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Scientific Muscle-Building Pt 2

From the Lab to Your Workouts

Rob Thoburn enjoys pestering scientists all over the world with questions on the muscle-building process. He’ll call them, send e-mail, send a carrier pigeon’whatever it takes to get answers to his questions. And we encourage him by showcasing what he learns in IRON MAN. If you’re like us, you’ll be riveted by what the sharpest minds on the planet have to say about hypertrophy (see, we know scientific words too).

Force vs. the Pump

If your muscles couldn’t generate force, you wouldn’t be able to lift weights. In fact, you’d be about as mobile as a cucumber. The more force your muscles generate, the more weight you can lift. Further, many scientists feel that force generation (a.k.a. tension) per se plays a critical role in stimulating your muscles to hypertrophy; that is, the more force you make your muscles generate, the more likely they are to grow.

But not all scientists feel that way. Some say metabolic factors are involved; others talk about hormonal factors; still others refer to a combination of factors.

Then there is the world you and I live in, the gym. Check out the training styles of legendary Serge Nubret, who did 40 sets for chest, or massive Jay Cutler, for example. Or just think about how long bodybuilders have praised the muscle-building virtues of the pump. Yes, there’s a good deal of real-world evidence to suggest that if you pump your muscles with as much blood as possible during your workouts, they’ll get bigger.

Could there be different kinds of hypertrophy? Maybe certain types of training (e.g., where the objective is to generate very high levels of force) produce one type of hypertrophy, while other types of training (e.g., where the objective is to achieve the best pump) produce another type. Or maybe different training methods can produce the same type of hypertrophy via different biological mechanisms?

Or maybe I’ve been smoking something. Boy, this muscle-building stuff can be confusing. Let’s go to the scientists:

‘You have sparked an interesting conversation here,’ said Troy Hornberger, Ph.D., of the Department of Bioengineering at the University of California, San Diego. (Hornberger worked in the lab of muscle hypertrophy expert Karyn Esser, Ph.D., at the University of Illinois; Esser is now at the University of Kentucky.) ‘In my opinion, there are two types of growth-promoting stimuli. One we probably all agree on is tension; however, I also think that there is a metabolic component to the growth-promoting stimulus of resistance exercise. My basis for that argument comes simply from comparing the physiques of powerlifters to bodybuilders.’

The fact of the matter is that I haven’t been smoking funny cigarettes. My brain is just crowded with muscle-building-related queries, most of them unanswered. That’s why I try to unload them on scientists all over the world, something I talked about in the first installment of ‘Scientific Muscle Building’ [December ’04].

Gary Kamen, Ph.D., a professor in the Department of Exercise Science at the University of Massachusetts Amherst, recently published a great review article on neuromuscular aspects of strength development in Research Quarterly for Exercise & Sport. I asked him about the observation that many bodybuilders seem to be able to build bigger muscles by doing the following, a reliable method of getting a great pump:

‘Lift moderate loads to the point of temporary muscular failure.

‘Perform multiple sets for each muscle or muscle group.

‘Rest relatively briefly between sets.

He replied in a personal communication:

‘If you take a look at the mass of articles on the effects of resistance training on muscular strength, I think you’ll begin to see the impact of large forces. ALL ‘I believe the reason moderate loads are effective in increasing size is due to the effect on capillarization, rather than hypertrophic effects. There certainly is considerable hypertrophy with moderate loads, but most of muscle size is water from the blood flow, and muscle has great capacity to increase blood flow. I believe this accounts for the muscle size increases you see with moderate forces.

‘Remember, too, that when moderate forces are lifted to failure, you're eventually lifting very high loads at failure, and these very high loads certainly have an impact on muscle fiber size and number. Perhaps fiber splitting (to increase muscle fiber size) is increased with moderate loads. I’m afraid we know very little about that.’

Time Under Tension vs. Time Under Pump?

Water or not, a pumped muscle looks good. I wish my muscles could stay pumped all the time, don’t you? But a pump may represent more than a short-lived cosmetic perk.

