My gym has two types of chest fly (= pectoral fly = butterfly) machines:

Type 1:

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Type 2:

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What are the pros/cons of using type 1 vs. type 2? E.g. injury prevention, effect on muscle growth, etc.

2 Answers 2


In my opinion, after using both of these machines as well as done dumbbell fly while supine on a bench, I prefer the free weights above either machine.

The hazard with machine 2 is easy to identify: it will tend to put a lot of strain on the elbow joints. Machine 1 does not suffer from this problem. But both machines have the potential to put excessive stress on the joints of the shoulders and arms, because they force the movement to occur along a predefined curve, rather than what is biomechanically natural to your body. What this means is that some people might use these machines for years and never have any issues, while others, no matter how they attempt to adjust the seat or arms, will find the motion painful or unnatural.

I would recommend using free weights instead, and start with a minimal amount of weight, concentrating on developing proper form and range of motion. This also has the benefit of activating stabilizing muscles. Then build up the weight, but never to an extent where exertion comes at the cost of precise form and complete control. With this type of exercise, the amount of weight isn't as important as the proper movement and muscle activation.

  • Thanks, interesting! Doesn't using free weights put more stress on the elbow joints than type 1? Commented Oct 21, 2016 at 2:49
  • 1
    @FranckDernoncourt In my experience--which again, is my own and I can't speak for others--no, because the idea with free weights is you only use as much weight as you can handle. If there's too much elbow stress your body will let you know immediately--you won't be able to do the exercise with proper form. And by developing the stabilizing muscles, over the long run, the free weights will be safer and encourage more proportional muscle development.
    – heropup
    Commented Oct 21, 2016 at 3:02
  • I'm a bit confused as to how machine 2 "will tend to put a lot of strain on the elbow joints". Can you explain why that is?
    – rrirower
    Commented Oct 21, 2016 at 16:35
  • @rrirower When I've tried that machine, I always find that to avoid feeling pain in my elbows, I have to bend my elbows rather than keep them relatively straight, as the photos show. I think this is because when I'm at the beginning of the movement, the initial resistance of the weight is too high and I am engaging muscles in my arms to overcome the load, rather than muscles in the chest. Yet, near the middle and end of the movement, the weight is too light, because the load is now being moved primarily by the pectoral contraction.
    – heropup
    Commented Oct 21, 2016 at 17:52
  • That sounds more like an adjustment issue with the machine rather than a flaw in the actual machine design.
    – rrirower
    Commented Oct 21, 2016 at 17:55

I'm going to slightly disagree with heropup's answer because I believe that the Pec Deck machine (type 1) and the Machine Fly (type 2) should not be discarded as training equipment since machine training does provide some advantages as well as disadvantages.

The two machines you show train different parts of the chest muscles. The Pec Deck provides a greater range of motion at the finish when the elbows come together. Compare that with the Machine Fly where the elbows are wider apart at the finish. This means that the Pec Deck is better for developing the inner chest. However, since the Machine Fly provides a greater overall ROM because of the alignment of the upper arms, the outer chest is targeted more effectively.

The design of the Pec Deck does not allow for the shoulders to assist in the exercise. This means better isolation work. While on the Machine Fly, the front deltoids can assist thus helping in building the outer chest.

The advantages of using these two machines are:

  • Gravity is not involved as it would be in a supine dumbbell fly.

  • Typically, no need for a spotter.

  • Less chance of injury because you can't go past parallel like you can in a supine fly potentially injuring the shoulders.

The disadvantages are:

  • Restricted movement – this may or may not be a disadvantage. It typically depends on the individual.
  • Typically used for isolation work so will not provide the same benefit as compound movements.

I'm a firm believer in using all available equipment to build a more complete physique. Machines do have a place in a training program, but, it's up to the individual to decide based on his/her goals what, if any, that place should be. I do not, however, suggest that they replace free weights. I believe they should be used to supplement a training program by providing resistance that is typically overlooked by those looking to build a more complete, balanced, and symmetrical physique.

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