Abstract:

The nervous system coordinates actions within the elbow flexors with extreme and complex precision.  Indeed, for decades, researches have been awestruck by its intricate methods of control.  It appears to utilize various mechanisms, which include: intricate calculations, recognition of mechanical advantages with changing lines of pull, and specified synergistic tandems.  Also recognized is the task-dependent protocol used by the NT to call specialized motor units "within" a single muscle into play.

The objective herein will be to uncover how varying angels of elbow flexion affect the biceps brachii, brachialis, pronator teres, and brachioradialis.  Additional care will be taken to detail specified actions at each of the aforementioned sites.  Furthermore, a strategic plan of action will be displayed, allotting the reader top scientific evidences toward the goal of maximized growth, as well as separation.

Introduction

In 1913, Sir Charles Sherrington wrote that muscles are synergistic when they "act mechanically in the same direction at the same joint” or those “which act similarly at two neighboring joints (59).”   Almost a century later, it has been noted by numerous scientists that the explanation of how the elbow flexors work together (as the definition of synergy suggests) is extremely complex and, in many cases, downright unpredictable (73, 13, 20, 12)!  Buchanan, along with easily the top experts in the world regarding the elbow joint, concluded the following in regards to the muscles which act on this region as well as the movements that take place therein:

“Suffice it to say that some kind of computational-predictive-feedback control strategy approach-may be needed to understand the solutions that the nervous system introduces to handle what is clearly a highly complex mechanical task (13) “

They propose that the nervous system literally strategizes each and every movement in a manner that is somewhat mind-boggling.  Thus, it is not enough to relay the actions of the elbow flexors to you.  Instead, we will need to review extensive and extremely complex literature.  I propose a layer-like attack to the subject.  Simply put, I will break down the elbow flexors in a wave-like pattern, or what you might call a reductionist approach.  The goal is to significantly expand your understanding of this stupendous system. 

Overview of Approach

1.  Anatomical Overview - Section one will cover the "basic" actions and anatomical locations of each elbow  flexor.

2.  Mechanical Terms - To understand how the nervous system recruits varying muscles, you must understand key Biomechanical terms.  I will define them in section two. 

3.  Discussion of Muscular Synergies between Elbow Flexors - As bodybuilders, you need to realize how the elbow flexors interact.  Much of this sport is the enablement of the artist (and that is what a true BB has to be) to target a specific muscle group. 

4.  Summary of Synergy - Here we summarize the results found and relay strategies to promote specified hypertrophy during workout routines.  Additionally, we discuss secondary elbow flexors - Certain muscles can increase elbow flexion strength, which are themselves not normally considered primary muscles with this action.  Nevertheless, by targeting them, you can significantly improve your ability to produce torque. 

We begin with a review.The scapula is a triangular bone which lies on the back of the rib cage.  Laterally it has a socket( glenoid fossa ) which articulates with the head of the humerus.  This is known as the shoulder joint.  The biceps is a two-headed muscle and both heads cross the shoulder joint.
 

1.  The short head is also known as the medial head, due to its closer location to the midline of the body.  Its origin (recall that the origin of a muscle group is the more mobile sect.  I.E. when the muscle shortens, it does so from insertion toward the origin) lies on the coracoid process of the scapula.  The coracoid is a hook-like protrusion which lies laterally and just above your clavicle.  Do you feel that bump?  That is where the short head attaches.  The short head tendon passes distally and then blends into the thick gaster or belly of the muscle.  It then continues downward for the length of the humerus.  Finally, its tendon travels past the humerus and inserts on the medial landmark of the lateral forearm bone, which you know as the radius.  The landmark it inserts on is known as the radial tuberocity.  Overall, the short head of the biceps adds inner thickness to the anterior arm.

2.  The long head is also known as the lateral head, due to its location further away from the midline of the body in relation to the short head.  It originates on the supraglenoid tubercle of the scapula.  Recall that the glenoid fossa is the "socket" which the head of the humerus forms a joint with.  Supra refers to the fact that a protrusion, directly above the glenoid fossa, can be found on the scapula.  Thus, the long head tendon attaches above the shoulder joint, and therefore crosses it (that is important!).  The tendon then spans out laterally and distally on the humerus.  Consequently, the tendon guided through what is known as the "bicipital groove," or intertubercular groove (28, 38,51). It is known as such due to the fact that it is in between two tubercles (which are protrusions on the humerus where the rotator cuff m. attach, see superficial muscles of the back part III). 

Key Anatomical Points Which Effect Actions

1.  The bicep’s origin crosses the shoulder joint.  Conclusion:  The position of the shoulder joint effects the bicep’s ability to contract.  Secondly, the biceps have actions at the shoulder.  Such consequences make them a  "multi-articulate" muscle.  Further down in the article, I will discuss how different shoulder movements effect the biceps.  There is an additional point of interest, however, and that is a multiple joint muscle has to be innervated by the nervous system in a more complex manner than a single joint muscle, for the simple fact that it has to control multiple joint movement (78, 29).  As you will see, the biceps are therefore extremely (more like insanely) complicated, and recruitment of certain aspects of it are indeed "task-dependent (79, 11)." 

2.  The insertion point of this muscle is fixed on a moveable bone (the radius).  As a consequence, contraction of the biceps effects radial movement, and radial movement effect the biceps’ line of pull!  Thus, we are in the presence of a muscle which operates at three different joints!  You can now see why the nervous system has such a tremendous job.

