The Deltoid (Rear and Lateral) Muscle Explained

Description: The deltoid muscle is considered the central muscle of the shoulder. 

Role: It assists with lifting the arms in three directions, using its three different portions. The frontal part (red) helps in lifting the arm upwards and forward; the middle part (green) helps with a sideways upward motion and the rear part (blue) lifts the arm backward.  

Potential damage: Once the deltoid loses sufficient strength, especially in its middle and rear parts, the body will tend to prioritize activity in the upper muscles of the shoulder and neck in order to lift the arm up. The risk of such over-compensation can lead to a painful chronic impingement or even a tear to the rotator calf muscles in the shoulder. 

This reverse-muscle function of using the upper shoulder and neck muscles instead of the weaker deltoid can also cause a strong pulling on the neck but also the alternative working muscles which attach to them. This may lead to entrapments of nerve roots in the neck, painful trigger points within these muscles, and bruised cervical joints. The so-called ‘mechanical headaches’ may also appear, as they are often caused by continual pulling by muscles on the soft tissue at the base of the skull.

Exercise: Either sitting or standing, slowly lift the arms up to the side, over 2 seconds and no higher than 80 degrees. Do so over one set of 15 repetitions, using light weights of 1-4kg.  

To train the middle deltoid, keep the arms in a neutral position with the thumbs pointing forward. When training the rare deltoid the thumbs will be pointing towards your body and into the thighs. For the frontal part, the thumbs need to point outwards.

Middle Deltoid: The back of the hands facing outside

Rear Deltoid: the back of the hands facing forward

Progress:

Number of Repetitions:________________________________________________

Time held for (if applicable):_____________________________________________

Comments (any questions, difficulty, pain, etc.):_____________________________

___________________________________________________________________

___________________________________________________________________

___________________________________________________________________