According to AZ Central, there are three primary muscles that a decline bench press works. These muscles include: the pectorals, triceps and deltoids. The pectorals are the muscles located in the chest area; the triceps the muscles on the back of the upper arm; and, the deltoids are the muscles located on the upper arm and shoulder.
As Pop Workouts explains, the two primary exercise methods for the decline bench press are the use of barbells and dumbbells.
When working out with barbells, Pop Workout recommends keeping the hands a little more than shoulder-length apart on the bar in order to create the most effective pectoral workout. Lower the barbell to a spot about an inch from the chest, and slowly lift the weights back up until the arms are in an extended position. Repeat for a safe amount of repetitions, and remember to exhale during upward movements and inhale on downward motions. A spotter is also recommended in order to prevent injuries.
When dumbbells are used, the workout method is slightly different. With a dumbbell in each hand, lower the weights, one to each side of the body. Once a slight stretch is felt, raise both weights back to the starting position: Both weights meet, on outstretched arms, above the face.