Thursday, October 19, 2006

Muscle truth: In science, the most widely accepted theory of muscle contraction is the sliding filament theory.

The question then becomes why so many different theories? The point is getting your muscles to work in the best fashion? If we have the best theory, and we understand the structures of muscles, understanding the changes in banding pattern resulting from the movements of thick & thin filaments past each other during contraction, then would we all not want to produce the best cross bridging or sliding of the filaments for the sport? After all what mind plays sport to play poorly?

For years we have made graphs using sEMG of the mechanical responses or the "twitch", of a muscle cell to a single action potential. We can watch the phases and application of the stimulus, along w/ the visible shortening of the muscle over the course of a time. Why then is their so many basic fitters. The real reason of this ongoing debate or guessing is the lack of money a professioinal fitter is willing to pay for the tools that show you your needs. They are not williing to pay for high-tech that is driven by the health care or insurance industry. There are people willing to pay for the service, they just can't find the professional to do it? So it really comes down to money driving things.

Even w/ the science, we have people claiming that they are professionals, they have been riding for years and they know. Or they have attended some fitting school for basic fitting. How slow the bike industry or world learns. Perhaps all fitters should be required to go to school for 10 years to learn and understand the topic thoroughly. But as we know, this is not the real world. The mass marketing iedas are focused on products. They are very basic and they have jumped into the bike fitting because they want to move their products and make money from (saddles,shoes, bikes,etc.) They have placed a lot of stress on the local dealer to use their system "if they want to move their brand."

Skeletal muscle is made of muscle bundle, leading to smaller msucle fiber, to even smaller myofibril. The myofibrill is then made of myofilaments of the molecular level F, G, H and I bands. It is know that actin filament and myosin filament

Skeletal muscle is the largest tissue in the body, accounting for 40 to 45% of the total body weight. But it seems that the structural charaoteristics of skeletal muscle are not well know?

The most striking feature of muscle fibers is the series of transverse light & dark bands forming a regular pattern along the fiber. Though skeletal muscle patterns appears continuous across a fiber known as myofibrils. Bundles of these fibrils are enclosed by a muscle cell membrane or sarcolemma. Each myofibril is about a micron in diameter. Between the myofibrils are large numbers of mitochondria,which are to be expected in cells that have such a high energy requirement. The myofibrils show the same pattern of cross striations as the fibers of which they are a par.

Skeletal muscle fiber are multinucleated cylindrical cells, 10 to 100um in diameter, and may be up to 1 ft.long. Generally each end of an entire muscle is attached to a bone by bundles of collagen fibers know as tendons. Some tendons are very long, and the site of attachment of the tendons to the tendon to the bone is far removed from the muscle. For example, some of the muscles which move the finger are found in the lower portion of the arm, between the elbow and the wrist.

Now lets get to the real properties of it all. The properties that you can't see w/ your eye. The properties of actin & myosin produce the cyclic activity of the cross bridges and they are responsible for contraction. Aggregation of myosin molecules form thick filaments, w/ the globular heads of the myosin molecules forming the cross bridges. The structure of actin has a thin myofilament composed of two helical chains of globular actin monomers.

Muscles can exert a "pull" but not a push. For ths reason, muscles are typically arranged in antagonistic pairs: one pulls a bone in one direction and the other pulls the same bone in the opposite direction. Such pairs of opposing extensors & flexors are found at the ankle & knee, as well as at other joints when either the flexor or the extensor contract, its antagonistic muscle need to permit the bone to move. To not understand what is really going on here is like riding w/ your brakes on!
Even more important is the understanding that the way you think and how you fire your muscles, has more to do than you know. In order to have the proper coordination, its your nerve impulses that more to do w/ the muscles than you know! Its what to think about that makes a difference,plus have the cleats, and your motor(legs) and hip angle correct for antagonistic pairs to function properly.

Back to the bottom of it all. Myosin, is the larger of the two molecules, and it is shape like a lollypop or golf club heads. They are oriented tail-to-tail in two halfs of the filament; the globular ends extend to the sides, forming the cross briges which binds to the reactive site on the actin molecule. Actin is also a globular-shaped molecule having a reactive site on its surface that is able to combine w/ myosin.

The globular end of the myosin molecule, in addition to being a binding site for the actin molecule, contains a separte binding site for ATP. I am not going to go inot that, but understand it is what makes things go. This active site has ATPase activity, and the reaction that is catalyzed is the hydrolysis of ATP!

Myosin has a very low ATPase activity. It appears that an allosteric change occurs in the active site of myosin ATPase when the myosin cross bridge combines w/ actin in the thin filaments, considerably increasing the ATPase activity. It is believed that the oscillatory movements of myosin cross bridges produce the relative movement of thick and thin filaments, resulting ultimately in the shortening of a muscle fiber.