A pump is basically a muscle swollen with blood. As your muscle cells generate force, or contract, during a set, blood vessels supplying the muscle are squeezed shut. At the end of the set the muscle relaxes and the blood vessels open up wider than before. That allows blood to enter the muscle more quickly. If you lift a heavy enough weight and don’t rest too long between sets, blood will eventually accumulate inside the contracting muscles. That causes them to become fuller in appearance.

Some of the water in the blood leaves the blood vessels and enters the space between muscle cells. It also enters the muscle cells themselves, causing them to swell. Swelling may serve as a hypertrophic signal. Or it may not. Back to the scientists:

‘Muscle [cell] swelling by osmotically active agents is also linked to hypertrophy. Amino acid transport is definitely linked to muscle swelling, at least in culture. Peter Taylor, who works downstairs, has published a number of articles on this. Therefore, the swelling (and thus the pump) might be beneficial.’
Henning Wackerhage, Ph.D.,
Lecturer in Molecular Exercise Physiology,
University of Dundee,
Dundee, Scotland

‘Unique features of high-volume training would be greater glycogen storage and capillary neoformation. Glycogen is stored with water, so increased glycogen storage can add to muscle bulk. New capillaries would add little bulk, particularly when they are collapsed when the muscle is inactive.’
Digby Sale, Ph.D.,
Professor of Kinesiology,
McMaster University,
Hamilton, Ontario,

‘An interesting question. I do always wonder what the stimulus for muscle hypertrophy is’and whether it is the need for high force production with fatigue or more force production while minimizing fatigue that works better’in other words, if you are able to support a muscle’s force-producing capacity and maintenance by providing it with adequate blood flow vs. creating an ischemic low-blood-flow environment under which the muscle is asked to generate force. In the latter, the force production will rapidly decay, and it will require recruitment of more motor units to lift the same weight.’ I think that having to tap into those motor units is definitely an essential requirement for hypertrophy, especially since those are the fast fatiguable fibers that get recruited last. Whether a lack of oxygen and removal of metabolic by-products enhances the stimulus for muscle hypertrophy, I don't know, but I would guess that a critical question to ask is this: Under which of the two conditions does muscle hypertrophy occur to a greater extent or faster’high blood flow during the lifting and after, only after or neither during nor after?’
Michael Tschakovsky, Ph.D.,
Associate Professor,
School of Physical and Health Education,
Queen’s University,
Kingston, Ontario, Canada ‘The molecular mechanisms triggering and maintaining muscle hypertrophy are not clear. There is scientific evidence for stretching and tension. Likely, metabolic by-products also have a role. There is experimental animal evidence of free radicals as inducers of muscle adaptation (maybe also for hypertrophy). This will also explain the findings with ischemic exercise and the need to accumulate sets without much rest in between. I also agree with your idea about fiber swelling (it works to induce muscle glycogen synthesis); it could work by causing stretching.’
Jose Calbet, Ph.D.,
Department of Physical
University of Las Palmas de
Gran Canaria,
Canary Island, Spain

‘I think that a very important consideration in muscle growth is blood flow. During exercise, blood vessels within the muscle dilate to allow greater blood flow through the muscle in order to meet the oxygen and glycogen demands of the active fibers. This increase in blood flow is the pump phenomenon that lifters experience when performing multiple sets at a sufficiently high intensity with short rest periods.

Now, my own personal opinion is that the increase in blood flow may cause greater hypertrophy due to more exposure of anabolic hormones to their receptors on muscle fibers. It is known, however, that the anabolic hormones are extremely potent (i.e., a very small amount of hormone released into the bloodstream can have dramatic effects on the target tissue). Thus, the time of exposure of the hormone to its receptor is very crucial. If there is an increase in blood flow through the muscle, then the hormone has more exposure time to its receptor, and that could result in more hormone-receptor binding.

