How to Get Your Biceps to Peak…and Other Notions of Muscle Hypertrophy
By Jose Antonio, Ph.D., CSCS
http://www.mensfitness.com/metrx/100802/biceps_peak.html

If you've spent any amount of time in the gym, then you've heard this idea before. Your favorite gym rat will claim that "preacher curls help give me a peak to my biceps while doing standing straight bar curls are good for overall mass of the biceps." Or perhaps you've heard that leg extensions are especially good for the medial (inner) aspect of the quad, your vastus medialis muscle. The vastus medialis muscle, better known as the "tear drop" muscle can be targeted specifically by doing leg extensions. Is this true? Or is it bodybuilding nonsense?

The idea that you can induce regional adaptations in muscle is not new. However, scientific evidence supporting such a notion is relatively new! Don't get me wrong. You and I are not going to do preacher curls 'till we're blue in the face and get a peak like Flex Wheeler. Sure genetics plays a role. However, within our own limits, we can shape our muscles to look different. We in essence have our own Olympic Gold medal or Olympia-like performances just waiting to be tapped.

ELECTROMYOGRAPHIC EVIDENCE
An EMG or electromyographic recording of muscle activity is often done to determine the extent of muscle involvement for a particular movement. An EMG signal is a recording of a muscles electrical activity from electrodes placed on the skin or within the muscle belly itself.

Using this technology, a group of Australian scientists examined the effects of different bench angles and grip widths on muscle activity around the shoulder. For example, in comparing two functionally distinct regions of the pectoralis major muscle (i.e., clavicular head and sternocostal head), they found that the clavicular head of the pec major (the part attached to the collarbone or clavicle) was more active during a narrow grip vs. wide grip, esp. during the flat and incline bench press. Relative to the sternocostal head, the clavicular head was more active during a narrow grip incline bench. On the other hand, the sternocostal head of the pec major (part attached to the breastbone or sternum) showed its greatest activity during a flat bench; however, if you wanted greater relative involvement of the sternocostal head vs. the clavicular head, a decline press with a narrow grip seemed to work best. And for best maximal involvement of the entire pectoralis major muscle, the wide grip flat bench resulted in the greatest measured electrical activity!

Another group of scientists examined how different heads of the biceps brachii muscle are activated during supination movements. If you've forgotten, supination is a movement that occurs around the radioulnar joint and occurs when you rotate your forearm such that your palms face up. And the biceps brachii is the primary muscle involved in supination! These scientists showed that when the elbow was flexed to 120 degrees, the short head (medial side) was activated more so than the long head of the biceps during supination. And the further the elbow was extended, the more the long head of the biceps came into play. Thus, if you want to stress the medial side of the biceps muscle, do supination movements at 120 degrees of flexion. Most gyms now have machines which allow isolated supination movements. So give it a shot; it'll be a good addition to your arm workout.

Further evidence for the functional differentiation within the biceps muscle is magnetic resonance imaging which demonstrate that a standing bilateral dumbell curl with your palms up (supinated) hits the medial or short head of the biceps brachii muscle more so than the lateral or long head. On the other hand, doing the same exercise with a neutral grip (slightly pronated) results in better activation of the lateral or long head.

And what about the notion that you can train your upper vs. lower abs? Here's an area where there is a big dispute concerning the role of the ab muscles. Many believe that the rectus abdominus is one muscle (which is correct) that is activated equally when you contract it (which is incorrect!). A study done at the University of Valencia in Spain compared the average EMG activity of the upper and lower abs during a curl-up and posterior pelvic tilt exercise. They found that it is true that the stomach crunch or curl does elicit greater rectus abdominus activity in the upper abs while doing posterior pelvic tilt exercises hits the lower abs better as long as they're performed correctly!

