Skeletal Muscle 101

[O-Train]

The "shaping" thread got me thinking about how many misconceptions there are regarding training and how muscles work. I assumed a lot of this stuff was more common knowledge than anything but maybe not.

So I'll give my take on things. Anyone can feel free to comment. Just keep in mind that what I'm saying is more than likely not up for debate. Otherwise I wouldn't discuss it.

So one thing that jumped out at me was "all or none." All or none refers to a muscle fiber contracting when a stimulus is above a certain threshold and not at all when the stimulus is below. It does not, I repeat, it does not apply to an entire muscle. Can you imagine if it did. A tiny movement would cause an "all or none" maximum force contraction in an entire muscle. If you think about this for more than a second it's obvious that it applies on the cellular level but not the muscular level. This is one of those "not up for debate" things.

Lets look at the triceps muscle. It has 3 heads. All three heads insert in roughly the same place except that the long head has an origin different than the other two (meaning one of it's attatchment points is in a different place). So given that a muscle has to be under tension to exert a pulling force on a bone it stands to reason that the position of the arm is important. Different exercises, depending on the position of the upper arm, will utilize the long head more or less. This is exactly the same reason that seated calf raises emphasis the soleus muscle and not the gastrocnemius.

With the chest, as I previously mentioned. The fibers that attach on the clavicle are more heavily recruited during an incline press. You don't need a university degree to understand why. You can just change your arm position and flex the muscle and feel the difference. Muscle pulls on bone and that's why it moves. Fibers in line with the lift being performed will be able to apply more pulling force to the bone. All areas of the muscle are being used during a heavy lift but it is the fibers in line with the applied force that are being used most heavily. This is especially true when using a sub-maximal load.

Different exercises will absolutely stress a muscle in different ways. Depending on the muscle, or group of muscles. This may influence the location of more muscular growth. If you know the attachment points of a muscle and it's actions (ie. what movements it produces). Then you would never need a personal trainer or anyone to tell you which areas a certain exercise will target.

Getting back to the original "shaping" discussion. You cannot change the length/size of your bones or the length of your tendons. A muscle will grow the way it is going to grow. With that being said, you can absolutely alter the development of a muscle using different exercises. If I want to emphasis the lower portion of my trapezius than I do exercises that focus on that area. It's as simple as that.

[HeavyD]

****in great post.... hit the nail on the head. 9 had to retire from that one i didn't know if i was in the Twilight Zone
, or what the hell

great piont on the all or nothing aswell.... if you look, he states all or nothing but then goes to say that the incline press focuses on the upper pec,how is this possible is its all or nothing?

very simply my piont is this, if someone came to us, complaining about a shallow upper chest, i think we would all recommend incline exercises, now yes when an athlete has nearly reached his peak, there is little to do as it is mostly genetics,

once again O hurley i respect the shit otta your word, so dont take it like i was just trying to piss ya off.

[O-Train]

great piont on the all or nothing aswell.... if you look, he states all or nothing but then goes to say that the incline press focuses on the upper pec,how is this possible is its all or nothing?


Who are you refering to? All or nothing gets misused a lot. I'll go into a bit more depth because what I posted wasn't 100% accurate just because I was trying to keep it simple. All or nothing really refers to motor units. Which is defined as a motor neuron and all the muscle fibers that it innervates. So each muscle has groups of muscle fibers that work together. Large muscles that need to generate a lot of force have larger more powerful motor units. They also tend to consist of larger, more powerful muscle fibers (Type II/Fast Twitch). This provides increased force output from the motor units but a less graded response. Meaning you have less fine motor control over larger muscles with larger motor units. So when an electrical stimulus travels down the motor neuron which is greater than the threshold value of the muscle fibers, they will all contract. Also, motor units are recruited in order from smallest to largest. I won't get into detail but feel free to read more about Henneman's Size Principle: http://jn.physiology.org/cgi/content/full/93/6/3024

The body likes to conserve energy so during an incline bench press the body will try to utilize the muscle fibers that are most capable of producing force. Those muscle fibers are the ones that are in line with the force being applied to the bone. These muscle fibers, because they are being more actively recruited, also recieve more damage. The body understands that to decrease the damage undergone by these muscle fibers it must make them stronger (and bigger). So through progressive training and repair you get more muscular development in the upper portion of your pec major. Also the anterior deltoid (which is more actively recruited during incline vs. flat) and other muscles also.
* When I say muscle fiber I'm refering to motor units but it is much easier to explain it this way.

