Chapter 14 - Muscle Contraction
It is presumed that the mechanism of contraction is the same for both .. The length-tension curve can be explained by the cross-bridge theory. As the resting muscle length increases, more cross-bridges cycling occurs when muscles are stimulated to contract. The resulting tension increases. Maximum. Differentiate between force-length and force-velocity of muscle contraction Force-Length Relationship: The relationship between sarcomere length and force The occurrence of another twitch contraction before complete relaxation of the.
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. 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.
Sarcomere length-tension relationship
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?.
Journal of biomechanics, 38 9 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.
Journal of sports sciences, 33 12 Shift of optimum angle after concentric-only exercise performed at long vs. Sport Sciences for Health, 12 1 Behavior of fascicles and the myotendinous junction of human medial gastrocnemius following eccentric strength training.
Preload, length-tension relation, and isometric relaxation in cardiac muscle.
Inter-individual variability in the adaptation of human muscle specific tension to progressive resistance training. European journal of applied physiology, 6 The variation in isometric tension with sarcomere length in vertebrate muscle fibres.
The Journal of physiology, 1 European journal of applied physiology, 99 4 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.
Length tension relationship | S&C Research
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.
Sarcomere length-tension relationship (video) | Khan Academy
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.
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.