Actions Discussed

For the above reasons, the actions below may not always be optimal, depending on the position of the forearm and/or shoulder joint.  Once again, my intentions are to introduce you to these actions now, and delve into the details later.

1.  Flexion at the Elbow - Note that the muscle fibers of this two-headed muscle are parallel (this has further implications).  When they contract, therefore, they pull the forearm muscles closer to the humerus, such as in a barbell curl.

2.  Supination - Recall that supination is the process by which the forearm is externally or laterally rotated, such that the palm of your hand faces upward.  It is confirmed that the biceps contribute tremendously to this movement (50, 58). 

3.  Flexion of The Shoulder Joint - Basamajian and Delucia found significant activation in the biceps during shoulder flexion (10); such results have much confirmation (60, 77, 14).  An example of shoulder flexion would be one arm dumbbell front raises. 

4.  It is fascinating to note that this muscle actually works as an abductor in cases (61).  "Abduction means to take a body part away from the midline or center of the body (40)." 

Purpose:  "Surface electromyography was performed for both heads of the biceps brachii in 11 healthy men while the muscles were under 30% maximum isometric shoulder flexion and abduction."

Test:  "Electromyographic activity was normalized as a percentage of maximal muscle contraction during 24 shoulder motions."

Results: "Electromyographic activity was detected in all motions examined, suggesting that the biceps muscle acts as a flexor and an abductor of the shoulder."

In the following paragraphs, I will explain to you the main factors which affect the amount of strength produced at the elbow joint.  A few key points to note are as follows:

1.  Some muscles have a greater mechanical advantage at force production than others.  Realize that, due to the fact that we are dealing with flexion, supination, and pronation, these mechanical advantages will vary.

2.  The line of pull changes during elbow flexion, forearm supination, and pronation for several muscles discussed and, with it, the mechanical advantages.  I will diagram when the advantages are optimized and when they are at their weakest.

3.  Muscles are constructed with notably different architectures.  These architectures effect the amount of force generated.  Such factors are covered below.

4.  The architecture of a muscle can also effect the degree of shortening it is capable of producing, as well as the speed of shortening.

We begin our discussion with the concept of "moment." 

Moment - In the event that a force causes a segment to rotate, the product (rotation) is known as a Moment, moment force, or torque (80).  Certain conditions must be met in order for the product "moment" to be produced.  They can be outlined as follows:

Note: Moment and Torque are interchangeable terms

1.  During rotation, a segment moves along a plane ( i.e. sagittal )around an axis.  For our purposes we will say that the axis, which is also known as the center of rotation, is fixed.  For example, your forearm rotates around the axis produced by the hinge joint of the elbow. 

2.  The rotation caused needs to be further looked into and, to do so, I want you to think of a wrench. 

If you were to take that wrench and use it to unscrew a bolt, you would do the following:  1. Attach the wrench to the bolt.  This attachment becomes fixed.  2.  Next you apply a force off-center to the axis of the bolt.  In other words, it will do you no good to push the wrench into the bolt.  If you were to do this, you would create no torque.  You must apply the force away from the center of the bolt and, when you do this, you will produce a Moment.  

You need to realize that torque is a measure of two concepts.  The first is force, and the second is known as Moment Arm, Lever arm, or force arm.  Each of those terms is interchangeable.  We will use moment arm here.  Thus, when determining the magnitude of a torque, which is how you would measure elbow flexion strength, you would use the following equation

Where T = Torque, F = Force, and MA = Moment arm.

You know that during arm flexion your biceps contract, and the tensile force that contraction produces is used to move the forearm closer to the humerus.  In your body, therefore, the force is muscular contraction (that's easy enough). Moment arm is determined by the following factors factors.  The first is rather easy to explain, and it refers to the measured distance away from the force application to the axis of rotation.  Below I will show a diagrammatical illustration of a wrench unscrewing a bolt.  The wrench is the long thin line and the circle represents the axis of rotation.  Note that rotation refers to a circular motion, hence the use of a circle.  The arrow pointing to the axis of rotation does not represent direction; it is simply pointing to the region.  The other two arrows, however, represent the force applied to the wrench "off center" and the magnitude of that force.  Note that the magnitude is represented by the length of the tail, while the direction is represented by the way the arrow is pointing.  

As you can see, the magnitude of force A, applied 12 inches away from the axis of rotation, is equal to the magnitude of force B.  With that in mind, we look at the distances.  The distance is represented by a straight line (that's the wrench).  Force B is applied 6 inches away from the axis of rotation and point A is applied 12 inches away from the axis of rotation.  Note that the torque of A is twice that of B.  This is due to the fact that the longer distance the force is applied, the greater the moment arm.  It is for this reason that a longer wrench can give a person a greater mechanical advantage than a shorter wrench and, additionally, where you apply the force is directly proportional to the magnitude of the "Moment" or "Moment Force" produced.  The total equation for Moment Arm looks like so:

MA = r X sin ( angle of application, thus torque is highly dependent on the direction of the applied force )

or

MA = The perpendicular distance from the axis of rotation and the line of force

Don't worry about the sine function( though I place notes on this subject below in case you are worried).  My main concern is that you realize that the Moment arm is not only determined by the distance the force is away from the axis (r), but also the direction which the force is applied.  Here is the point:  The closer to 90 degrees the angle of pull is, the greater the torque produced.
 

