The legs contain many muscle groups that support, balance, and propel the body. The muscles of the leg must provide tremendous strength while simultaneously allowing for subtle adjustments. In many cases, we do not notice the subtle adjustments our muscles constantly perform. Experts divide each section of the leg into several groups or regions to more easily describe the location of each muscle. The hip has four groups, the thighs have three, and the lower legs have four.
The majority of the muscles in the groin and buttocks areas belong to the gluteal group, which contains three primary muscles: the gluteus maximus, the gluteus medius, and the gluteus minimus. The gluteus maximus is the biggest and makes up a large portion of the hips and buttocks. The gluteus medius is a broad muscle that sits on the outer surface of the pelvis. Just below the gluteus medius is the smaller gluteus minimus. These muscles allow for anatomical motions such as extension, abduction, and rotation at the hip joint. The gluteus maximus also helps support the knee.
Unlike the other groups, the iliopsoas group possesses only two muscles. The iliacus and psoas major reside in the abdomen, connecting as they travel into the hips. They meet at the inguinal ligament and then insert into the lesser trochanter of the femur. Together, they are the strongest flexors of the hip, providing our ability to walk, run, and even stand. Because they are separate muscles that can act independently, they often perform different actions during movement and posture changes.
The muscles that bring the thighs together during adduction (movements toward the inner line of the body) belong to the adductor group. Within this group are the adductor brevis, adductor longus, adductor magnus, pectineus, gracilis, and the obturator externus. These muscles originate at the pubis and stretch to the inner areas of the thighs. The lateral rotator group consists of six muscles that can laterally rotate the femur in the hip joint. These muscles are the gemellus superior, gemellus inferior, piriformis, obturator internus, obturator externus, and quadratus femoris. All of these muscles begin at the hip bone and connect to the upper femur.
Within the thighs are some of the largest and strongest muscles in the human body. The main muscles in the anterior area of the thigh are the sartorius muscle and the quadriceps femoris. The sartorius is the longest muscle in the human body. It stretches obliquely from the upper middle to the lower inner portion of the thigh. It is a synergist muscle that helps other muscles move the hip and knee joints. The quadriceps femoris contains the rectus femoris, vastus lateralis, vastus intermedius, and the vastus medialis. These muscles act as powerful extensors for the knee. They cover much of the front and sides of the femur.
The hip adductor muscles enter the medial region of the thigh as they stretch downward. The gracilis, adductor longus, adductor brevis, and adductor magnus all belong to both the hip adductor and the medial thigh muscle groups. However, some experts include the pectineus muscle in the latter group. This is a flat muscle that begins in the anterior portion of the hip and upper thigh before merging into the medial area. Its primary responsibility is hip flexion, though it can also adduct the thigh.
The main muscles of the posterior thigh are responsible for knee flexion and hip extension. Many people refer to these muscles as the hamstrings. Three muscles that make up this group: the biceps femoris, semitendinosus, and semimembranosus muscles. Because they cross both the hip and knee joints, the hamstrings are biarticular muscles. While walking, the hamstrings act opposite to the quadriceps to slow knee extension. Some experts consider a portion of the adductor magnus another part of the hamstrings.
Near the front of the shin are the anterior muscles of the lower leg. This group includes the tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius muscles. Together, these muscles are responsible for dorsiflexion in the feet and toes. This refers to a motion of pulling the toes and feet upward. The tibialis anterior muscle can also invert the foot and point the sole toward the midline of the body. You can probably feel your tibialis anterior by placing a hand over the shin and moving the foot upward.
The peroneus longus and peroneus brevis are the outside muscles of the lower leg. These belong to the lateral muscle group. The peroneus longus can evert and plantarflex the ankle. Eversion of the ankle points the sole of the foot away from the midline of the body. Plantar flexion is an anatomical term that refers to the movement of pressing on a gas pedal or standing on tiptoes. The peroneus brevis sits under the peroneus longus and weakly assists the movements of the peroneus longus.
What people commonly refer to as the calf is the posterior region of the lower leg. The gastrocnemius, soleus, and plantaris muscles all lie in this area. All three muscles are capable of plantar flexing the ankle, though the gastrocnemius can only do so while the knee is extended. They each also connect to the Achilles tendon. The gastrocnemius also raises the heel while walking and can flex the knee. It is shorter and thicker than the soleus muscle, which is just underneath the gastrocnemius. The plantaris offers a minor assist to the gastrocnemius during plantar flexion.
Further within the rear of the lower leg are the deep posterior muscles -- the flexor hallucis longus, flexor digitorum longus, tibialis posterior, and popliteus muscles. The tibialis posterior acts opposite to the tibialis anterior. Rather than dorsiflexion, the tibialis posterior allows for plantar flexion of the ankle. The flexor digitorum longus can flex the four minor toes and can also plantarflex the ankle. Similarly, the flexor hallucis longus flexes the big toe and assists with plantar flexion. The popliteus can weakly flex and rotate the knee.
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