[rickyboy36]

Who are you refering to? All or nothing gets misused a lot. I'll go into a bit more depth because what I posted wasn't 100% accurate just because I was trying to keep it simple. All or nothing really refers to motor units. Which is defined as a motor neuron and all the muscle fibers that it innervates. So each muscle has groups of muscle fibers that work together. Large muscles that need to generate a lot of force have larger more powerful motor units. They also tend to consist of larger, more powerful muscle fibers (Type II/Fast Twitch). This provides increased force output from the motor units but a less graded response. Meaning you have less fine motor control over larger muscles with larger motor units. So when an electrical stimulus travels down the motor neuron which is greater than the threshold value of the muscle fibers, they will all contract. Also, motor units are recruited in order from smallest to largest. I won't get into detail but feel free to read more about Henneman's Size Principle: http://jn.physiology.org/cgi/content/full/93/6/3024

The body likes to conserve energy so during an incline bench press the body will try to utilize the muscle fibers that are most capable of producing force. Those muscle fibers are the ones that are in line with the force being applied to the bone. These muscle fibers, because they are being more actively recruited, also recieve more damage. The body understands that to decrease the damage undergone by these muscle fibers it must make them stronger (and bigger). So through progressive training and repair you get more muscular development in the upper portion of your pec major. Also the anterior deltoid (which is more actively recruited during incline vs. flat) and other muscles also.
* When I say muscle fiber I'm refering to motor units but it is much easier to explain it this way.

Very good post bro.You can tell you have studied this shit before.Ive got a question regarding something you said in your post.You say:
"These muscle fibers, because they are being more actively recruited, also recieve more damage. The body understands that to decrease the damage undergone by these muscle fibers it must make them stronger (and bigger)".

Now seeing this is true,the it should apply everywhere in that muscle.Now take an example where i do preacher curls.I can actually concentrate on the lower part of my bicep(not the head) and feel all the stress there.The next day even confirms this to me with D.O.M.S.Now if we take the reasoning of stress and fibre recruitment,then that part of the muscle will therefore "tear" and repair itself.If this is true then making the lower part grow or "EXTEND" is possible then.Now before you say its genetics and you cant(whcih i agree you cant extend a muscle) please explain to me why the whole bicep will grow instead of just the bottom part where ALL THE STRESS AND RECRUITMENT TAKE PLACE.

Thanks!

[Socially_Inept]

good post

[O-Train]

Very good post bro.You can tell you have studied this shit before.Ive got a question regarding something you said in your post.You say:
"These muscle fibers, because they are being more actively recruited, also recieve more damage. The body understands that to decrease the damage undergone by these muscle fibers it must make them stronger (and bigger)".

Now seeing this is true,the it should apply everywhere in that muscle.Now take an example where i do preacher curls.I can actually concentrate on the lower part of my bicep(not the head) and feel all the stress there.The next day even confirms this to me with D.O.M.S.Now if we take the reasoning of stress and fibre recruitment,then that part of the muscle will therefore "tear" and repair itself.If this is true then making the lower part grow or "EXTEND" is possible then.Now before you say its genetics and you cant(whcih i agree you cant extend a muscle) please explain to me why the whole bicep will grow instead of just the bottom part where ALL THE STRESS AND RECRUITMENT TAKE PLACE.

Thanks!

