How Specifically Can We Isolate Muscles?


We can target even a region along a muscle fiber’s length through different functions and ranges of motion though why is unclear.

The curvature of muscle fibers changing based on range of motion, such as the shortened state that leads to cramping during a concentration curl, may also selectively develops, in this case, the proximal or upper region of the outer biceps via cell swelling. We know that overstretch preferentially develops the distal region by adding sarcomeres in-series. The active and passive tension also varies due to the different sarcomere lengths throughout the range of motion, with the midpoint optimal for overall active tension.

We should probably trust our sensations regarding where we feel it, since the science is complex and not fully explanatory at the moment.

bodybuilding pose lat spread bob gallucci

This should give you some direction in designing your own bodybuilding program, understanding the potential for isolation. It should also help you to make sense of the countless exercises available.

You may doubt if it is necessary to approach the finer degrees of isolation described here. This all depends upon what you want, along with what you are already getting, from your current exercises. I encourage you to keep an open mind, at least giving further isolation a try.

Note that isolation is not possible; emphasis is the better word. Nonetheless, isolation is an important keyword. It communicates the intention to focus on an area, even when other muscles are working, so I will continue using it.

Finally, I want you to have enough information to explore more deeply and arrive to your own conclusions. Therefore, I will present a pure bodybuilding perspective first and then explain my opinion afterward.

Let’s start by looking at the possibilities, beginning generally and moving toward specificity.

Tiers of Isolation

Leave no stone unturned: that is, try everything, leave nothing unattempted.

– Euripedes

  1. Function
  2. Muscle Group
  3. Muscle Head
  4. Muscle Fiber
  5. Region Along a Muscle Fiber’s Length

By function, I mean using a muscle group on a basic compound movement such as a push, a pull, or a squat.

Going from inactivity to even just a few compound exercises will transform someone’s physique. Proceeding beyond the functional though, which means something like squatting alone to work the calves, to adding a heel raise to isolate the gastrocnemius, will lead to another tremendous improvement.

After this, we can delve further by working muscle heads. Externally rotating the hips to point the toes outward on the heel raise will focus on the medial or inner head of the gastrocnemius. Internally rotating the hips to point the toes inward will emphasize the lateral or outer head.

On a muscle fiber level, we may be able to further isolate within a muscle head. The side deltoid provides a good example where this could be worthwhile; a lateral raise leaning back or forward may emphasize the front and rear portions of the side deltoid respectively.

Each tier of isolation, as we get more specific, will have a further but lesser difference on muscle development.

The implication though is that, as a bodybuilder, you should consider proceeding all the way to the end.

Many do not even contemplate this despite yearning for a better physique. They may claim to be avoiding overtraining, feel that isolation is harmful, unnecessary, or impossible, or give some other excuse that is self-limiting. They may ignore the wisdom of professional bodybuilders attaining the most developed physiques in the world. They also ignore the latest science, instead defaulting to a basic knowledge of gross anatomy.

In summary, they fail to pursue their goal the very best they can.

The final tier of isolation, addressing a region along a muscle fiber’s length, is clearly the most controversial and speculative. Contracting a muscle fiber seems to pull on each end of the strand equally; you should not be able to selectively apply tension within a region. This makes sense when examining the evidence, such as other muscles contracting to prevent unwanted movement at non-active joints.

Reasoning by analogy can mislead us though. Here are some sound reasons to doubt that we figured it all out:

  • We know some muscle fibers do not extend from origin to insertion.
  • EMG studies reveal muscle compartments for functional differentiation, described as “muscles within muscles.” One study shows the latissimus dorsi as having six compartments! Another shows medial versus lateral activation of the lats, though this may occur due to interference from other muscles.
  • Described in the research as nonuniform muscle hypertrophy, some studies show regional development in portions of the quadriceps and triceps.
  • Strength is highly specific to range of motion, with the nervous system alone not explaining why this is so.
  • Fibers may somehow shorten and lengthen unevenly on different exercises to disable certain regions. This may allow areas less affected to contract harder by remaining closer to an optimal length.
  • Some research shows a distinction between the upper and lower abs, which would seem impossible despite its unusual structure.
  • Perhaps factors that influence muscle growth beyond tension like micro-tearing or occlusion are applied unevenly with different positions and movements.

It is a shame then that many completely ignore the routines of the most qualified experts, the bodybuilders, since their experience would best summarize the complexity of it all. They should at least be seen as source of potentially valuable advice.

