Knowing the major muscle groups (Pt5)
In this 5th and final post on the major muscle groups of the body, we’ll discuss muscles of the lower leg, the back of the thigh, and hip.
The lower leg can be divided into three compartments, the anterior (front), lateral (side), and posterior (back). There are a total of eleven muscles in the lower leg, all of which operate the foot. These muscles are referred to as extrinsic muscles, while the muscle located on the foot itself are referred to as intrinsic muscles. There are three in the front, three on the side, and five in the back. We’ll focus on two of theses muscles, which form the superficial layers of the calf.
Gastrocnemius: Located just below the back of the knee, the two bellies of the Gastrocnemius are what give the calf muscles their contoured shape. They descend about half way down the lower leg and are easily the most superficial and accessible muscle of the lower leg. Due to the fact that Gastrocnemius crosses both the knee and ankle joint, it can just as effectively flex the knee as it can plantarflex the foot. The lower portion of the muscle blends with another lower leg muscle known as Soleus to form the Achilles tendon. The Gastrocnemius is a powerful muscle capable of lifting your entire body weight, making it most active when running or jumping.
Soleus: Sometimes referred to as the body’s “second heart”, the Soleus muscle plays a very prominent role in pumping blood back to heart. The upper portion of the muscle is buried beneath the superficial bellies of the Gastrocnemius, but its lower half is easily accessible and palpable. Although Soleus does not cross the knee joint, it does blend with Gastrocnemius to form the Achilles tendon. The main function of this muscle is to plantarflex the foot. Unlike the Gastrocnemius, which is known for its short bursts of power, the Soleus is a workhorse muscle, essentially working anytime you’re on your feet.
Hamstrings: The hamstrings as they’re commonly referred to, are the major muscle group found in the back of the upper leg and thigh. There are three distinct and individually named muscles, which surprisingly occupy less space at the back of the leg than one would imagine. The lateral portion of the Quadriceps and the medial Adductors fill in a big portion of the posterior thigh. Yet these three slender muscles are capable of performing several actions that affect the hip and knee in variety of ways.
Biceps Femoris: The most lateral of the hamstrings, Biceps Femoris has two distinct bellies. One belly originates at the sitz bones and the other shorter head, starts half way down the femur. Both heads then blend together to form a common tendon, which crosses the knee joint to attach on the fibula. This portion of the hamstrings can: flex the knee, laterally rotate the knee (when flexed), extend the hip, laterally rotate the hip, and tilt the pelvis posteriorly.
Semitendinosus & Semimembranosus: The only major difference between these two muscles, which happen to form the medial hamstrings, are their insertion points. They both originate on the sitz bone and they both perform the exact same functions. Semitendinosus overlies the deeper Semimembranosus, but they both cross the knee joint. Instead of blending together to form on common tendon and one insertion point, they each maintain their tendon and attach at slightly different points on the tibia. The Semis can: flex the knee, medially rotate the knee (when flexed), extend the hip, medially rotate the hip, and tilt the pelvis posteriorly.
Moving up the leg and into the hip, we come to an area with many layers of muscle collectively referred to as the ‘glutes’. There is of course Gluteus maximus, which is the most superficial layer of the glutes and one that we’re all familiar with. Beneath this muscle however, lie two other muscles named “gluteus”: Gluteus medius and Gluteus minimus. Both these muscles are key players in moving as well as stabilizing the hip. Then we have the ‘deep six’ lateral rotators – a grouping of six slender muscles that fan out around the head of the femur in the hip socket. As the name implies, they laterally rotate or roll the leg and hip out. One of these lateral rotators is called Piriformis.
Piriformis: If you’ve ever had sciatica or experienced sciatica-like pain, then you’ve probably heard of the Piriformis. The reason for this is that, out of the deep six lateral rotators, the Piriformis is the only one the runs directly over the sciatic nerve. The other five lie beneath it. If for some reason the Piriformis becomes strained or inflamed from overuse or trauma, that extra bit tension could compress the sciatic nerve causing an entrapment.
The Piriformis muscle originates on the sacrum and attaches to a part of the femur called the greater trochanter. As mentioned, it’s a strong lateral rotator of the hip and leg. When the leg is stationary, it can also rotate the body to the opposite side. For that reason, an activity or sport that involves quick cutting or twisting movements could potentially cause trouble for the Piriformis.
Iliotibial Band: Although technically not a muscle, this thick band of fascia covers the outer part of the hip and thigh and serves as central tendon for two muscles: Gluteus maximus and a muscle called Tensor Fascia Lata (TFL). The vertical fibers of the IT band originate and are an extension of both these hip muscles. This thick tendon like structure runs the length of the outer leg and inserts just below the knee on the tibia. The IT band essentially transmits the power of the Gluteus maximus and TFL to help move the hip and leg. More importantly, the IT band helps to stabilize the hip and knee when standing, walking, and running.
