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ISSA, International Sports Sciences Association, CPT, Strength, Bigger Muscles or Stronger Muscles?

Bigger Muscles or Stronger Muscles?

Reading Time: 8 minutes 50 seconds

BY: Alex Hoffmann

DATE: 2019-12-10

Getting big and getting strong are two different things!

Believe it or not, these are not the same... Here's why

As a trainer, you hear just about everything from your clients. Each one has a different goal.

Client #1 says:

"You know what? I really just want to get big."

Client #2 says:

"Me? I just want to increase my 1 RM, but you know, not look crazy huge."

You have different clients and they have different needs. While having bigger muscles does lead to the potential for having greater strength, generally speaking, optimizing muscle size and optimizing muscle strength are two different things.

And you can work with your clients to achieve one or the other. It just takes different strategies, each backed by exercise research.

What Do the Textbooks Say?

As a certified trrainer you can go back to your fitness textbook and find the chart that tells you how to use weight training to achieve greater strength or hypertrophy.

In most texts the recommendations are about the same[1 3 4]:


· Load: >85% 1RM

· Reps: <6

· Sets: 2-6

· Rest: 2-5 min.


· Load: 67-85% 1RM

· Reps: 6-12

· Sets: 3-5

· Rest: 30-90 sec

This is a good general rule for achieving one goal or the other, but not everyone agrees with it. Some people may find success with something a little different.

If we go to the research to find out whether these recommendations are the best or not, we find that the results are a little cloudy.

Some studies show these textbook recommendations as effective, while others will show that they just don't work for everyone.[2,5,7]

To get a better understanding of what it all means and how you can use the information to help your clients, let's dig a little deeper.

Muscles 101

Let's start with some basic muscle physiology.

Muscle tissue consists of two types of muscle fiber (note we are avoiding muscle fiber subtypes):

  • Type I Muscle Fiber. Also known as slow twitch fibers, type I muscle fibers use oxygen more efficiently and can be used over longer periods of time; think endurance. These are our smaller, least powerful muscle fibers that have little potential for hypertrophy.

  • Type II Muscle Fiber. This is the fast twitch type of muscle fiber that can burn energy quickly for short bursts of strength. These are our larger, more powerful muscle fibers that have great potential for hypertrophy. The two most commonly discussed types of type II muscle fiber are type IIa (fast oxidative glycolytic) and type IIb (fast glycolytic).

This leads us to the Size Principle of Motor Unit Recruitment. One motor unit is a nerve and the muscle fibers to which it is attached.

In each muscle, we have smaller, weaker type I motor units that are easily excitable and more resistant to fatigue, and larger, more powerful type II motor units that are hard to excite, but less resistant to fatigue once they are activated.

The Size Principle states that when the central nervous system recruits motor units for muscle contraction, it begins with the smallest, weakest, more easily excited type I motor units first and progresses to the larger, stronger, more-difficult-to-excite type II motor units only when force needs to be maintained or increased.

In other words, lifting at a low intensity (i.e. a light weight) will only stimulate smaller motor units.

In order for the larger, more powerful type II motor units to be activated, greater intensity is needed.

So How Do Muscles Get Stronger?

How can we use this information to help our clients who want to get stronger, but not bigger? We have to consider the amount of weight lifted, the number of reps, and the rest period.

1. Maximal Weight

The Size Principle implies that to get stronger we need to activate all of the motor units, and that requires a heavy enough weight, or great enough resistance, to trigger the high-threshold, type II motor units. This is why the standard recommendation for load is >85% 1 RM. Furthermore, lifting a near maximal weight will provide the additional benefit of stimulating synchronous activity of motor unit recruitment. In order for maximal force to be generated, all motor units in a given muscle must be activated at close to the same time. In an untrained individual, motor unit activation will occur at slightly different times, and therefore lead to inefficient movement. This works much like rowers in a boat rowing in synch vs. the rowers rowing at different times. One of the simplest ways to enhance motor unit synchronization is through heavy load resistance training.

