Stretching Yoga Injury Knee Health Fitness Strength End Range Flexibility Isometric Strength

Flexibility, Mobility & Isometrics

Flexibility, Mobility and Isometrics are the three pillars of strength in your yoga practice. Let’s look at how they are different, how they compliment each other, and how they can be used to make you stronger in the right ways.

What is flexibility?

I think it’s important to start by discussing what flexibility is in relation to yoga. Flexibility pertains to the range of motion available in a given articular joint. In this case, we’ll look at the knee.

As I mentioned in a previous post, almost every major joint operates as a pulley or lever system. The muscles crossing the joint counteract one another in a complementary way to make the joint move or to stabilize it.

Using the example of the knee, the quadriceps work to extend—straighten— the knee, while the hamstrings work to flex—bend— the knee. This is a simplified version of a complex movement involving lots of little muscles, but you get the point.

When the quadriceps and hip flexors fully engage, the hamstrings relax. However, if your hamstrings are locked up and tight, reaching full extension may prove difficult, and you will find that it is nearly impossible to straighten your leg.

However, were you to continually work on straightening your leg day after day, you’d find that the fascia, tendons, and muscles would eventually begin to back off. Unless you have some sort of injury, you would be able to straighten your leg. You would have increased your range of motion and in essence increased flexibility.

The main thing I want to address here is something known as “end range”. This concept is a bit contradictory in the minds of some folks, specifically chronic yoga enthusiasts. End range by definition means that you can maneuver your joint into either a passive or active terminal extension. Passive end range in the knee's case would be extension without effort, active would be 'muscling' your way into end range. ‘Terminal'  means the absolute range of motion you can achieve without injury.

Sure, being able to get into end range is considered a full range of motion. However, constantly putting yourself in a state of terminal end range is not necessarily a good thing. This is where the disconnect happens for a lot of people in their yoga practice.

When a joint is placed at end range, the burden of keeping the joint stable is often placed entirely on the fragile ligaments and connective structures of that joint. You’re basically hanging your body weight on connective tissues.

Say, for example, you are in Warrior Three and you are able to get your knee completely straight. If you were to just arbitrarily straighten your knee, it would look and feel like it’s about to buckle backward, which, even if it doesn’t happen, is a dangerous position to put your poor knee in. However, if you were to find just a little bit of tension in the muscles surrounding the knee, you can stabilize the knee joint through strength rather than relying on the soft tissues and other structures to compensate for muscle laxity.

We’ll get back to this in a minute, so let’s look at the difference between flexibility and mobility.


Mobility is the ability of a joint to go into full range with control.

There has been a lot of confusion about the difference between mobility and flexibility as of late. Although they are definitely cut from the same cloth, the concept of mobility goes beyond being able to touch your toes. Being fully mobile in a joint complex means you are able to go into your full range of motion while being able to execute movement and stability in or near end range positions.

Mobility is best illustrated in the practice of gymnasts, dancers, and well-trained yoga practitioners, but take this ridiculous example instead:

I do not recommend even considering to attempt this, btw.

This example of Jujimufu being absurdly strong at end range (and in general) helps to illustrate the difference between the two. Yes, he is doing the splits, but where an hyper-flexible person would simply collapse and rupture (probably multiple muscles) due to lacking tensegrity and strength, he is mobile in his ability to control the movement and remain stable throughout.

Somehow. I hope.

Mobility in contrast to flexibility involves strength and coordination to move the joint through an entire range of motion without losing control of joint stability. Mobility is strength at end range, and to become strong at end range, you need to be able to master isometrics.

What does isometric mean?

Try this:

With your back flat against a door jamb, ball your hand into a fist and curl your fist toward your bicep-- like you're curling a dumbbell. Now, with your whole back flat on the wall and your arm fully curled, lift your elbow as high to the ceiling as you can. Fully contract and hold it for about ten seconds.

If you do this correctly, you’ll notice that your bicep starts working really f’ing hard because the anterior aspect of your arm is maximally contracted. This is an isometric hold at contracted end range. All the muscle involved are completely engaged and you are simply holding it.

When the full range of motion of any joint, in this case, the elbow and wrist and partially the shoulder, moves through a range of motion there are three phases known as concentric, isometric and eccentric.

Simple example: when you lift a fork to your mouth, your arm flexes concentrically; when you lower it back down, it is an eccentric movement phase. The moment where you hold the fork to your mouth is isometric.

Isometric strength and mobility go hand in hand because isometric control and strength allow you to be stable at end range. However, being able to hold a position at any point in the range of motion creates coordination, strength, and stability; it's the key to a truly strong yoga practice.

Let’s once again look at our yoga example in Virabhadrasana (Warrior) III

As mentioned, a lot of folks, whilst yogaing, are tempted to straighten their leg completely while in this position which creates an ugly buckling effect in the knee joint. I would argue that they are missing out on a heap of benefits while putting their knee in a potentially dangerous position. Just because you can get your knee locked straight does not mean you should.

Instead, try to find a slight bend at the knee and hold there. If you are utilizing the pulley system wherein the quads and hip flexors are engaged with the hamstrings also slightly engaged, you are implementing an isometric hold creating an equal distribution of force on both sides of the knee. You'll also find that it's a more work, aka a lot more strength gain.

Thus, you stabilize the knee and become universally stronger on both sides of the joint while mitigating the strain on those itty-bitty ligaments, in this case, the ACL, MCL, and PCL.

Think about the cables on either side of a bridge; if the cables are weak on one side, that bridge is gonna collapse.  You do not want your knee to do that.
Yoga is not simply about stretching and becoming hyper-flexible; if you truly want to get strong in your physical yoga practice, you need to determine what actually needs to be lengthened and which weak muscles need to be strengthened.  Simply repeatedly going to end range can be dangerous. Use isometrics to your advantage and increase your mobility instead of trying to prove to yourself and everyone else how sloppily flexible you are.

Hope this helps. Comments welcome as always. Until next time...


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