We can even examine a small forearm muscle such as the extensor carpi radialis longus (ECRL) muscle. You're thinking what the hell or where the hell is this muscle with a monstrously long name. The ECRL performs wrist extension and radial deviation (movement of the hand sideways towards the thumb). It originates at the lower end of the lateral surface of the humerus and attaches to the base of the second metacarpal. Even a muscle such as this is differentially activated depending on how you utilize it. For example, when you do wrist extension alone, the proximal ECRL is activated more so than the distal ECRL. However, when you do radial deviation, only the proximal ECRL is activated! The distal ECRL is in essence silent or inactive.

MUSCLE GROWTH!
OK, EMG signals are fine and all, but does this mean that muscles can grow in specific regions. Or does a muscle hypertrophy by generally enlarging all parts? We know in animals that stretch overload will cause greater growth in the proximal and distal region while fiber number is greater in the middle region vs. other regions of the muscle belly. Also, that rats undergoing hypertrophy of their plantaris muscle (a plantarflexor) showed the greatest growth in the middle and distal region with the least in the proximal region. Furthermore, we now have evidence in humans that regional differences exist with regards to muscle growth.

In a study done at the University of Texas Southwestern Medical Center in Dallas, twelve weeks of training the elbow flexors in elderly men resulted in regional response with regards to hypertrophy. The greatest increase in cross-sectional area occurred in the distal belly of the elbow flexor muscles with little if any change proximally (near the origin of the muscle). This demonstrates that muscle does not respond in a uniform manner! In fact, you could say that training seemed to produce a more "lop-sided" muscle!! Is this a normal response? Did a specific exercise cause this? It's hard to say since these subjects performed various arm exercises (barbell curls, dumbell curls, hammer curls, etc.).

Moreover, a Japanese group examined five men after 16 weeks of unilateral triceps brachii exercises (consisting of the French press exercise) found that maximal muscle growth occurred at the distal end of the arm vs. the middle and proximal regions.

A study done in the United Kingdom examined ten young adults (5 men and women) and had them perform leg extension exercises concentrically with one leg and eccentrically on the other leg. They trained three times per week for twenty weeks doing four sets of ten reps with a minute rest between sets. The measured the cross-sectional area of the quadriceps muscles at two levels: at 25% and 75% of the femur's (thigh bone) length measured from the knee joint. Interestingly, both the concentric and eccentrically trained leg produced increases in muscle cross-sectional area, but only in the upper region of the quad with no change occurring closer to the knee. Although, it is generally accepted that it is the eccentric part of a muscle contraction that is "more important," it is apparent that at least in previously untrained persons, concentric contractions alone may provide a sufficient hypertrophic stimulus.

In a similar study done at the University of Nebraska Medical Center, they trained previously untrained male college students to perform six sets of 10 reps of unilateral knee flexion/extension and elbow flexion/extension of the non-dominant limbs concentrically on a isokinetic device three times a week for eight weeks. The contralateral limb served as the control. They found that there was regional hypertrophy within the same muscle! For instance, the elbow extensors (triceps brachii) experienced growth at the proximal and middle levels but not distally (near the elbow) with the greatest changes occurring in the middle. For the leg extensors (i.e., quads), only the rectus femoris (at all three levels), the vastus lateralis (middle level), and vastus intermedius (middle level) increased in cross-sectional area. For the leg flexors (hamstrings), the biceps femoris (middle level) and the semitendinosus (distal level) increased in size with no change in the semimembranosus.

It isn't clear why certain muscles grow while others did not. Furthermore, it is difficult to make comparisons between studies since they often use different exercise protocols and different technology to analyze changes in muscle growth. It isn't clear why within the same muscle, only certain parts grow. But what is clear is that you do not get a generalized of muscle in response to exercise. For instance, the University of Nebraska Medical Center study demonstrated how difficult it was to induce growth in one of the hamstring muscles, the semimembranosus. Why is this muscle such a hardgainer? Is there a better exercise for that part of the hamstring muscle group?

