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Muscles to order Can you really change the shape of a muscle?

Muskeln auf Bestellung Kannst Du die Form eines Muskels wirklich verändern?

There are very few absolute truths in the world of bodybuilding. Remember when it was considered proven that squats were bad for your knees and "safer" alternatives like leg extension machines came into fashion? Remember the days when everyone knew for sure that dietary fats were bad for you and that a high protein intake would make you explode faster than you could say protein shake? Remember the days when experts laughed at bodybuilders because these muscular fools thought they could actually change the shape of their muscles? It seems like yesterday's facts are becoming today's fallacies.

But wait, you might say, it's a fact that you can't change the shape of a muscle by working out! Everyone knows that so-called "shaping exercises" are bogus, right? Well, according to Dr. Jose Antonio and author Mike Meija, there might be something to that old idea after all. We'll let you decide.

Bodybuilding or body sculpting?

During the Renaissance, mankind witnessed some of the best sculptors the world has ever seen. Men like Michelangelo and Leonardo da Vinci were famous for their ability to take a simple object like a piece of marble and transform it into a visual masterpiece.

Fast forward to today and you'll find that modern technology has made this kind of old-world craftsmanship virtually obsolete. But there is still one group of people who appreciate such attention to detail: Bodybuilders!

You only need to go to any gym and you will see these people working on every inch of their body. You'll see them maltreating their muscles with exotic exercises of all kinds from every conceivable angle to ensure the most symmetrical development possible. But can bodybuilders really shape their bodies by isolating specific parts of a muscle? Or is this simply a pipe dream and a throwback to the training ideologies of the 1970s?

A new look at regional hypertrophy

The question of whether it is possible to target specific areas of a muscle has been hotly debated for years. Many experts in the field of strength training believe that once a muscle has been stimulated to contract, all the fibers that make up that muscle will respond in the same way, which would mean that any growth will occur evenly across the entire muscle.

These experts do not accept the view that you can activate different regions of the same muscle by varying the exercises you perform. On the other hand, there are those who believe that it is not only possible to target specific parts of a muscle, but that this can also change the shape of a muscle!

One such expert is Dr. Jose Antonio. Dr. Antonio, who is widely regarded as one of the country's leading scientists, has recently written a comprehensive literature review on the subject of local hypertrophy. Since this review, published in the Journal of Strength and Conditioning Research, is quite scientific in nature, Dr. Antonio has allowed me to present my interpretation of his findings to a wider audience. Among the more interesting points he addresses are the following:

- Why an individual muscle cannot simply be described as a collection of muscle fibers running from attachment point to end point.
- Studies show that you can selectively recruit different segments of a muscle not only depending on the type of exercise used, but also depending on the weight used.
- There is no single "best" exercise that can maximize the growth potential of a particular muscle.

To make Dr. Antonio's position easier to understand, I've categorized his results into three main areas:

  • Muscle fiber type
  • Subdivision of skeletal muscles
  • Electromyography (EMG) studies

Muscle fiber types

There are two basic types of skeletal muscle: slow-contracting and fast-contracting muscle fibers, each with different characteristics:

  • Slow-contracting muscle fibers are your endurance fibers. They are highly oxidative (meaning that they rely on oxygen for energy production), do not develop high levels of tension and are extremely resistant to fatigue.
  • The fast contracting muscle fibers are divided into two groups
    • Fast oxidative glycolytic fibers (FOG) or type IIa fibers: these fibers have both a high oxidative and a high glycolytic (anaerobic) capacity. These are the fibers you use the most during activities such as basketball or middle-distance running.
    • Fast glycolytic fibers (FG) or type IIb fibers. These fibers are your little power plants. They are the fibers you rely on during short, maximal sprints or training with maximum weights. These fibers contract powerfully and quickly, but fatigue just as quickly.

Admittedly, this is an oversimplification of the classification of the different muscle fibers, but for the purpose of this article, it is quite sufficient.

Why do you need to know all this? Because these different muscle fibers are recruited based on the intensity of your efforts. In other words, how hard you train dictates which fibers are recruited to perform a particular task. For example, according to the usual progression of muscle fiber recruitment, the slow-contracting fibers are recruited before the fast-contracting fibers. As the intensity (or in this case the amount of weight you use) increases, your nervous system begins to recruit fast-twitch fibers to a greater extent.

