Eccentric and Concentric Motions in a Shoulder Press


The shoulder press is a fundamental exercise in bodybuilding and power lifting. It's widely used because it's highly effective for building muscle mass and increasing strength. The shoulder press involves two phases: concentric, or muscle shortening, and eccentric, or muscle lengthening. Learning which muscles are involved during each phase is crucial for maximizing your mind-muscle connection and performing the lifts as efficiently as possible. Focusing your mind on the correct muscles also helps to recruit more muscle fibers and increase the amount of weight you can lift.

Shoulder Press Basics

The shoulder press is most commonly performed using barbells and dumbbells. You can do the exercise in a standing or seated position. Grip a barbell or two dumbbells, holding the weight in front of your shoulders with your arms bent. Press the weight overhead by extending your elbows, and then return down to the starting position. For safety reasons, never do a shoulder press with the resistance behind the head to avoid injury to the rotator cuff of your shoulders.

Concentric Motions

During the upward phase of the shoulder press, your anterior deltoid, lateral deltoid and supraspinatus contract to produce shoulder abduction, or lateral movement of your arms. This is the main movement of the shoulder press. If you want to build your deltoids to your maximal potential, then it is crucial you focus your mind on these muscles during this phase to help better execute the movement and lessen the chances of injury. The secondary motions during this exercise are upward rotation of your shoulder blades, caused by the concentric contractions of your mid-trapezius and serratus anterior, and elbow extension, caused by the concentric contractions of your triceps and anconeus. You should also try to focus your mind on these muscles, but this may be difficult when first starting out. With practice, you will develop a better mind-muscle connection. Beginners should first focus on the primary movers before focusing on the assisting muscles.

Eccentric Motions

To return the barbell or dumbbells down to the starting position, you must eccentrically contract the aforementioned muscles. To adduct your shoulders, rotate your shoulder blades down and flex your elbows. The same muscles that perform the concentric contractions will also perform these eccentric contractions. Instead of shortening, now these muscles will lengthen. Just as you were focusing on these muscles during the upward phase, you must focus on the downward phase. Your muscles are in a more vulnerable position when being stretched, and you risk a muscular tear if you're not being careful. Focusing lessens your risk of injury.


The shoulder press, although highly effective, can be dangerous over time, depending on the shape of your acromion, a bony structure in your shoulder blades. In simple terms, if you have a hooked acromion bone, known as type 3 acromion, you have a high risk of developing shoulder impingement. This is a syndrome that involves inflammation of your biceps long head tendon, supraspinatus tendon, and sub-acromial bursa sac, causing pain in the shoulders each time you raise your arms overhead. To minimize your risk of developing shoulder impingement, regardless of the shape of your acromion, do shoulder presses in the scapular plane: internally rotate your shoulders until your elbows are pointing slightly forward and maintain this position as you execute the movement. Also, never sacrifice form to lift heavier weights. This is a common mistake that gym-goers make, and it exponentially increases your risk of serious injury. Always use a weight that does not compromise your range of motion to remain as injury-free as possible.