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The human body is a complex system of muscles, ligaments, and joints that work together to enable a wide range of movements. One important aspect of this system is the ability of certain muscles to rotate, either internally or externally, which allows for dynamic motion and flexibility. Internal rotation, also known as medial rotation, refers to the movement of a body part towards the centre of the body. This involves several muscles, including the subscapularis, deltoid, teres major, and latissimus dorsi, each serving a specific function in facilitating smooth and controlled internal rotation. Understanding these muscles and their roles is crucial for maintaining joint stability, preventing injuries, and promoting overall physical health and mobility.
| Characteristics | Values |
|---|---|
| Internal rotation | Medial rotation |
| Muscles involved in internal rotation of the arm/humerus at the shoulder | Anterior part of the deltoid muscle, subscapularis, teres major, latissimus dorsi, pectoralis major |
| Muscles involved in internal rotation of the thigh/femur at the hip | Tensor fasciae latae, gluteus medius, gluteus minimus, gluteus generalis, anterior fibers of gluteus meralis, adductor longus, adductor brevis |
| Muscles involved in internal rotation of the leg at the knee | Popliteus, semimembranosus, semitendinosus, sartorius |
| Muscles involved in internal rotation of the eyeball | Superior rectus muscle, superior oblique muscle |
| Rotator cuff muscles | Supraspinatus, infraspinatus, teres minor, subscapularis |
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What You'll Learn
- Shoulder internal rotators: Subscapularis, Deltoid, Teres Major, Latissimus Dorsi, Pectoralis Major
- Hip internal rotators: Anterior fibres of Gluteus Medius, Tensor Fasciae Latae, Gluteus Minimus, Adductor Longus, Adductor Brevis
- Thigh/femur internal rotators: Gluteus Maximus, Sartorius, Popliteus, Semimembranosus, Semitendinosus
- Knee internal rotators: Piriformis, Rectus Femoris
- Eyeball internal rotators: Superior Rectus, Superior Oblique
Shoulder internal rotators: Subscapularis, Deltoid, Teres Major, Latissimus Dorsi, Pectoralis Major
The shoulder's internal rotators are the subscapularis, deltoid, teres major, latissimus dorsi, and pectoralis major. These muscles are responsible for internal rotation, which involves the limb rotating towards the midline along a vertical axis. The normal range of motion for internal rotation is 70° to 90°.
The subscapularis is one of the four muscles that constitute the rotator cuff, along with the supraspinatus, infraspinatus, and teres minor. The rotator cuff is crucial for stabilizing the glenohumeral joint by compressing the humeral head against the glenoid. The subscapularis is supplied by the axillary nerve, which wraps around the humeral surgical neck.
The deltoid muscle is shaped like an inverted triangle and can be divided into anterior, middle, and posterior parts. Its functions are related to the shoulder joint and include arm flexion, internal rotation, abduction, extension, and lateral rotation. The deltoid is supplied by the axillary nerve, which can be damaged during shoulder dislocation or reduction attempts, leading to potential deltoid paralysis.
The teres major is located inferior to the teres minor and has a tendon that inserts near the insertion of the latissimus dorsi and subscapularis. It originates from the inferior angle and lower part of the lateral border of the scapula and attaches to the medial lip of the intertubercular sulcus. The teres major is involved in arm adduction and internal rotation.
The latissimus dorsi is the largest skeletal muscle of the upper body and originates from the lumbar vertebra and pelvis. It inserts under the deltoid on the humerus (upper arm bone) and may have a small additional insertion on the scapula (shoulder blade). The latissimus dorsi is a prime mover of shoulder extension, adduction, and internal rotation.
The pectoralis major is a large muscle on the anterior surface of the chest wall and is involved in shoulder adduction, flexion, and internal rotation. It has a tendon that inserts under the deltoid on the upper arm, near the insertion of the latissimus dorsi and rotator cuff muscles.
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Hip internal rotators: Anterior fibres of Gluteus Medius, Tensor Fasciae Latae, Gluteus Minimus, Adductor Longus, Adductor Brevis
The hip joint is a ball-and-socket joint that allows for a wide range of movements, including internal and external rotation. The muscles responsible for internal rotation of the hip are primarily the anterior fibres of the gluteus medius, gluteus minimus, tensor fasciae latae, adductor longus, and adductor brevis. These muscles work together to medially rotate the thigh at the hip joint.
The gluteus medius and gluteus minimus are fan-shaped muscles that lie deep within the gluteal region. The gluteus medius is larger and located between the gluteus maximus and minimus. The gluteus minimus is the smallest of the gluteal muscles and is similar in shape and function to the gluteus medius. These muscles are innervated by the superior gluteal nerve and work together to abduct and internally rotate the thigh at the hip joint, stabilising the pelvis.
The tensor fasciae latae is a small, fusiform-shaped muscle located towards the anterior edge of the iliac crest. It is the most anterior of the gluteal muscle group and is innervated by the superior gluteal nerve, just like the gluteus medius and minimus. The tensor fasciae latae is unique among this group as it is the only muscle that crosses the knee joint, allowing it to act on the leg as well.
The adductor longus and adductor brevis are two of the hip adductor muscles, which are responsible for bringing the lower extremity towards the midline of the body. The adductor longus is the most frequently injured muscle in athletes, with strains causing groin pain. These adductor muscles also have a secondary function of flexing the hip joint.