1.  The further the insertion point is from the axis of rotation, the greater the distance and, therefore, the greater the moment arm.  This translates to a greater Moment, Moment Force, or Torque. 

2.  Think of the arrows above as being fixed, like the biceps tendon is fixed.  The fixed point is the attachment site.  Now, as you move your arm, the "angle of application" changes.  Think of the angle of application changing in a similar manner to how the arrow changed its direction in the last illustration, as compared to the illustration that was at 90 degrees.  Thus, we realize that how much, or how little your forearm is flexed (in degrees), will directly effect the "size" of the moment arm and, with it, the magnitude of Torque produced.  Dr. Murray and Dr. Delp confirmed this in the journal of Biomechanics by stating the following:

"Flexion/extension and pronation/supination moment arms of the brachioradialis, biceps, brachialis, pronator teres, and triceps were calculated from measurements of tendon displacement and joint angle in two anatomic specimens and were estimated using a computer model of the elbow joint. The anatomical measurements revealed that the flexion/extension moment arms varied by at least 30% over a 95 degrees range of motion. The changes in flexion/extension moment arm magnitudes with elbow flexion angle were represented well by the computer model (49)."

Vital Concepts Outlined:

·         The greater the length of the moment arm, the greater the force production of a muscle.

·         The smaller the length of the moment arm, the greater an angle will be over a given distance, relative to the amount of shortening a muscle will go through.  Thus, if muscle A has a longer moment arm than Muscle B, it will have to shorten more to move a joint through 30 degrees than muscle B does to create the same angle. 

The second statement seems confusing, but it is actually fairly simple.  Recall that rotation carves out a circle.  A smaller moment arm would carve out a smaller circle, while a larger moment arm would carve out a larger circle.  Check it out:

The following conclusions of moment arms for elbow flexion were derived from van Zuylen , van Velzen , van der Gon (1988), Murray , Delp , Buchanan (1995), and Murray , Buchanan , Delp (2000).

Magnitude of Moment arms

1.  The Brachioradialis has the largest.
2.  The Biceps Brachii is in second place.
3.  The Brachialis comes in third.
4.  The Pronator teres has the smallest MA.

As stated, however, moment arms peak at a certain level of elbow flexion (49, 76, 48,55).  Here is a breakdown:

Peaks of Moment Arms

1.  The brachioradialis peaks at approximately 90 degrees of elbow flexion (49, 76, 48, 55).
2.  The biceps brachii peaks also at approximately 90 degrees of elbow flexion, and has been shown to vary up to 110 degrees of elbow flexion (49, 76, 48, 55).  Recall that the elbow has been shown to flex at an average of 135-150 degrees of flexion (30, 31, 62, 63). 
3.  The brachialis peaks at approximately 100 degrees of flexion, and up to 120 in some individuals (49, 76, 48, 55).
4.  The pronator teres peaks at approximately 75-80 degrees (49, 76, 48, 55. )

In conclusion, the Lever arms of the elbow flexors peak at the top range of motion.  For the three larger muscles it peaks between 90 and 120 degrees, and including all muscles at 75-120 degrees.  Thus, if we only analyze this aspect of torque, the greatest moment is realized at this range of motion.  However, we know that force of contraction is also key to producing torque.  We must therefore analyze each muscle’s force production capabilities before making absolute conclusions.

Physiological Cross Sectional Area

As you know, a muscle group can be broken down into hundreds of thousands of muscle fibers, and the connective tissue which binds these fibers together, so as to increase their mechanical capabilities, as well as provide support (look for a biomechanical issue on CT in the future). Each cylindrical muscle fiber is, in turn, made of repeating sarcomere units.  Recall that sarcomere units contain the contractile filaments of the muscle cell, known as actin and myosin. 

·         See the following Articles for discussion on muscle contraction:  1.  Anatomy of a muscle, 
2.  All Or None and Whole Muscles, 3.  Pain and Tension

From my Biomechanics article, you understand that tension can be defined as follows:

While performing the bench press, the force which your contracting muscles exert against a barbell is defined as tension, whereas the force which is exerted against the muscle by the barbell is called the load.  – Quote Biomechanics And Sport – An Introductory Viewpoint (80).

Tension is created when myosin thick filaments bind to actin thin filaments.  The more myosin bound to actin in a muscle group, the greater the tension produced.  Thus, a muscle's ability to produce tension is related to the number of muscle fibers it contains as well as the size of those cells (81).  Adam Knowlden discussed in "Mobility Training and the Application of Proper Warm-up for Body Builder Mobility Training and the Application of Proper Warm-up for Body Builderss" that "The maximal tensile strength of a muscle (its resistance to pull) is approximately 77 to 80 pounds per square inch."

How, then, can we determine which of the elbow flexors has the greatest capability to produce force?  One way is to measure what is known as the "Physiological Cross Sectional Area."  This is a very proficient process, but before I explain it to you, it is vital to describe further the architecture of the current muscles being discussed.  There are two "basic" forms of fiber arrangements in the body.

1.  Parallel Arrangement - Here, muscle fibers run parallel to the long axis of the whole muscle. 

Advantages: The fibers in this arrangement run "almost" the entire length of the muscle.  This means that there are several sarcomere units in one muscle group.  Given that all sarcomere units have similar capacities for shortening, it follows that the more sarcomeres contained within a muscle group, the greater its capability to shorten.  Thus, this type of muscle would be able to move a joint through a tremendous range of motion, a concept directly related to its ability to greatly shorten.

