What is the infraspinatus muscle?
The infraspinatus is a thick triangular muscle located in the shoulder region. It is one of the four muscles that make up the rotator cuff and its primary function is to externally rotate the arm and also help to stabilize the shoulder joint. (1)
Origin, insertion and function
Origin
The infraspinatus muscle originates from the infraspinous fossa, which is a depression located on the posterior (back) of the scapula (shoulder blade).
Insertion
The infraspinatus muscle inserts on the greater tuberosity of the humerus, which is a bony prominence located on the upper arm bone.
Function
External rotation of the arm: The infraspinatus muscle is responsible for externally rotating the arm. This means it helps to turn the arm outward, away from the body.
Stabilization of the shoulder joint: The infraspinatus muscle, along with the other muscles of the rotator cuff, helps to keep the head of the humerus (upper arm bone) in the socket of the scapula (shoulder blade). This helps to maintain the stability of the shoulder joint.
Abduction of the shoulder: The infraspinatus muscle also helps to abduct the shoulder, which means it helps to lift the arm away from the body.
Assist in horizontal adduction: It also assist in horizontal adduction of the arm, which is movement of the arm towards the body in a horizontal plane.
Injuries or strains to the infraspinatus muscle can cause pain and weakness in the shoulder, and may limit an individual’s ability to perform activities such as reaching, lifting, or throwing.
Common signs of weak infraspinatus muscles
- Difficulty lifting the arm out to the side or above the head
- Pain or discomfort in the shoulder or upper arm when lifting the arm or reaching overhead
- A feeling of weakness or instability in the shoulder
- A popping or clicking sensation in the shoulder when moving the arm
- Limited range of motion in the shoulder
- Tenderness or pain when pressing on the muscle or when it is stretched
- Pain or discomfort when lying on the affected shoulder
- Tendinitis or rotator cuff tear
It’s important to note that these signs can also be caused by other conditions such as rotator cuff tears, impingements and other shoulder injuries. A professional diagnosis from a doctor or physical therapist is recommended to determine the cause of symptoms and develop an appropriate treatment plan.
Exercises to strengthen the infraspinatus
Exercises that can help to strengthen the infraspinatus muscle include:
External rotation: Stand with your arm at your side and a light weight (such as a small dumbbell) in your hand. Keep your elbow at your side and rotate your arm outwards, away from your body. Slowly lower the weight back to the starting position. Repeat for several reps.
Resistance band external rotation: Anchor a resistance band to a stable object at about chest height. Hold the band with the affected arm, with the elbow at the side and the forearm parallel to the floor, and rotate the arm outwards, away from your body. Slowly return to the starting position. Repeat for several reps.
Shoulder horizontal adduction: Stand with your arms at your side, holding a light weight (such as a small dumbbell) in each hand. Keep your elbows straight and bring your arms together in front of your body, as if you are clapping your hands. Slowly return to the starting position. Repeat for several reps.
Reverse Fly: Stand with your feet shoulder-width apart, holding a light weight (such as a small dumbbell) in each hand. Hinge forward at the hips, keeping your back straight and your core engaged. Your arms should be extended straight below your shoulders. With your elbows slightly bent, raise your arms out to the side, squeezing your shoulder blades together. Slowly lower back to the starting position. Repeat for several reps.
It’s important to consult your doctor or physical therapist before starting any new exercise program. They can evaluate your specific condition and recommend the most appropriate exercises for you. They can also help you to ensure that you are performing the exercises correctly and safely to avoid any injuries.
References:
- Williams JM, Sinkler MA, Obremskey W. Anatomy, Shoulder and Upper Limb, Infraspinatus Muscle. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK513255/