab the right cable with your left arm. This is the same as a cable crossover exercise.
4. Hunched over, hinging at the hips. Keep your spine straight and your shoulders rolled back. You want to avoid having a hunch at the top of your back.
5. With your elbows bent slightly, raise the cables up to shoulder height, flapping your arms like a bird does with its wings. Bring your arms back down to the waist, but don’t come all the way down to your sides. Keep tension on the cable throughout the exercise. Do not pull your elbows behind your back.
6. Repeat for 10-20 reps, depending on the weight of the load and your training phase. If you can’t complete at least 10 reps with a full range of motion, or without pulling your elbows behind your back, then you need to take the weight down.

Lateral Raises vs. Rear Delt Raises

The rear delt fly is going to look similar to a lateral raise, and they do have a lot of things in common, including which muscle groups they target. The lateral raise is a great deltoid isolation exercise, with some upper back benefits. So is the rear delt fly. 

The main difference in a lateral raise vs. a rear delt fly, is that, in the rear delt fly, your arms are going behind your back.

In a lateral raise, they’re just going up and down to shoulder height. The critical form difference between the two is that the rear delt fly involves bending your back and hinging at the hips.

In case you ever wondered why you sometimes see people hinging at the hips while doing a lateral raise at the gym, this is probably why. Bringing the weights behind your back targets the back even better. The lateral raise is more of a deltoid isolation exercise than the rear delt raise is, although both are generally considered isolation exercises.

The primary muscle group for both is the anterior, medial, and posterior deltoids. The rear delt fly just incorporates more synergist muscles from the back.

You can use any pec fly machine to turn it into a rear delt fly machine. This reverse fly exercise isolates the rear deltoids, or posterior deltoids, while incorporating the lats, traps, and rhomboids as muscle synergists.

The primary benefit of using the fly machine is to increase the resistance without sacrificing your form.

Cables and free weights also provide a great deltoid training modality, but these exercises are usually limited to, and best conducted with lighter weights.

If you have trouble with form during your shoulder exercises, there are several  shoulder stability exercises that can be done to help. Although it should not be relied upon solely to engage the shoulders and back, the fly machine is a handy tool to isolate the deltoids and simultaneously target the muscle in the upper back.

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