What Makes Muscles Grow?

by Brad Schoenfeld

What makes muscles grow? Brad Schoenfeld, author of The MAX Muscle Plan, answers this big question in our new, exclusive Burn the Fat Blog interview with Tom Venuto… Read on to discover what the latest research says about the mechanisms of muscle growth, how much hormones really affect the muscle building process, how to use periodization to gain the most muscle in the least time while avoiding injury and overtraining. plus much more…

Tom Venuto: Brad, congratulations on your new Book the MAX muscle plan. When i first read it, I was surprised (pleasantly so), because knowing you are one of the top experts in the research and science side of the exercise game, I guess I was expecting something very science and theory-heavy…

But when I started flipping through the pages, I saw that almost your entire book is a practical, step by step program for gaining muscle. You give the theory very quickly and succinctly in chapters one and two and then you’re right to the program – exercises, sets, reps, schedule and even exercise photos. What made you decide to create it this way?

Brad Schoenfeld: First, thanks for the nice feedback about the book as well as inviting me to do this interview, Tom. I have great respect for the work you do as well as your commitment to staying on top of the research. So coming from you, the comments are particularly meaningful.

As for your question, The MAX Muscle Plan is a consumer-oriented book. As such, I did not want to bog it down with a lot of technical info. I figured that readers are primarily looking for practical information on how to get results and therefore spent the majority of the book focusing on mapping out the routines, including the requisite sets, reps, exercises and other variables. That said, I felt it was important to at least cover the scientific aspect as this forms the basis of the routine.

Further, a certain amount of science is necessary to provide readers with the ability to tailor the routine to their individual needs – something that’s essential to any exercise regimen. I did my best not to get too “sciencey” and I’m glad that it came across as such.

Tom Venuto: Since you are a “science guy” though, I can’t resist. Can you – as briefly and simply as possible, for the lay person – give a punch list of what the latest research says about the mechanisms of hypertrophy? In other words, what really makes muscles grow?

Brad Schoenfeld: The primary factor in hypertrophy (growth) is the force exerted on a muscle. This is known as “mechanical tension”; without tension, muscles simply do not have an impetus to adapt and get bigger. But while tension drives hypertrophy, it’s not the only factor involved in the growth process.Given sufficient tension (and there is debate as to what the minimum threshold for tension actually is), metabolic stress has been shown to augment the hypertrophic response.

Simply stated, metabolic stress is a buildup of metabolites primarily resulting from training in the anaerobic energy system (specifically fast glycolysis), There are a number of theories as to why metabolic stress promotes muscle growth. Based on current research, it seems to be related to a variety of factors local myokines, systemic factors, reactive oxygen species, cell swelling and perhaps others.

Moreover, muscle damage also seems to play a role in muscle development. Provided the damage is not too severe, there is evidence that structural trauma to fibers leads to greater remodeling of the tissue.

We are still a long ways away from understanding how all these factors come together to produce muscle growth, but theoretically there is a “sweet spot” where results are optimized and this seems to be in the moderate rep range with multiple sets performed.

Tom Venuto: Staying on that mechanisms of muscle growth note, for years, hormones have been said to be one of the major keys – BOTH in advertising claims as well as in the scientific literature. They say, do things- in your nutrition, training and lifestyle – that optimize hormones, and you optimize muscle gains. It makes sense even intuitively, but this belief has been scrutinized more closely recently and experts are starting to question just how important hormones are in the overall scheme of things. I guess the practical question is, how much can you really manipulate your hormones through NATURAL means such as changing your training style or the foods you eat, and if you CAN manipulate the hormones acutely, how much does that really affect muscle growth over time?

Brad Schoenfeld: The role of acute hormones in muscle growth is an interesting topic and is the source of a great deal of controversy in the scientific community. I actually have a journal article on metabolic stress that addresses this topic scheduled for publication early next year.

Without getting into too much technical detail, the jury is still out to whether these hormonal spikes are involved in hypertrophy, and if so, to what extent they exert actions. The evidence to date is actually quite conflicting. Confounding matters further, there is a paucity of data on trained subjects (which is a major limitation of hypertrophy research, in general).

What seems to be fairly clear is that acute hormonal elevations do not play a major role in hypertrophy–if in fact there is an effect, the overall impact would be modest at best. Training strategies that generate significant metabolic stress (bodybuilding style training that employs high volumes with moderate reps and fairly brief rest intervals) will tend to heighten the acute hormonal response, but it is not clear as to whether this is a contributing factor in the growth response.