THE NUCLEAR DOMAIN
In order to understand why or how muscle can respond regionally, it is important to understand the underlying biology of muscle cells or fibers themselves. An individual muscle is much more than just fibers attaching at tendons or bones with a single muscle-nerve interaction. Neuromuscular compartments, which can be described distinct regions of a muscle, are each innervated by an individual nerve branch and therefore containing motor unit territories with a unique set of characteristics. In other words, different portions of one muscle may be called into play depending on the task demands of the situation.

Furthermore, this compartmentalization is evident at the subcellular levels. There is something that muscle biologists refer to as the DNA unit or nuclear domain. The nuclear domain can be defined as the theoretical volume of cytoplasm associated with a single myonucleus. In English, that means each nucleus controls its own little territory. What happens in one part of a muscle fiber does not necessarily happen in other parts of a muscle.

WHAT DOES THIS ALL MEAN?
Does this mean we can all shape our bodies to look like Lee Labrada? No! But we can still shape our muscles to some degree. It may take some tweaking here and there. Mere comparison of the physiques of Olympic weightlifters and bodybuilders demonstrate what effects different training regimens have. You don't normally see a large teardrop (vastus medialis) muscle or prominent sartorius (long strap muscle that starts at the hip and crosses the front of the thigh) muscle on Olympic weightlifters, do you? Certainly, diet and genetics plays a role in the size and shape of the muscle. However, the issue of androgen use may negate any differences in the type of training performed. So at this point, all we can really say is that the different athletes in the strength/power sports demonstrate strikingly different phenotypes or physiques and that these differences are due to many factors (i.e. training, diet, genetics, drugs).

However, if you're a natural bodybuilder (somewhat of an oxymoron), the use of different angles, grips, and exercise selection may produce different hypertrophic responses in different muscles as well as within different regions of a muscle.

PRACTICAL ADVICE ON HOW TO TARGET A SPECIFIC REGION OF MUSCLE
Keep in mind that the following recommendations are based on the limited data available; and it would behoove you to utilize the principle of variation in your training regimen. Nonetheless, you add these variations to your training program as part of an overall training scheme:

1) pectoralis major - if you're interested in developing the upper portion (clavicular head) relatively more so than the sternocostal portion, it is best to do a narrow grip incline bench; if you want to target the sternocostal region relatively more than the clavicular region, a narrow grip on the decline bench is best. And furthermore, for the greatest activation of the entire pectoralis major muscle, then the wide grip bench press is the king of the chest exercises.

2) biceps brachii - if you want to target the short head (medial side), you can do supination exercises with your elbow flexed to ~120 degrees (bend your arm so that your forearm is nearly touching your biceps) or you can do unilateral dumbell curls with your palms up; if you want to target the long head more, try doing unilateral dumbell curls (i.e. hammer curls) with your palms in a neutral position or you can do supination movements (turning of the palms upward) with your elbows extended past 90 degrees (i.e. your arm is between a right angle and fully straightened).

3) triceps brachii - to target the distal portion of the triceps brachii group, French presses (dumbell press overhead) will do wonders; interestingly, isokinetic elbow extensions seem to target the proximal and middle portions of the triceps.

4) rectus abdominus - for the upper abs, curl-ups or crunches are best; for the lower abs, posterior pelvic tilt exercises will help tremendously!

5) quadriceps femoris - the "quads" are actually four separate muscles each having the same function, except the rectus femoris, which also performs hip flexion. Although, regional adaptations occur in each of these muscles, it isn't clear which exercises target each region the best; however, for maximal stimulation of the "entire" quad, doing leg extensions with the leg outwardly rotated (toes pointed out) seems to work best!

The previously described exercises are to be used as an adjunct to your training program. They are not meant to be the exclusive exercises for these bodyparts. It is evident that your muscles are much more complex than just a bunch of fibers attaching at an origin and insertion. In order to maximally stress the muscle unit as a whole, it is imperative that you do a variety of exercises. Of course, if you're in a performance sport such as powerlifting, emphasis should be placed on those exercises specific to the sport; but in bodybuilding or general fitness, you've got more room to experiment with different exercises. So get back to the lab more affectionately known as the gym and do some experimenting!