You Can’t Ignore The TWO Joint MUscles!


Want the Perfect Teaser?

Do you have that client who can’t straighten their legs in supine? Who cramps every time they do a bridge? How about that client who just can’t straighten their legs in teaser? We often respond with “don’t worry, you’re just not strong enough yet” or “you just need to learn to turn off your hip flexors.”  I admit it…  I’ve used these phrases.  But the good news is that these bodies are actually performing exactly as they should.  It’s the Two Joint Muscle that is causing the difficulty … and it’s supposed to! 

Most muscles cross a single joint and are responsible for moving the bones or “levers” of that joint toward or away from each other. Two Joint Muscles or TJM’s are muscles that cross two joints of the body and therefore perform more than one joint function.  For example, the Rectus Femoris (considered one of the quads) actually crosses both the hip and knee joints and performs hip flexion and knee extension. It both lifts and straightens your leg. (For a list of TJM’s, See the Sidebar below.)

Advantages of TJM’s

These joints are designed for efficiency of movement — Less energy is required to move two joints with the same muscle than engage two different muscles.  For this reason, most of the TJM’s are used for power movements like walking, running, jumping, climbing, etc. In addition, the Muscle gets put on a stretch before it contracts - giving it maximum power for an explosive movement. 

Consider the Gastrocnemius or large calf muscle in the back of your lower leg.  It crosses both the knee and ankle joint so it performs both knee flexion (kicking yourself in the butt) and plantar flexion (pointing your toe).  When you’re walking or running the leg and foot first lengthen out in front for your foot strike (knee extension and dorsi flexion) which puts the gastroc on a stretch. As you take the stride and your leg goes behind you, the gastrocnemius flexes the knee and points the toe so you can push off the ground -- An efficient demonstration of the TJM at work!

A Big Disadvantage

There is one important disadvantage to Two Joint Muscles (Also called Biarticulates) that rears its ugly head quite often. And it’s a game changer:

Performing both functions simultaneously weakens the combined effort!

Try This… Stand up and extend your leg behind you. Now flex your knee by bringing your foot to touch your butt. Ouch! Feel that cramp? That is the two joint muscles trying to perform both functions (hip extension and knee flexion) to their max. The result is weakness and cramping!

Now try this one:  Sit on the floor or chair and lean back on your sitz bones, hands on the floor behind you. Lift both legs into tabletop. Now straighten your legs and hold.  Can you do it? Feel a cramp in the Quad? That your Rectus Femoris - It’s a TJM!

Whoa! Wait a minute! Does that mean it’s normal to cramp in the quad when I try to straighten my legs in Teaser!! Yes! Yes! It’s totally normal!  It’s the TJM doing exactly what it’s supposed to do!  It’s burning out because it’s trying to lift the hip and straighten the knee at the same time. What a relief… it’s not you! You’re not weak! You’re just experiencing the challenge when a TJM tries to perform both functions simultaneously.

Once you become aware of these Biarticulates and what they do - you will realize how they can NOT be ignored! They will make their presence known both when you need them (like during a hill sprint) and sometimes when you don’t (like when you are attempting the most perfect Teaser!)  Paying attention to the Two Joint Muscles can be a game changer in how we train ourselves our clients to improve all movement from simple everyday to high powered sports!

Now consider this ... The converse applies:

To get maximum efficiency out of a TJM - take it out of the two joint function!

Bending your knees in Teaser or Roll Up will get rid of the cramp. Take knee extension out of the mix so that hip flexion can be performed properly.  If you want to maximize work on the Rec Fem, take the leg out of hip flexion by supporting it. (Try Teaser with legs supported by the Spine Corrector or Arc)

Did you ever look closely at the hamstring machine at the gym.  It has a slight “A” frame shape. Ever wonder why? It’s to allow for a slight bend in the hip (flexion) to maximize the hamstring curl portion of the movement.

Sidebar: The Two Joint Muscles


  1. 1.Rectus Femoris

  2. crosses hip and knee

  3. performs hip flexion and knee extension

  4. 2.Sartorius

  5. crosses hip and knee

  6. performs hip flexion (with abduction and lateral rotation) and knee flexion (the“tailor’s” position)

  1. 3.Tensor Fascia Latae

  2. crosses hip and knee

  3. performs hip flexion, hip abduction, and internal rotation (The “hackysack” move)

  1. 4.Hamstrings (Semitendinosus, Semimembranosis, Biceps Femoris - Long Head)

  2. cross hip and knee

  3. perform hip extension and knee flexion

  1. 5.Gastrocnemius

  2. crosses knee and ankle

  3. performs knee flexion and plantar flexion


  1. 6.Biceps (Short Head)

  2. crosses shoulder and elbow

  3. performs elbow and shoulder flexion

  4. also pronates

  1. 7.Triceps (Long Head)

  2. crosses shoulder and elbow

  3. performs elbow and shoulder extension

Train in Multiple Planes

We don’t always want to train the muscle in isolation - especially for sports or movements where the TJM’s are critical for speed or explosive power!  The best approach is to work joints in multiple planes and angles!

Take the TJM’s in the arm for example.  The Triceps (Long Head) crosses both the shoulder and elbow therefore performing shoulder extension (sending arm behind you) and elbow extension (straightening the arm). That’s a Tricep Kickback or a Pressdown.  If we always train in this plane - we will only condition one of the triceps.  We must add overhead movements where the shoulder is in flexion to hit the rest. That’s Shave Back of Head or Overhead Tricep Press or Skullcrushers!

The Biceps (Short Head) both bends the elbow and lifts the arm so to train the entire muscle group you need to perform bicep curls with arms low (like Concentration Curls) and arms raised (like in Rowing). To fully train both heads of the Bicep we must work in multiple planes and angles!