Muscle fibers run the length of the muscle. So with any skeletal muscle you have a tendon, the belly of the muscle and another tendon. Each individual muscle fiber runs the entire length of the muscle. They are very long skinny cells. If a muscle fiber grows than it grows along the length of the muscle not just at the ends. You know the suspension bridges with the bundles of steel cable? Muscles are very similar. If the cables are required to support a greater load than the diameter of the entire length of cable needs to increase, not just at one end or the other. If you are feeling an exercise predominantly near the ends of the muscle, more than likely it is the tendon you are feeling. In your example of preacher curl the elbow joint is fixed in place. During portions of the lift, the muscle will have to work harder. Because the elbow is fixed in place your arm can't move into a position of better leverage. This may be why you feel this particular exercise near the elbow as opposed to the biceps other attachment. To really figure it out you would need a complex free body diagram that would change during the entire ROM of the lift. Muscles always grow in strength and size more quickly than tendons. They also repair more quickly than tendons (this is due to increased blood flow to the muscle).

[Atarii]

Thank god someone posted this now I have a place to refer people who seem to think other wise..

Very easy to follow, it's in depth enough to get the idea of what is happening and great post over all,

Thank you!

[cog]

Well it's definitely not the tendon that I'm feeling when I am doing preachers with strict style.The swelling is predominantly in the lower bicep,and my belief is that this area will grow more than the far end of the muscle from this movement.Unless you're a genetic freak you need to do them.

[declan]

Good read bro. I hope this would help dispel "shaping myths" among beginners.

[AlladdinSane]

Yeah, yeah... but i want to see my abs. How many sit-ups do I have to do, or can you recommend any other exercises that might help?

[O-Train]

Yeah, yeah... but i want to see my abs. How many sit-ups do I have to do, or can you recommend any other exercises that might help?

lol. You forgot to mention a well defined jaw bone. We all know that woman only care about abs and a pretty looking face...

[O-Train]

I want to talk about DC training and why I think it works. I'm still not sure that fascial stretching is critical. It very well could be taking place and allowing the muscle to grow more. I'm just not sure, so I'm going to attempt to explain why the training program is effective using other avenues.

Muscle fibers (read motor units) are recruited in a pre-determined order based on their size and threshold. So slow twitch muscle fibers are always being used. When the stimulus (weight) becomes great enough progressively more fast twitch muscle fibers will be recruited to help. The slow twitch muscle fibers are still active during this time. There are two types of fast twitch muscle fiber (IIa and IIb).

Quick blurb I found explaining fast twitch fibers better:
Type IIa Fibers
These fast twitch muscle fibers are also known as intermediate fast-twitch fibers. They can use both aerobic and anaerobic metabolism almost equally to create energy. In this way, they are a combination of Type I and Type II muscle fibers.

Type IIb Fibers
These fast twitch fibers use anaerobic metabolism to create energy and are the "classic" fast twitch muscle fibers that excel at producing quick, powerful bursts of speed. This muscle fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types, but it also has a much faster rate of fatigue and can't last as long before it needs rest.

This is also a good article and it's fairly easy to read: http://www.thinkmuscle.com/articles/haycock/hst-07.htm

So the biggest and most important fibers are type II and more specifically IIb. By using a rest-pause style with heavy weight you are more heavily recruiting all of the important tpe II fibers. (At least I think so). Also, they do not get a chance to fully recover so more cellular damage is occuring. When you combine this with a controlled eccentric phase you get a lot of time under tension for those important large muscle fibers. Then you finish it off with an extreme stretch which further loads the muscle. When you stretch a tight muscle you arn't stretching. What is happening is that muscle is contracting and resisting the stretch. Because the tight muscle is being forced into a stretched position it is undergoing a lot of damage at the cellular level. So basically DC training inflicts a lot of damage to the important large fast twitch muscle fibers. It does so in a short period of time kind of like a "holy shit" stimulus for the body.

