Can you really change the shape of a muscle?
by Mike Meija
There are very few absolute truths in bodybuilding. Remember when squats were "proven" to be bad for your knees and much "safer" alternatives like the leg extension machine came into vogue? Remember when everyone knew for sure that dietary fat was bad for you and that high protein intake would nuke your kidneys faster than you could say MRP? Remember when experts laughed at bodybuilders because the big goons thought they could actually change the shape of their muscles? It seems that yesterday's facts are fast becoming today's fallacies.
Wait a minute, you might be saying, it is a fact that you can't change the shape of a muscle with training! Everyone knows that so-called "shaping exercises" are bogus, right? Well, maybe. According to Dr. Jose Antonio and author Mike Meija, there just might be something to that old idea after all. We'll let you decide.
Bodybuilding or Body Sculpting?
Back in the days of the Renaissance, mankind was witness to some of the greatest sculptors the world has ever known. Men like Michelangelo and Leonardo da Vinci were renowned for their abilities to take a simple object like a piece of marble and painstakingly transform it into a visual masterpiece. Fast forward to today and you'll find that modern technology has made this type of Old World craftsmanship all but obsolete. But there's still one group that appreciates such fine attention to detail: bodybuilders!
Just walk into any gym and you'll see them laboring over every inch of their physiques, blasting their muscles with exotic exercises performed at all sorts of peculiar angles, all in an effort to ensure the most symmetrical development possible. But can they really sculpt their bodies by isolating specific parts of a muscle? Or is this just wishful thinking and a throwback to the training ideologies of the 1970s?
A New Look at Regional Hypertrophy
The idea of whether or not it's possible to target specific areas of a muscle is one that's been hotly contested for years. Many experts in the field of strength training feel that once a muscle has been stimulated to contract, all the fibers that comprise that muscle respond in a uniform manner, meaning that any growth will be proportional throughout the entire muscle belly.
These experts offer little acceptance to the notion that you can activate different "regions" of the same muscle simply by varying the types of exercises you do. On the other hand, there are those who feel that it's not only possible to target specific parts of a muscle, but that doing so can actually alter the shape of the muscle!
One such expert is Dr. Jose Antonio. Widely recognized as one of the leading researchers in the country, Dr. Antonio has recently written a comprehensive literature review on the subject of regional hypertrophy. Because the review (which appears in a recent edition of the Journal of Strength and Conditioning Research) is rather scientific, he's graciously agreed to allow me to present my interpretation of his findings to a more diverse audience. Among some of more interesting points he addresses are:
? Why an individual muscle can't simply be described as a compilation of muscle fibers that run from origin to insertion.
? Studies show that you can selectively recruit different segments of a muscle depending not only on the type of exercise you do, but how much weight you use.
? There's no single "best exercise" that can maximize the growth potential of a particular muscle.
In order for you to better understand Dr. Antonio's position, I've categorized his findings into three main areas: fiber type, the compartmentalization of skeletal muscle, and electromyography (EMG) studies.
Fiber Type: Which Twitch is Which?
There are two basic fiber types of skeletal muscle: slow twitch and fast twitch, each of which displays vastly different properties. Slow twitch, or Type I fibers, are your endurance fibers. They're highly oxidative (meaning that they rely on oxygen as their primary fuel source), don't develop a great deal of tension, and are extremely resistant to fatigue. Next up are your fast-twitch fibers, which are subdivided into two different groups: fast oxidative glycolytic (FOG) or Type IIa, and fast glycolytic (FG) or Type IIb fibers.
FOG fibers have both a high oxidative and a high glycolytic (anaerobic) capacity. These are the fibers you use most during activities like basketball or middle distance running. Your fast glycolytic fibers are your little powerhouses. These are the guys you call upon to run a 40-yard dash or lift a maximal weight. They contract forcefully and quickly, but fatigue just as fast. Granted, this is somewhat of an oversimplification of how the various fiber types are classified, but it'll do for the purposes of this article.
Why do you need to know all this? Because these different muscle fibers are recruited based on your intensity of effort. In other words, how hard you're working dictates which fibers you'll rely on to complete a given task. For instance, according to the usual progression of muscle-fiber recruitment, slow-twitch fibers are recruited before fast twitch fibers. As intensity (or in this case the amount of weight you're lifting) increases, your nervous system begins to recruit fast twitch fibers to a greater degree.
However, there are certain situations, such as when you're doing heavy negatives, where it's possible to preferentially recruit your more powerful fast-twitch muscle fibers.(7) According to Dr. Antonio, this would seem to suggest that it's possible to selectively recruit different types of fibers depending on the type of exercise you're doing.
What makes this idea of selective recruitment even more intriguing is the fact that these different fibers are randomly scattered throughout a given muscle. Therefore, if it were indeed possible to zero in on a specific fiber type, the end result would be a non-uniform hypertrophy, which would in essence change that muscle's shape. Admittedly, this is more commonly seen with fast-twitch fibers, which tend to hypertrophy proportionately more than slow twitch, especially at heavier resistances.(1,5)
However, as Dr. Antonio points out, this doesn't mean you should completely ignore the growth potential of your slow-twitch fibers. There may in fact be a way to train that would enable them to attain similar development. The point is, there's no single training protocol that will consistently produce growth in all your different muscle fibers. That's why it's imperative that you periodically vary the amount of weight you use as well as your set and repetition schemes in order to keep making gains.