2. Fewer Reps

As a side effect of lifting near your one repetition maximum, the number of repetitions you will be able to perform will naturally be fewer. Think about it: your one repetition maximum literally means that most weight you can lift one time. Therefore if we are lifting a weight that is near our one rep max, repetitions will be kept to a minimum simply because the resistance is too great to generate numerous successive repetitions. Generally speaking, if you are able to lift a resistance more than six times in a row, it is not heavy enough to stimulate your highest threshold motor units nor force synchronous motor unit activity. A word of caution: however, near maximal lifting (>85% 1 RM) can be dangerous for a novice lifter, and thus one should have some training experience before attempting to develop maximal strength through this manner.

3. The Rest Interval

Now, what about the two to five minutes rest interval recommendation?

This can be related to our understanding of the metabolic pathways, specifically regeneration of adenosine triphosphate and creatine, but that can get a little complicated.

An easier way to explain it is that the central nervous system needs full recovery in between sets in order for coordinated motor unit activity and maximal motor unit recruitment to occur in the subsequent sets[6]. Maximal strength output requires optimal performance of both variables. Lastly, the stronger an individual is, the more rest he or she will likely need between sets when working with a near maximal resistance.

And How Do Muscles Get Bigger?

Now you might be thinking that this is common sense, right? Lifting heavy weights make you stronger, but is this also the best strategy for getting bigger muscles?

The quick answer is no. It is not likely that following the recommendations for increasing muscle strength will lead to optimal muscle hypertrophy. Here's why:

1. Protein Degradation

Resistance training initiates protein degradation, the breakdown of muscle tissue and in turn creates the right conditions for rebuilding bigger muscles during rest and recovery periods.

Protein in muscle tissue breaks down with strength training and only then can it rebuild itself into bigger tissue. The amount of protein degradation that occurs depends on how we approach our training. Obviously, the extent to which our muscle rebuilds depends on the quality of our post training recovery (an issue separate from the discussion taking place in this article).

Protein breakdown is stimulated by two different factors:

  1. The amount of weight lifted. Heavier weights lead to greater degradation per rep.

  2. The number of reps. Consecutive repetitions further contribute to degradation.

2. Heavier Weights, Higher Reps

With this in mind, in order to make our muscles bigger, we need to use a weight that is not only heavier, but also one that we can lift for a high number of reps.

This is the reason why the load and rep recommendation of 67%-85% 1 RM for 6-12 reps is the starting guideline for muscle hypertrophy.

This load/rep ratio satisfies the two factors that stimulate protein degradation: heavy weight, high rep scheme, so that you get maximum muscle building during recovery. As you can see, while lifting a near maximal load (>85% 1 RM) for low repetitions (i.e. <6) would meet the first requirement needed to stimulate protein degradation, it would not meet the second requirement, and therefore is not the theoretical optimal load/volume ratio to be used to stimulate maximum hypertrophy.

On the other hand, lifting a light weight (i.e. <67% 1 RM) for a high number of repetitions (i.e. 25 reps) would meet the second requirement needed to stimulate protein degradation, but not the first requirement, and therefore is not the theoretical optimal load/volume ratio to use to stimulate maximum hypertrophy.

3. And...the Rest Interval

The rest interval recommendation for hypertrophy is 30 to 90 seconds. Why less recovery time than for increasing muscle strength?

Well, one reason is that some studies have shown this rest interval range leads to elevated levels of serum growth hormone during exercise (6). Growth hormone is important in stimulating muscle growth, hence the resulting hypertrophy.

Is the Textbook Answer Right for Everyone?

Now you can see that there is a reason that most fitness textbooks will give you this particular set of recommendations for hypertrophy and strength. They act like building blocks, a starting point.

As a trainer you can use this starting point to develop individualized programs for each client.

It is important to remember, however, that these guidelines were developed based on theory, and haven't been consistently replicated in peer-reviewed studies.