I do feel there is benefit in training to enhance metabolic stress regardless of any potential contribution from systemic hormones–as previously mentioned, there is compelling evidence that such training does enhance hypertrophy. From a practical standpoint, I wouldn’t advocate trying to increase acute hormonal output through foods or supplements -I’ve not seen any evidence that these strategies have any merit.

Tom Venuto: I’m a huge fan of programs that include periodization and yours is one of them. Can you give the simple definition of what periodization is for a reader who might not be familiar with the concept?

Brad Schoenfeld: Sure. Periodization refers to the systematic manipulation of program variables (exercises, sets, repetitions, frequency, etc) to optimize a given fitness goal. The primary benefit of periodization is that it helps to prevent overtraining. When properly implemented, it allows for sustained progress without hitting a plateau. In my opinion, every serious lifter should invoke some type of periodization into their program; if not, they will ultimately short-change results.

Tom Venuto: I know there are different kinds of periodization. What kind do you recommend for hypertrophy and why?

Brad Schoenfeld: The approach that I outline in the MAX Muscle Plan is a modified linear periodization program that begins with an 8 week strength phase, then moves to a 4 week metabolic phase, and concludes with a 12 week hypertrophy phase. Each phase is designed to build on the one preceding it.

Within these phases, I employ a “step-loading” approach that varies intensity over the course of a training block (phases are subdivided into one month “blocks”). For example, in the hypertrophy phase reps will be 10-12 the first week, 8-10 reps the second week, and then 6-8 reps in the third week. This is then followed with a week of “unloading” where intensity is decreased to facilitate restoration and recuperation. The end result is a wave-like loading pattern that provides and optimal combination of intensity and recuperation.

In addition, volume is systematically increased over the course of each block. This is primarily accomplished through an increase in training frequency as opposed to increases in the number of sets per session. As with intensity, the frequency of training is reduced during the unloading periods to allow for recovery. I’ve found this model extremely successful for maximizing hypertrophy in a broad range of clients–from recreational lifters to elite bodybuilders.

Tom Venuto: Overtraining: Big concern or are a lot people actually not training hard enough or with enough volume?

Brad Schoenfeld: Overtraining is a concern for anyone who trains hard. An important thing to point out is that overtraining is highly dependent on the individual. Genetics play a big role, as do factors such as nutritional status, sleep, and other factors.

Thing is, volume is positively correlated to hypertrophy, at least up to a given point. Higher training volumes have consistently been associated with greater muscular gains. This is why I preach the importance of periodizing volume over the course of a training cycle. You need to train with high volumes, but if you do so for too long, you end up overtrained.

The solution is to progressively increase volume and build in the unloading microcycles. The goal should be to structure the program so that volume culminates in an overreaching response (in the MAX Muscle Plan this involves training 6-day-a-week for two to three weeks) and then following this with a short active recovery period where the muscles supercompensate and maximal hypertrophy is achieved.

Tom Venuto: Cardio during a muscle gain program – yes or no?

Brad Schoenfeld: It really depends on intensity and volume. Without question, high volume, high intensity cardio routines are a recipe for impaired muscle growth. You simply can’t sustain high levels of growth if you combine such a regimen with resistance training.Lower intensity and/or volume bouts of cardio, on the other hand, can potentially be implemented into a hypertrophy-oriented routine without negative effect BUT you need to be very careful that you don’t overdo it.

The signaling pathways for resistance training and aerobic training are contradictory. Some researchers have coined the term “AMPK-PKB switch” whereby aerobic training promotes catabolic processes (AMPK is involved in pathways associated with protein breakdown) and resistance training promotes anabolic processes (PKB is involved in pathways associated with protein synthesis).

While the concept of a “switch” is a bit overly simplistic (most of the evidence points to anabolism and catabolism taking place along a continuum), there is little doubt that concurrent training has the potential to undermine muscle growth and lead to overtraining.

It also should be noted that experienced lifters will have great difficulty trying to simultaneously gain lean mass while losing body fat. If you’ve been training for a number of years, you generally need to focus on one or the other assuming the goal is optimization.

