What Happens When You Stretch

• "When you stretch, the muscle fiber is pulled out to its full length sarcomere by sarcomere, and then the connective tissue takes up the remaining slack. When this occurs, it helps to realign any disorganized fibers in the direction of the tension. This realignment is what helps rehabilitate scarred tissue back to health." This was interesting, and raised several questions for me. I would like to know what about scar tissue makes fibers disorganized and how it happens, as well as if there is any benefit from stretching out the connective tissue, which 'takes up the extra slack.'
• "This triggers the stretch reflex (also called the myotatic reflex) which attempts to resist the muscle length by causing the stretched muscle to contract. The more sudden the change in muscle length, the stronger the muscle contractions will be (plyometric, or 'jump,' training is based on this fact). This basic function of the muscle spindle helps to maintain muscle tone and to protect the body from injury." This caught my attention both because it could be relevant to my more effective joint project and because it sounded like an ingenious method of preventing injury, one I never even knew existed.
• "Some sources suggest that with extensive training, the stretch reflex of certain muscles can be controlled so that there is little or no reflex contraction in response to a sudden stretch. While this type of control provides the opportunity for greatest gains in flexibility, it also provides the greatest risk of injury if used improperly." This is interesting because it seems like the stretch reflex should be automatic, which leaves me wondering how one learns to control it, and if it takes a conscious effort to do so.

Relate and Review
    The article "What Happens When You Stretch" discusses what happens in your body when you stretch out a muscle- it's a surprisingly complicated process. The sarcomeres begin to lengthen as each overlapping pair of muscle fibers is pulled apart, although depending on the intensity of the stretch, some fibers will stay in place instead of stretching like all the other fibers. However, when you stretch, intrafusal fibers, more commonly known as muscle spindles, send signals to the brain and cause the stretch reflex, which makes the muscle contract. This reaction is particularly strong if the stretch is sudden. When the tension becomes too high, though, it causes a lengthening reaction, allowing the muscles to stretch in order to prevent injury.
    This article helped me to understand more about the physiology of muscles. It supplemented the lessons we have been learning on muscle contraction by teaching me more about the opposite function of muscles- stretching. I enjoyed learning about stretching, because I have always wondered how it works, but I still have many more questions. Why is it that, as a young child, I was more flexible than I am now? If you stretch too far, could you damage your connective tissues? How does stretching prevent injury?

Designing a More Effective Joint

Abstract

In this project, I redesigned the knee joint in order to prevent injuries to the medial collateral ligament. The medial collateral ligament (MCL) is often torn when someone experiences a blow to the outside of the knee, causing the MCL, which is located on the inside, or medial edge, of the knee, to stretch and then break. To prevent this injury from occurring, I redesigned the joint so that the two sections of the MCL- the deep medial collateral ligament and the superficial medial collateral ligament- were joined into one thick ligament. This new layout will prevent grade three tears (tears going all the way through the MCL), as well as hopefully most grade two tears, which go only partway through the MCL.

Body

I redesigned the knee joint to prevent tears to the medial collateral ligament, more commonly known as the MCL. The knee joint connects the femur, patella, fibula, and tibia together using several different ligaments including the anterior cruciate ligament, posterior cruciate ligament, patellar tendon, lateral collateral ligament, and medial collateral ligament (composed of superficial and deep sections), as shown below. It is extended using the quadriceps and flexed with the hamstrings.

Sometimes, usually during sports, a person will experience a blow to the outside of their knee, causing the knee to bend inwards which in turn stretches and then tears the medial collateral ligament. This will usually heal on its own or with a brace of some sort, but it can take a while to heal, depending on its severity. Common symptoms include pain, swelling, and, in severe cases, instability of the knee.

In order to prevent tears to the MCL, I propose that that we join the superficial medial collateral ligament and the deep medial collateral ligament, making it thicker and therefore much harder to tear.

Discussion

When I started this project, I had no idea where I was going to go with it. After searching for a while, I came up with two ideas: make the medial collateral ligament thicker, or make it more elastic. First, I explored whether I could make the MCL stretch more easily, so that when someone did get hit in the side of the knee, it would bend instead of tear. Eventually, this led me to reading about joint hypermobility (double-jointedness), which seemed like just what I was looking for. However, as I read more about it, I realized that hypermobility actually caused a lot of instability in the joints. This meant that while the MCL would stretch farther, it would actually take a lot less force to stretch it to the point that it would tear.

Abandoning the idea of hypermobility, I moved on to my other idea: increasing the thickness of the medial collateral ligament. I did more research on the structure of the MCL and found out that it was actually composed of two parts: the deep MCL and the superficial MCL. Then, I considered whether I could thicken either the superficial and deep MCL or just one of the two, but then realized that would necessitate the removal of the bursar in between them, causing the two ligaments to rub directly up against one another. Instead, I decided to combine the two ligaments, forming one doubly thick medial collateral ligament. This new ligament would prevent tears- it would still be possible to form mild, microscopic tears (grade one) or, in extreme cases, partial tears (grade two), but complete, or grade three, tears would be almost completely eliminated. Joining the two sections of the MCL would likely inhibit movement at the knee joint, but the MCL would not get torn in half, so I have achieved my goal for this project.

This assignment taught me many things, not just about the medial collateral ligament but also about the body, and even myself and my own problem-solving skills. During the course of my research, I realized that even though the human body is quite fragile and prone to injury, evolution has designed us that way for a reason. Each potential injury is a trade-off; by leaving us vulnerable to one injury, our body gains more mobility, or prevents a worse injury. I also learned about the MCL, which I knew nothing about prior to this project. One thing that particularly intrigued me was how it stabilized the knee, because I never really thought about how that worked before. Finally, I learned that when I encounter a roadblock, like when my first idea about more elastic ligaments didn’t work, I am able to step back and find another solution.

This project didn’t directly relate to the muscles we are currently learning about in class, since it was more focused on ligaments, but it did help provide a bit more understanding as to how joints work; they rely not just on the muscles and bones and cartilage we have already learned about, but also on many other important structures such as the ligament I just researched.

Short of completely redesigning the knee joint, which, if it were even possible, would require extensive surgery, there are many ways that one can prevent tears to their MCL. First, you could avoid activities like football, where you are likely to get hit on the outside of your knees, and if you do participate in such activities, you should wear a brace.  Also, when playing sports, make sure you do not make any sharp turns while your foot is planted on the ground, as that could also cause injury to the MCL. Finally, you should strengthen the muscles around the knee joint in order to stabilize it even more.

Works Cited

Pallas, Andrew. Beating Sports Injuries. Hauppauge: Barron's, 2002. Print.

"MCL Tear." UCSF Medical Center. The Regents of the University of California, n.d. Web. 8 May 2017.

Chen, Lan, William N. Levine, Paul D. Kim, and Christopher S. Ahmad. Pub Med Central. National Center for Biotechnology Information, 7 Dec. 2007. Web. 8 May 2017.