contractions/shortening and lengthening of muscles

Hi guys

A debate in my class today made me realise how much some people (possibly myself) didn't understand how the body moves and what the role of muscles are!

We were asked to explain what muscles work concentrically and eccentrically in a downward phase of a squat. I personally got stuck on the contraction of the hamstrings at the knee because to me, i feel it isn't a contraction, but a movement...shortening to be exact.

The debate was carried on further by trying to explain the movement of the tricep in an eccentric bicep curl. Most people in my class said that the tricep contracts to control the movement of the arm as it extends, again i was not convinced! (at this point i thought to myself "i shouldn't have said anything" haha) this is how i see it.

As the arm extends with the weight in hand, all control is in the anterior muscles of the arm i;e biceps, ant. delt, wrist flexors, brachial radialis etc. I don't see how the tricep does anything apart from shorten in length passively NOT actively.

I even tested it myself, i picked up a 10kg dumbell and lowered my arm slowly whilst palpating my tricep with my free hand....just as i thought no contraction at all it was floppy and relaxed all the way through the motion!?

I figured the same happened with the squat, as your butt gets closer to the ground quads are contracting eccentrically but the hamstrings at the distal end are being stretched but aren't contracting. At the proximal end, the hamstrings are eccentrically contracting, stretching out under tension along with the glutes (hip extensors).

Can someone clarify this for me cos personally i think what i am picturing is write but i may have taken the word 'contract' too literally?

cheers guys

First thing to remember:

If a muscle shortens, it contracts concentrically (towards the center). If it lengthens, it contracts eccentrically (away from the center). No exceptions.

Why? Because it actually costs ATP to relax! At the tissue level, the resting state of the working myosin heads is actually in constant contact with the active site of the actin filament. When we die, our muscles are constantly burning ATP at the cellular level. When it's all gone, there's no more energy to keep the muscles relaxed, and you get a complete tetanic contraction (rigor mortis) that lasts until the proteins start breaking down.

That's a simplified explanation, but should serve to help you make the conceptual connection to the idea that if a muscle changes length, a contraction of some type is occurring. There is no such thing as truly passive muscle length change, at the tissue level. There are always messages being sent to the muscles that cause the length change to happen.

So, now that you understand this, let's move on

Start at the knees. What muscles cross the knee? Popliteus, gastrocs, all hamstrings, etc. Just look at origin and insertion, and make a list.

Next, list the actions of these muscles ON THE KNEE. Example: rectus femoris: knee extension. It does hip flexion too, but don't think about that right now. We're just looking at the knee. Example 2: Hamstrings: knee flexion.

Now, which way does the knee move during the downward phase of the squat? Into flexion. Therefore, you can say for sure that any knee EXTENSORS are working eccentrically.

I mentioned these muscles for a reason: They also perform actions at the hips.

Rectus femoris: Hip flexion

Hamstrings: All but the short head of biceps femoris cross the hip joint, and participate in hip extension.

Now, the hip is flexing as you go down, and so is the knee. For simplicity's sake you could assume that since the hip is flexing, which should cause concentric contraction for rectus femoris, but the knee is also flexing, which should cause ECCENTRIC contraction, that there is no change in length and that you have an isometric contraction. On the other hand, the other three quadriceps are just knee extensors, and since flexion is opposed to extension the movement must be eccentric.

Remember, when we list a muscle action we are talking about what it performs CONCENTRICALLY!

 *throws you a scuba tank* Ok, now hang on, because we're going to dive right in:

The truth is a little more complicated when muscles have actions on two or more joints, and figuring out what is going on requires goniometers (or knowledge of a particular subjects goniometric data at the knees and hips throughout several reference points of the squat ROM). Goniometers measure joint angles. This information will let you say something like this: "Oh, during this part of the upward phase, perhaps the first 40 degrees of the upward squat, there's more hip extension than knee extension. That means that the hamstrings are getting shorter, and the rectus femoris is getting longer, because even though opposing functions are happening at the same time, there is MORE hip extension than knee extension, and that means that the rectus femoris is lengthening more than it is shortening. It can't do both at the same time, so it must be lengthening, and that's an eccentric contraction!"

You will then do this for every single muscle involved in the joints of interest. YAY!!!

Thanks Josh,

I was hoping you would reply to this...but i'm still not clear on one thing, bare with me here;

If we apply the same logic to the hip flexors during the downward phase of a squat, would you still say they were performing a concentric action??...The way i see it is gravity pulls me down towards the ground without me having to actively contract my hip flexors to flex my hip. almost as if I'm just being folded up through natural downward force.