We also avoid coming to our own verdicts through trial and error. We place our full trust in experts confidently stating that they know it all, deferring responsibility. We ignore that even anatomy can differ among trainees. We cling to our most satisfying information, hanging onto something pedantic because it seems more legitimate and impressive to others and ourselves. We ignore that research can be wrong, misleading, or irrelevant to our goals.

Before dismissing the final or any degree of isolation then, I suggest finding out for yourself.

Conduct experiments. Touch the muscle as it works. Feel where active tension is developing. Perform more sets of an exercise than usual, and for that exercise alone, and notice where soreness develops. Pay attention to where you are building muscle after adding a new exercise.

Example: Isolating the Biceps

Here is a sequence through the tiers of isolation for the biceps. For each tier, it shows the areas addressed followed by an exercise for it:

  1. Function: Elbow Flexion including the Biceps Brachii (Dumbbell Row)
  2. Muscle Group: Biceps Brachii (Medium-Grip Barbell Curl)
  3. Muscle Head:
    1. Short Inner Head (Wide-Grip Barbell Curl)
    2. Long Outer Head (Close-Grip Barbell Curl)
  4. Muscle Fiber:
    1. Inner Fibers (Dumbbell Curl w/ Wrists Outside Elbows + Supination)
    2. Middle Fibers (Medium-Grip Barbell Curl)
    3. Outer Fibers (Dumbbell Curl w/ Wrists Inside Elbows + Supination)
  5. Region Along a Muscle Fiber’s Length:
    1. Upper-Middle Region (Incline Curl)
    2. Middle (Middle) Region (Medium-Grip Barbell Curl)
    3. Lower-Middle Region (Preacher Curl)
    4. Upper-Inside Region (Incline Curl w/ Wrists Outside Elbows)
    5. Middle-Inside Region (Dumbbell Curl w/ Wrists Outside Elbows)
    6. Lower-Inside Region (Preacher Curl w/ Wrists Outside Elbows)
    7. Upper-Outside Region (Cable Concentration Curl w/ Peak Contraction)
    8. Middle-Outside Region (Dumbbell Concentration Curl)
    9. Lower-Outside Region (Preacher Curl w/ Wrists Inside Elbows)

These are not the only exercises available. By understanding the parameters determining the region addressed, we can understand the intention behind any selection.

Parameters for Isolation

The final tier of isolation is simplified by dividing a muscle group into 9 sections. For these sections then, what parameters determine which region is addressed?

They are:

  1. Initial Setup
  2. Positioning (Angle)
    1. Top or Outer
    2. Middle
    3. Bottom or Inside
  3. Range of Motion
    1. Stretched Third (Outer or Top) (Inside or Bottom)
    2. Middle Third (Middle)
    3. Shortened Third (Inside or Bottom) (Outer or Top)

The initial setup determines the muscle group addressed while positioning and range of motion each occupy either a horizontal or vertical axis.

Initial Setup

This includes factors that cannot be systemized, such as joint actions and positions. For the initial setup, think different exercises like a row versus a pull-over. We just name these exercises outright and then describe the joint actions and positions when explaining good form.

Here are some things to think about:

  1. Consider the positions and movements of other joints for even subtle changes. Horizontal adduction, or the flye motion performed with bent elbows on a machine, versus horizontal flexion, with a fairly straight elbow such as on a cable cross-over, will change the number of muscles involved beyond the chest. The cable cross-over will bring in the shoulders and biceps more.
  2. Consider unusual movements like rotations. Rotations, or movements taking place within the transverse plane, will better isolate some smaller muscles if desired. The superficial infraspinatus of the upper back is targeted through external shoulder rotation. Even though a rotation often hits deep muscles, such as the subscapularis through internal shoulder rotations, this still may expand your chest measurement if this is your goal.
  3. Consider pure movements. Scapular depression performed alone, versus contributing on a dip or a pull-down, will allow you to focus on the pectoralis minor. Once again, working these deeper muscles could expand your overall measurements as a bodybuilder.
  4. Activity at a specific joint is another factor to consider. This is non-conclusive, but some EMG studies and bodybuilders report that something like hip extension on a stiff-legged dead-lift may activate the upper portions of the hamstrings more so than leg curls taking place at the knee. The muscle regions near the active joint therefore may be emphasized.

