Lengthening and Shortening 

Concentric and Eccentric Contractions

Well, as far as horses go, you might be expecting me to be talking about cavaletti!  And they are fabulous for this!  Anything where the horse is figuring out and deciding for itself what to do, we can start having communication, and that makes my life easy.   

These next few pages, though, are going to be more about the person.  And, depending upon your background, maybe a little bit more of a mind-bender.

Background

My very simple idea of muscles was that they contracted or they relaxed.  And for me, contraction meant get bunchy and shorter.  Relaxed meant they let go of being contracted and went back to whatever shape they started in.  OR, if the agonist (okay, is that like agony?) muscle was bunching up, the antagonist muscle would relax and passively stretch.  (Mind you, you, the person, would be actively contracting, as in bunching up, something, the agonist muscle and the antagonist muscle would be 'passively' 'stretching.')  Muscles worked in pairs and took turns being bunchy or getting stretched by the bunchy muscle. 

Enter in some education.

Firstly, muscles don't actually stretch like silly putty.  Maybe you knew that.   They change shape by rearranging spindles, by sliding them past each other.  Theoretically.

Maybe that'll come in one of the follow on pages ... Here's the practical part:

Lengthening is a Contraction, too

Well, knock me over with a feather.  

The easiest way for me to understand this is that if you lifted you arm, say to pick up a halter, the you're contracting the muscles on top of the arm to lift it.  So far, so good.

When you go to put the halter down, you're now also contracting your muscles.  (?) While they're getting longer.  (?)  

Which, makes sense when you really pay attention.  If you weren't contracting your muscles as you put the halter down, gravity would take over and your arm and the halter would fall like a rock.  Which generally it doesn't.  The slowing of the descent is because the muscles on top are contracting.

Of course, there's names for this.  When the muscle gets longer, it's called eccentric contraction.  When it gets shorter, it's called a concentric contraction.  Muscles can do both, sometimes contracting eccentrically and sometimes contracting concentrically.  Short and bunchy: Concentric.  Long and lean: Eccentric.  

Biceps is lengthening with Eccentric Contraction. Triceps is shortening with Concentric Contraction.		Biceps is shortening with Concentric Contraction. Triceps is lengthening with Eccentric Contraction.

It's easier for me to think of lengthening contractions when I'm preventing a limb from clanging back down to the ground, but it can also happen when limbs are being lifted.  This is where it gets interesting.

Something to Experiment With

Exploration 1: Lifting the weight up (you don't really need a weight!)

first part:  movement by concentric only Doing a curl, lifting the hand towards the shoulder, the bicep muscle is contracting concentrically.   (getting bunchy.) How does it feel if, as you do this, you pretend the bottom muscles are doing nothing other than getting stretched by the action of the top muscles? contrasted with:  movement by eccentric only While doing a curl, lifting the hand towards the shoulder, with the bicep muscle 'along for the ride,' how does it feel if, as you do this, you pretend the bottom muscles are lengthening actively and in doing so pushing the elbow away from the shoulder, levering the lower arm up into the air? contrasted with:  movement by concentric and eccentric  While doing a curl, lifting the hand towards the shoulder, with the bicep muscle is contracting concentrically, how does it feel if, as you do this, you pretend the bottom muscles are lengthening actively and in doing so pushing the elbow away from the shoulder, levering the lower arm up into the air?

Exploration 2: Lowering the weight first part:  movement by concentric only Doing a curl, moving the hand away from the shoulder, the triceps muscles are contracting concentrically.  (getting bunchy.) How does it feel if, as you do this, you pretend the bicep muscle is doing nothing other than getting stretched by the action of the triceps? contrasted with:  movement by eccentric only While doing a curl, moving the hand away from the shoulder, the triceps muscles are 'along for the ride,' how does if feel if, as you do this, you pretend the biceps are lengthening actively and in doing so pushing the forearm away from the shoulder? contrasted with:  movement by concentric and eccentric  While doing a curl, moving the hand away from the shoulder, the triceps muscles are contracting concentrically (and getting bunchy,) how does if feel if, as you do this, you pretend the bicep muscle is lengthening actively and in doing so pushing the forearm away from the shoulder?

Did anything about this surprise you?  Or change how your arm moved?  Was one way easier than another?  More fluid?  With greater range of motion?

Similar explorations can be done observing the swing of the lower leg under the upper leg, or the leg in its entirety any time you're walking or running.  Or with any set of muscles.  Any time your moving your bones.  Like during stretching, yoga, dancing, or riding.

The "New" Idea

What if the muscle lengthening, eccentric contraction, contributes to changes in the relationships between bones?  What if it's not just a matter of muscles getting short and bunchy, dragging the other muscles into a "stretch."  It's not only about concentric contractions.  And maybe eccentric contraction isn't only about defying gravity.   What if eccentric contractions happen all the time?  

Did you give this a whirl?  What did you notice?  Share if you like!

More to come!

Lynn

4/1/20