‘Furthermore, we have consistently found that the delayed-onset muscle soreness that is a characteristic of a large volume of eccentric muscle actions is not necessary for muscle fiber hypertrophy. DOMS is due to microtrauma and is largely caused by the eccentric component of exercise. We have found the same amounts of hypertrophy coming from exercise that involves only concentric movement, during which there is very little microtrauma. Thus, hypertrophy is not a function of muscle damage.’
Travis Beck, Ph.D. candidate,
University of Nebraska-Lincoln

‘I am not a bodybuilder myself, but it was my understanding that there has been a change of training methods, from long sets (10 to 15 reps) toward far shorter sets (four to six reps). In terms of increasing muscle mass, that makes sense to me. Moreover, long, fatiguing sets are ineffective because only the last (most difficult) reps probably will provide an adequate stimulus. That said, bodybuilding is not only about size. The number of blood vessels in the muscle (capillarization) may also be important because the more small blood vessels there are in a muscle, the better possibilities you have to pump up the volume during competition. I can very well imagine that for the improvement of capillarization, it may be beneficial to do somewhat longer sets (eight to 10 reps).’
C.J. (Jo) de Ruiter, Ph.D.,
Vrije Universiteit Amsterdam,
Faculteit der

Occlusion Training and the Pump

As I explained above, when you lift weights, your muscles generate so much force that they frequently squeeze shut, or occlude, their own blood vessels. When the muscles relax, the blood vessels open up even wider, causing blood to rush in.

Dr. Takashi Abe is a professor at Tokyo Metropolitan University’s Department of Exercise and Sport Science. He has conducted several studies on occlusion, or Kaatsu, training, which involves cutting off blood flow to the working muscle by application of a pressure cuff. He has found this method of training to be remarkably effective for increasing muscle size, both personally and with his study subjects. Here’s what Dr. Abe had to say (remember, English isn’t his first language):

‘Now, I am writing a Kaatsu resistance-training paper that I present at ACSM 2004. I would like publishing it shortly.

In my experience, Kaatsu training is most effective technique for stimulating muscle hypertrophy. Using a classical resistance-training method (80 percent of 1RM, three sets, three times a week), my quadriceps muscle cross-sectional area increased 7 percent following four months. On the other hand, my quadriceps muscle CSA increased 8 percent following two weeks of Kaatsu training (20 percent of 1RM, three sets, two times a day). I hope you will read this paper shortly.’

How does occlusion training increase muscle size? One scientist suggested to me that the application of a pressure cuff to the muscle provides additional mechanical tension that results in greater hypertrophy. Others postulate that occlusion causes greater recruitment of fast-twitch cells, the muscles cells that have the greatest potential for hypertrophy.

There’s another possibility. The occlusion caused by the pressure cuff may produce a greater pump, ultimately leading to more muscle cell swelling. I proposed this idea to Dr. Abe, who commented:

‘I am thinking about plasma volume shift from circulating blood to active muscle. After Kaatsu-training session midthigh (or arm) girth increased over two centimeters’just 10 minutes of training. Of course, hematocrit increased after training (43 percent to 50 percent). This girth change is equal to 8 to 9 percent increase in thigh-muscle CSA. I think the acute size change is one of the important stimuli for synthesis of contractile protein. We have to do more research.’

Taking Science Into the Gym

I’ve spent a considerable amount of time corresponding with many of the world’s leading research scientists on matters related to building bigger muscles. One thing I can tell you with certainty is that the mechanism(s) by which lifting weights makes muscles hypertrophy is (are) anything but clear.

Some scientists say that the pump may play a causal role in hypertrophy; the bulk of those I’ve spoken with, however, feel that it plays no such role.

But I’m stubborn’and, arguably, a little ignorant too. I’ve seen too many massive muscles built with methods that seek to maximize time under pump (as opposed to the commonly cited time under tension) to believe that the pump has no role in muscle growth. And what about those studies by Dr. Abe and his colleagues? Thus, I bring this article to a conclusion with some suggestions for how you can put some of the pump science discussed here to powerful muscle-building use in your own workouts.

R.O.B. Training. Occlusion training is impractical and, in my experience, rather painful. William Kraemer, Ph.D., of the University of Connecticut tells me that you can get a similar effect simply by keeping rest periods brief, something I espouse in R.O.B. (Rest Only Briefly) training (see for details).