However, there are certain situations, such as performing heavy negative repetitions, where it is possible to preferentially recruit your more powerful fast-twitch muscle fibers (7). According to Dr. Antonio, this seems to suggest that it is possible to selectively recruit different muscle fibers depending on the type of exercise you are performing.

What makes the idea of selective muscle fiber recruitment even more interesting is the fact that these different fibers are randomly distributed across a given muscle. So if it were actually possible to selectively use a specific muscle fiber type in isolation, the result would be non-uniform hypertrophy, which would essentially change the shape of the muscle.

Admittedly, this can be observed more often in fast-contracting fibers, which tend to hypertrophy proportionally more than slow-contracting fibers, especially at heavier resistances (1, 5).

However, Dr. Antonio emphasizes that this doesn't mean you should completely ignore the growth potential of slow-contracting fibers. In fact, there may be a way to train that allows these fibers to achieve similar development. The point is that there is no single training protocol that will consistently produce growth in the range of all your different muscle fibers. For this reason, it is imperative that you periodically vary both the amount of weight you use and your set and repetition scheme in order to continue to make progress.

Skeletal muscle subdivision: divide and conquer

What lends further credence to the whole concept of targeted training is something known as skeletal muscle subdivision. Simply put, this describes the fact that a muscle can be divided into several separate segments depending on how it is activated by your nervous system.

Dr. Antonio explains this as follows: "An individual muscle is more than simply a collection of muscle fibers that run across the entire muscle belly and are activated by a single muscle-nerve interaction. In other words, different areas of the same muscle can be activated depending on the demands of the specific situation."

A perfect example of this is the trapezius - a large kite-shaped muscle that makes up a significant portion of your upper back. Because of the way this muscle attaches to your skeleton, the trapezius can be divided into three separate areas (upper, middle and lower), each of which can be isolated by a specific exercise (1).

For example, while an exercise such as shoulder raises (shrugs) will train the upper area, a rowing exercise will train the middle area of your trapezius more effectively. Lastly, a lat pulldown, which requires you to pull your shoulder blades down, will work the lower portion of the muscle best.

This is just one of countless examples of why it's important to include a variety of exercises in your training program to ensure well-rounded muscle development.

EMG: A closer look

Still not convinced that it's possible to isolate certain parts of a muscle? A look at the relevant studies might change your mind. In his article, Dr. Antonio refers to several studies that have used electromyography (EMG) measurements to determine the actions of muscles surrounding a specific joint. An EMG measurement measures the electrical activity of a muscle both at rest and during its contraction.

The fact that many muscles do not show a consistent EMG response during certain exercises suggests that there is a region-specific response to resistance exercise (2, 3). In fact, one study showed that after 6 months of performing leg extensions, subjects showed a 19% increase in muscle mass in both the upper and lower quadriceps, while the increase in the middle region was only 13% (8).

A similar study conducted in the upper body concluded that 12 weeks of triceps training produced significant growth in the middle portion of the muscle, while there was virtually no change in other areas (4).

Perhaps the best example of a region-specific EMG response involves abdominal muscle training. For years, there has been an ongoing debate among fitness experts as to whether the abdominal muscles can be divided into upper and lower segments. Many argued that because the primary muscle in this area - the rectus abdominus - is a long muscle (running from the pubic bone to the costal cartilages of the fifth, sixth and seventh ribs), any abdominal exercise should stimulate the entire muscle equally. However, this turned out to be factually incorrect!

It has been clearly shown that the upper and lower segments of the rectus abdominus have different innervations, which means that they can respond selectively to different exercises (6, 9). While a crunch movement will place more stress on the upper region, reverse crunches and hanging leg raises should also be included in the exercise program to work the lower abs. (And yes, it's okay to talk about "upper" and "lower" abs!)

In addition to the EMG research cited by Dr. Antonio, there is also an exciting new book that uses a different type of technology to show how muscles respond to resistance training. In his book Target Bodybuilding, respected scientist Dr. Per A. Tesch uses magnetic resonance imaging studies to show not only which muscles, but also which areas of a muscle are preferentially loaded during a selection of different popular bodybuilding exercises (10).

