Everybody knows there are three hamstring muscles. Some people realize that there are actually four. Very few people recognize all nine. Are you ready to take your anatomy knowledge to the next level? Let’s do it!

hamstringsDefinition of Hamstring

“The word “ham” is derived from the Old English ham or hom meaning the hollow or bend of the knee, from a Germanic base where it meant “crooked”. It gained the meaning of the leg of an animal around the 15th century.[7] String refers to tendons, and thus, the hamstrings are the string-like tendons felt on either side of the back of the knee.[8]” Wikipedia

It’s true, if you feel behind your knee joint, there are some very prominent cords (tendons) that are easier to feel when the knee is flexed (bent). These are the muscles traditionally taught to be hamstrings.

I’d like to propose that we have nine hamstrings, not four. In the hollow behind your knee, there are nine tendons. You can’t feel all of them easily, but they are there. Let’s call them “knee flexors”. At the end of the day, your brain doesn’t have names for the muscles, it knows their actions.

When you want to flex your knee, the brain recruits any muscles that have the ability to perform this action AND that are strong enough to meet the demand (force) being placed on them.

Wikipedia says that the “three true” hamstrings cross both the knee and hip. All three perform hip extension and knee flexion. They each contribute to motion in the frontal and transverse planes as well. Let’s stick with knee flexion in the sagittal plane (the plane of walking, cycling) for now. You have several other muscles performing knee flexion.

Introducing your nine knee flexors: 

True Hamstrings (knee flexion and hip extension)
Semimembranosus: ischial tuberosity TO posterior (back) superior (upper) tibia
Semitendonosus: ischial tuberosity TO medial (inner) superior (upper) tibia
Biceps Femoris long head: ischial tuberosity TO head (upper) of fibula

These are the big cords that can be felt behind the knee joint. If you follow each cord, you’ll find it’s insertion. Then, you can forget the complicated terms and know by sense where they attach.

The 4th Hamstring (knee flexion only)
Biceps Femoris short head: head (upper) of fibula TO lower lateral third of femur

The Lower Hamstrings
Gastroc Nemius lateral – achilles tendon (calcaneus) TO lateral condyle of femur
Gastroc Nemius medial – achilles tendon (calcaneus) TO medial condyle of femur
Plantaris – achilles tendon (calcaneus) TO lateral condyle of femur

Two More Hamstrings
Popliteus – posterior tibia TO lateral condyle of femur
Sartorius – (ASIS) anterior superior iliac spine TO pes anserine of tibia

*The pes anserine is on the superior (upper) medial (inner) tibia.

True Hamstrings?

If hamstrings are knee flexors, then two could be considered “true hamstrings”. The popliteus and short head of biceps femoris are the only two out of theses nine that ONLY flex the knee. They don’t have any direct impact on other joints. 

Stop Memorizing
In my anatomy courses, I emphasize that trainers only memorize one thing. The insertions of the muscles.  You don’t even need to know the complex names of the insertions, just where they attach by feel.  I call both sides insertions, because it gets confusing trying to remember which is origin and which is insertion.  It’s no wonder people have a hard time learning anatomy and avoid it.  

Your body doesn’t use these labels and doesn’t take them into account when moving joints, so don’t confuse yourself needlessly.

If you know the attachment (insertion) points of a muscle, you can always figure out the actions and then create exercises. See how….   

Muscle Actions
Get a rubber band or balloon (something stretchy) and find each side of the muscle on the body. Put one end of the stretchy item on each insertion point on yourself or a partner. Explore what joint actions will shorten the rubber band by moving the joint in different directions. Some movements will lengthen the rubber band (stretch) and others will shorten (contract) it.

Most personal trainers are kinesthetic learners. Getting a feel for where each muscle is on your own body can be easier then learning the complicated names.    

Why Does Anatomy Matter?

Knowing your muscle attachments…

1. Builds respect and awareness for your body.
2. Enhances your knowledge, which fuels confidence.
3. Assists you in communicating with medical professionals to increase credibility.
4. Helps you create specific exercises for clients.


Creating Specific Exercises For Clients

Each of the nine muscles above has unique functions. Some of the muscles work together. You have three muscles attaching to the calcaneus, impacting plantar flexion. Each one travels superior (upward) to a different place on the posterior femur giving it other independent actions such as internal or external rotation of the tibia.

You have three muscles attaching to the ischial tuberosity, impacting hip extension. Each one travels inferior (downward) to a different place on the lower leg causing other independent actions such as hip internal and external rotation.

Internally rotating the tibia and/or femur while performing plantar flexion, knee flexion or hip extension will change which muscles are recruited. Practice these motions slowly in isolation with your eyes closed and you’ll begin to feel the subtle differences.  Add force to the movements if you need help feeling them.

For example: Sit on a chair with feet on the floor and gently press one foot into the floor.  Use friction to pull the heel back, to create knee flexion.  Now, internally rotate the tibia (turn your foot in) and try it again.  Compare the right and left sides.

There are many small movements like this that can be done to identify imbalances in the muscles.  We all have repetitive patterns that cause muscle imbalances. Correcting them requires awareness, anatomy and action (and patience). 

It is complicated, but you can figure it out with some time spent exploring. Knowing the muscle attachments is the first step. Get a partner, it’s more fun that way!

Muscle Imbalances

Ever have a client complain of one side being stronger than the other? Or more sore? Or weaker than the other? Have you ever seen a client do an exercise and one side looks different than the other? Small discrepancies in strength of specific muscles can account for these differences right to left side.

The primary job of a personal trainer is to strengthen muscles. By learning the specific attachments and contracting each muscle individually (as best as possible) you can identify which individual muscles are weaker than the others. It takes time.

It’s what makes the difference between a personal trainer and a professional trainer.     

Test Yourself and Categorize to Memorize
1. Which two muscles are ONLY knee flexors?
2. Which three muscles attach to the ischial tuberosity?
3. Which three muscles attach to the calcaneus?
4. Which seven muscles cross two joints?
5. Which five muscles attach to the superior (upper) tibia?
6. Which two muscles attach to the fibula?

If you found this helpful, please share it with others and check out NFPT’s Anatomy Program!

1.  popliteus and short head biceps femoris
2. semimembranosus, semitendonosus, long head of biceps femoris
3. gastroc nemius lateral, gastroc nemius medial, plantaris
4. semimembranosus, semitendonosus, long head of biceps femoris, gastroc nemius lateral, gastroc nemius medial, plantaris, sartorius
5. popliteus, plantaris, sartorius, semimembranosus, semitendonosus
6. biceps femoris long head, biceps femoris short head

Beverly Hosford

Beverly Hosford, MA teaches anatomy and body awareness using a skeleton named Andy, balloons, play-doh, ribbons, guided visualizations, and corrective exercises. She is an instructor, author, and a business coach for fitness professionals. Learn how to help your clients sleep better with in Bev’s NFPT Sleep Coach Program and dive deeper into anatomy in her NFPT Fundamentals of Anatomy Course.