I checked the definition for contractions and the encyclopedia says this:

• In concentric contraction, the force generated is sufficient to overcome the resistance, and the muscle shortens as it contracts. This is what most people think of as a muscle contraction.
• In eccentric contraction, the force generated is insufficient to overcome the external load on the muscle and the muscle fibers lengthen as they contract. An eccentric contraction is used as a means of decelerating a body part or object, or lowering a load gently rather than letting it drop.
• In isometric contraction, the muscle remains the same length. An example would be holding an object up without moving it; the muscular force precisely matches the load, and no movement results.

So, this brings me back to my original boggle!.....how can a muscle shortening be the same as it concentrically contracting?? How can a muscle stretching be the same as eccentrically contracting??

If we could remove the tricep from the arm during a eccentric bicep curl, surely there would be no change in performance of the movement?? The arm would still extend under the control of the bicep?

Basically i agree with exactly about what your saying happens to the muscle during a functional process, but i disagree with the terminology of labelling a relaxed shortening of a muscle a concentric action/contraction.

To me this is one of the most interesting topics on here!....thanks for you time man!

cheers

Not going to steal Josh's thunder but a couple points. Next time to squat do NOT rely on gravity, actively pull yourself down. This goes for any eccentric, lowering a shoulder press..pull it your lats down etc.

How stable would a joint be without the antagonist attachment?

Nic: I'm all about having more people's thunder in here You are totally right, and that's a great point. This has helped me a whole lot for a long time... actively stabilizing joints is very important. It doesn't take much, but that little bit is a BIIIG difference to me.

Bio: Nic probably has more time than I do right now, and more knowledge in this area, so listen when he speaks

You can disagree all you like, but your muscles won't care at all. You are trying to combine external and internal influences, and worst of all you're using Wikipedia as your primary source We all use wiki, but it can't replace proper education.

Muscles don't care about anything except resistance. If they shorten, it is concentric. Period. If they lengthen, it is eccentric, period.

I dont have any more time tonight, sorry!

Nic: haha thanks, don't worry i don't just drop to floor with 40kg on my shouders (front squat).

The point i am making is on the terminology only. If a concentric contraction is a muscle shortening and the force generated surpasses the resistance (That's what it says in all the dictionaries, not just wiki). Then how can that be the same as a muscle shortening WITHOUT any resistance. it's like opening a door (door is a hinge joint too), if i push a door open...there's no force pulling it open at the same time. So imagine me pushing the door open is the eccentric bicep contraction...the only thing the hinge can do on the other side is get shorter passively.

Also, you can't activate your hip flexors in a squat....unless you pull yourself down at a greater force than gravity...which would NOT be a good idea with weight on your back. BUT, I understand that antagonist's on certain parts of the body (the stabilizers) can be actively contracted to help stabilise a joint under tension through ROM like the arms and knee's.

Concentric contraction - muscle shortens as force generated surpasses resistance

Eccentric contraction - muscle lengthens as reistance surpasses force generated

Isometric contraction - muscle stays the same length and meets resistance

shortens - gets passively shorter (i.e tricep in a eccentric bicep curl)

lengthens - gets passively longer (i.e tricep in a concentric bicep curl)

You're missing the inherent muscle tone that is always present in the body. Gravity is assisting the motion.

Your base understanding of function and force balance at the joints needs more study.

Put a rubber band of equal strength on each side of your door. Now when you move it as both sides are equal it will stay where it is, but there is always tension. Very simplified example of course.

Oh and you can very much use your hip flexors in a squat. This is very key for advanced lifters.

The rubber band is a good example! I'm remembering that one.

OP: There is no such thing as passive movement of a muscle in real human motion. As Nic has said, your education is lacking. I would focus on understanding that the body is always using the muscles surrounding the articulating joints to some degree.

Glad you like it

Thanks for the reply Nic!

I was unaware of an inherent muscle tone

So, you're saying that regardless of the muscle being used to articulate the joint or not...it always has tension in it?? which in turn makes the tricep's role in a eccentric bicep curl a concentric contraction because the fibres are always in some tension? adding load just makes it a stronger concentric contraction?

Just as a side note: Squating specialist coach Mark Rippetoe has posted a squating seminar on the crossfit journal website and on there he explains how the hip flexors aren't doing anything during the downward phase of a squat!? The stability comes from the trunk muscles which are performing iso-metrically to keep the intervertebral relationships the same as you decend and come back up. The only way you could use your hip flexors in a squat is if you bolted your feet to the floor and pulled yourself down.

But if your saying that the muscle is in constant state of some tension anyway, then i understand where you're coming from. But if a muscle is never relaxed then whats the point in calling it a concentric or eccentric contraction...why not just call it getting longer and getting shorter?