The book is designed to help the reader eliminate any guesswork from training. Want to know how a specific grip affects biceps development? Are you looking for the best exercise to give your triceps that characteristic horseshoe shape? Or maybe you're more interested in the effects that the positioning of the feet during squats has on muscle engagement during squats.

Whatever you want to know, just turn to the relevant page of the book and you'll get a detailed insight into the effects each specific exercise has on your muscles.

Practical applications

What does all this mean in practice? How can you use this information to your advantage in the gym? The way I see it, you have several options. You can either isolate specific areas of a particular muscle or you can try to cover everything by working a muscle from every conceivable angle in every training session.

For example, let's say you're training your pecs. Is it better to focus mainly on the upper area of the pecs during one training session and primarily on the middle and lower area during the next training session? Or should you try to perform at least one exercise on the flat bench, one exercise on the incline bench and one exercise on the reverse incline bench during each training session? Considering the fact that very few of us have perfectly symmetrical development, I would say that option number 1 is the better choice.

Admittedly, the ability to bring those "little problem areas" up to par with the rest of your body in terms of development is fascinating - at least to me. No more scoffing at underdeveloped lower latissimus or weak inner calves. That being said, once you've corrected these minor imbalances, you'll have plenty of time for a more well-rounded approach.

Final thoughts

Putting all this science to one side for a moment, there is also plenty of practical advice to support the effectiveness of targeted training. Looking at all the athletes who train with weights, there is no doubt that bodybuilders consistently show the most impressive levels of muscle development. This is because their primary goal is not to train to improve their ability to perform a particular sport, but to achieve the highest level of muscle size, shape and symmetry.

In doing so, they realize that there is no "best" exercise and no ultimate program to continuously grow their muscles. Perhaps the rest of us can now begin to appreciate what bodybuilders have known for decades: it is possible to change the shape of a muscle! And maybe as a result, you'll be able to sculpt a body that would have made Michelangelo envious.


  1. Antonio, J. Nonuniform response of skeletal muscle to heavy resistance training: can bodybuilders induce regional hypertrophy? J. Strength Cond. Res.14(1):102-113. 2000.
  2. Barnett, C., V. Kippers, and P. Turner. Effects of variations of the bench press exercise on the EMG activity of five shoulder muscles. J. Strength Cond. Res. 9:222-227. 1995.
  3. Glass, S.C., and T. Armstrong. Electromyographical activity of the pectoralis muscle during incline and decline bench presses. J. Strength Cond. Res. 11:163-167. 1997.
  4. Kawakami, Y., T. Abe, S.-Y. Kuno, and T. Fukunaga. Training-induced changes in muscle architecture and specific tension. Eur. J. Appl. Physiol. 72:37-43 1995.
  5. Kraemer, W.J., S.J. Fleck, and W.J. Evans. Strength and power training: Physiological mechanisms of adaptation. Exerc. Sport Sci. Rev. 24:363-398.1996.
  6. Lipetz, S., and B. Gutin. An electromyographic study of four abdominal exercises. Med. Sci. Sports 2:35-38. 1970.
  7. Nardone, A., C. Romano, and M. Schiepatti. Selective recruitments of high-threshold human motor units during voluntary isotonic-lengthening of active muscles. J. Physiol. 409:451-471. 1989.
  8. Narici, M. V., H. Hoppeler, B. Kayser, L. Landoni, H. Claasen, C. Gavardi, M. Conti, and P. Cerretelli. Human quadriceps cross-sectional area, torque, and neural activation during 6 months of strength training. Acta Physiol. Scand. 157:175-186. 1996.
  9. Sarti, M.A., M.S. Monfort, M.S. Fuster, and M.D. Villaplana. Muscle activity in the upper and lower rectus abdominus during abdominal exercises. Arch. Phys. Med. Rehab. 77:1293-1297. 1996.
  10. Tesch, P.A. Target Bodybuilding. Human Kinetics, Champaign Ill. 1999.

By Mike Meija

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