In general, be open-minded toward different positions, stances, and grips, even when the anatomy at first glance would seem to make it inconsequential. Our nervous system achieves movement without caring how our muscles are worked, so manipulating the initial setup has great value for a bodybuilder.

Positioning (Angle)

Positioning, as I define it here, means applying a different angle to the same initial setup. This could mean changing the angle of a bench, and placing a joint inside or outside of the resistance such as elbows relative to the wrists on a curl.

Range of Motion

This parameter would determine the region emphasized along a muscle fiber’s length, depending on the length of the whole muscle.

Working the muscle in a shortened or lengthened state can come about in two ways:

  1. Restricting the range of motion to that portion. (Curls within the top range only for the shortened state or the bottom range only for the stretched state.)
  2. Using an exercise with the proper strength curve to emphasize that state, regardless of the range of motion used. (An incline curl, with the resistance furthest away from your elbow near the top, feels most difficult in a shortened state. A preacher curl, with the resistance furthest away from your elbow near the bottom, feels most difficult in the stretched state.)

The 2nd option seems most popular, though some bodybuilders use the fullest range of motion on every exercise regardless in the hopes of attaining complete muscle development.

According to this logic, it seems then that a stretched or shortened state at the dominant joint is most important. Making it feel toughest with close to a straight elbow on the curl, as occurs when using the preacher curl, is more important than having the shoulder flexed by the preacher bench, which shortens the muscle. On an incline curl, despite stretching the muscle at the bottom with the shoulder extended, the resistance feeling heaviest near the top is more important.

Example: Isolating the Chest

Let’s go through the parameters with an example for the chest:

  1. Initial Setup: Bench Press (horizontal adduction emphasizing the middle length), Flye (horizontal adduction emphasizing the stretched length), or Cross-Over (horizontal adduction emphasizing the shortened length).
  2. Positioning (Angle)
    1. Incline (Upper Chest)
    2. Flat (Middle Chest)
    3. Decline (Lower Chest)
  3. Range of Motion
    1. Presses (Middle Chest)
    2. Flyes (Outer Chest)
    3. Cross-Overs (Inner Chest)

We can then sort out the combinations to know which exercises target each region along a muscle fiber’s length:

  1. Upper-Middle Region (Incline Bench Press)
  2. Middle (Middle) Region (Flat Bench Press)
  3. Lower-Middle Region (Decline Bench Press)
  4. Upper-Inside Region (Cross-Overs at Upper Chest)
  5. Middle-Inside Region (Cross-Overs at Middle Chest)
  6. Lower-Inside Region (Cross-Overs at Lower Chest)
  7. Upper-Outside Region (Incline Flyes)
  8. Middle-Outside Region (Flat Flyes)
  9. Lower-Outside Region (Decline Flyes)

My Opinion on Isolation Tiers

I have spent a lot of time testing the pure bodybuilding perspective, trying to reconcile it with anatomy and the latest science.

In the end, my experience does not support any significance to isolating along a muscle fiber’s length. I have not noticed any sort of nonuniform development, at least as a natural bodybuilder. This seems supported by the length-tension relationship and how muscle fibers operate in general.

Several examples can support this belief. For instance, you will feel it in the lower biceps region on the preacher curl because the underlying brachialis is contracting, along with the passive tension generated due to a lengthened biceps while at the bottom.

Any time I thought I was isolating a region, like the inner chest, I realized the same level of tension, either in a stretched or shortened state, was applied evenly throughout the whole fiber length. Sometimes I wondered if the inner chest was comparatively less disabled than the rest of the chest, so even though this portion was contracting at a poor length, it was still being emphasized. The soreness though occurred throughout the whole length and without any uneven development.

It is easy to confuse the shortening sensation, that cramps the muscle, and the lengthening sensation, that stretches it to create passive tension, with an active muscle contraction, which it is not.

Trying to address a region along the fiber length, which means including stretched and shortened states, leads to poor active tension. Active tension is the main stimulus for more muscle size. This form of tension is emphasized in the middle range of the right exercises.

This approach also protects the joints by avoiding the extremes, as shown through stabilizing and destabilizing forces.

This makes compound exercises optimal for the largest muscle groups. For example, the elbows are furthest away from the shoulders at about the midpoint of a bench press, which makes the exercise feel toughest at the correct length for the chest.

This means that the flat press, the incline press, and perhaps a decline press or dip are sufficient for the entire chest. No flyes or cross-overs are needed.

