Single fibres isolated from the tibialis anterior muscle of Rana temporaria were The descending limb of the length-tension relation extended between and Changes in sarcomere length during isometric tension development in frog. Length changes of consecutive. mm long segments of frog single muscle fibres were studied by photoelectric recording of opaque markers placed on the. Single twitch fibres were dissected from anterior tibial muscles of the frog, Rana pipiens, The relationship between tension and average sarcomere length was .
It is currently still unclear whether the changes after acute exercise and after long-term training are caused by the same, similar, or different factors.
However, more recently studies have found that workouts involving only concentric training are also able to produce shifts in the angle of peak torque to longer muscle lengths Guex et al. However, markers of muscle damage are not related to the extent of the change in the angle of peak torque after exercise Welsh et al.
Indeed, Guex et al. Where such studies have been carried out, they have most commonly used eccentric training. These studies have found conflicting results. In the long muscle length group, the angle of peak torque did not change after training.
In another study design, Guex et al.
Sarcomere length-tension relationship (video) | Khan Academy
The subjects in both groups trained using knee flexion muscle actions, but one group performed the exercise lying down, with the hip in 0 degrees of flexion full extensionwhile the other group performed the exercise seated, with the hip in 80 degrees of flexion.
However, a minority of trials have also reported no increases Kawakami et al.
This suggests that increases in muscle fascicle length are partly responsible for the change in the angle of peak torque after strength training, although other factors are likely involved. The effects of muscle length during strength training on angle of peak torque are unclear, but longer muscle lengths may lead to greater shifts in the angle of peak torque. Muscle fascicle length does tend to increase after strength training, particularly after eccentric training.
The relationship between the change in the angle of peak torque after strength training and the increase in muscle fascicle length is unclear, but there does appear to be a moderately-strong relationship, at least after eccentric training. Effects of dynamic resistance training on fascicle lengthand isometric strength. Journal of Sports Sciences, 24 05 Effects of isometric training on the knee extensor moment-angle relationship and vastus lateralis muscle architecture.
European journal of applied physiology, 11 Muscle architecture adaptations to knee extensor eccentric training: Effect of testosterone administration and weight training on muscle architecture.
Training-specific muscle architecture adaptation after 5-wk training in athletes. Influence of concentric and eccentric resistance training on architectural adaptation in human quadriceps muscles. Journal of Applied Physiology, 5 Damage to the human quadriceps muscle from eccentric exercise and the training effect. Journal of sports sciences, 22 Altering the length-tension relationship with eccentric exercise.
Sports Medicine, 37 9 Effects of eccentric exercise on optimum length of the knee flexors and extensors during the preseason in professional soccer players. Physical Therapy in Sport, 11 2 Is the force-length relationship a useful indicator of contractile element damage following eccentric exercise?.
Pressure volume loops Video transcript So I'm going to draw up the length-tension relationship. This will be the key idea we're going to talk about in this video.
And it's very related to some stuff we've already talked about. So we've talked about, for example, the Frank-Starling curve. And that was talking about how if you stretch out heart cells, and all of the things within heart cells-- all the proteins-- that it actually changes the force of contraction. 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. 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.
Sarcomere length-tension relationship
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. 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.
The stimulating electrodes are attached to a Narishige micromanipulator on a stand behind the frog; adjust the electrode pair so the sciatic nerve can be elevated over both electrodes. Make sure no extraneous tissue shorts out the stimulation clear view underneath the raised nerve.
Use single shocks to watch the leg twitch. If you don't see a strong twitch when you stimulate, check the settings on the stimulator, and check that the sciatic nerve is lifted up and electrically isolated on the stimulating electrodes. To begin with, we won't care to isolate only the fiber headed for the muscle in quesion--we'll watch the whole leg twitch.
Notice where the stimulator "trigger" and the 'scope are connected on the NI rack box; make appropriate matches in your VI for recording the twitch. What is the latency in msec from stimulation to contraction start? What is the duration of a twitch? Slowly increase the stim. One lab partner will move the force transducer micromanipulator and flick the stimulator switch. The other partner will call out "ready, go" when the VI has started its search for a trigger, and will record max and min responses on an EXCEL spreadsheet.
To insure response over the full range, offset the scope to a negative voltage, so the scope itself doesn't saturate its output. Start with a relaxed setting in which you see no twitch. Don't change the 'scope gain once you start recording data.
Stretch by 1 mm at a time and keep repeating the stimulation. You should get to a state of stretch in which the size of the twitch decreases from maximum. You may have to stop at a point where the force transducer has reached its maximum limit. How repeatable is the data? Can you notice fatigue or creep of the muscle?
Make sure you have length going "the right direction" from short to long. Arrange that the length where the twitch is first nonzero is the rest length of the muscle. Is there any part of the curve with a negative slope?
Subtract passive from total to see the active-only LT curve. Was there any influence on the passive data of a "stretch reflex" mediated by the spinal cord?
Or evidence of plastic deformation? If there is time, insert the pin electrodes from the Blaberus Lab into the gastrocnemius muscle and observe the EMG waveform that results from a twitch-causing stimulation. Can you reassemble the preamp circuit if some wires are removed?
Explain how sliding filament theory accounts for negative L-T curve. Explain how sliding filament theory accounts for L-T curve below L0.