The internal rotation of the hip is a complex movement involving the coordination of these muscles. Their activation and recruitment during different hip flexion postures vary, with the gluteus medius and tensor fasciae latae showing high to very high magnitudes of activation during internal rotation exercises.
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Thigh/femur internal rotators: Gluteus Maximus, Sartorius, Popliteus, Semimembranosus, Semitendinosus
The thigh or femur internal rotators include the gluteus maximus, sartorius, popliteus, semimembranosus, and semitendinosus muscles. These muscles work together to facilitate internal rotation at the hip and knee joints, contributing to various movements and functions.
The gluteus maximus is the largest and most superficial muscle of the gluteal group. It plays a role in extending, externally rotating, abducting, and adducting the thigh at the hip joint. Deep to the gluteus maximus lies the gluteus medius, which internally rotates the thigh at the hip joint and stabilizes the pelvis.
The sartorius muscle is the most superficial muscle in its layer. It assists in the flexion of both the hip and the knee. Additionally, it acts as a lateral rotator of the thigh at the hip and a medial rotator of the knee when the knee is flexed. The sartorius muscle is crucial for movements that require simultaneous hip and knee flexion, such as stair climbing.
The popliteus muscle is located in the deep posterior compartment of the thigh. While it has a function in knee flexion, its primary role is as an internal rotator of the tibia.
The semimembranosus and semitendinosus muscles are part of the hamstring group, which also includes the biceps femoris. These muscles flex the knee and play a role in internal rotation. They work in synergy with the sartorius muscle to enable the leg to be moved into a figure-4 position, similar to a tailor's sitting posture.
The gracilis muscle, which is the most medial muscle of the group, also contributes to internal rotation at the knee joint. It crosses over both the hip and knee joints, allowing it to act on both.
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Knee internal rotators: Piriformis, Rectus Femoris
The piriformis is a flat, pear-shaped muscle located in the gluteal region. It is one of the six short external thigh rotators, alongside the superior and inferior gemelli, quadratus femoris, and obturator internus and externus. The muscle passes through the greater sciatic foramen and divides the gluteal region into superior and inferior parts. The piriformis also serves as a landmark for the gluteal region, with several nerves and vessels named based on their spatial relationship with this muscle.
The rectus femoris is one of the four quadriceps muscles, along with the vastus medialis, vastus intermedius, and vastus lateralis. The muscle is situated in the middle of the front of the thigh and has a fusiform shape. Its functions are to flex the thigh at the hip joint and extend the leg at the knee joint. The rectus femoris is not dominant in knee extension when the hip is flexed, as it suffers from active insufficiency. However, it is a direct antagonist to the hamstrings at the hip and knee.
In terms of knee internal rotators, the piriformis muscle externally rotates the thigh and laterally rotates the femur during hip extension. It also abducts the femur during hip flexion, which is critical for walking as it prevents falling by shifting the body weight to the opposite side. The rectus femoris, on the other hand, is involved in extending the leg at the knee joint. While it is not the dominant muscle in knee extension when the hip is flexed, it still plays a role in this movement.
Injuries to these muscles can occur. Piriformis Syndrome can occur when the lateral rotators of the hip are tight and exert pressure on the sciatic nerve, causing pain in the lower extremity. Rectus femoris strain, also known as hip flexor strain, is a common injury in sports like football and soccer. It usually occurs as a partial tear but can also be a full tear due to forceful movements related to sprinting, jumping, or kicking.
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Eyeball internal rotators: Superior Rectus, Superior Oblique
The superior rectus and superior oblique muscles are two of the seven extraocular muscles responsible for controlling the movements of the eyeball and the superior eyelid. These muscles are involved in the internal rotation, or intorsion, of the eyeball, with the superior oblique serving as the primary internal rotator and the superior rectus as the secondary internal rotator.
The superior oblique muscle is an extraocular muscle that originates from the body of the sphenoid bone and runs anteriorly, parallel to the medial wall of the orbit. Its tendon passes through a cartilaginous pulley, known as the trochlea of the superior oblique, before attaching to the posterior surface of the sclera of the eye. This unique trajectory allows the superior oblique to direct the gaze in multiple directions while stabilising the eyeball by counteracting head movements.
When the eyeball is in a neutral position, the primary function of the superior oblique muscle is to perform abduction (movement away from the nose) and depression (inferior movement) of the eyeball. However, its most notable role is in the internal rotation or intorsion of the eyeball, specifically the movement of the superior pole of the eye medially. This internal rotation is most effective when the eye is in an abducted position.
The superior rectus muscle, while also contributing to internal rotation, primarily elevates the eyeball. It originates from the anterior aspect of the orbital floor and attaches to the sclera of the eye, posterior to the lateral rectus muscle. The superior rectus muscle elevates the eyeball by pulling it upward and helps in intorsion, particularly when the eye is in an adducted position.
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Frequently asked questions
The internal rotators of the arm/humerus at the shoulder include the anterior part of the deltoid muscle, subscapularis, teres major, latissimus dorsi, and pectoralis major.
The subscapularis is the main internal rotator of the shoulder. It is the largest and strongest cuff muscle, providing 53% of total cuff strength.
The internal rotators of the thigh/femur at the hip include the tensor fasciae latae, gluteus generalis, anterior fibers of gluteus medius, adductor longus, and adductor brevis.