This is why I think DC training and the extreme stretches work. I might not have explained it quite right but this is what I think is happening. Workouts need to cause cellular damage. Cellular damage is what forces muscles to become bigger and stronger. Otherwise the body doesn't adapt because the amount of muscle it has works just fine. And that of course is one of the other reasons DC works so well. Constant progression. I won't get into the exercise selection, exercise rotation or the use of different exercises on different days. It has a lot to do with new stimulus and something people like to refer to as "muscle confusion".

I am biased towards DC training because I can see the thought that went into it. There are a lot of really good things about the program. Even though I personally modified the program I would be the first to warn people against this. Don't fix what isn't broken and don't attempt to fix something unless you know which parts are working and which parts may need a bit of a tweak.

[buildinthaskinnys]

I want to talk about DC training and why I think it works. I'm still not sure that fascial stretching is critical. It very well could be taking place and allowing the muscle to grow more. I'm just not sure, so I'm going to attempt to explain why the training program is effective using other avenues.

Muscle fibers (read motor units) are recruited in a pre-determined order based on their size and threshold. So slow twitch muscle fibers are always being used. When the stimulus (weight) becomes great enough progressively more fast twitch muscle fibers will be recruited to help. The slow twitch muscle fibers are still active during this time. There are two types of fast twitch muscle fiber (IIa and IIb).

Quick blurb I found explaining fast twitch fibers better:
Type IIa Fibers
These fast twitch muscle fibers are also known as intermediate fast-twitch fibers. They can use both aerobic and anaerobic metabolism almost equally to create energy. In this way, they are a combination of Type I and Type II muscle fibers.

Type IIb Fibers
These fast twitch fibers use anaerobic metabolism to create energy and are the "classic" fast twitch muscle fibers that excel at producing quick, powerful bursts of speed. This muscle fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types, but it also has a much faster rate of fatigue and can't last as long before it needs rest.

This is also a good article and it's fairly easy to read: http://www.thinkmuscle.com/articles/haycock/hst-07.htm

So the biggest and most important fibers are type II and more specifically IIb. By using a rest-pause style with heavy weight you are more heavily recruiting all of the important tpe II fibers. (At least I think so). Also, they do not get a chance to fully recover so more cellular damage is occuring. When you combine this with a controlled eccentric phase you get a lot of time under tension for those important large muscle fibers. Then you finish it off with an extreme stretch which further loads the muscle. When you stretch a tight muscle you arn't stretching. What is happening is that muscle is contracting and resisting the stretch. Because the tight muscle is being forced into a stretched position it is undergoing a lot of damage at the cellular level. So basically DC training inflicts a lot of damage to the important large fast twitch muscle fibers. It does so in a short period of time kind of like a "holy shit" stimulus for the body.

This is why I think DC training and the extreme stretches work. I might not have explained it quite right but this is what I think is happening. Workouts need to cause cellular damage. Cellular damage is what forces muscles to become bigger and stronger. Otherwise the body doesn't adapt because the amount of muscle it has works just fine. And that of course is one of the other reasons DC works so well. Constant progression. I won't get into the exercise selection, exercise rotation or the use of different exercises on different days. It has a lot to do with new stimulus and something people like to refer to as "muscle confusion".

I am biased towards DC training because I can see the thought that went into it. There are a lot of really good things about the program. Even though I personally modified the program I would be the first to warn people against this. Don't fix what isn't broken and don't attempt to fix something unless you know which parts are working and which parts may need a bit of a tweak.


How can dc training be credited for your progress if you modified it? essentialy dante created it so if you arent training the way he instructs you to then essentialy you arent really training dc style no?

Essentially you just created your own style of then training no?

Ive come to the realization that training styles or programs are just gimmicks that help people make money.

These I believe are the three most important factors in gaining muscle size or strength. 1. load 2. frequency 3. Intensity.

Throw in a rest pause here, and a drop set there, mix in a stretch or a partial rep and VOILA! You have your own personalized training program.:popc

[O-Train]

How can dc training be credited for your progress if you modified it? essentialy dante created it so if you arent training the way he instructs you to then essentialy you arent really training dc style no?

Essentially you just created your own style of then training no?