Many cycles are needed to produce a degree of shortening during muscle contraction, the myosin bridge must be able to detach from the actin and then rebind again. This is accomplished by the binding of ATP to the myosin in the cross bridge, forming what is know as a low-energy complex. The low-energy complex has only a weak affinity for actin; the actin-myosin bond is broken, allowing the cross bridges to disociate from actin. Shortly after this event, a conformational change occurs in the myosin -ATP complex & a "High Energy" complex is formed. The high energy complex has a high affinity for actin, and the cross bridges are able to rebind to the actin. In this manner, the cross bridges are able to bind and dissociate from actin in a cycle of coordinated actions.

The bridges swivel in an arch around their fixed postions on the surface of the thick filaments, much like the oars of a boat. When bound to the actin filaments, the movement of the cross bridges causes the sliding of the thick & thin filaments past each other. Since one movement of a cross bridge will produce only a small displacement of the filaments relative to each other, the cross bridges must undergo many repeated cycles of movement during contraction.

The analysis of leverage in musculoskeletal systems has several applications that are useful for the true movement professional. The advantages derived from knowing muscle mechanic are emphasized in the follow.

The magnitude (amount) and direction (angle of pull) of a muscle or muscle group on a bone is very exacting. Exact magnitudes of the components can be determined by rather sophisticated techniques, but what is more important to understand here are the relative magnitudes of the two components of a muscle's force on a bone. Thus, the greatest torque may be generated by a muscle whose direction of pull is correct to the shaft of its bone. In all sports this can be determined.

Now lets think about the basic fits. Or all the science of being more aero. You will hear everthing. But if the muscles don't work, don't expect to faster. Perhaps the biggest debate are in the tri bike fits. Even w/all the sicence to date, there is still a ton of "old school" thinking and many claims? I guess its becasuse you have to this to your muscles to better run or swim? Back to the turth about movment.

It is important to understand that several joint positions change in the course of a movement, the muscle-to-bone angle changes as well. Certain positions of the joints allow for greater rotary muscle torque; these muscle torques are related to the angle of the muscle attachment as well as the lenght of the muscle at any given instant.

Take the action of the hamstring muscle at the knee. The largest force arm that can be achieved by the hamstring muscle at the knee is that produced when the muscle pulls at its best angle to the leg bone. In other words the cross-bridging of the actin & myosin. If the muscle line of pull is off then the systems fails. When the muscle angle is greater than the correct determined degree (continued flexion of the knee), the rotary component diminishes.

The length-tension relationship is significant here because the muscle is a two-joint muscle. This is huge because who knows what size & shape of hip, sit bones one was given when they picked their mom and dad? If the hip joint is held in a position of extension, (i.e., in a standing position,) the tension able to be produced in the muscle continues to decrease as the muscle shortens to flex the knee.

Because the hamstring muscle is a two-joint muscle, certain adjustments to the length of the muscle is shortening at the other end (i.e.,as the knee flexes, the hip may be flexing.) Your saddle and location of your center of mass behind the botom bracket is very important. Thus the length of the muscle may be maintained, because it shortens to flex the knee while it lengthens w/ flexion of the hip. Consequently, if the hip is flexed as the knee is flexed, the muscle does not lose the tension advantage of its resting length, as it would if it were merely flexing the knee.

The ability to maintain the length of a two-joint muscle during its contraction may allow the muscle greater tension. The angle of attachment of the hamstring muscle in different positions will change the torque in knee flexion. So a zone of hip angle works best as we are moving in & out of balance.

That is one reason we measure your hip size/shape, plus find your sitbones, as that is where the hamstrings are attached. Our constraints and measurements allow you the best chance of finding the correct degrees of pull for a more effective action & myosin contractions.

After that we can even show you a graph of the mechanical response, the twitch, of a muscle cell to a single action potential. That allows you to control your stimulus.

Muscles fibers, like nerve fibers, have a refractory period, that is, a very short period of time immediately following one stimulus, during which they will not respond to a second stimulus. The refractory period in skeletal muscle is so short (about .002 second) that muscles can respond to a second stimulus while still contracting in response to the first. The result of this is the summation of contractions, which leads to a greater than normal shortening of the muscle fiber.

Some to know about fatigue. If we have to work some muscles more because you don't know the best movement, you deplete that muscle stores of glycogen. This may actually be felt by the individual before the muscle reaches the exhausted condition.

In contrast to true muscle fatigue psychological fatigue may cause an individual to stop exercising even though his muscles are not depletet of ATP and are still able to contract.

An athlete's performance depends not only upon the physical state of his muscles but also upon his will to perform. But if the muscles are not allowing for their best shortening "Game Over."

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