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The muscles of the thigh are responsible for a variety of movements, acting on both the hip and the knee joint. There are many muscles in the thigh, but they can be categorised into the anterior, posterior and medial compartments.
These compartments are separated by layers of fascia (sheets of connective tissue).
It is also very important when studying muscles that you are comfortable with anatomical terminology, because these articles use many anatomical terms. For more information, please check out our Anatomical Terminology Article.
Diagram - The fascial compartments of the thigh. Pink represents the anterior compartment, green is the medial compartment and blue represents the posterior compartment
Image: public domain
The muscles of the anterior compartment of the thigh are innervated by the femoral nerve, apart from the psoas major (see Iliopsoas below). Between them, these muscles extend the knee joint (the quadriceps femoris, described below) and flex the thigh at the hip joint (the iliopsoas, rectus femoris, sartorius and pectineus).
Diagram - Muscles of the anterior thigh. Note that the vastus intermedius is tucked underneath the rectus femoris and is, therefore, not visible
Creative commons source by OpenStax College [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
This muscle is the longest in the body and runs in an oblique fashion across the anterior thigh. It is long, thin and is the most superficial of the anterior compartment muscles. It runs from the anterior superior iliac spine (the bony point at the front of the pelvis) and passes inferomedially (downwards and towards the midline) to the medial tibia.
It flexes, abducts and laterally rotates the hip joint and flexes the knee joint.
This is a flat muscle that runs from the anterior surface of the pubis (the front part of the pelvic bone) to the pectineal line of the femur (a ridge on the back of its upper part). Its placement within the body allows it to flex and adduct the hip joint. It is supplied by the femoral nerve, and sometimes also by a branch of the obturator nerve.
There are three vastus muscles that contribute to the quadriceps femoris group of muscles. These muscles are responsible for extension of the knee joint. They all attach to the patella via the quadriceps tendon, and the patellar ligament then joins the patella to the tibia. They are:
- Vastus Lateralis - originating from the lateral lip of the linea aspera (a rough ridge down the back of the femur)
- Vastus Intermedius - originating from the anterior surface of the femoral shaft
- Vastus Medialis - originating from the medial lip of the linea aspera
This muscle is the fourth muscle of the quadriceps femoris. It originates from the ilium (the upper part of the pelvic bone) and attaches to the patella, then to the tibial tuberosity (the bump at the top of the shin) via the patellar ligament. It flexes the hip and extends the knee.
This muscle is a combination of both the psoas major and iliacus muscles, hence the name.
Together, they flex the hip joint. The psoas major is supplied directly by branches of the L1 to L3 spinal nerves, and the iliacus by the femoral nerve.
The posterior compartment is simpler: it has only three muscles, and they share the same actions. Collectively, these muscles are known as the hamstrings and are involved with extension of the hip and flexion of the knee. They are innervated by the sciatic nerve.
Diagram - Posterior compartment (Hamstring) muscles on the right leg highlighted in red
Creative commons source by OpenStax College, edited by Dr. Thomas Burnell [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
This muscle has two heads. The long head originates at the ischial tuberosity (the bony part of the pelvis you sit on), whilst the short head originates at the linea aspera of the femur. Together, they insert into the head of the fibula. The common tendon of the two heads can be felt (palpated) on the outer side of the back of the knee. The two heads are innervated by two different branches of the sciatic nerve: the long head by the tibial branch, and the short head by the common fibular (also called common peroneal) branch. Its main action is flexion of the knee. It also contributes to extension of the hip, and to lateral rotation of the hip and the knee (the knee rotation happens only when the knee is flexed).
This muscle lies medial to the biceps femoris. It originates from the ischial tuberosity and attaches to the medial tibia. It is primarily responsible for flexion of the knee joint and extension of the hip, but can also medially rotate the thigh. It is innervated by the tibial branch of the sciatic nerve. When looking at the back of the thigh, the two can be hard to tell apart. Semitendinosus is the one with a very long tendon at the bottom, which attaches to the medial tibia.
This is the most medial of the posterior muscles. It is deep to the semitendinosus muscle. Like semitendinosus and the long head of biceps femoris, it originates from the ischial tuberosity. It attaches to the medial tibial condyle (the rounded inner part of the top of the tibia). In addition to extension of the hip and flexion of the knee, it can medially rotate the thigh. When looking at the back of the thigh, the two can be hard to tell apart. Semimembranosus is the most medial of the hamstrings (a memory aid: membranosus and medial both begin with 'm').
These muscles mainly produce hip adduction (moving the thigh towards the midline). They are innervated by the obturator nerve, except the hamstring part of adductor magnus (see below), which is supplied by the sciatic nerve.
Diagram - Medial compartment of the thigh. Note that the Obturator Externus is not illustrated, but would be deep to pectineus and superior to adductor muscles
Creative commons source by Beth ohara, edited by Dr. Thomas Burnell [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]
These are a group of muscles found in the medial thigh. They are primarily responsible for hip adduction and originate from the pubis (adductor magnus also arises from the ischium, the lower back part of the pelvic bone, including the ischial tuberosity). There are three muscles in this group:
- Adductor brevis - a short muscle that lies beneath adductor longus. It attaches to the linea aspera on the posterior femur.
- Adductor longus - a long, fan-shaped muscle that inserts into the middle third of the linea aspera.
- Adductor magnus - the largest muscle in the medial compartment. It is also the deepest of the medial compartment muscles. This muscle can be divided into two regions, an adductor region and a hamstring region. The adductor region contributes to hip flexion and is supplied by the obturator nerve, whilst the hamstring region contributes to hip extension and is supplied by the tibial part of the sciatic nerve.
Obturator Externus is the most superior of the medial compartment muscles. It originates from the membrane covering the obturator foramen (the big hole in the pelvis made by the ischium and pubis) and attaches to the greater trochanter (the bony lump at the top and outer side of the femur). In addition to adduction, it also contributes to lateral rotation of the thigh.
Gracilis is the most superficial and most medial of the muscles in the medial compartment. It originates from the pubis and descends to the medial surface of the tibia. It, therefore, also contributes to flexion of the knee in addition to hip adduction.
For Pathologies and Conditions affecting the Thigh area, check out our Conditions of the Thigh article.
Edited by: Dr. Marcus Judge and Dr. Maddie Swannack
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