Personally i think the only way to test it would be to remove someone's hip flexors and get them to squat! haha

The hip flexors stabilize the joints.

Rippetoe is right if what he meant to say is that quite a few of them do not provide any substantial controbution to the actual movement, but he is dead wrong if he thinks they are taking a nap. Some help stabilize the hip, one helps stabilize the spine, two (at least) perform knee extension to some degree, etc.

Hip flexors (partial list of muscles and actions during a squat):

Iliacus: stabilizes hip directly

Psoas: stabilizes hip (indirectly) and spine (direct lumbar spinal extension)

Rectus femoris: knee extension, hip flexion; primarily a knee extensor in squats

Sartorius: hip rotation (direction depends on degree of rotation), hip flexion, knee extension.

Tensor fascia latae: hip abduction, hip rotation

As you can see, these muscles all do important things. They don't necessarily contribute directly to upward or downward motion, but they are directly involved in stabilizing your joints. How do you ensure you hinge exclusively at the hip if you do not use the muscles that move the joint (and the muscles that stabilize all the vertebral joints, which include psoas, a primary hip flexor)? How do you keep forces centered in the acetabulum with out them? :answer: You can't.

yer good point...i'm sure he didn't mean they were 'dead' in the movement. The question he asked his students was "what were the hip flexors doing during the downward phase of a squat?...Is it concentric or eccentric or neither?" and then he went on to say how gravity was taking the tension out of the hip flexors.

Also in regards to the psoas being a primary hip flexor....In Dr. Evan Osar's seminar about the psoas..(i think it's fitnesseducationseminars.com) he had a women who had her right psoas removed because of a tumour and tested negative for hip flexion but positive for hip/trunk/midline stability!!? the case study is on his website...you might like to check it out

I always use the drawbridge example....Which i adapted to the eccentric bicep curl! when a drawbridge lowers there's nothing pulling it down only gravity. The chain (biceps) is lowering the bridge under tension. Now, if we imagine that same bridge as the femur and the chain on the bridge as the psoas. That would mean that it would be attached to the bridge at a sub-optimal position which would be near the proximal end i.e the lesser trochanter, and not the distal end i.e the tibia via patella (end of the bridge). Mechanically, the RecFem has a far greater advantage of lifting the femur than the psoas.

So it makes sense to say that the psoas isn't a primary hip flexor but a primary hip stabilizer. Which i know is what you said it does indirectly but i just wanted to use the drawbridge example as an awesome way to show it.

One final question: If the hip flexors are stabilizing the joint on the way down and the same goes for the tricep in the eccentric bicep curl....how come it's all floppy and relaxed as like i wasn't moving my arm at all?? i can put my hands on my hip flexors at my hips in a squat and as i go down, i feel nothing but flop....so if they are this floppy...how are they providing tension to stabilize??

Nic Branson said:

Not going to steal Josh's thunder but a couple points. Next time to squat do NOT rely on gravity, actively pull yourself down. This goes for any eccentric, lowering a shoulder press..pull it your lats down etc.

How stable would a joint be without the antagonist attachment?

Nic I just want to ask about using the antagonists such as the hip flexors and hamstrings on the eccentric. I tried this with a bodyweight squat and when doing it I got a deeper range of motion with good form(keeping my back straight). Now here is where I get confused, when doing a squat with TUT such as 4-0-2 I feel my hamstrings and hipflexors contract, and feel A LOT of tension going through my legs when doing the eccentric. The thing is when I'm getting out of the bottom position of the squat its hard for me to let go of the tension in my hip flexors for tat brief second, and I'm not trying to be inefficent in my concentric phase. Is this where muscle control comes in? As in over time I will be able to relase the tension at the bottom, and then contract my agonists with efficency after using my antgonists in the eccentric?

Finally is there a limit to how hard I should "pull myself" down into the squat? As in should I only contract so much when going down in the eccentric so I don't make myself inefficent, or does the more tension I get from my antagonists when going down become more beneficial? When going SUPER SLOW  something like 10-0-10 I can generate a lot of tension on my eccentric from my antagonists and as I get lower the contraction gets stronger. 

Muscle Control indeed

Your focus is to build the tension in your agonists by pulling against them, the tension also increased the stability to drive harder out of the bottom. No need to go crazy with the tension. Controlled tension is the key.

Make sense?

In some ways, one of TaiJiQuan's main focus (and other martial arts to a lesser extent) is to teach the body to release the antagonists residual tension.

Very, very hard to acquire

FredInChina said:

In some ways, one of TaiJiQuan's main focus (and other martial arts to a lesser extent) is to teach the body to release the antagonists residual tension.