Note also that muscles with shorter tendons such as the biceps can shorten more than muscles with longer tendons such as the gastrocnemius. 
 

Cross Sectional Area Discussed

The cross sectional area of a muscle group is self-explanatory.  You begin by finding the thickest aspect of a muscle and cut right across it in such a way that the slice taken out is perpendicular to the long axis.  This works in a parallel group, but does not comprise the physiological (functional) aspect of pennate muscle groups.  This is due to the fact that a cross section would only cut through part of the muscle fibers in a muscle group.  Enter the PCSA.  Here you cut through an area which goes through all the fibers in that muscle.  Thus, in a pennate arrangement one would end out slicing through the long axis, as the muscle fibers obliquely insert into the tendon.  When done, you find that pennate muscle groups have larger PSCAs than do parallel muscle groups. 

The PSCA of Each Muscle Group below is derived from An KN, Hui FC, Morrey BF, Linscheid RL, Chao EY 1981, Lemay MA, Crago PE 1996, and Murray WM, Buchanan TS, Delp SL 2000 (48, 45, 34):

1.  Brachialis - This pennate muscle group has the largest physiological cross sectional area at approximately 6.25 cm^2
2.  Biceps Brachii - This parallel muscle group is second with a physiological cross sectional area at approximately 4.5 cm^2
3.  Pronator Teres - The PT comes in third at 4.0 cm^2
4.  Brachioradialis - This parallel muscle group comes in fourth with a very small cross sectional area relative to the other muscle groups at 1.4 cm ^2

In summary:

Brachialis - Large PSCA, but 3rd in moment arm size.  Thus, it has a great capacity to generate force, while its moment arm is adjusted to allow it the capability to move the elbow joint through a large range of motion.  Again, it can produce notable torque due to its large CS and can move the elbow through an excellent range of motion, but due to its pennate arrangement cannot shorten as quickly as the biceps.

Biceps Brachii - has the second highest PSCA and the second highest MA.  It can produce notable force and, due to its shortening capacity, can make up for a lower ability to produce joint movement, as it can shorten greatly due to the length of its fibers.

The other two muscles as you will see are meant to support the former.

Length Tension Relationships
    
A concept discussed in previous articles was that of the "Length Tension Relationship."  In a nutshell, it means that a muscle reaches a certain length in which contraction is optimal.  If it is stretched too much, the thin filaments are pulled out of the reach of the thick filaments (labeled c ).  Conversely, if the length is too short, there will be far too much interference .

The length tension relationship in all of the elbow flexors is easy to remember.  They are designed to produce optimal contractile force when the elbow joint is fully extended, and this force lessens in a proportional manner to the amount of flexion produced. 

Therefore, the optimal moment arms occur at the top range of motion, while the optimal lengths are reached at the bottom.  Such a design makes sense.  As the muscle fatigues on the way up, the mechanical advantage increases.  When does strength peak then?  Studies show that it occurs in a compromising manner, when the moment arm and optimal length are high but not maximized, at approximately 80-90 degrees of pure elbow flexion (39, 19). 
 

You can shock the elbow flexors into growth and target extra muscle fibers by taking advantage of this area of optimal strength.  The technique, of course, is as follows:

1.  Go to failure in a full range of motion.
2.  Cheat the weight all the way up and perform barbell curls, from 90 degrees of elbow flexion all the way up until you have reached failure again.

It is a classic regimen, and the above clearly explains why you can accomplish this feat.  I must, however, emphasize that the ability for a muscle to develop maximal contractile force is a major reason for hypertrophy.  Eccentric training has been shown in literally endless studies to produce a greater force of contraction than concentric training (52, 64, 82) and, at the same time, has delivered a greater stimulus for growth and adaptation to further bouts of hardcore training (22, 72).  The ability of a muscle to contract at 100 percent efficiency, whether eccentrically or concentrically, does not change as far as the length tension relationship for a concentric or eccentric contraction.  That is, at the bottom range of motion, contractile force is optimized for any type of tensile force produced by the musculature and, as discussed, stressing the muscle when it can produce maximal force is extremely conducive to the stimulation of growth (47). 

To this end, we re-analyze the biceps brachii.  Recall that it is a multiarticulate muscle group.  As such, movements at the shoulder joint can enhance or decrease the biceps optimal length.  In a multiarticulate muscle group, when a decrease in angle occurs at two joints at once, the muscle may accumulate so much slack and shorten to such an extent that it can barely produce any tension.  Such an occurrence is deemed "active insufficiency."  AI occurs in the biceps when both the shoulder and biceps are flexed simultaneously, meaning that at this stage other elbow flexors would be relied on rather than the biceps. 

With that said, I am going to give you an amazing tool for enhancing hypertrophy in this muscle group.  You see, the biceps act as a shoulder flexor and, when you contract this muscle, they not only flex the elbow, but also cause shoulder flexion (60, 77, 14, 61).  When shoulder flexion and elbow flexion occur at the same time, you may produce momentum, which is good for cheat reps, but you will not get optimal tensile force in the biceps brachii.  Thus, theoretically, if you were to extend the shoulder joint (extend your arm backward) while simultaneously flexing the elbow, maximum tensile build up would occur in the target muscle!  Are there studies on this?  Indeed there are.  In the scientific Journal of Muscle Nerve, in ‘98 it was found that maximum contraction took place when the shoulder was "hyperextended (1)."  Recall that extension of the shoulder joint occurs when it brings the humerus backwards to your sides; anything past this is hyperextension.  Thus, by holding the humerus straight backward, past extension, while simultaneously flexing at the elbow joint, you can increase muscle growth.

