Deltoid


Where is my Deltoid?

You have a left and right deltoid. Basically, they are your shoulder cap muscles, and are important lifting muscles for everyday home usage as well as for weightlifting sports!

Location:

Lateral (side) Shoulder

Name Breakdown: 

Delt-oid"Delt"=for "delta" the greek letter Δ) 

All together: The Reason for the name is because the deltoid makes an upside-down triangle on the shoulder. Its base is actually on the top of the shoulder and is wide and wraps around the front, to the side, and then to your back (This is why there are the 3 different motions for the deltoid!) The pointed tip is actually lower down and is on the side of your arm, so all three motions still pull on and move your arm upwards, it just depends on if it is up&foward, up&to-the-side, or up&back


Why This Matters

Application for Workouts

The Deltoid (shoulder cap muscle) has a large range of functions and uses in its range of motion. As a result, we often have to incorporate a variety of different movements to fully stimulate the muscle. All of these movements result in lifting of the arm upwards, but how they vary is in the angle and rotation of the arm as you do so.

Sometimes this comes by having a very inclusive shoulder day, and other times we split up the different movements the deltoid can do in its range of motion, and hit those on different days paired with other muscles that do those same movements. I'll give an example of both:

On a Shoulder day:

  • Front Delts: you would likely do an incline bench press, shoulder press, or front dumbbell raises to hit the front deltoids. The front delts lift your arm out straight in front of you.
  • Middle Delts: you could do lateral raises or standing rows to target the middle deltoids. The middle delts bring your arm up to the side, like doing a jumping jack.
  • Rear Delts: you could do rear/bent over/machine rear delt raises, or back movements such as a low row for the Rear Deltoids. The rear delts bring your arm back, like doing a  pull down.

If you prefer to spread out your shoulder movements:

  • Front Delt: included in Chest days
  • Middle Delt: included in days that you prefer to use middle delt exercise. i.e. you might like doing standing rows on back days, but lateral raises on chest days.
  • Read Delt: included in Back days

Emphasis on Bodybuilding

Shoulders are an important muscle for bodybuilding because having larger shoulders contribute to having that tapered look that brings an aesthetic build to the stage. 

Shoulders are also hard to grow for a lot of people. They are versatile muscles capable of withstanding a great deal of use throughout the day. When you hit the gym, it can be the same. You have to train them hard and often to see the results you want when compared to other muscles.

Because they are so important to daily life and to lifting, it is important to keep them healthy. I stretch before and after every workout, as well as do a warm-up sequence before I begin to make sure not only my deltoids, but my scapular complex is activated and in alignment to prevent injury. Always be sure to have complete control of the weight to prevent injury, maintain health, and continue seeing improvements.


Origin:

1) Front/Anterior Head: Clavicle (Collar bone)(Lateral 1/3rd)

The front belly of the deltoid is located in the front of the shoulder. It sits directly adjacent to the upper chest (clavicular head of the Pectoralis major). People who perform a lot of pressing motions typically have a very developed Front Head when compared to the other two heads. This muscle is most important in the front poses.

2) Middle Head: Acromion process of the scapula

The middle head is the one that gives you that roundness on the side when you look at yourself head on in a mirror. This muscle is important for shoulder development in both the front and back poses.

3) Rear/Posterior Head: Spine of the scapula.

The rear delt wraps backward from the upper arm to the back of the shoulder on the scapula bone. The muscle covers the infraspinatus (one of the shoulder cuff muscles). It is very important in back and side poses.

Insertion:

All three heads of the deltoid blend together to insert onto the upper arm. The insertion onto the bone causes a bump on the bond called the deltoid tuberosity. This insertion is located on the humerus bone very close to the top and on the side.

The importance of this is that you should always focus on trying to move your upper arm, rather than moving your forearm, despite where the weight is located.

When doing any sort of front, lateral, or rear delt movement, you should focus on moving the arm up, and either to the front, side, or back, respectively, depending on which of the heads you are targeting.

Action:

1) Front/Anterior Head:

The primary action of the front head of the Deltoid is to move the arm forwards. The anatomical term for this is Flexion of the shoulder, or Flexion of the arm AT the shoulder. This movement is somewhat similar to when you lift your arm up to point at something in front of you. A good example of this movement is the Front Shoulder Raises.

2) Middle Head:

The middle head of the Deltoid is responsible for lifting your arm up and out to the side, like doing a jumping jack. The anatomical term for this movement is called Abduction of the shoulder, or Abduction of the arm AT the shoulder. A good example of this movement is the Lateral Shoulder Raises.

3) Rear/Posterior Head:

The primary action of the posterior head of the Deltoid is to move the arm backwards. The anatomical term for this is Extension of the shoulder, or Extension of the arm AT the shoulder. This movement is somewhat similar to when you do a pull-up, but with your arms a little bit more raised rather than directly at your sides. A good example of this movement is the Rear Delt Fly Machine.

Antagonist:

When a muscle acts as antagonist, it is trying to resist the action of a different muscle. Since the deltoid has 3 different heads and 3 different motions, it has 3 different opposing directions as well. Given the contrasting nature of the front and rear deltoids, these heads can be antagonistic to each other; The major antagonists however are latissimus dorsi and pectoralis major.

  1. The latissimus dorsi does both arm extension and arm adduction, therefore it opposes the action of the front head.
  2. The pectoralis major does both arm flexion and arm adduction, therefore it opposes the action of the rear head.
  3. Since the middle head does arm abduction, the latissimus dorsi and pectoralis major work together to oppose the middle head.

Nerve Supply:

The deltoid is innervated by the Axillary nerve. This nerve also innervates the teres minor muscle. Damage to this nerve (such as pinching) would result in poor ability to lift the upper arm.

This nerve comes from the Posterior Cord of the Brachial Plexus. The Brachial Plexus is the  main set of nerves that innervate different parts of the arm, forearm, shoulder, back and chest. Depending on what nerves or parts of the Brachial Plexus may be pinched, you could have different combinations of muscles working improperly. 

The posterior cord is associated with back and shoulder muscles, such as the rotator cuff muscles, deltoid, and latissimus dorsi.

Blood Supply:

The deltoid is supplied by the posterior humeral circumflex artery. This is the main artery travels with the axillary nerve through the armpit from front to back. 

Blood Flow: Heart -> Aorta -> -Brachiocephalic Trunk -> Subclavian Artery -> Axillary Artery -> posterior humeral circumflex artery.


Example Exercise Videos to Work this Muscle

Focus on Front Delts

Focus on Middle Delts

Focus on Rear Delts