Monday, 30 March 2015

1 of 3 Hamstrings: Biceps Femoris

We've covered SemiTendinosus & SemiMembranosus, so
Today we're talking about the 3rd and most lateral hamstring

Biceps Femoris.
Biceps: referring to the fact that this muscle has "two heads" or 'origins' - not to be confused with
biceps brachii (which is your ARM flexor!)

Femoris: referring to the femur (aka thigh bone)

Biceps Femoris muscle attachment points:

This muscle has two points of origin or "heads". The long head refers the origin that is furthest away from the insertion point. The long head is also more superficial & the short head origin is deeper.  And of course the short head would be closest the the insertion point.


Long Head: Ischial Tuberosity * & the sacrotuberous ligament
Short Head:  linea aspera and lateral supracondylar line of the femur.

Insertion: head of the fibula and the lateral tibial condyle


 The other two hamstrings attach on the inside (medial side) of the knee, whereas Biceps Femoris attaches to the lateral (outside) edge of the knee.

 *did you know that all three hamstrings share the same origin of ischial tuberosity?
Ischial tuberosities aka "sits bones", you know those points of the pelvis, butt bones if you will? here's a visual:

The hamstring muscle bellies turn into skinny tendons that cross the knee.
Because they cross both joints, the muscle actions will happen at the hip AND the knee:

Biceps Femoris Muscle Actions:

same actions as the other two hamstrings:

When we're talkin' hamstrings, there are two main actions that come to mind:
- Extension of the thigh at the hip joint (aka coxal joint)
- Flexion of the leg at the knee joint (aka the tibio-femoral joint)

But wait there's more!

Apparently Biceps Femoris also assists in:

'posterior tilt' of the pelvis at the hip joints
(tucking your tailbone down)

Biceps femoris is the only hamstring muscle that can laterally rotate the thigh @ the hip joint
AND the leg @ the knee joint - when the knee is flexed (!)

There are three hamstrings, located on the back of (posterior) thigh bone (thigh bone = femur).  
More specifically, they are tucked between Vastus Lateralis (quad group)
and Adductor Magnus (adductor group)

The term 'Hamstring' apparently comes from 18th century England. Butchers would display pig carcasses in their shop window by hanging them from the long tendons at the back of the knee. 
((I tried to find an image of this with no luck but I also didn't search too hard 
- maybe it's better that way ;))