The leg is divided into the upper leg (thigh) and lower leg (calf) .
The upper leg consists of one bone, the femur, whereas the lower leg consists of two bones, the tibia (located on the big-toe side) and fibula (on the little-toe side) . The knee is a hinge joint formed at the junction between the femur and the tibia. Two movements occur at the knee joint: flexion and extension.
During knee flexion, the lower leg bends toward the back of the thigh.
During knee extension, the lower leg moves away from the thigh so the leg becomes straight.
The hip is a ball-and-socket joint between the upper end of the femur and the pelvic bone. Six main movements occur at the hip joint: flexion, extension, abduction, adduction, internal rotation, and external rotation. During hip flexion, the thigh bends up toward the abdomen, whereas during hip extension, the thigh moves backward toward the buttocks. The thighs separate apart during hip abduction, and the thighs come together during hip adduction. The ankle is a hinge-type joint between the lower tibia and fibula and the talus bone in the foot. During ankle dorsiflexion, the toes lift off the floor and the foot moves toward the shin. During ankle plantar flexion, the heel lifts off the floor and the foot moves away from the shin.
The quadriceps femoris, located in front of the thigh, has four separate heads:
- Rectus femoris arises from the front of the pelvic bone.
- Vastus medialis arises from the inner edge of the femur.
- Vastus lateralis arises from the outer edge of the femur.
- Vastus intermedius arises from the front surface of the femur and lies underneath the rectus femoris.
The four heads merge together, attach onto the patella (knee cap), and then insert via a single (patellar) tendon onto the tibia, just below the knee joint. The main function of the quadriceps is to extend the knee and straighten the leg. Because the rectus femoris arises from the pelvic bone, contraction of this muscle also flexes the hip joint.
The hamstrings, located behind the thigh, are a group of three muscles that originate from the ischium bone of the pelvis.
- Biceps femoris passes behind the outer aspect of the thigh to attach to the head of the fibula bone, just below the knee.
- Semimembranosus passes behind the inner aspect of the thigh, attaching to the upper tibia bone behind the knee.
- Semitendinosus passes behind the Inner aspect of the thigh, attaching to the upper tibia bone adjacent to semimembranosus.
All three hamstrings span both the knee and hip joints. Therefore, they serve dual functions: flexion of the knee and extension of the hip.
The gluteus maximus arises from a large area on the rear of the pelvic bone, passes down behind the hip joint, and attaches to the upper femur. This powerful muscle causes hip extension. Good exercises for building the gluteal muscles are the squat, deadllft, and lunge.
Other thigh muscles include the following: Hip adductors (Inner thigh):
Gracilis; adductor longus, magnus, and brevis
Hlp abductors: Tensor fascia latae; gluteus medius and minimus
Hip flexors: Sartorius, iliopsoas, rectus femoris
The lower leg contains 10 different muscles. The calf comprises two muscles:
- Gastrocnemius is the visible muscle of the calf. The two heads (medial and lateral) of the gastrocnemius arise from the rear of the femur bone. immediately above the knee joint.
- Soleus arises from the rear aspect of the tibia and lies underneath the gastrocnemius.
The tendons of the gastrocnemius and soleus fuse to from the Achilles tendon that passes behind the ankle joint and attaches to the calcaneus (heel bone). The calf muscles cause plantar flexion of the ankle. the movement required for standing on tiptoes. The relative contribution of the two calf muscles depends on the angle of knee flexion. The gastrocnemius is the prime mover when the leg is straight. and the soleus becomes more active as the knee bends. Note that the gastrocnemius crosses both the knee and ankle joints. and therefore serves a double function: knee flexion and ankle flexion.
The following are other lower-leg muscles:
Ankle extension (dorsiflexion) : Tibialis anterior
Ankle eversion : Peroneus longus and brevis
Ankle Inversion : Tibialis posterior
Toe flexors and extensors: Flexor digitorum longus, flexor hallucis longus, extensor digitorum longus, and extensor hallucis longus.
Source: wikipedia.org | book – Bodybuilding Anatomy by Nick Evans