Ive come to the realization that training styles or programs are just gimmicks that help people make money.

These I believe are the three most important factors in gaining muscle size or strength. 1. load 2. frequency 3. Intensity.

Throw in a rest pause here, and a drop set there, mix in a stretch or a partial rep and VOILA! You have your own personalized training program.:popc

You're absolutely right, I have modified DC training in a couple different ways. My original intent was just to give my point of view on fascial stretching and what I think might actually be happening. I got kinda carried away. I credit a lot of what I've learned to reading and trying DC training. It caused me to think a lot more about what I do in the gym and why I do it. Instead of what most people do which is doing something because it was recommended to them or because someone else is doing it.

I would imagine a lot of people do things in the gym that are unique to them, or a small group of people. I remember that Dante doesn't recommend doing rest-pause sets for stiff leg deadlifts. I thought to myself, why not, it's a great exercise, why not optimize my results with rp sets. Its something I had to experience for myself before I realized it isn't a good idea. I modified the way I work calves so that it is similar to everything else and I like it a lot more. My calves respond better to an increased load than they do to the super slow reps that Dante recommends. Everything is a work in progress.

For people that don't have a lot of experience programs are great to follow. It's taken me years to kinda figure out what I think I should be doing. In 10 years I'll probably look back and wonder what the heck I was thinking.

[buildinthaskinnys]

I think you gotta keep rethinking everything you do, to a certain degree of course. I tryed DC, that is to say with best intentions and to the best of my knowledge and didnt really make any gains, this is where I decided to rethink my training for myself as opposed to following a program blindly. And though the westside barbell site I found out about a book called the science and practice of strength training, I designed my own routine and within week and a half set a personal record on my bench. Im not gonna knock any program but Im certainly not gonna follow what one person says anymore.

From now on I create my own muscle destiny.:flagC

[rickyboy36]

Heres something i found at Promuscle that was posted late yesterday which makes good sense.Im not sure who the credit goes to,but here it is anyways:

The existence of the so-called "upper", "lower", "inner" and "outer" pectorals along with the assertion that it is possible to isolate one or more of these to the relative exclusion of the others in training, are among the most firmly entrenched myths in Strength Training and Bodybuilding circles. In fact none of these truly exist as either separate and distinct muscles or regions in a functional sense. Even though it could be argued that there appears to be a structural distinction between the upper and lower pectorals (and some anatomy texts do in fact support this distinction though not all do) because the pectoralis-major does originate from both the sternum and the proximal or sternal half of the clavicle along it’s anterior surface (it also has connections to the cartilages of all the true ribs with the frequent exception of the first and seventh, and to the Aponeurosis of the external oblique muscle), this is considered to be a common (though extensive) origin in terms of the mechanical function of the muscle. Thus the pectoralis-major is in fact for all practical purposes one continuous muscle with a common origin and insertion, and functions as a single force-producing unit. The terms upper, lower, inner and outer are imprecise and relevant only in order to make a vague subjective distinction between relative portions of the same muscle for descriptive purposes. They are vague and imprecise terms because there is no clearly delineated or universally defined border between them.

Further it is not physically possible either in theory or practice to contract one region of a single muscle to the exclusion of another region or regions (as a Biomechanics Professor of mine once demonstrated to a bunch of us smart-ass know-it-all’s taking his course, using EMG analysis). When a muscle contracts it does so in a linear fashion by simultaneously reducing the length of its constituent fibers and thus its overall length from origin to insertion. Even where a single muscle is separated into multiple functional units that are clearly defined such as the triceps (which are referred to as “heads” by Anatomists and Biomechanists), because they share a common point of insertion in order for one head to shorten all must shorten. This only makes sense if you think about it because otherwise there would be “slack” in one when the other shortened, which as we know does not occur. Note that there are some special cases where one head of a muscle must actually lengthen when the other shortens (e.g. the posterior head of the deltoid in relation to the anterior head during the positive stroke of fly’s), the point however is that even in these special cases there is no “slack” because there is in fact contractile activity (whether concentric or eccentric) throughout the muscle.