Some make the argument that isolation for the large muscles may reduce fatigue on secondary muscles. Lots of pressing could wear out the triceps and shoulders even with the chest as the prime mover. These would still be suboptimal exercises.

Keep an open mind though, remembering the doubts I raised at the beginning. We must admit that our knowledge could be incomplete.

Nonetheless, here is how I view the tiers of isolation:

  1. Function
  2. Muscle Group
  3. Muscle Head
  4. Muscle Fiber

Working each superficial large muscle head should be your priority as a bodybuilder.

Small and often deeper muscles can be addressed as desired. They receive indirect work as you add variety.

If your goal is to simply increase the measurement of a body part, it could be worthwhile. Aesthetically it may look odd for some muscles though, like a well-developed sartorius for the thigh.

Minor but impressive superficial muscles, like the serratus anterior, may get enough stimulation through your overhead movements and protraction while pressing, but you can experiment with pure scapular protraction.

Isolating at the muscle fiber level seems unnecessary for many muscle heads, but keeping this tier allows for…

  1. medium options.
  2. hyper-targeting of certain muscle heads.
  3. possibly addressing compartmentalization.

A medium option could be a regular curl or heel raise. This means elbows and wrists aligned and toes forward.

For these muscles though, the biceps and the gastrocnemius, I do not think these are helpful. I suggest focusing on each head alone. This would mean curls with elbows both inside and outside of your wrists while supinating and heel raises with toes pointing outward and inward. Two exercises should be all you need for each muscle group, with no neutral option required.

Certain muscle heads, if you perceive a weakness, may respond to further targeting. This can be simplified by dividing the head into three slices. You may want to try lateral raises while upright, while leaning forward, and while leaning backward on an adjustable bench to fully develop the side deltoid. An upright row with a wider grip may be more than enough though.

Compartmentalization is tricky because even though it is shown in the research, it may not matter enough for bodybuilding. If the lats really do have multiple compartments that affect development noticeably, then a bent-over row, pull-down, and T-bar row would address the inferior, superior, and middle fibers well. These would be good additions to address other back muscles anyway, so this debate may be mostly academic.

This all raises a lot of questions. Luckily, a balanced program with a variety of exercises for each major muscle head along with reasonable ranges of motion would cover many angles.

Here is how I view the parameters for isolation:

  1. Initial Setup
  2. Positioning (Angle)
    1. Top or Outer
    2. Middle (For quite a few muscle groups, a middle option seems unnecessary.)
    3. Bottom or Inside
  3. Range of Motion (Use a near-full range of motion, avoiding the extreme endpoints. May matter slightly for muscles, heads, and fibers but not regions along the fiber’s length.)

Range of motion is worth discussing further.

Active and passive insufficiencies show the futility of training muscles near the endpoints, yet range of motion could matter when addressing muscle heads.

We know that the supraspinatus initiates the lateral raise. The vastus medialis may work a bit harder near terminal knee extension than the vastus lateralis. The medial head of the triceps may also work more so than the other heads near full elbow extension. We know the brachialis works harder at extreme lengths for the biceps brachii, and shoulder hyperextension on rows allow for the trapezius and rhomboids to be emphasized.

Different pennation angles for muscle fibers within a muscle supports using enough range of motion to hit them all optimally as well.

Finally, a stretched muscle may be emphasized slightly over a non-stretched muscle, such as the long head of the triceps on an overhead arm extension.

Despite the shift in muscle emphasis throughout the range of motion, you could still make the argument that the middle position generates the most tension for all heads anyway.

I suggest establishing a near-full range of motion but ignoring the extreme endpoints as determined personally.

This fuller range of motion has other benefits. The pre-stretch improves the contraction on the positive phase of the repetition along with giving you enough space to exert some power, bringing in the fast-twitch fibers. You may also address secondary growth factors like attaining a better pump or further micro-tearing.

Other Factors for Isolating Muscles

These factors delve further into the parameters. They will eventually receive articles of their own:

  1. Direct Resistance
  2. Disablement
  3. Countercurrent & Concurrent Movements

Direct Resistance

You want the muscle fibers to have the best line of pull when facing the resistance.

This is why you internally rotate the shoulder, or “pour from the pitcher,” on lateral raises, to allow the side deltoid a better position than the front deltoid. This also explains why the upright row, performed correctly, can be a great exercise for the side deltoid.

Pulling up higher on your torso, to align with the teres major on a row or pull-down, will emphasize it. This principle also explains why a pull-over motion on a cable machine done at your side will focus on the coracobrachialis.

