What Muscles Does the Flat Bench Press Exercise Work?

Chest

The chest is the primary muscle worked with bench press. The pectoralis muscle of the chest is a large, fan-like sheet of muscle that starts at the sternum in the middle of the rib cage as well as up at the collarbone. The muscle inserts into the are of the upper arm near the shoulder. Different areas of the chest are targeted depending on if you’re working incline, flat or decline bench press. Flat bench press concentrates work on the center of the chest muscle that originates from the sternum as opposed to the area originating from the collarbone.

Triceps

Though the chest gets all the attention in reference to bench press, the triceps are actually the prime movers that allow the exercise to happen. The triceps allow the arm to bend and straighten and are the warhorse of the exercise while the chest ends up the hero of the battle. The triceps assist quite a bit as you straighten your arms and push to return the bar away from the chest. It’s not unusual to take a close grip -- shoulder width or slightly narrower -- to use flat bench as an exercise to target the triceps alone.

Shoulders

As with the triceps, the shoulders -- primarily the front deltoids -- assist in moving the weight during bench press. The shoulders go through a much smaller range of movement during the exercise than the arms so the shoulders don’t engage to quite the same extent as the triceps. But the front deltoids are asked to provide a good push to assist the triceps and chest as the arms straighten. It’s important to make sure the barbell moves up and down at the level of your chest to target the work squarely on the chest on not stress the shoulders. There can be a tendency for the bar to dip toward the neck and head or away toward the waist on either the upward or downward path, which can tweak the shoulders.

Other Assistors

Though bench press focuses on developing the muscles of the chest, the whole body actually plays along in the exercise to a certain degree. Your core automatically engages the moment you un-rack the bar and are forced to steady and control the immediate instability of 45 pounds or more stretched out across the length of the barbell. Pushing to straighten your arms also uses the core and the upper provides some assistance during this phase to isolate the muscles of the chest. The legs come into play only to keep you steady. A little push through the heels can help move the weight as you straighten your arms again but the glutes should stay glued to the bench at all times. Make sure it’s your chest getting the workout and not your legs.