Length-tension relationship :: Sliding filament theory
The effect of resting fiber length on muscular contraction is referred to as the length-tension relationship. This lesson will describe the. The Length-tension Relationship. For muscles to contract, the muscle proteins called actin and myosin must interact with each other. This occurs when they are . I have a test in kinesiology tomorrow and can't really grasp the length tension relationship is normal terms. Like I can't explain it which is what I.
Let's take a look at the frog's gastrocnemius, or calf muscle: The calf muscle would shorten if it were removed from the body. If you were to remove the muscle from the body of the frog, its length would shorten. Therefore, the muscle is stretched to its resting length within the body. As the muscle is stretched, so are the muscle fibers that make up the muscle organ. As it turns out, the natural resting length of our skeletal muscles maximizes the ability of the muscle to contract when stimulated.
If the resting length is shorter or longer, contraction is compromised. The effect of resting fiber length on muscular contraction is referred to as the length-tension relationship. This lesson will describe the anatomical arrangement of the muscle at rest and explain how this helps with muscular contraction. Length-Tension Relations Let's do an experiment using the gastrocnemius muscle of a frog to examine the relationship between resting muscle fiber length and contraction.
First, remove the gastrocnemius from the frog. Then, clamp the muscle between a fixed position and a force transducer, which is an instrument that will record how much contraction occurs when the muscle contracts. We can move the clamp to change the resting length of the muscle - in other words, how long the muscle is before it contracts.
We will then record contraction after stretching the muscle 1mm each time. Let's start with a short length at which the muscle is pretty loose. When the muscle contracts at this short resting length, we see a small amount of force development, as illustrated by the small blip on the picture below.
Length-Tension Relationship in Training - RDLFITNESS
When the muscle is loose, only a small amount of force develops during contraction. Now, let's stretch the muscle a little bit, so we increased its resting length by just 1mm. As you can see below, the muscle contracts with more force at this longer resting length. And so now there is some space between the z-disc and this myosin right here. So there is some space between these myosins and the z-discs. In fact, I can draw arrows all the way around. And so there is a little bit of work to be done.
But I still wouldn't say that it's maximal force. Because look, you still have some overlap issues.
Length-Tension Relationship in Skeletal Muscle
Remember, these myosins, right here, they're not able to work. And neither are these, because of this blockage that's happening here. Because of the fact that, of course, actin has a certain polarity. So they're getting blocked. They can't do their work. And so even though you get some force of contraction, it wouldn't be maximal. So I'll put something like this. This will be our second spot. This will be number two.
Now in number three, things are going to get much better. So you'll see very quickly now you have a much more spread out situation. Where now these are actually-- these actins are really not going to be in the way of each other.
You can see they're not bumping into each other, they're not in the way of each other at all. And so all of the myosins can get to work.
So the z-discs are now out here. My overall sarcomere, of course, as I said, was from z-disc to z-disc. So my sarcomere is getting longer. And you can also see that because now there's more titin, right? And there isn't actually more titin.
I shouldn't use that phrase. But the titin is stretched out. So here, more work is going to get done. And now my force, I would say, is maximal. So I've got lots, and lots of force finally. And so it would be something like this. And so based on my curve, I've also demonstrated another point, which is that, the first issue, getting us from point one to point two, really helped a lot. I mean, that was the big, big deal. Because you needed some space here.
Again, this space really was necessary to do work at all. And now that we've gotten rid of the overlap issue, now that we've gotten these last few myosins working, we have even more gain.
But the gain was really-- the biggest advantage was in that first step. Now as we go on, let's go to step four. So this is step four now. As we go here, you're going to basically see that this is going to continue to work really well.
Because you have your actin, like that, and all of your myosins are still involved in making sure that they can squeeze. So all the myosins are working.
And our titin is just a little bit more stretched out than it was before. And our force of contraction is going to be maximal. And you're going to have-- and so here, I'm drawing the z-discs again. They're very spread out. Our sarcomere is getting longer and longer.
And our force of contraction is the same. Now let's just take a pause there and say, why is it the same? Why did it not go up? Well, it's because here, in stage three, you had 20 myosin heads working.
Up here, you had something like 16 out of 20 working. Here, we said maybe zero out of 20 right? And here, you again have 20 out of So you still have an advantage in terms of all of the myosins working. But there's no difference between 0. Because again, all the myosins are working.
So now in stage five, we kind of take this a little too far, right? So let me actually just make a little bit of space here. We take this a little bit too far in the sense that our actin is going to slip out all the way over here.
And it's going to be out all the way over here. So we've got a huge, huge gap now. And, of course, our titin is completely stretched out. It's about as stretched out as our titin is going to get. This green titin protein. And now the question is, of course, would you get any force? And the answer's probably no. Because the myosins aren't even touching the actins anymore. So really, again, you have zero out of 20 myosins at work.
Length-Tension Relationship in Training
And of course, that means that then the amount of force would be zero. So we go back down to zero. So this is part five.