Tom Venuto: There’s a growing culture of “evidence based” fitness professionals today, which we can both agree is a good thing. On the other hand, this has also turned into a lot of “dueling abstracts” on forums and arguments that if the “real science” doesn’t confirm it – it’s bs, aka, its “bro science.” It’s kind of amusing sometimes because the conclusion you are led to believe when observing this from a distance, is that the best bodybuilders in the world – the winners and champions in both the natural and the open federations – are doing it all wrong (ponder that oxymoron for a while, right?) As a guy who has a practical background in bodybuilding as well as a education in the academic side of exercise physiology, I’m curious how you, personally Brad, reconcile the results of your own experience with what the research says? How would you recommend a competitive bodybuilder do it?

Brad Schoenfeld: This is such a great point, Tom, and I’m glad you brought it up. Now I’m the first to preach that we must base our training approaches on what we know through science. Controlled experimental is imperative to assess training variables and approaches in as an unbiased fashion as possible. Otherwise all we have is bro-science where people do endless sets of concentration curls to increase their biceps “peak” and gazillions of crunches to whittle away their love handles.

That said, research has significant limitations. Resistance training, in particular, is generally limited by small sample sizes (most studies have less than 20 or 30 subjects, making them highly underpowered) and differences in methodology (including many instances where the routines employed have no relationship to how serious lifters actually train).

Another extremely important point that often goes unrecognized is the huge variations in the hypertrophic response of subjects often seen in research. Studies will report means (i.e. averages) but this does not reflect the fact that some people saw big-time gains with a given approach while others did not gain any muscle. These, and numerous other limitations must be taken into account to draw valid conclusions from the research. Otherwise we are left with “dueling abstracts” that mean little in practical terms.

On the other hand, personal experience is always an important component in devising programs that have practical application. By definition, an evidence-based approach involves harnessing the prevailing body of current research and combining this with personal experience and the needs of the individual. So to dismiss one’s experience is misguided. Basic bodybuilding principles have stood the test of time–if they didn’t work, the guys who are huge would be doing something different.

We need to embrace this fact and realize there is a lot to be learned from those whose competitive goal is to get big. But this doesn’t mean that bodybuilders couldn’t be doing even better if they trained more scientifically. I’ve worked with a number of high level competitors who’ve been able to substantially improve their mass and symmetry by altering their approach in a more scientific manner.

It’s also essential to remember that individuals respond differently to training. Just because a bodybuilder gets jacked from a given routine doesn’t necessarily mean that a hard-gainer will see anything close to the same results. Although humans are inherently similar, we are also vastly different in our physical adaptations. This is consistent with the principle of individuality, and has been borne out quite conclusively in the research..

So bottom line is that we need to harness both research and experience in our training efforts; they are inseparable for creating optimal programming. Exercise is both a science and an art. There are basic tenets of training that need to be followed, but we also must draw from our experiences to maximize results on an individual level.

Tom Venuto: Thanks Brad, I really appreciate you sharing with our readers. If someone wants to get more information about you and your book, what is the best place to find it?

Brad Schoenfeld: The book is available in all major bookstores, but the best bargain is probably Amazon.com. They are offering the book at a significant discount (~40% off, the last I checked). The Max Muscle Plan (@ Amazon)

About the Author:

Brad Schoenfeld, MSc, CSCS, CPT, is widely regarded as one of the leading strength and fitness experts in the United States. The 2011 NSCA Personal Trainer of the Year is a lifetime drug-free bodybuilder who has won numerous natural bodybuilding titles, including the All-Natural Physique and Power Conference (ANPPC) Tri-State Naturals and USA Mixed Pairs crowns. As a trainer, he has worked with numerous elite-level physique athletes, including many top pros. Brad was elected to the NSCA Board of Directors in 2012. Schoenfeld is the author of eight other fitness books, including Women’s Home Workout Bible, Sculpting Her Body Perfect, 28-Day Body Shapeover, and the best-seller Look Great Naked (Prentice Hall Press, 2001).

Brad is a former columnist for FitnessRX for Women magazine, has been published or featured in virtually every major fitness magazine (including Muscle and Fitness, MuscleMag, Ironman, Oxygen, and Shape), and has appeared on hundreds of television shows and radio programs across the United States. He also serves as a fitness expert and contributor to www.bodybuilding.com, www.diet.com, and www.t-nation.com. Certified as a strength and conditioning specialist by the National Strength and Conditioning Association and as a personal trainer by both the American Council on Exercise and the American College of Sports Medicine, Schoenfeld was awarded the distinction of master trainer by IDEA Health and Fitness Association. He is also a frequent lecturer on both the professional and consumer levels. He is currently pursuing his PhD in health science at Rocky Mountain University, where his research focuses on the mechanisms of muscle hypertrophy and their application to resistance training.