Dumbbell Shoulder Press on Stability Ball

Muscles involved:

Shoulder joint:

• Deltoid
• Rotator cuff (subscapularis, supraspinatus, infraspinatus, and teres minor)
• Trapezius
• Rhomboid
• Levator scapulae

Arms

• Triceps
• Biceps
• Forearm muscles

Abdomen:

• Rectus abdominis (straight abdominal muscle)
• External oblique (external oblique abdominal muscle)
• Internal oblique (internal oblique abdominal muscle)
• Transversus abdominis (transverse abdominal muscle, 'corset muscle')

Lower back and spine:

• Erector spinae
• Lumbar multifidus
• Quadratus lumborum

1. Sit on a stability ball with your feet approximately shoulder-width apart and the dumbbells on your knees.
2. Raise your knees one at a time and bring the dumbbells into their starting position: Your hands are approximately level with your ears. Your elbows are beside your torso. Your palms are turned forward.

1. Focus on your elbows and press them straight upward until they are above shoulder height. At the end of the movement, your arms are almost fully extended. The dumbbells move toward each other but do not touch.
2. Lower your arms back down in a controlled manner until the dumbbells are level with your ears.
3. Repeat.

The three heads of the deltoid

The deltoid muscle pulls on the upper arms from three directions. During the shoulder press, all three of these "heads" of the shoulder muscle are engaged. However, it is primarily the anterior head (pars clavicularis) that does most of the work, followed by the lateral head (pars acromiaca). The posterior head (pars spinalis) is engaged considerably less.

The shoulder press can be performed in various ways that can shift the load between the heads, but not by much. In most cases, the front of the shoulder produces three times as much effort as the side, which in turn produces an average of three times as much effort as the rear.

Why use a stability ball

Exercises are often performed on a stability ball so that the core muscles have to make a greater contribution. However, it should also be taken into account that other muscles must also perform more stabilizing work. 

Research has shown that when the shoulder press is performed standing, the shoulders (all three heads) produce greater effort. The researchers point to the additional need for stabilization when the exercise is performed standing. This would imply that the standing variation is 'more effective' at engaging the shoulder muscles. Although this has not been investigated, you can possibly imagine that the shoulders have to stabilize even more when you are seated on a stability ball. However, you may question the extent to which the stabilizing work of the core and shoulders could come at the expense of the maximum effort the shoulders can produce. 

Another possibility, however, is that people often use compensatory movement in the seated variation. The standing variation forces you to stand upright so that you do not fall backward. This limits the possible contribution of the chest muscles. On a bench with a backrest, you often see that the backrest is already set too far back. People then slide their buttocks forward a little more, causing them to lean back even further. The shoulders then have to produce less effort because the chest, especially the upper chest, can make a greater contribution.

Dumbbells or barbells?

The same study also found that the shoulder press with dumbbells engaged the shoulders (all three heads) more intensely in every case than the barbell variation. Here too, the greater need for stabilization was mentioned as a possible cause.

In addition to the shoulder muscles having to perform more stabilizing work with dumbbells, the exercise's range of motion is also greater. With dumbbells, the hands can move toward each other at the top of the movement, at the point where the barbell version has reached its endpoint.

• Barbell shoulder press
• Seated barbell shoulder press
• Shoulder press machine
• Dumbbell shoulder press