One of my favorite variations of R.O.B. training is as follows: After warming up thoroughly, increase the load to 80 percent of your one-repetition maximum for the selected exercise. Complete as many reps as you can. Upon reaching’or coming within one rep of’failure, pause just long enough that you can squeeze out another one to three reps. Repeat the process until one minute has elapsed. After one week increase it to two minutes. If you’re not used to training like that, one such set per muscle or muscle group will be fine to start with. The method I just described makes your muscles generate high forces in frequent bursts while taking only very short ‘breaths’ in between. It produces a tremendous pump and very pleasing increases in muscle mass and muscle hardness.

Dr. Nao Ishii’s method. Dr. Nao Ishii of the University of Tokyo has studied occlusion training with Dr. Abe. He’s also studied other methods. Here are his comments on R.O.B. training, occlusion training and his own method. Give it a try.

‘Yes, I quite agree with you where multiset exercises with short interset rest period and middle weight strongly stimulate muscular hypertrophy. About this point, please read Takarada, Y., and Ishii, N., ‘Muscular Hypertrophy Induced by Low-Intensity Resistance Training With Short Rest Period in Aged Women’ (J. Str. Cond. Res. 16 123-128: 2002).

‘Many factors involved in resistance-exercise training may be related to muscular hypertrophy. These include mechanical stress, metabolic stress, oxygen environment (reduction/oxidation stress), changes in blood circulation within muscle, heat stress, etc.

‘We researchers do not yet know what is the most important among those factors for gaining muscular size effectively and efficiently. My group, including Dr. Takashi Abe, has studied occlusive training for many years, and found that moderate suppression of muscular blood flow during resistance exercise with light load (even 20 percent 1RM) causes marked increase in muscle size. Probably normal training with short rest period shares some mechanism with the occlusive training in that muscular contraction stronger than ~40 percent MVC (maximal isometric force) suppresses the blood circulation within muscle, and combination of such type of contraction and brief rest period causes accumulation of metabolic subproduct such as lactate within muscle, enhanced secretion of growth hormone and activation of local growth factors such as IGF-I and hepatic growth factor.

‘Also, slow lifting exercise may have a similar effect, at least to some extent, for gaining muscular size. On the other hand, isometric exercise may be less effective in production and accumulation of metabolic subproduct than exercises with actual movements. These notions are written in Ishii, N.: Factors Involved in the Resistance-Exercise Stimulus and Their Relations to Muscular Hypertrophy (in Nose, H., et al., eds. Exercise, Nutrition and Environmental Stress. Cooper, MI. 119-138; 2002).

‘What is the best exercise method for gaining muscle size? would be a kind of enormous question. It may depend on age, training career and genetic background.’ In general, middle intensity, large volume and short interset rest period are essential, as you have suggested.

‘Among other things, however, the so-called descending method’i.e., successive RM bouts with gradually decreased weight are repeated with interval of ~30s’is effective for both beginners and competitors. One typical way is: Start with 85 percent of 1RM and go to failure, and then use 70 percent of 1RM, then 50 percent of 1RM. We have shown that such a method is highly effective in stimulating growth hormone secretion and gaining muscular size in the Journal of Strength and Conditioning Research article mentioned above. From my own experience, it is true.’

X-Rep training. Have you ever seen Ronnie Coleman train? He moves the weight up and down in an abbreviated, or partial, range of motion that hovers about the point of peak tension. By focusing on that portion of each movement wherein the muscle is squeezing the hardest (both on itself and its blood vessels) he achieves a very pump-friendly workout and trains key muscle fibers hard.

IRON MAN Editor in Chief Steve Holman and Jonathan Lawson train at the IRON MAN Training & Research Center, where they recently developed X Reps, a method of training that also employs abbreviated reps and specially selected exercises. The X-Rep technique provides a powerful occlusion effect, or blood-flow stoppage, like the one that the Japanese researchers found so effective. So with X Reps you get a lot of hypertrophic components in any one set.

Check out the method at You’ll see the results in Steve’s and Jonathan’s before and after photos, taken one month apart during the X-Rep-development experiment. As science is proving, occlusion methods like X Reps have a lot of potential to significantly increase muscle mass quickly. (There is a complete occlusion workout that includes X Reps and growth hormone activation in the new e-book X-treme Lean, available at

Editor’s note: Read plenty of free articles, purchase Rob’s e-books and join the R.O.B. Club forum at IM

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