How The Elbow Flexors are Recruited!

I have conducted extensive research on elbow mechanics.  In doing so, I came across a fascinating study conducted by  T. S. Buchanan, G. P. Rovai and W. Z. Rymer in the prestigious Journal of NeuroPhysiology (73).  I found their results summed up elbow flexor research astoundingly.  Thus, we begin this aspect of the article by summarizing their findings.

The purpose was stated as follows:  "We studied the patterns of electromyographic (EMG) activity in elbow muscles of 14 normal human subjects. The activity of five muscles that act in flexion-extension and forearm supination-pronation was simultaneously recorded during isometric voluntary torque generation, in which torques generated in a plane orthogonal to the long axis of the forearm were voluntarily coupled with torques generated about the long axis of the forearm (i.e., supination-pronation)."

If that sounded somewhat technical, the point to understand is that they tested activity levels in several muscles which act at the elbow.  As you recall, differing angels can have profound effects on activation of any one muscle.  They tested this extensively, including analyses under differing forearm actions such as supination and pronation.  What did they find?  I think it will no doubt astound you.

1.  Firstly, they discovered that pure synergy between elbow flexors was rare.  They state the following:  "we found that pure synergies in this sense are quite uncommon. For example, we observed that the elbow flexors biceps brachii and brachialis acted synergically for joint torques generated in very few directions (73)."  When they state, "in this sense," they are referring to unified synergy (44).  This model predicts great amounts of synergy between all muscle groups so as to simplify the job of the nervous system (44).  It turns out, through numerous studies, that this is far more complex than was expected when dealing with the elbow flexors (71). 

2.  How come?  Several reasons.  For one, you cannot tell what a muscle's function is by simply reviewing its gross anatomy; instead, you must rigorously test its function by task. 

3.  They found that the brachialis was "rather constant during pronation and supination movements."  In other words, the muscle stayed active, despite forearm position.  Why is that the case?  Take a look at its insertion point.  The brachialis attaches to the relatively immobile (although it moves slightly) ulna.  Thus, pronation or supination does not effect its mechanical advantage.  It is for this reason that the brachialis is deemed the workhorse of the elbow flexors (84).  However, as you will see, this does not mean that its activity cannot lower under various conditions (41), only that it is a mainstay player in the target motion. 

4.  They found that "the Biceps acted as a strong supinator and increased activity with supination resistance (73)."  Recall that the biceps have a moment arm for supination.  They utilize a wheel and axel system to cause movement in the forearm joint.  If you are interested in the mechanics of such a system, I describe it in detail in my second article on Bone Mechanics.  Note that as the difficulty of supination increased, so too did the biceps activation.  To this end I recommend various supination techniques for maximized growth (described shortly).

5.  Further into their dissertation it was reemphasized that "the interactions between elbow flexors is truly complex, especially for muscles which can flex and supinate (73)."  As you recall, the biceps brachii is a multi-articulate muscle.  As such, innervation of it is more complex than single joint muscles.  This is why he stated that not only were the interactions complex, but an emphasis should be placed on those with more than one capability!  Hang on to that because I will reveal some astonishing facts latter on this very subject.

6.  Buchanen et al. also noted that when the biceps brachii were most active, the brachialis and brachioradialis were least active, and vise versa!  It was also noted that the brachialis and brachioradialis actually did show great synergy.  Thus, headway began to be made, and you could hear the excitement in their writings! 

"There are three points of interest. First, these plots clearly demonstrate a positive, near-linear relationship between the BRA and the BRD. When one muscle is active, the other is active as well, regardless of torque direction or joint angle...Second, the BIC did not normally share this relationship.  In fact, the BIC was most active when the BRA and BRD were least active (73)."

We can therefore surmise several key points.  For example, as a sculptor, you have the ability to hone into the brachialis and brachioradialis at times when the biceps are less active, and can therefore more selectively "target" certain aspects of your arms for the desired effect.

For more on the artistic aspect of the sport, I would refer you to my colleague, Mr. Knowlden's genius article entitled:  Monumental Masterpiece - Creating A Cerebral Portrait.  That is a must for any true and serious hypertrophy athlete. 

8.  In the article referenced above, Adam made an incredibly true statement.  Allow me to quote him:

"The philosophy of shaping a muscle in retrospect to the ideals of this sport is inherent. But how exactly would one go about this task?

There are multiple ways in which to accomplish this undertaking. But the fundamental principle to shaping a muscle is a utilizing of a variety of angles (42)."

It is exactly this statement which was found to be the overwhelming case in their study.  In fact, they state, and I quote, "The degree of muscle synergy changes with each angle, showing that varying tasks, varies activated musculature (73)." 

The authors of HYPERplasia have emphasized this fact, numerous times, and it is due to the overwhelming scientific evidence to support the claim.  For example, Dr. Van Zeulan, one of the world’s most outstanding experts on motor control, asserts that "The relative activation of the muscles depends on the elbow angle. Changing the elbow angle affects the mechanical advantage of different muscles differently. In general, muscles with the larger mechanical advantage receive the larger input (79)."  Tax et al., after performing extensive testing procedures on the elbow flexors, made the following statements in regards to task dependency:

"First of all, the concept of one single activation parameter (total synaptic drive?) cannot account for the motor-unit behavior observed during our experiments: the relative contribution of the two force-grading mechanisms is different for different tasks. (69).”

