October 22, 2024, 11:21 am | Read time: 6 minutes

The deltoid muscle surrounds the shoulder joint and is involved in all its movements, both in many everyday activities and in sports exercises. FITBOOK editor Nuno Alves explains the anatomy of the deltoid muscle and its functions – and describes exercises for strengthening and stretching it.

Anatomy of the deltoid muscle

The deltoid muscle consists of three parts: an anterior (pars clavicularis), a middle (pars acromialis), and a posterior (pars spinalis). Depending on the part, there are also different origins.

Origin

• Pars clavicularis: The anterior part originates from the lateral third of the collarbone (clavicle).
• Pars acromialis: The middle part originates at shoulder level (acromion), the highest point of the shoulder blade.
• Pars spinalis: The origin of the posterior part is the spine of the scapula (spina scapulae).

Attachment

All three parts of the deltoid muscle attach to the side of the upper arm bone (humerus), more precisely to the deltoid tuberosity, a rough bony elevation.

Functions of the deltoid muscle

As already mentioned, the deltoid muscle is involved in all arm movements. Specific functions result from the involvement of the three different parts:

• Forward movement of the arms (anteversion) through the pars clavicularis
• Outward movement of the arms (abduction) by the pars acromialis
• Backward movement (retroversion) of the arms through the pars spinalis

The deltoid also protects the shoulder joint from injury and acts as a synergist to other shoulder muscles in many everyday and sports movements.

Special features of the deltoid muscle

The deltoid muscle tends to weaken, which can lead to muscular imbalances and thus severely disrupt the shoulder anatomy. Targeted strengthening of the deltoid muscle is therefore advisable.

Exercises for the deltoid muscle

As the deltoid muscle is involved in all directions of movement of the arm, there are numerous exercises to specifically strengthen it depending on the part involved. These can be done with or without weight, on a pulley, or on a machine. You can focus on the different parts. Here are some variations.

Body-driven exercises

Pike push-ups

Pike push-ups primarily train the front and middle part of the deltoid. They also strengthen the triceps and the upper part of the chest muscles. The exercise can be used as a preliminary stage or preparation for handstand push-ups.

This is how it works:

1. Start in the push-up position with your hands shoulder-width apart on the floor.
2. Walk your feet towards your hands until your bottom is pointing upwards and your body forms an inverted ‘V’ shape.
3. Bend your elbows and lower your head towards the floor in front of your hands.
4. Straighten your arms again.

Handstand push-up

Handstand push-ups train the shoulders very effectively and are admittedly not for beginners. Even advanced users find them difficult because many people can’t do a clean handstand. Alternatively, you can use the wall as an aid.

This is how it works:

1. Get into a handstand (against the wall if necessary), positioning your hands either slightly wider or shoulder-width apart (more strenuous!).
2. Slowly bend your elbows and lower your head towards the floor; the movement should be controlled.
3. Straighten your arms and push your upper body back into the handstand position.

Variation: Crossfit, in particular, often involves using your legs to push yourself out of the floor with momentum.

Equipment training

Many gyms are equipped with several machines specifically designed to train the deltoid muscle. Below, we describe the shoulder press and the lateral raise machine.

Shoulder press on the machine

The shoulder press involves pressing the weight upwards while sitting. Depending on the machine, you may also be able to adjust the angle of the backrest and train the front section more intensively. The triceps and the upper part of the chest muscles are also involved.

Side lift machine

The lateral raise machine, also known as the deltoid machine, involves lifting the weight with the forearms and elbows. The elbows and parts of the forearm usually press against a pad.

With the deltoid or delts machine, users lift the weight by pressing their elbows and sometimes their forearms against padded armrests.

Dumbbell training

Front raise with dumbbells

This primarily focuses on the deltoid pars clavicularis muscle, i.e., the front part of the deltoid muscle.

This is how it works:

1. Standing, hold a dumbbell in each hand and raise your arms either simultaneously or one after the other, stretched out in front of you to slightly below shoulder height.
2. Slowly bring your arms back to the starting position in a controlled manner.

Side raise with dumbbells

This variation primarily trains the middle part of the deltoid muscle, i.e., the pars acromialis.

Here’s how it works:

1. Hold a dumbbell in each hand and raise your arms sideways to shoulder height.
2. Slowly lower the dumbbells back down.

Using the cable pulley

Front raise on the cable pulley

In principle, this exercise is similar to the dumbbell version. However, you either use the one-handed grip and train one arm at a time, or you use a short bar and grip it with both hands. In both cases, you stand with your back to the cable pull.

Side raise on the cable pulley

For this exercise, you should choose the one-handed grip and position yourself stably (primarily in the core area) and with a slightly wider stance to the side of the cable pull. Then, as with side raises with dumbbells, simply raise your arm sideways to slightly below shoulder height.

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Stretching exercises for the deltoid muscle

When stretching the deltoid muscle, you should try to take the different parts into account. The following two exercises can be used for this.

Stretching the posterior part of the deltoid muscle

To do this, place your right arm over your chest at about collarbone level with your fingers pointing to the left. With your left hand, grasp your right upper arm and gently pull it further to the left side until you feel a stretch in your shoulder. Then do the exercise in reverse with the left arm.

Stretching the anterior part of the deltoid muscle

For this stretch, the fingers should interlock behind the back with the arms extended. Then try to actively pull your arm upwards until you feel a stretch.