Reverse fly The reverse fly / pec dec machine is a great exercise to target the posterior deltoid (back of the shoulder). Here are some tips to performing the exercise: Hand position - set-up at or slightly above shoulder height. Not too high, not too low (determined by the position of the seat and body). - starting slightly high and ending subtly low can help reduce upper trap activation. - throwing your hands back as far as possible (indicated by the red line top left) can cause the rhomboids