Caldwell, in the European Journal of Physiology, postulates that, "motor unit recruitment thresholds have demonstrated the existence of task-specific motor units within the muscles controlling the elbow (15)."  In other words, differing tasks ( i.e. which would correspond to changing exercises up), can call differing muscles into play, as well as specific aspects within a single muscle group, ultimately allotting the athlete an even greater ability to target areas.

Buchanan and colleagues conclude with their ultimate findings as follows:

”For virtually every other muscle pair, the degree of coactivation depends on the particular task at hand. It follows that the concept of synergy is applicable only under restricted conditions, thereby reducing and perhaps even eliminating the hypothetical advantage arising from this approach, because a new synergic relation would have to be defined for virtually every new motor task. This is similarly stated, although in different terms, by Macpherson (1988). She argues that although a simple muscle-synergy organization is incomplete, a more robust task-dependent synergy that is tuned or modified as needed is more likely (73).“

They noted that muscular synergy between the elbow flexors was "task dependent."  It was additionally concluded that they agree with Macpherson’s conclusion that synergy is modified as needed.  My favorite aspect of his conclusion is that they believe that the nervous system "strategizes."  Thus, rather than stating complete muscular synergy, we can use the term "strategic synergy!"

Essentially, they find that there is virtually no position in which equilibrium between all muscle groups is reached.  "If this analysis is correct, the selection of muscles may well be a computational task in which the nervous system calculates or otherwise computes precisely the sole set of muscle forces necessary to achieve the required net torque...Suffice it to say that some kind of computational-predictive-feedback control strategy approach-may be needed to understand the solutions that the nervous system introduces to handle what is clearly a highly complex mechanical task.“  And you thought flexing your elbow was simple.  That is incorrect.  Essentially, what bodybuilders have been stating for years about the ability to target differing aspects of a region by varying tasks and angles was and always has been correct!  It is the latter, overtly simplistic view which does not agree with experimental evidence (79, 12, 71).

As stated, the above results summarized numerous findings.  In a 1998 edition of Neurophysiology, similar conclusions were made (71).  Buchanan teamed up with several other great scientists by the names of David P. J. Almdale, Jack L. Lewis, and W. Zev Rymner.  They confirmed task dependent synergies, but also came to further startling conclusions.  They believe that such a system of complexity is best described by the nervous system (specifically interneurons) "containing a map of joint torque for a certain direction and would be accessed by appropriate descending pathways, when such torque directions were commanded (71)."  It is concluded that muscular synergy can best be described by two mechanisms.  The first is that the nervous system recruits certain muscles depending on their mechanical advantages.  It is remarked that "in this case, each muscle is a single variable in the set of equations governed by Newton’s laws (71)."  I find that astonishing, however, he also believes that "Of course, there is another possibility: that the system is redundant and that it is the role of the nervous system to choose one of a number of possible combinations of muscles that will produce the desired outcome."  Ultimately, it is concluded that a possible combination of the two may be the factor. 

From the above, we can deduce that a very complex system is involved in coordinating muscular synergies, but when we move through all the incredible design of the nervous system and its ability to calculate for each and every task at hand, we do see key patterns arise.  As stated, we know that when the biceps are at their peak activation, the brachialis and brachioradialis are not.  We shall explore this through further vital literature. 

Kulig et al., in the Journal of Medicine and Science in Sports and Exercise, tested the biceps brachii and the brachialis during various speeds of contraction, specifically varying the eccentric aspect of a repetition (41). Each participant performed one protocol with one arm, while performing a second with the opposite limb. To take the time factor out, they made sure that each experiment lasted 144 seconds. It is vital to control the environment to the highest extent in such procedures. Note also that to correct for any problems, "the right and left arms were selected randomly."  With one arm they lifted the weight in one second concentrically, and lowered it in an equal time period.  However, in the opposite arm, the participants lifted the weight for one second, but lowered it in five for the eccentric portion of the repetition. Naturally, the latter protocol performed fewer repetitions. Results revealed that "The biceps brachii was found to be preferentially recruited during the fast protocol compared with the brachialis, whereas the brachialis was found to be preferentially recruited during the slow protocol (80)."

The reason for their conclusions can be analyzed several ways. One of which would be that the biceps have a parallel architecture, compared to the pennate structure of the brachialis. Recall that the former can shorten faster than the latter. Also recall that the nervous system recruits elbow flexors based on the task at hand (33, 53, 15). It would make sense for the nervous system to recruit the parallel group, as opposed to the pinnate, in a faster protocol. Therefore, by emphasizing slow eccentric contractions, one can preferentially target the brachialis over the biceps brachii, and vice versa.  To show you my point, Graves et al. studied a range of people, from young to elderly, and found that those who had a higher reliance on the biceps brachii, as opposed to the brachialis during elbow flexion, could accelerate through a given range of motion quicker with the former than the latter (33), lending more credence to why the nervous system would recruit the biceps to a greater extent during rapid movements.  This study has been confirmed in other journals.  For example, Tax et al., in the Journal of Experimental Brain Res., found a marked change in motor recruition in the biceps, even when conditions outside of speed were similar. They conclude the following: "It is suggested that the central activation of the alpha and/or gamma motoneurone pools of m. biceps brachii is different for force tasks and slow movement tasks, even if the same torques are exerted and/or movements are made (70)." The above studies confirm that elbow flexors are both task dependent, as well as speed of contraction conscious.

