Monday, 23 March 2015

1 of 3 Hamstrings: SemiMembranosus

Last week we got into the Hamstrings! 
We started with SemiTendinosus and Today we're talking SemiMembranosus

(see how I've capitalized the T in SemiTendinosus -and the M in SemiMembranosus? I just wanted to note that that is something that I do to help me distinguish between the two ;)

  SemiMembranosus  also lives deeper than - and larger than - SemiTendinosus.

okay, now forget T  :


SemiMembranosis muscle attachment points:

Origin: Ischial Tuberosity *

Insertion: Posterior surface of the medial condyle of the tibia
((approx behind and just below the knee joint))

 *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 tibia is a lower leg bone, the larger one that mid way down we refer to as our shin (bone)
This muscle also attaches to the medial meniscus of the knee ( a pad of cartilage wedge between your femur (thigh) bone and your tibia.  Medial Meniscus helps to reduce friction in the knee joint.

Here is a view of the back of the knee (aka Posterior view)

Posterior View of knee joint. 
not shown: Lateral menisus (also wedged between just on the outside (lateral) side of the knee joint.

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:

SemiMembranosus Muscle Actions:

same actions as last week's SemiT

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 SemiMembranosus also assists in:

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

medial rotation of leg at hip joint
(imagine standing on one leg and then turn the lifted ankle INwards)
But wait!
-WHEN the knee is flexed, it is said that medial rotation of the knee @ the t/b joint is possible 
(say whaaaat? sounds unfortable - I imagine it's just a micro movement -barely noticable)

Standing up and sitting down would be really difficult to do with our hamstrings!
Hamstrings can get tight from too much sitting :(

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)

One more Ham to go!