Muscle Contractions

Hello!

A few weeks ago I posted a blog about ATP (Read Here) and how our body uses this energy everyday.  One of the question that is often asked hand in hand with ATP is "how do muscles work"? The contraction of muscles is very complex (as are most mechanics in the body, which you are starting to realize) so I thought I would take the time and explain how we are able to show off our muscles at the beach, perform a crunch or even just walk around, so you could see how this process works.

I thought I would keep things simple for this post.  Yes this diagram is simple in physiological terms!

Let's use this picture to help use grasp what a muscle breaks down to.

First, let's meet the major players of the muscle:

Skeletal Muscle: The collection of many smaller objects to form what you think of when you say muscle.  Think of those matryoshka doll that fit into each other, after one is put into the other the eventually form into one whole doll. 

Fascia: For those who work with me know about this tissue that covers separates and holds muscles in position.  They know it from the foam roller and other myofascial release techniques we do lol. 

Fascicle: The first little doll inside the muscle (see above) which contains muscle fibers.

Muscle Fibers: The next little doll to pop out contain many little structures, which will play a huge role in contraction of the muscle. Muscle fibers come in different types, the most common you hear about are; slow titch and fast twitch.

Myofibrils: This next doll contains the tiny little structures that we will be spending our focus on: the filaments.

Filaments: The last little doll is made up of actin and myosin.  We will be focusing on myosin, or thick filaments and actin, thin filaments.

Now that we know a few of the key players in the muscle, let us discuss what a sarcomere is.  You can think of this sarcomere as a bonus doll out of the filaments section to a degree, because many sarcomeres are require for contraction. A sarcomere is a portion of the myofibrils in between the "Z-Line". If you look at the picture above, you'll see these Z-lines with an H-Zone between them.  These portions continue all the way through the myofibrils. In short what has to happen is that these sarcomeres have to shorten and lengthen as a team in order to make the muscle contract and relax.  This is known as the sliding filament theory.

The sliding filament theory is the process of making these little portions of actin come closer together or over top myosin, which then takes place throughout the sarcomere and thus, a contraction is formed. Essentially we need the top picture to look like the bottom, by a process where myosin attaches and pulls actin over itself. So how does this happen? Let us use a step by step process to make things simpler: (I posted some diagrams on how the process can be further broken down, but only a few as I don't want to crash this site)

Calcium enters the picture

1. An impulse (action potential)  triggers Calcium (Ca++) to release from its home and enters the picture (more specifically from the sarcoplasmic reticulum down the transverse tubules )

Calcium kicks tropomyosin out and allows the myosin heads to attach to actin.

2. Calcium allows for the myosin (played by the tan heads) to attach to the actin (blue orbs) by removing a barrier known as tropomyosin that blocks it's destination on the actin bands.

ATP is converted to ADP+Pi to allow the myosin the pull actin

3. ATP is converted (ADP+Pi) and allows for the tan heads to yank the blue orbs over top each other (shortening) and a contraction has been achieved.  It should be noted that this pulling constantly continues during contraction until the next step.

Calcium leaves the party and myosin lets the actin go back to it's relaxed position.

4. Once energy is no longer present and calcium cannot clear the path for myosin, the tan heads will release and allow for the blue orbs to revert back to their starting point, until the next time this process begins.

The concept of muscle contraction is not an easy one to convey, without going far too in depth and adding many pictures and models.  What I have displayed here is a very very bare bones and simplistic view of some anatomy and conceptual mechanics on how this process works.  It took me weeks to build my model of in depth analysis of the sliding filament theory for my exercise physiology course, so you can imagine how many pages this post could be to describe it all.

Contracting a muscle, as most processes in the body, is a very complex and dynamic activity.  What I would take away from this post would be: 

1.Muscles are broken down into many substructures

2. At the core of it all, the tiny filaments of actin and myosin are the major players in muscle contraction

3. The sliding filament theory is how a muscle contracts, by myosin pulling actin over itself.

4. ATP and calcium are the fuels needed to make this process move.

As you type, move your head or any other tiny action that requires muscle movement, remember that this sliding filament theory is constantly taking place and that your body really is always hard at work behind the scenes, even for the smallest of movements. If anyone would like any further detail of the information provided today feel free to post below or you can visit the facebook page as well.  I hope everyone has a very safe and enjoyable holiday.  Please enjoy the weekend and remember to appreciate the complexity of your body! Speaking of complex, I've added a few more diagrams of something called an action potential, which is another fundamental component of our body functions. Muscle contractions would not occur without these little guys, so in essence, this step would be included in the overall picture I posted above, but for shock value, I thought I'd show you how much more goes into something as simple as flexing your biceps than you might think. There are also a couple diagrams expanding our initial blog post as well.

The is the anatomy of a neuron, which the process of an action potential takes place.

Of course I could put up many more models, because each process is started and followed by another process so it all depends what part of the physiological chain you want to stop at.

Thanks for reading! 

"Without education, you are not going anywhere in this world"- Malcom X

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*I am not a doctor or a licensed physician.  I am in no way diagnosing anything and recommend that you speak to your physician before making any medical/supplemental/nutritional decisions.

*I am not a registered nutritionist or dietitian. The information presented is for education purposes only.

References

1. Powers,S. Howley, E. (2007) Exercise Physiology Theory and Application to Fitness and Performance 6th edition (141-160) NY: McGraw Hill

2. Howley, E. Franks, B. (2007) Fitness Professional's Handbook 5th edition (340-342) NY:  McGraw Hill