Dr. Basmajian and Dr. Luca performed intense studies on the elbow flexors, and their patterns of activation also confirmed Buchanin's observations on muscle synergies.  I will summarize these scientists’ findings below:

1.  The biceps brachii, when the forearm is supinated, is activated with or without weight.  In fact, it shows the most activity of all positions when the forearm is supinated.  This suggests that it is a main player in elbow flexion and does not play the role of reserve here.  However, even when supination occurs, differing speeds can vary activation, as we have discussed.

2.  The Brachialis is active during all elbow movements; however, I have also shown above that speed of contraction can effect it, namely during supination movements when the biceps are most active, corresponding to the time when the brachialis could be lowered in activity for varying movements. 

3.  When the forearm is pronated, they found that the biceps were inactive when no resistance was applied to the forearm.  They were slightly called into play when resistance was applied, however, but again activity was very low.  The nervous system is obviously calling into play muscles with desired functions and optimal lines of pull.  You see, when the forearm is pronated, the tendon of this muscle is wedged between the radius and ulna and cannot generate an optimal moment. 

It is at a mechanical disadvantage.  As you no doubt may have predicted, the brachioradialis was most active during full pronation, and of course the brachialis was also extremely active. 

4.  When the forearm was neutral (i.e. hammer curl), the biceps were partially activated, while the brachioradialis and brachialis were highly active.  To further understand this, realize that the biceps act as both a supinator of the forearm and a flexor of the elbow.  The nervous system, therefore, will not fully activate the biceps, as the result would supinate the forearm rather than maintain a neutral position.  In order to more fully understand this, I feel a discussion on the concept of compartmentalization is in order. 

Studies have confirmed the existence of neuromuscular compartments (83).  One compartment is a "portion" of a muscle which is supplied by a particular nerve branch.  This compartment contains, in many cases, motor units with distinct functions.  Further, the number of muscle fibers in a neuromuscular compartment varies.  Van Zuylen et al. explains by stating that, "Most muscles are not activated homogeneously; instead the population of motor units of muscles can be subdivided into several subpopulations (79)."  These scientists further state that:

"Inhomogeneous activation of the population of motor units in a muscle is a general finding and is not restricted to some multifunctional muscles (79)."  The term inhomogeneous refers to differing activation.  In other words, all muscle fibers are not recruited for one task in a single muscle; rather, differing tasks can call a specific portion of a muscle into play.  Recall that I stated above that you cannot simply look at a muscles anatomy and predict how the whole thing will react to a certain action.  Van Zuylen confirms this here:  "On the other hand, motor units in muscles are not necessarily activated if their mechanical action contributes to a prescribed torque. For example, there are motor units in the m. biceps that are activated during flexion torques, but not during supination torques."  What was explained is extremely vital to this article and your training.  It was noted that certain parts of the muscle were activated during flexion, but not during supination.  This is the concept of compartmentalization and there is much experimental evidence for it. 

Let us review Dr. Chaunad’s studies on the subject.  He analyzed a cat's biceps femoris and found that, "The BF muscle consists of three neuromuscular compartments: anterior (BFa), middle (BFm) and posterior (BFp). Each compartment is innervated by a separate nerve branch.”  It was found that each compartment had distinct neuromuscular functions (16).  English and Letbetter studied the gastrocnemius (the large posterior calf muscle) and found that, "The lateral gastrocnemius is more complex and contains three distinctly identifiable heads, each of which is a unipennate band of fibers coursing between a proximally attached aponeurosis of origin and a distal aponeurosis of insertion (21)." 

In the Journal of Physical Therapy, English et al. summarizes the "partitioning hypothesis" as follows: 

1.  " The partitioning hypothesis is based on the fact that an individual muscle is arranged in a more complex array than simply fibers attaching at aponeuroses, tendons, or bones with a single muscle nerve innervation."

2.  They state that neuromuscular compartments "are distinct subvolumes of a muscle, each innervated by an individual muscle nerve branch and each containing motor unit territories with a unique array of physiological attributes."

3.  Finally, they assert what many other Scientists have confirmed:  "These data are complemented by physiological studies, the results from which suggest that partitions may have functional or task-oriented roles; that is, different portions of one muscle may be called into play depending on the task demands of the situation."

Is there evidence for neuromuscular compartments in the biceps brachii?  The answer is yes.  First, we need to consider that the more this muscle is studied, the more complex its actions become.  It doesn't even shorten uniformly!  Many have hypothesized that muscles acted as one large sarcomere unit.  In the Journal of Applied Physiology, Dr. George Pappas and colleagues blew this theory sky high!  They actually found that the biceps shorten "nonuniformely."  Results revealed that "mean shortening was non-uniform along the centerline of the muscle during active elbow flexion. Centerline shortening in the distal region of the biceps brachii was significantly less than shortening in the muscle midportion."  In other words, different portions of the muscle shortened at differing rates than others (34).  Segal et al., however, sealed the deal with an amazing finding!  Here is a summary (65):

"Electrophysiological evidence suggests that the human biceps brachii muscle is organized into functional neuromuscular compartments." 

