The Pec Fly/Rear Delt Machine is often overlooked in the weight room because there are so many different ways to work the chest (pectoralis) muscles. For example, you can do a chest fly with dumbbells or by using cables. Some of these variations offer the benefit of training other muscles that help to stabilize the body—such as the abdominals and the back muscles.
The chest fly or “pec deck” is a great way for both beginners and those with experience to target the chest muscles without worrying about the balance required when using a bench, a ball, or when standing. It’s also a useful machine if you have a lower-body injury and need to avoid standing.
The fly machine is ideal for increasing chest strength and muscle mass by targeting the pectoralis muscles. You have two sets of pectoral muscles on each side of the front of your chest: the pectoralis major and the pectoralis minor. This exercise primarily benefits the pectoralis major—the larger of the two muscles that are responsible for movement at the shoulder joint.
You use these muscles for many day-to-day activities, such as pushing open a heavy door, picking up a heavy grocery bag, or lifting a child. The pectoralis muscles also control the chest and ribcage when you take a deep breath.
This exercise is particularly helpful if you are new to training these muscles. The chest fly is performed fully seated and supported by a back pad so it is easy to practice good posture and form while using the machine. Additionally, the seated position helps you put your full effort into the chest muscles.
Since you are seated while using the chest fly machine, this method of strengthening the chest muscles is safe, effective, and great for beginners.
The first step is to adjust the equipment. Almost all machines have a seat pad that lifts or lowers. This is the first adjustment you’ll want to make.
Move the seat pad height so that the handles are at chest height and when you sit down you can place your feet comfortably on the floor with the back pad supporting your spine. When you extend your arms out to the side to grab the handles, your elbows and wrists should be level with your shoulders (not higher or lower than your shoulders).
You may also need to adjust the arm levers if you have shorter or longer arms. Note that not all machines allow for this adjustment. When extended, your elbows should be slightly bent.
Next, you’ll need to choose a weight setting. When you first begin using the machine, start with a weight that feels slightly easy until you get comfortable with the movement. The complete movement is often described as opening and closing your arms like a butterfly.
- Sit up tall and relax your neck and shoulders. Your feet should be flat on the floor.
- Grab the handles so that your palms are facing forward. Note that some machines have a foot bar that you need to push in order to release the handles and bring them forward.
- Press your arms together in front of your chest with a slow, controlled movement. Keep a slight, soft bend in the elbows with wrists relaxed.
- Pause for one second once your arms are fully “closed” in front of your chest.
- Bring your arms slowly back to the starting position, opening your chest and keeping posture strong and upright.
Perform two sets of seven to 10 repetitions to start. Take a short break between sets. As your fitness level improves, add one to five repetitions to each set. You can also add a third set. Add more weight and repetitions if you complete all of the repetitions without fatigue. Your last set should be challenging but not so hard that you can’t complete it with proper form.
Below are some common mistakes to avoid.
Holding Your Breath
As you perform the chest fly machine exercise, it can be tempting to take a deep breath in and hold it as you engage your chest muscles and bring your arms together, a technique called bracing.
This method of forced breathing (also called a Valsalva maneuver) isn’t necessary for lighter weight exercises. It can be helpful as you increase weight and the movement becomes more difficult. However, to start with, it’s important to release your breath and reset with each repetition.
Breathe With Each Movement
Exhale as your arms bring the handles together in front of your chest and inhale as you return the handles back to the open position.
Using Your Legs
It may also be tempting to press into your feet to steady your body and give that closing movement more power. But remember, the purpose of this exercise is to train the chest muscles, not your legs. If you notice that you are using your legs to gain momentum, decrease the amount of weight you are lifting.
Arching Your Back
Some exercisers arch their backs during this exercise. This can cause injury to the lower back. Maintain good posture during both the opening and closing phases of this exercise by sitting tall with your back maintaining contact with the pad behind you.
Lift and lower the weight using slow, controlled movements. If you go too quickly, you will be using momentum rather than training your muscles.
Modifications and Variations
Customize this exercise as needed with the following options for modifications and variations.
Need a Modification?
Most machines require you to extend your arms (almost) completely to grab the handles. When you close your arms to perform the exercise, it should feel like you are hugging a beach ball.
However, there are other models of the machine that have elbow pads instead of handles. On these machines, your arms maintain a 90-degree angle or L-shape at your elbows as you open and close your arms. This type of machine may be useful for people with hand or wrist injuries.
Up for a Challenge?
If you want to work your abdominals, try using only one side of the fly machine at a time. That means you’ll have one arm that is working while the other arm rests. To maintain good posture, your abdominal muscles—particularly the oblique muscles on the side of your body—will have to work extra hard.
Safety and Precautions
The best way to stay safe is to become familiar with the equipment before using it. Since there are different machine variations and manufacturers, you may need to make more than one adjustment to maintain good form. Consult with a gym trainer if you need help adjusting a specific machine.
Look for a foot press if the handgrips feel like they are behind your body. When you start the closing phase of the movement, your arms should be slightly in front of your chest. If they feel like they are behind your chest, find the foot press or for another adjustment on the back of the machine to bring your arms forward.
While you should feel the effort in your chest (and to a lesser extent, in the biceps and shoulders), you shouldn’t feel any sharp or intense pain in your shoulders or wrists. If you do, stop using the machine and ask for assistance.