Pec Deck Fly Machine

The pec deck fly machine isolates the pectorals by moving the arms together in front of the body along a fixed path. That path is the whole reason the machine exists: with the back against a pad and the arms guided, the shoulders and triceps cannot take over the way they do in a press, and the chest is left to do the work alone. It is one of the easiest chest exercises to perform correctly, which makes it valuable at the end of a session when free-weight technique starts to deteriorate and you still want quality volume. Setting the seat so the handles sit level with your shoulders is what keeps the movement in a safe arc. Do not chase range by letting the arms travel far behind the body, since the stretch there is taken by the shoulder joint rather than the muscle.