sliding filament theory

[anniehall]

Hi,
I've been reading and trying to understand the practical way of understand this concept when it comes to explaining it to future clients. Can anyone help me. All the textbooks talk in a way that I just don't understand!
Thanks!

[dos]

From http://bio.winona.edu/berg/ANIMTNS/SlidFila.htm...

Two adjacent sarcomeres are shown going through cycles of contraction and relaxation. If the thin filaments are attached to something such that a load can be developed, tension will develop on the sarcomeres as they shorten. Click here to see the key for this animation. Note that as the sarcomere contracts, the Z lines move closer together. The myosin thick filaments "walk" their way along nearby actin thin filaments. Since the structure of the thick filament allows the myosin to "walk" in both directions and since the myosin fibers do not stretch, the thin filaments of opposite polarity are pulled together.


Does that help at all?!? [img]smile.gif[/img]

[bryanc]

Um...what practical significance does the sliding filament theory have with respect to your training clients?

[dos]

I was actually thinking the same thing.....

[Jean-Paul]

It may not have any real significance, but it is good to have a full and in depth understand of the physiology of exercise don't you think? We don't share probably a fraction of what the knowledge on fitness we actually possess, but should you ever get an intense questioning from a client it sure helps if you know it well enough to explain it.

[wingsfan]

Originally posted by bryanc:
Um...what practical significance does the sliding filament theory have with respect to your training clients?

if i recall from another thread, annie is studying up to take either the NCSA-CPT or the CSCS exam or maybe it was one of the other one's.

[rem1956]

Probably the CSCS. I am studying for the same and I recognize the concept and terminology. I struggled with that concept for a while, but think I am foinally getting it. However, thanks dos....fresh prespectives are always nice.

[anniehall]

thanks for the info. Yes JP answered the question perfectly. I still don't get it. In dummy terms. Let's say I do a bicep curl. What's happening in the sliding filament theory during concentric and eccentric action? I'm just trying to understand it for a practical perspective or am I way off?

[vin]

Originally posted by anniehall:
thanks for the info. Yes JP answered the question perfectly. I still don't get it. In dummy terms. Let's say I do a bicep curl. What's happening in the sliding filament theory during concentric and eccentric action? I'm just trying to understand it for a practical perspective or am I way off?

While I can't answer your question, as it's been a while since I studied that - I can tell you that it was a difficult concept for me to really understand. If you're using the NSCS text (like I was), read it over a few times and do the exercise they give you at the end of the chapter for it - that's what finally helped me to 'get it' (although, since then I've 'lost it' )

[Craig]

Annie,

Referring to the diagram above (posted by Dos):

When you do a "biceps curl", the tension meter in that diagram starts moving from 0-100%. And the model of the sliding filaments start to come together. That is the concentric motion.

In the eccentric motion, everything is moving apart. However, its not accurate to say that tension goes from 100% to 0% in an eccentric contraction, b/c you can still produce force during eccentric movements.

This is course material from a 1st or 2nd year University level kinesiology program.

Craig

[bryanc]

There isn't really a "dummy way" to explain the sliding filament theory (which, in terms of being relevant and practical to training clients, is questionable, since there's now some research that shows that the sliding filament theory does not adequately explain some observed phenomena of muscle contraction).

Muscle contraction involves three proteins--two chain proteins and one globular one. The two chains proteins are actin and myosin. Actin is a thin filament. Myosin is thicker. You can picture actin as a thin piece of string. You can picture myosin as a thicker piece of string with little blobs hanging off it at regular intervals. The globular protein is called tropomyosin and it normally sits on the actin filament covering bits of it that are important for actin-myosin binding. When the signal for muscle contraction happens, calcium binds to the globby tropomyosin and makes it move away from the binding site. One of the little globby bits of myosin then is naturally attracted to the binding site on the actin filament and so it gloms onto the binding site. This happens all over the actin and myosin filaments.

Then, through the magic of ATP->ADP conversion, energy is spent and the globby myosin bits change their shape and , unified, pull the actin filament like so many slaves, chained at the ankles, pulling on a rope (the slaves don't move, the rope does. The rope is the actin filament). Then the myosin globby bit lets go, tropomyosin moves back into place and the whole cycle begins again.

More later. I have a patient and then class right now.

[Kaiser]

Originally posted by Craig:
This is course material from a 1st or 2nd year University level kinesiology program.

It's also in Chapter 1 of the CSCS text, which may be why she is asking. Thanks for all the answers guys...like Vin, I had 'lost' this info, but your answers have allowed me to 'find' it again. [img]smile.gif[/img]

[Jean-Paul]

However, its not accurate to say that tension goes from 100% to 0% in an eccentric contraction, b/c you can still produce force during eccentric movements.

Expounding on what Craig just said, when you extend your arm, you are contracting your triceps, and getting uniform extension (lengthening) of the biceps. When you draw your wrist to the shoulder you are extending the triceps and uniformly contracting the biceps. When you are raising your arm with a dumbbell you are uniformly contracting your biceps, but when you lower the weight, you aren't so much contracting the tripeps to extend your arm. Your biceps are still working, so you basically have non-uniform contraction and extension of the biceps in the eccentric portion of that movement. That is why you are still producing force in the eccentric portion of the movement, and technically, that is where hypertrophy occurs.

[Jean-Paul]

Oh, Bryans explanation went up before I was done typing this. I like that explanation a lot.

[bryanc]

Ok, so during concentric and eccentric contractions:

According to the sliding filament theory, the actin and myosin and tropomyosin proteins are doing the same stuff. Concentrically, the filaments continue to slide to produce movement. Eccentrically, the filaments don't slide physically as much in relation to one another, but myosin and actin still bind and unbind from one another. However, within each motor unit, not all myosin globs bind to all actin binding sites--nor do 100% of motor units contract. Think about the slave analogy again where not every slave pulls the rope, but only a proportion of them pulls at any given time. So the rope can be pulling away from them and they can control the rate at which it pulls way from them by controlling how many slaves pull on the rope at any given time.

How eccentric contractions contribute to hypertrophy is still not understood.

That's as close as I can get to "dummying down" the sliding filament theory.

[poopy pants]

Excellent post bryanc...ever thought of going to med school? [img]smile.gif[/img]

[bryanc]

Laf.

Man, going to lecture for the first time in four years is going to take some major adjusting to (8:30am lectures!!!). And I miss my office. And the fact that the gym was down the hall. And the fridge in my office (I gotta lug food around with me). Oh, and the research too. Gotta find me a cool project to do so I don't go mad.

[poopy pants]

Originally posted by bryanc:
Laf.

Man, going to lecture for the first time in four years is going to take some major adjusting to (8:30am lectures!!!). And I miss my office. And the fact that the gym was down the hall. And the fridge in my office (I gotta lug food around with me). Oh, and the research too. Gotta find me a cool project to do so I don't go mad.

Major adjustment no doubt, and less posting time too I take it.