That is not to say however, that all fibers in different areas, or heads are necessarily shortened to the same degree during a particular movement. Depending on the shape of the muscle, the joint geometry involved, and the specific movement being performed, fibers in one area of a muscle or head may be required to shorten more or less than in others (or even to lengthen) in order to complete the required movement. For example during a decline fly though muscle fibers in all regions of the pectoralis-major must shorten as the upper arm is drawn towards the median plane of the body, because of the angle of the arm in relation to the trunk the fibers in what we commonly refer to as the lower pecs will have shortened by a greater percentage of their overall length than those in the upper region of the muscle by the completion of the movement. Conversely when performing an incline fly there is greater shortening in the fibers towards the upper portion of the muscle than in the lower.

Many proponents of the so-called “isolation” approach to training claim that this proportionally greater shortening of the fibers equates to greater tension in the “target” region than in others, and therefore stimulates greater adaptation; but this is completely at odds with the cross-bridge model of muscle contraction which clearly shows that as fiber length decreases tension also declines due to increasing overlap and interference in the area of the cross-bridges. Some also contend that the fibers called upon to shorten to a greater degree tend to fatigue faster than others and that therefore there is greater overall fiber recruitment in the region where this occurs, and thus a greater stimulus to growth; but there is no evidence to suggest that a fiber fatigues faster in one position than in another in relation to other fibers in the same muscle. In fact it has been shown that Time Under Tension (TUT) is the determining factor in fatigue and not fiber length. In fact fiber recruitment tends to increase in a very uniform fashion throughout an entire muscle as fatigue sets in.

The ability to “isolate” a head, or region of a muscle to the exclusion of others by performing a particular movement, or by limiting movement to a particular plane and thus develop it to a greater degree, is a myth created by people who wish to appear more knowledgeable than they are, and has been perpetuated by trade magazines and parroted throughout gyms everywhere. It is pure non-sense and completely ignores the applicable elements of physiology, anatomy, and physics in particular. Quite simply the science does not support it, and in most cases is completely at odds with the idea.
Regardless of the science however, many people will remain firmly convinced that muscle isolation is a reality because they can “feel” different movements more in one region of a muscle than in others. This I do not dispute, nor does science. There is in fact differentiated neural feedback from motor units depending on the relative length of the component fibers, and this feedback tends to be (or is interpreted by the brain as) more intense when the fibers in question are either shortened (contracted) or lengthened (stretched) in the extreme. However this has to do with proprioception (the ability to sense the orientation and relative position of your body in space by interpreting neural feedback related to muscle fiber length and joint position) and not tension, fatigue, or level of fiber recruitment. Unfortunately it has been seized upon and offered up as “evidence” by those looking to support their ideas by any means available.

Muscle shape is a function of genetics and degree of overall development. As you develop a muscle towards its potential, it does change in appearance (generally for the better) but always within the parameters defined by its inherent shape. A person who tends to have proportionately more mass towards the upper, lower, inner or outer region of his or her pectoralis-major will always have that tendency, though it may be more or less apparent at various stages in their development, and in most cases appears less pronounced as overall development proceeds. That is not to say that training a muscle group from multiple angles is totally without value. In fact we know that even subtly different movements can elicit varying levels of fiber recruitment within a muscle in an overall sense (i.e. in terms of the percentage of total available fibers) due to differences in joint mechanics, and neural activation patterns, as well as varying involvement of synergistic and antagonistic muscle groups involved. So by all means experiment with different angles in your training, but don’t expect to be able to correct so-called “unbalanced” muscles this way, or to target specific areas of a particular muscle. Work to develop each of your muscles as completely as possible and shape will take care of itself. If you want to worry about “shaping” you should pay more attention to the balance between different muscle groups and work to bring up any weak groups you may have in relation to the rest of your physique.<?:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" />

Author: His credentials and experience consists of being a Medical Specialist in the US Army, an instructor and personal trainer at Bally Fitness. He is also an ISSA Certified Fitness Trainer, and an ISSA certified Specialist in Performance Nutrition.