Very, very hard to acquire

I guess that could be the case here  I heard advanced powerlifters flare their lats HARD when bench pressing, and after that I guess they must have the muscle control to release the tension from the antagonists to let their agonists work on the concentric phase.

Nic Branson said:

Muscle Control indeed

Your focus is to build the tension in your agonists by pulling against them, the tension also increased the stability to drive harder out of the bottom. No need to go crazy with the tension. Controlled tension is the key.

Make sense?

I get the idea NIc, thanks! I guess its definitely going to take a while before I really am able to relax my muscles (specifically hip flexors) when coming out of the bottom of the squat as well as other lifts and exercises 

Try a different approach. Do 1-3 squat jumps before you squat next time.

"Okay, someone needs to explain to me how weak hip flexors are involved in this. How is it that resisting the load on a heavy bar as you perform an eccentric contraction down to the bottom of your squat involves active hip flexion? Yes, the hips and knees are coming into the position of flexion, but do you think you are actually pulling 405 down into the bottom with your hip flexors? I thought the weight pushed you down. Or is there some arcane, esoteric aspect of biomechanics that eludes me here? I see these comments occasionally, and it appears to me that we are using our hip extensors rather thoroughly when we squat, and that the hip flexor muscles (flexion in this case being the proximal function of these muscles, the rectus femoris, sartorius, and tensor fascia latae) are working distally to resist knee flexion, and then to actively extend the knee."

Just to show that i am not the only one with this opinion.

The opinion is not the same, I know Mark. He's talking more about the degree of activation.

Fluidity said:

I guess that could be the case here  I heard advanced powerlifters flare their lats HARD when bench pressing, and after that I guess they must have the muscle control to release the tension from the antagonists to let their agonists work on the concentric phase.

At the bottom of the bench a hard lat flare will actually get the moving the first couple of inches for you. Also as you are not protracting during a bench press the inhibition caused by the lat flare is minimal.

bio-mechanix said:

 

Here is another one of Mark Rippetoe's comments in "ATG squatting [archive] - startingstrength.com

 

Mark Rippetoe

09-18-2007, 10:00 PM

 

"Okay, someone needs to explain to me how weak hip flexors are involved in this. How is it that resisting the load on a heavy bar as you perform an eccentric contraction down to the bottom of your squat involves active hip flexion? Yes, the hips and knees are coming into the position of flexion, but do you think you are actually pulling 405 down into the bottom with your hip flexors? I thought the weight pushed you down. Or is there some arcane, esoteric aspect of biomechanics that eludes me here? I see these comments occasionally, and it appears to me that we are using our hip extensors rather thoroughly when we squat, and that the hip flexor muscles (flexion in this case being the proximal function of these muscles, the rectus femoris, sartorius, and tensor fascia latae) are working distally to resist knee flexion, and then to actively extend the knee."

 

Just to show that i am not the only one with this opinion.

 

Do you want to be right, or do you want to have a better understanding of how your body works?

From Dr. Osar's site:

http://www.fitnesseducationseminars.com/uncategorized/the-psoas-part-3-management

Halfway down the page:

 

CONCLUSION

The psoas is an extremely unique muscle functioning in a variety of roles:

• as a connection between the trunk and the lower extremity
• as a stabilizer of the spine, pelvis, and hips during activities of daily living
• as a decelerator of the trunk and hip during gait.

 

 

Nic: The opinion is the same, In his seminar he says exactly what i was saying

Quote Mark: "How is it that resisting the load on a heavy bar as you perform an eccentric contraction down to the bottom of your squat involves active hip flexion? Yes, the hips and knees are coming into the position of flexion, but do you think you are actually pulling 405 down into the bottom with your hip flexors?"

I said the same thing earlier and you said "

Nic Branson said:

Oh and you can very much use your hip flexors in a squat. This is very key for advanced lifters.

 

Next time to squat do NOT rely on gravity, actively pull yourself down. This goes for any eccentric, lowering a shoulder press..pull it your lats down etc.

 

I'm not debating out of ignorance honestly!.....But until someone can prove that the muscles do what you say then i will stick with what sounds more mechanical and physically logical. However i will research this further and try and find some journals/articles.

Josh: Of course i want to understand better how the body works....But i just can't see why the body would waste time contracting a muscle that doesn't need to be contracted.

I'm sure if i research more of this, it will suddenly click and i will realise what you guys were trying to tell me

cheers

Well since your mind was already made up I am not sure why you wasted our time.

I know Mark personally, your quote only signifies what we agree on as not pulling the entire weight of the load down. In any case I've wasted enough time here.