Anatomy And Function Of The Hamstrings


The hamstrings are muscles that just about everyone is at least somewhat familiar with. If you’re someone with tight hamstrings, then you might think you are very familiar with exactly where those hamstrings are located. But the hamstrings are much more than just something to stretch out in yoga. They’re necessary for fundamental movements like walking and running. And understanding the anatomy of the hamstrings can help us understand how they function. In this article, we’ll dig a little deeper into the anatomy and function of the hamstrings.

Which muscles make up this group?

The “true” hamstrings include three separate muscles: semitendinosus, the semimembranosus, and the long head of biceps femoris. What distinguishes these muscles from other muscles or portions of muscles that function alongside them, is that the hamstrings cross both the knee and hip joints. Biceps femoris actually has a second “head”, or section of the muscle. But it only crosses and affects the knee joint, as we’ll see below. So, it is not considered a true hamstring.

Where are the hamstrings located?

The specific location of each of these muscles ultimately tells us something about what they can do. All three of the hamstrings (biceps femoris long head, semimembranosus, and semitendinosus) attach to ischial tuberosity of the pelvis (sit bone) at their proximal end. From there, they each take a different path. The long head of biceps femoris takes the lateral path. It’s the cord-like muscle we can easily feel just above the back of our knee. It attaches at its distal end onto the head (top) of the fibula (the smaller of our lower leg bones). 

Our other two hamstrings take a medial path from their proximal attachment at the sit bone. Both semimembranosus and semitendinosus run down the medial side of the back of our thigh. Semitendinosus then attaches at its distal end on the pes anserine, which is an area of the tibia near the tibial tuberosity. Semimembranosus attaches at its distal end on the posterior medial condyle of the tibia (the inside and top part of the back of the tibia).

Why does understanding the hamstrings' anatomy help us understand movement?

The hamstrings are not one muscle. They are three separate muscles that work together in some of their actions. But during other functions, some of the individual muscles do different actions from one another.

If all three of the hamstrings attach to the sit bones on the pelvis, then it makes sense that they could work together to move the pelvis. And this turns out to be true, unsurprisingly. All three of these muscles can contribute to pulling the pelvis into more of a posterior tilt. Likewise, all three hamstrings function to extend the thigh at the hip joint and to flex the knee.

But in other movements, the actions of the individual hamstring muscles diverge. Remember that we have two hamstrings (semimembranosus and semitendinosus) which attach more towards the medial side of our lower leg. So these two muscles contribute to medial rotation of the knee when it’s flexed. In contrast, biceps femoris attaches on the lateral side of the lower leg. As you might guess, it contributes to the lateral rotation of the knee when it’s flexed.

Functional movement

In sports, we might start to think of our hamstrings as just those tight muscles which restrict our movement. But they are so much more than that! The specific action that we mentioned above, extension of the thigh at the hip, is a critical part of walking. When we are walking, the hamstring muscles on one side assist with that movement by pulling the thigh back, a little bit like loading a spring. Other muscles can then take over to bring our leg from behind us into our next step. The hamstrings then contribute eccentrically by slowing down the swing of that leg just before we place our foot.

That the hamstrings also attach at the knee has an implication in gait, or walking, too. They contribute to flexing the knee as we pick up our foot so we can swing it through for our next step. The short head of biceps femoris pitches in and works with the true hamstring muscles during this action. 

No muscle works alone

One thing that’s important to understand about muscles and their actions though, is that no muscle works alone! Muscles work together to create or resist an action. One or more of the hamstrings work as synergists with other muscles in all of their functions.

In the action of pulling the thigh back before we take a step, all three hamstrings are working with gluteus maximus, which is actually our most powerful hip extensor. Adductor magnus, which also attaches to the sit bone, contributes to the hip extension as well. Sartorius, gracilis, popliteus, and gastrocnemius all work along with the hamstrings when we flex the knee.

What can anatomy tell us about how to effectively stretch our hamstrings?

As I said above, one of the actions of all three hamstring muscles is to posteriorly tilt the pelvis on the hip joints. So let’s think about that. If you are actively using your hamstrings in a seated forward bend—maybe because they are just short and tight from sports and you find it difficult to relax them—how easy do you think it will be to stretch them? Probably, not so easy, right? So, if this is you, then it might be helpful to find a way to place the pelvis in a more neutral position before you try to stretch those hamstrings. You might do that by sitting up on a yoga block or bolster.

Why can anatomy help us understand how to work with hamstring pain?

I’ve covered this question in more detail in other articles, so I’ll just touch on it here. Anatomy can tell us a lot about how a muscle functions. And it can tell us something about how and why a muscle might be dysfunctional.

In the case of the three hamstrings, remember that we said that they cross both the hip and knee joints. This means that the tension on both the hip and knee joints influences what we feel in the hamstrings. So whether we’re feeling pain at the sit bone end of these muscles, or pain at the distal end below the knee, it’s important to take a look at what’s happening at the other end of the muscle when we try to find the cause of the pain.

The hamstrings are important muscles in functional movement like walking. Understanding their anatomy helps us understand more fully how they function. And, understanding the anatomy of the hamstrings, can help us understand why they might be dysfunctional. Now that you have a better understanding of hamstring anatomy, take that information with you next time you go for a walk and see what you notice.

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