Compartmentalization: Divide and Conquer
Lending further credence to this whole "target training" concept is something known as the compartmentalization of skeletal muscle or, in laymen's terms, the fact that a muscle can be divided into several distinct segments depending on how it's activated by your nervous system. As Dr. Antonio explains, "An individual muscle is more than just a collection of fibers spanning the entire muscle belly with a single muscle-nerve interaction. In other words, different portions of the same muscle can be called into play, depending on the task demands of the situation."
A perfect example would be your trapezius, the large kite-shaped muscle that comprises a significant portion of your upper back. Because of the way it attaches to your skeleton, the trapezius can be divided into three separate regions (upper, middle and lower), each of which can be isolated by a particular exercise.(1)
For instance, while an exercise like shrugs will hit the upper region, a rowing movement will more effectively target the middle segment of your traps. Finally, a lat pulldown, which requires you to depress, or lower your shoulder blades, will best work the lower segment of the muscle. This is just one of countless examples as to why it's important to incorporate a variety of exercises into your routine to ensure the most well-rounded development.
EMG: A Closer Look
Still not convinced it's possible to isolate certain parts of a muscle? A look at some of the research might just change your mind. In his article, Dr. Antonio refers to several studies that have used electromyography (EMG) to determine the actions of muscles surrounding a particular joint. EMG measures the electrical activity of a muscle both at rest and as it contracts.
The fact that many muscles don't exhibit a uniform EMG response during certain exercises suggests that there's a region-specific response to resistance exercise.(2,3) In fact, one study showed that after six months of doing leg extensions, subjects demonstrated a 19% increase in size in both the upper and lower regions of the quadriceps, but only a 13% increase in the middle portion of the muscle!(8) A similar study done on the upper body found that 12 weeks of triceps training produced significant growth in the middle portion of the muscle with virtually no change anywhere else.(4)
Perhaps the best example of regional specific EMG responses involves abdominal training. For years there's been a running debate amongst fitness professionals as to whether or not the abs can be divided into upper and lower segments. Many contend that since the main muscle of the abdominals, the rectus abdominus, is one long sheet of muscle (it runs from your pubis to the costal cartilages of your 5th, 6th and 7th ribs), that any abdominal exercise you do will stimulate the entire muscle equally. This is factually incorrect!
It's been clearly demonstrated that the upper and lower segments of the rectus have different innervations, meaning that they can selectively respond to different exercises.(6,9) So, while a crunch will hit the upper region, reverse crunches and hanging leg raises should be included to work the lower abs. (And yes, it's okay to say "lower" and "upper" abs!)
In addition to the EMG findings cited by Dr. Antonio, there's 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, noted researcher Dr. Per A. Tesch uses magnetic resonance imaging (MRI) to show not only which muscles, but also which portions of the same muscle are emphasized during a variety of popular bodybuilding exercises.(10)
The book is designed to help readers take all the guesswork out of training. Want to know how a particular grip affects biceps development? Looking for the best exercise to give your triceps that distinctive horseshoe shape? Or, maybe you're more interested in the effect that foot position has on muscle involvement during squats. Whatever the case, all you have to do is turn to the corresponding page of the book and you'll get an in depth look at the effect each exercise has on your muscles. The book is available through Human Kinetics. You can call them at 800-747-4457.
So, just what does all this mean? How can you put this information to work for you in the gym? The way I see it you've got a couple of options. Either you can isolate specific regions of a particular muscle each time you train it, or you try and cover all your bases by blasting the muscle from every angle imaginable in each workout.
For example, let's say you're training chest. Is it better to focus mainly on the upper segment of the pecs one workout and the mid to lower segments the next? Or should you try and do at least one flat, incline and decline movement every workout? Given the fact that few of us sport perfect symmetrical development, I'd say option one is the best way to go.
Admittedly, being able to bring those little "problem areas" up to par with the rest of your physique is intriguing, at least to me. No more being ridiculed for sub par lower lat development or weak inner calves. Besides, once you fix these little imbalances, there's plenty of time for a more well-rounded approach later on.
Putting all this science aside for just a moment, there's also plenty of practical evidence to support the efficacy of target training. Of all the athletes who train with weights, there's no arguing that bodybuilders consistently display the most impressive levels of muscular development. That's because, rather than train to improve their ability to perform in a given sport, the bodybuilder's primary goal is to achieve the highest degree of muscular size, shape and symmetry.
In doing so, they realize that there's no "best" exercise, no ultimate program that will continually enable their muscles to grow. Perhaps now, the rest of us can begin to appreciate what bodybuilders have known for decades: It is possible to change the shape of your muscles! And who knows, as a result, perhaps create a physique that would make even Michelangelo jealous.
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."