Shorty Swan here to help you understand your hamstrings. Let's talk about where they are and what they do. Stay tuned for #hammies posts with exercises and more! There's a lot to cover so let's jump right in. 


Your hamstrings are the set of three muscles that make up the back of your thigh. (Must admit they are one of Shorty's favorites!). All three hammies cross over the back of your knee joint and articulate your hip joint. This is important for understanding how they move your body and how to stretch them properly when they are tight. 

Let's do a roll call:

1. Biceps Femoris 2. Semitendinosus  3. Semimembranosus

Biceps Femoris

This hammie has a long head and a short head as it's name indicates. The long head originates at the ishcial tuberosity or sitz bone and the short head originates at the linea aspera which is a ridge located in the middle of the back of your femur or thigh bone. Both heads thread together, pass over the  back of the knee, and insert on the lower leg. The long head inserts on a lateral edge of the tibia and the short head inserts on the lateral head of the fibula.  (Some of you are very familiar with your sciatic nerve and should note it innervates both the long and short head of Biceps fem.)

What does my Biceps Femoris do? 

Great question. The long head acts on hip extension using it's attachment to the ischial tuberosity. Both heads act on knee flexion aka bending your knee. Because this hamstring is positioned laterally, it supports lateral rotation of the flexed knee or extended hip. 




Semitendinosus originates at the ischial tuberosity or sitz bones too, sharing a tendinous attachment with the Biceps Femoris.  Then it travels medially, or towards center line, and inserts on the inside front corner of the shaft of the tibia. 


What does it do?

With it's shared origin to Biceps Fem. comes shared function. Semitendinosus extends the hip and flexes the knee. However, due to its medial insertion it contributes to medial rotation of the knee or inward rotation. 



Semimembranosus originates at the ischial tuberosity. (Those ischia are a busy attachment site!) It continues down and inserts on the inside back corner of the shaft of the tibia. This is the most medial of your hamstrings meaning it sits closest to your midline.  Semimembranosus is deeper than Semitendinosus as well as  a bit wider 


What does it do?

Are you picking up the pattern ? :) Again Semimembranosus shares function where it shares attachment with it's hamstring neighbors. It acts on hip extension, knee flexion and medal rotation of the knee. 


When you think about the insertions of these three muscles on the inside and outside of your knee you can easily put together how balance, strength, stability and ROM for these #hammies plays into knee heath and stability. We will get further into healthy hamstring functions in another post!