Muscle Physiology - Functional Properties
Tension development during isometric tetani in single fibers of frog semitendinosus muscle occurs in three phases: (a) in initial fast-rise phase;. The steepness of the cardiac length-tension relation arises because the degree of . study of the filament lattice of striated muscle in the living state and in rigor. The length-tension relationship is also observed in cardiac muscles. in the passage from the resting to the active state is a function of the length of the fibre.".
And actually, force of contraction is very much related to this length-tension relationship as well. So I'm going to put that up here.
Length-tension relationship :: Sliding filament theory
And instead of using that terminology, though, we're going to use the term tension. I mean, you can essentially think of them the same way. But classically, the word tension is what everyone uses. So we're going to use that same word. And then, as far as length, specifically the length that we're talking about is the length of a sarcomere. So I'm going to write sarcomere here.
And the sarcomere, just keep in mind, is really going from one z-disc to another z-disc. So to draw this out, to actually write it out maybe, we can start with myosin. And so maybe this is our myosin, right here. And I'll draw some myosin heads here. And maybe some myosin heads on this side, as well. And, of course, you know it's going to be symmetric looking, roughly symmetric.
So this is our myosin.What is the length tension relationship of muscles?
And actually, I'm going to make some copies of it now, just to make sure that I don't have to keep drawing it out for you. But something like that.
And we'll move it to be just below so that you can actually see, when I draw a few of them, how they differ from one another. So I'm going to put them, as best I can, right below one another. And we'll do a total of, let's say, five. And I think, by the time we get to the fifth one, you'll get an idea of what this overall graph will look like. So these are our five myosins. And to start out at the top, I'm going to show a very crowded situation. So this will be what happens when really nothing is spread out.
It's very, very crowded. And you recall that you have actin, this box, or this half box that I'm drawing, is our actin. And then you have two of them, right? And they have their own polarity, we said. And they kind of go like that. And so, in this first scenario, this very, very first one that I'm drawing, this is our scenario one. We have a lot of crowding issues. That's kind of the major issue, right? Because you can see that our titin, which is in green, is really not allowing any space.
Or there is no space, really. And so, these ends, remember these are our z-discs right here. This is Z and this is Z over here. Our z-discs are right up against our myosin. In fact, there's almost no space in here. This is all crowded on both sides. There's no space for the myosins to actually pull the z-disc any closer.
So because there's no space for them to work, they really can't work. And really, if you give them ATP and say, go to work. They're going to turn around and say, well, we've got no work to do, because the z-disc is already here. So in terms of force of contraction for this scenario one, I would say, you're going to get almost no contraction. So when the length is very low, so let's say this is low.
Maybe low is not a good word for length. Let's say this is, I'll use the word short. The sarcomere is short. And here the sarcomere is long. So when it's short, meaning this distance is actually very short, then we would say the amount of tension is going to be actually zero.
Because you really can't get any tension started unless you have a little bit of space between the z-disc and the myosin. So now in scenario two, let's say this is scenario two. And this is my one circle over here. In scenario two, what happens?
Well, here you have a little bit more space, right? So let's draw that. Let's draw a little bit more space. Let's say you've got something like that. And I'm going to draw the other actin on this side, kind of equally long, of course.
I didn't draw that correctly. Because if it's sliding out, you're going to have an extra bit of actin, right?
And it comes up and over like that. So this is kind of what the actin would look like. And, of course, I want to make sure I draw my titin.
Titin is kind of helpful, because it helps demonstrate that there's now a little bit of space there where there wasn't any before. 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. Remember, these myosins, right here, they're not able to work. Intensity of eccentric exercise, shift of optimum angle, and the magnitude of repeated-bout effect. Journal of applied physiology, 3 The effects of eccentric hamstring strength training on dynamic jumping performance and isokinetic strength parameters: Physical Therapy in Sport, 6 2 Fatigue affects peak joint torque angle in hamstrings but not in quadriceps.
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Proceedings of the Royal Society B: