I have discussed chest development in a post last year that I need to re-post again eventually. Realistically all you need to develop your chest is an incline press, flat press, & fly variation. No need to over do it. On another note, let’s single out chest fly’s & talk about why they can be beneficial for hypertrophy. 

First things first, I would like to mention that selectorized machinery & cables should come first when performing fly’s. This is SPECIFICALLY when aiming for concentrated tension or macro-musculature activation. I would not recommend completely axing out free weight fly variations from your regimen though.

Why are cable chest fly’s phenomenal to integrate within your training program?

• Unlike dumbbells, cables provide tension throughout the entire range of motion, even at the top where dumbbells tend to lose resistance. This continuous load helps increase fiber engagement. 

You can hit different parts of the pectorals by adjusting the height of the cables:

• High-to-low: Lower chest emphasis
• Mid-level: Middle chest focus
• Low-to-high: Upper chest activation

Studies are limited, but expert insight has noted the adjusting of cable angles can help engage/favorite the area you are aiming the stimulate.

One of the major reasons that plays a key role in favoring cable or machine fly variations for chest growth is due to the fact that they are safely loadable. Increase load in order to maximize mechanical tension safely. Dumbbells or other free weight modalities are a bit more difficult to overload safely. 

Read this post on mechanical tension to understand why it the primary driver for hypertropy: https://www.cptlij.com/blog?id=67c9164f15cd4e7a11afb4ba

So where is the research? We need more clinical trials & studies on this.

Electromyography (EMG) studies have shown that cable crossovers elicit high activation of the pectoralis major, comparable to the barbell bench press. One study reported that bent-forward cable crossovers achieved 93% of the muscle activation seen in the barbell bench press, which was set as the reference at 100% .

https://www.johnnyhazell.com/post/best-pectoral-chest-muscle-exercises-backed-by-sciencd?utm_

EMG studies have indicated that the pec deck machine fly achieves muscle activation levels nearly equivalent to the barbell bench press. One study found that the pec deck fly elicited 98% of the muscle activation compared to the barbell bench press . https://www.johnnyhazell.com/post/best-pectoral-chest-muscle-exercises-backed-by-sciencd?utm_

Dumbell flyes vs. bench press study in trained males: https://pubmed.ncbi.nlm.nih.gov/33239937/