Baraka_Guru

The chest can be a difficult area to work because it depends on compound movements and support from other muscles such as the shoulders and triceps. I actually recommend against machine "butterfly" (pec decs), as they typically put too much stress on your shoulder rotation, potentially dislocating it. You're better off using something more natural like the dumbbell fly, which would give you a better workout anyway. The movement is less restrictive and uses more synergy from your shoulders in a way that doesn't put them at risk.

Also try alternative movements such as piston dumbbell chest press, which forces you to unilaterally lift the weight on each side. Quite challenging if you haven't done it. Dumbbells in general give you a better workout because of the requirement to keep them balanced. Avoid machines if possible, though many people use them to avoid the spotter requirement of heavy free weights.

Try other things such as incline presses and dumbbell pullovers, which will hit movements in your pecs that they might not be accustomed to. That's where you will find some further growth.

How is that for starters?

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Knowing that death is certain and that the time of death is uncertain, what's the most important thing?
—Bhikkhuni Pema Chödrön

Humankind cannot bear very much reality.
—From "Burnt Norton," Four Quartets (1936), T. S. Eliot