As a bodybuilder, this also shows the possible value of machines for certain movements. You may find it easier to maintain strictness for direct resistance.


The largest muscle involved in a movement tends to be the prime mover unless it has poor leverage or is otherwise disabled.

To target the brachioradialis of the forearm, you need to use a pronated or reverse grip to disable the larger biceps from taking over on a curl.

Active insufficiency applied to the gastrocnemius, by using a seated heel raise, will isolate the soleus.

Concurrent & Countercurrent Movements

Multiarticulate muscles, which attach to more than one joint, have special properties that can be manipulated for bodybuilding purposes. This involves the range of motion through concurrent and countercurrent movements.

A concurrent movement occurs when the muscle lengthens at one joint and shortens at another. This happens naturally in many compound movements that humans perform.

Concurrent movement takes place for the rectus femoris on a squat or the biceps during a row or pull-up. Since the muscle maintains its length, it does not contract very intensely, instead maintaining a lower level of constant tension to facilitate movement.

Concurrent movement can be useful for bodybuilding. It explains why the squat focuses on the vasti (vastus medialis, vastus lateralis, and vastus intermedius), the row on the brachialis (at least for the elbow flexors), and the close-grip bench press on the lateral and medial heads of the triceps.

A countercurrent movement occurs when the muscle either shortens or lengthens at more than one joint simultaneously.  It feels somewhat unnatural against resistance, occurring in everyday life more rarely. This occurs when kicking a ball for the rectus femoris.

Countercurrent movement allows for a more intense contraction though. It also explains techniques done intuitively by bodybuilders. The scoop motion on a curl, with elbow flexion, wrist supination, and slight shoulder flexion would involve all the functions of the biceps. Some research shows it may actually develop the peak of the biceps, or the fibers closest to the middle of the outer head.

At a minimum, multiarticulate muscles must be addressed through a single-joint or isolation movement to get worked well. A leg extension is required to work the rectus femoris, and a leg press or a squat alone would be inadequate. A movement like a resisted kick on a cable machine, with both hip flexion and knee extension, would be best though if more development is desired.

How Specifically Can We Isolate Muscles?

I understand this post dealt with a great deal of information. Much more can be said, such has how to put it all together, along with going further into many subjects mentioned here.

This should make it clear that bodybuilding is its own art and science, related to but separate from pursuits like powerlifting or general fitness.

Therefore, we need to accept the rules of the game, how things really are and not how they ought to be. Efficiency does not equal effectiveness. We observe the value of specialization in so many other areas of life, yet disdain it in fitness.

Progress on the basics is not enough.

One of the greatest mistakes we can make in training, and all of our lives really, is to not know what we want. Without setting goals, we wander around aimlessly, failing to dig deeply enough so as to mine the most precious gems, to earn the very best results.

Notice that the huge arm of a bodybuilder is well-developed. Imagine a twisting arm pose. A large brachialis separates the biceps from the triceps. The long head of the triceps is especially pronounced, hanging below the lateral head. The outer biceps creates a tremendous peak.

Imagine the average trainee striking the same pose. This arm looks like it has two small parts: a biceps and a triceps. The bodybuilder displays 4 prominent parts instead.

As the largest muscle will tend to dominate a movement, all of these muscles and muscle heads require isolation to optimize. You could perform concentration curls for the long outer head of the biceps. Hammer curls will hit the brachialis. Close-grip bench presses or rope push-downs would take care of the lateral head of the triceps. Perhaps an unusual exercise, like a pull-over and arm extension, would manipulate the range of motion through countercurrent movement to focus on the long head of the triceps.

Every way you can isolate more specifically will lead to new muscle growth.

Research has mounted that supports much of the traditional bodybuilding way of training. This means isolation, variety, mostly moderate rep ranges, enough volume, and so forth.

Ask yourself, what are my goals? My weaknesses? My capabilities? My preferences? How much time can I invest?

The focus of this website is now to optimize natural bodybuilding. The natural part of this statement is an important distinction. While it means we more easily develop proportion, the V-taper, and other admirable qualities, we also need to be realistic about our limits.

I suggest isolating each superficial muscle head, with the possibility for muscle fibers as well, while using a near-full range of motion. I believe this is the furthest tier of isolation for bodybuilding.

Consider your own experiments, with the pure bodybuilding perspective in mind, to decide for yourself.

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