Good point.

"The purpose of this study was to determine whether there was an anatomical basis for these compartments. Dissection of the biceps revealed both architectural and nerve branching pattern compartmentalization within the muscle. Although the biceps brachii is grossly subdivided into long and short heads, these heads are further subdivided into roughly parallel architectural compartments. Moreover, these architectural compartments usually receive a private nerve branch, thus supporting the notion that the human biceps brachii has neuromuscular compartments."

Thus, there is not only functional evidence, but now anatomical evidence for neuromuscular compartmentalization in the biceps.  However, there is much more supporting evidence for the above.  Brown et al. conducted a study which was rightfully named, "Further evidence of functional differentiation within biceps brachii (11)."  They studied whether supination during various phases of flexion could activate different portions of the muscle.  It was found that when the elbow joint was fully extended (or actually when extended below 90 degrees), that the long head of the biceps was more activated than the short head during supination movements, and the short head was more activated when the elbow was flexed past 120 degrees of flexion than the long head (11).  Thus, if you were seeking greater inner biceps thickness, you would perform resisted supination with the elbow highly flexed, and if you wanted to target the outer biceps you would perform supination movements while the elbow was below 90 degrees of flexion (2). 

ter Haar Romeny BM, van der Gon JJ, Gielen CC discovered something truly astonishing.  These scientists studied the long head of the biceps.  In doing so, it was revealed that motor units in the lateral aspect of the muscle were specialized for flexion of the elbow joint, motor units located medially were activated for supination of the forearm, and motor units located in the center of the head were specialized for both movements superimposed on one another (11, 37).  Another interesting study, which lends support to the aforementioned results, was conducted by Dr. Nato and colleagues.  These scientists electrically stimulated different portions of the short and long head of the biceps.  Though not as precise as the nervous system, they found that in one person electrical stimulation of the long head caused the action of flexion without supination (54).

The point to be emphasized is that the nervous system must hone several complex mechanisms for biceps recruition when the muscle is neutral and still activated.  Such a fact corresponds well with the findings that certain subcategories of motor units are specialists at various movements.  However, I would also point out that several other mechanisms must take place.  For example, certain Pronators of the forearm may have to resist supination torque during neutral flexion. 

5.  Dr. Basmajian and Dr. Luca discussed a few more key findings in elbow flexor coordination. 

A.  The brachioradialis can mid pronate and mid supinate.  Thus, from a position of full pronation, the BR can supinate to the point that brings the forearm to a neutral standpoint.  Additionally, from a fully supinated position it can do just the opposite.

B.  The pronator teres, when vigorously resisted, assists in pronation torque.

C.  Both the brachioradialis as well as the pronator teres are not normally recruited unless they face resistance.  This leads researchers to believe that both of these muscles serve as "reserves," which would explain why the brachioradialis is activated more when the biceps are not as activated or when vigorously resisted.  In fact, I postulate that this is one of the main reasons you see a synergistic effect between the brachioradialis and the brachialis.  You see, the brachialis is almost always active, but when its activity lowered, such as in a fast contraction, Basmajian noted that the brachioradialis actually increased in activity.  Thus, during fast contractions it can actually act as a synergist with the biceps brachii.  These authors believe this is due to stabilizing the elbow joint.  However, Buchanin showed such convincing synergy that I believe it is a combination of the brachioradialis acting in reserve with the brachialis, and the nervous system preferably recruiting these two muscles in tandem. 

I will conclude this analytical section with the presentation of one more theory on the multiarticulate Biceps Brachii.  It was written by Dr. Herman and Dr. Flanders in the prestigious Journal of NeuroScience.  They effectively tested the BB, and how it reacted to differing tasks.  According to these authors results, the activity in the muscle was so complex and so "task-oriented" that it actually violated the size principle.  Recall that this principle states that smaller motor units, such as slow twitch units are always recruited before fast twitch motor units.  They feel, however, that: "this elegant functional simplicity of the size principle/common drive concept is not without drawbacks. When applied to human arm movements it would predict rigidity within a system whose flexibility is, in fact, amazing. The directional aspects of everyday reaching movements are manifold, requiring a versatility that might make it necessary to allow for task-specific, differential activation of different subunits of the same muscle, resulting in deviations from a fixed recruitment order (54)."  Their overall hypothesis was varied from the compartmentalization hypothesis.  They noted extreme difficulty in pinpointing a pattern utilized in the biceps muscle.  However, they also noted that differing aspects of the musculature were active for varying tasks.  Here is a summarizing conclusion on their thoughts:

”If differences in mechanical action exist across units within a muscle, the population of units optimally fit to produce a required force vector will change with limb position and force direction during a movement."

The point is this:  Muscle fibers with the greatest mechanical advantage are selectively recruited.  Though this violates the size principle, it is postulated that, overall, it saves energy.  Naturally, that which has the greatest m. advantage would in turn have to use less energy than a population of motor units which did not have such an advantage.

Overall, I would conclude that it is again a combination of all the factors mentioned.  Indeed, the Nervous system is a strategizing machine.  With every movement you make, it calculates with a precision that boggles even the most prestigious and qualified scientists.  All agree on this:  The movements at the elbow joint are insanely complex, synergies in some form or another are strategized and, finally, differing portions of a muscle group can be called into play depending on the task at hand.  Thus, you have the ability to sculpt your physique with an incredible flare!