The recommendations don't take into account key variables such as training frequency, training experience, mode of exercise, total number of exercises per muscle group, client somatotype, supplementation, nutritional intake, or recovery quality.

Furthermore, programming ideologies such as supersets, drop sets, compound sets, half reps, negatives, periodization format, and others play a significant role in the type and rate of adaptation that occurs.

Program Design

The theory of exercise is the science of program design; the ability to make adjustments to a program based on client progress and your own unique experiences is the art of program design.

The science of program design can provide a wonderful starting point from which to develop a programming outline, but it is ultimately the art of program design that will determine your clients' results.

The best coaches and trainers I've encountered are able to integrate both into their philosophies.

Individual Differences

Program design is highly variable depending on the individual differences you see in your clients. There are many gray areas, and in my experience there are no absolutes when it comes to program design, no rights or wrongs.

As professional trainers, only seeking out sources that support our own preconceived programming ideas will severely stunt our growth.

Success in training is a process of taking the time to learn the theory of generalized programming recommendations, recording our own unique experiences, carefully considering the programming ideas of others, and being flexible enough to adapt our programs based on results.

Choosing the path of a being a trainer means that we will always be students of fitness. As the science evolves and changes, we have to as well.

So if your client's goal is to develop strength or hypertrophy, the recommendations provided in textbooks are a nice starting point for theory-driven program design. However, it's up to you to create your own programming design art to ensure you optimize the results for each of your unique clients.

Ready for more? Step up your knowledge and training with the ISSA's Master Trainer certification course.

ISSA, International Sports Sciences Association, CPT, Strength, Bigger Muscles or Stronger Muscles?

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1. Baechle, Thomas R., and Roger W. Earle. Essentials of Strength Training and Conditioning. Third ed. Champaign: Human Kinetics, 2008.

2. Campos, Gerson, Thomas Luecke, Heather Wendeln, Kumika Toma, Fredrick Hagerman, Thomas Murray, Kerry Ragg, Nicholas Ratamess, William Kraemer, and Robert Staron. "Muscular Adaptations in Response to Three Different Resistance-training Regimens: Specificity of Repetition Maximum Training Zones." European Journal of Applied Physiology 88.1-2 (2002): 50-60.

3. Clark, Micheal, Scott Lucett, and Rodney J. Corn. NASM Essentials of Personal Fitness Training. Third ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2008.

4. Hatfield, Frederick C. Fitness: The Complete Guide. 8.6.6 ed. Carpinteria: International Sports Sciences Association, 2013.

5. Mangine, Gerald T., Jay R. Hoffman, Adam M. Gonzalez, Jeremy

6. Townsend, Adam J. Wells, Adam R. Jajtner, Kyle S. Beyer, Carleigh H. Boone, Amelia A. Miramonti, Ran Wang, Michael B. Lamonica, David H. Fukuda, Nicholas A. Ratamess, and Jeffrey

7. Stout. "The Effect of Training Volume and Intensity on Improvements in Muscular Strength and Size in Resistance trained Men." PHY2 Physiological Reports 3.8 (2015).

8. Salles, Belmiro Freitas De, Roberto SimÃo, Fabrício Miranda, Jefferson Da Silva Novaes, Adriana Lemos, and Jeffrey M. Willardson. "Rest Interval between Sets in Strength Training." Sports Medicine 39.9 (2009): 765-77.

9. Schoenfeld, Brad J., Nicholas A. Ratamess, Mark D. Peterson, Bret Contreras, G. T. Sonmez, and Brent A. Alvar. "Effects of Different Volume-Equated Resistance Training Loading Strategies on Muscular Adaptations in Well-Trained Men." Journal of Strength and Conditioning Research 28.10 (2014): 2909-918.

10. Zatsiorsky, Vladimir M., and William J. Kraemer. Science and Practice of Strength Training. Second ed. Champaign: Human Kinetics, 2006.

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