He was a bodybuilding competitor in the late 80's and has trained others for competitions as well, including his wife Gena who is a nationally qualified Figure competitor, and he competed again in April of 2004 at the NPC Northern Bodybuilding competition! His wide range of education includes having a Bachelor's degree from Colorado State University which included course work in Anatomy &amp; Physiology,Biology, Diet &amp; Nutrition, Kinesiology and Drugs. The last 20 years of his life can be summarized as having a passion for bodybuilding &amp; fitness and always furthering his mind through education.

[O-Train]

Hmmm, interesting. I think a lot of what this article is saying is probably true. I'm not sure if it's 100&#37; accurate though, but probably a lot of what I say isn't either. It's a long article so I'm going to go through it bit by bit. Some of it I don't think anyone could provide a definite answer for. I'll just talk about the things I understand.

The triceps have a common insertion point but what he failed to mention or realize is that the long head has a different origin. You know the thick rubber bands that are small compared to a regular one that is larger? Pretend you are holding one of each and trying to stretch them both simultaneously. Both rubber bands will be under tension when you stretch them but the larger band will hardly stretch at all compared to the smaller one. The long head has an origin on the scapula instead of the humerus. It crosses the shoulder joint.

Edit: I'm not totally sure what arm position will produce the most tension in the long head. I know that because this head crosses the shoulder joint that the position of your humerus does matter but I need to look into this more...I think I figured it out. The long head also produces extension about the shoulder joint not just the elbow joint. So probably one of the best exercises you could do is something like a rolling tricep extension (see tricep exercise thread or youtube). This exercise would incorporate both functions of the long head.

Here is a picture I got from wikipedia that shows the three heads of the triceps. Just google triceps muscle if you want to read more or see a clearer picture. See the head that is going in behind other muscles? That's the long head, totally different origin.

[O-Train]

I'll mention that I agree that all areas of muscle will contract as a single force producing unit (as he said). I also agree with how he talks about muscle shape. What I don't agree with is that all areas of the muscle will be recruited to the same degree, fatigued at the same rate and incur the same cellular damage.

So here we go, Sliding Filament Model of muscle contraction... Cross bridges work exactly like a ratchet system within each muscle fiber. This article explains it really well: http://www.tiem.utk.edu/~gross/bioed/webmodules/muscles.html

Basically when contractile units are too far apart or too close together the muscle is not under tension.

So during an incline fly (using his example). We have fibers in the upper portion of the pec major which are shortening more and producing more force than fibers not directly in line with the application of force. Doesn't it just make intuitive sense that this area of the muscle that is doing more is also recieving more damage and so, because of adaptation, experiencing more growth? I mean sure, at the very apex of the lift those fibers, because of extreme crossover, are not under a lot of tension. But what about the rest of the lift when they are under the most tension and also producing the most force? It just makes sense to me that this area can absolutely be targeted.

So you have 2 muscle fibers in the pec major. Again using the incline fly example. One inserts way down on the sternum and one up high on the clavicle. Lets say both fibers are Type IIb so they are big and fatigue quickly. One is shortening considerably more than the other and producing considerably more force (which requires energy...). Which fiber fatigues more quickly? It just seems really obvious to me. If I'm wrong I guess I'm wrong...but it won't change the way I lift.

The guy doesn't properly understand the Sliding Filament Model.

[O-Train]

The other thing he says is that there is a structural difference (and there absolutely is, there is no disagreement in any good anatomy texts) without a functional difference? Why is that? Why are some areas of the pectoralis major structurally different (point of insertion) if this difference produces no functional benefit? Why would humans have evolved this way? Is the upper portion of the pec major a vestigial feature of the human body? NO. I'm glad he didn't discuss the anatomy of the back. It may have been harder for him to "explain" why even though the upper and middle/lower portions of the trapezius are exactly the same muscle they serve totally different functional purposes.