How to Use a Chest Fly Machine: Techniques, Benefits, and Variations

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Also Known As Pec Fly, Machine Fly, Pec Deck, Butterfly

Equipment Needed: Chest fly machine

The chest fly 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 other variations offer the benefit of training other muscles that help to stabilize the body—such as the abdominal muscles and the back.

But if you are a beginner (or even if you have more experience) the “pec deck,” as it is commonly called, is a great way to target the chest muscles without the worry of having to balance or stabilize on a bench, a ball, or simply standing upright. It can also be a smart machine to use if you have a lower-body injury and need to avoid standing.


The chest fly machine targets 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. The chest fly machine primarily benefits the pectoralis major—the larger of the two muscles.

Your pectoralis major is a fan-shaped muscle that is responsible for movement at the shoulder joint, primarily adduction (when your arms move towards the midline of your body at the shoulder joint), shoulder flexion (movement of your arms away from your body), and for shoulder rotation.

You use your pectoralis major muscles for many activities of daily living. When you push a heavy door open or move a heavy object away from your body with your arms, you’re engaging the chest muscles. When you pick up a heavy bag of groceries or lift your child, you are also using your pecs. Lastly, you’ll feel your pectoral muscles engage to control the chest and ribcage when you take a deep breath.

The chest fly machine is particularly helpful for beginners when they are starting to train these important chest muscles. You are fully seated and supported by a back pad so it is easy to practice good posture and good form while you are using the machine. Additionally, the seated position helps you to put your full effort into the chest muscles.

Since it provides a seated and supported position, the chest fly machine provides an effective, safe method of strengthening the pectoral (chest) muscles for beginners because there is no added stability challenge.

Step-By-Step Instructions

The first step to using a chest fly machine is learning to set up 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 so that 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, the elbows and wrists should be in line with the shoulder (that is, not higher or lower than your shoulders). Your arms should also not be behind your body but rather in line with the front of your chest.

You may also need to adjust the arm levers if you have shorter or longer arms. Not all machines allow for this adjustment. When extended, you should have a slight bend at the elbows.

Next, you’ll need to choose a weight set. 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.

  1. Sit up tall. Relax the neck and shoulders. The feet should be flat on the floor.
  2. Grab the handles so that your palms are facing the front. (Note: some machines have a foot bar that you need to push in order to bring the handles forward enough so that you can grab them).
  3. Press the arms together in front of your chest with a slow, controlled movement. Keep a slight, soft bend in the elbows with wrists relaxed.
  4. Once the arms are fully “closed” in front of your chest, pause for one second.
  5. Slowly bring the arms back to the starting position, opening the chest but keeping posture strong and upright.

To begin, perform two sets of 7-10 repetitions. Take a short break between sets. As your fitness level improves, add 1-5 repetitions during each set. You can also add a third set.

Add more weight if you complete all of the repetitions without fatigue.


Common Mistakes

As you perform the chest fly machine exercise, you’ll want to maintain relaxed breathing. It can be tempting to take a deep breath in and hold it as you engage your chest muscles and bring your arms together. But this method of forced breathing (called a Valsalva maneuver) has been shown to increase heart rate and blood pressure and should be avoided.

It may also be tempting to press into your feet to steady the 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, lower the amount of weight you are lifting.

Lastly, some exercisers arch their backs during this exercise. This can cause injury to the lower back. Be sure that you maintain good posture during both the opening and closing phases of this exercise. Sit tall, with your back maintaining contact with the pad behind you.

Modifications and Variations

Machine Variations

Most chest fly machines require that you extend the arms (almost) fully to grab the handles. When you close the arms in front of you to perform the exercise, it should feel like you are hugging a beach ball.

However, there is another type of machine (generally older models) that have elbow pads instead of handles to grip. On these machines, you maintain a 90-degree angle at the elbow as you open and close the arms. Your arms maintain an L-shape throughout the movement. This type of machine might be best for anyone with a hand or wrist injury.

Up for a Challenge?

If you want to work your abdominals while you are using the chest press machine, trying using only one side of the machine at a time. That means you’ll have one arm that is working while the other armrests. However, in order to maintain good posture, your abdominal muscles—particularly the oblique muscles on the side of your body—will have to work hard.

Safety and Precautions

The best way to stay safe on the chest fly machine is to get to know the equipment before using it. Because the machine has different variations (and manufacturers) yours may have more than one adjustment that needs to be made in order for you to maintain good form.

Before adding weight, adjust the seat and do a few repetitions with no weight at all. Simple move through the mechanics of the exercise to make sure you feel comfortable.

Again, look for a foot press if the handgrips feel like they are behind your body. When you start the closing phase of the movement, the arms should be slightly in front of the chest. If they feel like they are behind your chest, look for 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 the chest (and to a lesser extent in the biceps and shoulders), you should not feel any sharp or intense pain in the shoulders or wrists. If you do, stop using the machine and ask for assistance.


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