Muscle Hypertrophy

Introduction to hypertrophy

As defined by Merriam-Webster, hypertrophy means “excessive development of an organ or part; specifically: increase in bulk (as by thickening of muscle fibers) without multiplication of parts.”

For bodybuilders, hypertrophy is one of the primary goals of training (along with shape and proportion). Unfortunately, enormous volumes of misinformation exist surrounding the principles of muscle hypertrophy.

There are many factors to consider when training for hypertrophy. These factors include exercise selection, resistance, training intensity, training volume, repetition cadence, rest intervals, movement patterns, and non-training factors such as nutrition and recovery.

However, there are vastly different perspectives on which factors are most important and how those factors should be manipulated; for example:

So, which is optimal?

What does the research say?

Peer-reviewed research has indicated that each variable of the above-listed factors can lead to hypertrophy.

However, if you go online or speak to personal trainers, bodybuilders, or every day gym-goers, you will likely hear people telling you that one specific factor is optimal. Some may even say a single factor, or their preferred training protocol, is “the only way.”

Historically, some of the most common invalid claims are that muscle hypertrophy requires heavy weight and/or maximum intensity (some level of muscle failure). The trends in current research indicate that neither are true.

Program design: putting it all together

Each variable listed above can promote muscle hypertrophy; however, these variables also require coordination with each of the others.

Resistance and effort/exertion are both factors you can manipulate to increase or decrease your training intensity, as described in Progressive Overload. Training intensity should be viewed as being inversely correlated with training volume, but this is not necessarily a direct or linear correlation.

Generally, a higher training intensity would require a lower training volume and vice-versa. If both resistance and exertion are high, your training volume will almost certainly be lower. If both resistance and exertion are low, your training volume would need to be higher to achieve an appropriate level of stimulus.

In a situation where one intensity factor is high and the other is low (e.g., heavy resistance to volitional fatigue, or light-to-moderate resistance to concentric or absolute failure), your training volume may be high, moderate, or low. This would depend largely on your training status and other factors such as rest intervals.

Ultimately, the training variables are just that—variables—meaning there is no one-size-fits-all. You will be able to learn more about manipulating these variables in Art of Anatomy‘s program design (coming soon; sign up for email updates).

Physiologic principles of muscle hypertrophy

Like many topics in research, you’ll likely be able to find research that supports whatever opinion you have and/or debunks any claims against your favored style of training. For muscle hypertrophy, many of these research findings have merit regardless of your opinions.

To simplify the research trends, there are three major physiologic principles to consider—beneath which each of the aforementioned factors (resistance, volume, etc.) will fall. These principles are mechanical tension, metabolic stress, and muscle damage. Spoiler: muscle damage is a non-factor, and it is included on this list to describe how research has debunked this old-school belief.

Mechanical tension

When reading through research on the topic, mechanical tension appears to be the most dominant factor driving muscle hypertrophy. Even without knowing any of the peer-reviewed research, most people are already aware that your muscles need to be challenged with resistance (tension) in order to grow.

For example, we do not use cardiovascular exercise (e.g., walking on a treadmill) as a technique to target muscle growth; instead, various types of resistance training are widely used to increase muscle mass.

Within the category of mechanical tension are exercise selection, resistance, volume, intensity, and specialty sets.

To simplify it tremendously, your muscles need to be challenged with resistance, and they need to both shorten and lengthen under resistance; isometric contraction (where the muscle does not lengthen or shorten; e.g., planks) of any muscle against resistance does not elicit notable muscle hypertrophy.

Of course, there are lower limits and upper limits for which you will not experience growth. For example, one set of an exercise for a given muscle is unlikely to increase muscle mass. On the other hand, excessive training volume can also inhibit growth.

As described above, there is evidence that supports nearly every training variable; ultimately, you need to find what’s most comfortable and most effective for you, and utilizing multiple variables is likely the best option. For example, you may prefer heavier resistance, lower volume, and longer rest intervals on compound movements and lighter resistance, more volume, and shorter rest on isolation exercises.

In Art of Anatomy‘s Program Design (coming soon), each of these factors will be outlined with specific recommendations based on a combination of many years of formal education, research evidence, practical experience, and discussion with some of the world’s best bodybuilders and trainers.

Metabolic stress

Metabolic stress is a broad term describing the metabolites (or byproducts) of chemical processes of your body during exercise. The most relevant metabolite of resistance training is lactate. Lactate, or lactic acid, is the primary metabolite following bouts of resistance training as it is the byproduct of glycolysis—the dominant energy pathway for working muscles.

As previously mentioned, you will likely be able to find research that supports or rejects any theory. The research on metabolic stress is yet another example of this scenario. In a review by Brad Schoenfeld—world-renowned researcher on exercise and hypertrophy—he states,

In other words, accumulation of metabolites (namely, lactate) may promote muscle growth. However, in a separate review analyzing the role of lactate (or lactic acid, abbreviated La⁻), the authors (which include Brad Schoenfeld) stated,

Granted, these are two simple quotes pulled from two reviews of other peer-reviewed research. The purpose here is to simply show that metabolite accumulation during exercise could be a factor in maximizing muscle growth. Then again, it may not be a major factor.

Muscle damage

Muscle damage does not appear to be a factor for muscle hypertrophy. Including it on this page is simply to provide the evidence on the topic.

Some people may still believe the purpose of resistance training is to cause micro-tearing in the muscle fibers so they heal thicker and stronger—increasing both strength and mass. However, research trends reveal an opposing conclusion; it appears the micro-tearing theory for muscle hypertrophy is untrue.

For beginners—those who are resistance training for the first time (or for the first time after a long period of deconditioning)—muscle damage is more prevalent. It is important to note that beginning lifters experience measurable muscle damage and minimal hypertrophy in their first few weeks of training.

With consistent resistance training, however, muscle damage is reduced over time (e.g., within 3-5 weeks), but hypertrophy becomes more notable. Damas, Libardi, and Ugrinowitsch suggest hypertrophy is negligible in the first couple weeks (assuming 2-3 training sessions per week), modest by 4-6 weeks, and significant by 6-10 weeks.

Likewise, these researchers suggest muscle damage is nearly a direct inverse of the hypertrophy response for beginning lifters. Muscle damage is significant in the first couple weeks, modest by 4-6 weeks, and negligible (or non-existent) beyond 6-10 weeks of training.

Hypertrophy: described by Art of Anatomy

When describing muscle physiology, the word hypertrophy is most often simply described as an increase in cell size. While this is not entirely inaccurate, breaking the word down to its roots provides a significantly more valuable explanation.

The missing piece in all that research

The first part of the word, hyper-, means “above, beyond, or in excess” while the second part, -trophy, describes nourishment (from the Greek term trophḗ, meaning “nourishment” or “food”). Therefore, the word hypertrophy literally describes excessive feeding/nourishment.

When you break the word down, you will recognize that an increase in muscle cell size is actually the result of hypertrophy or excessive feeding. To achieve this result, there are two major factors to consider. One factor of hypertrophy is part of its definition: you must provide appropriate nourishment!

The other factor is the exercise routine, itself. You must perform an appropriately targeted exercise routine. Specific to your ability to maximize the growth of a target muscle, you must consider the following general principles of hypertrophy in your routine.

Depleting the target muscle’s glycogen (energy)

Glycogen is the storage of glucose (sugar) within the muscles. With high-intensity muscle contraction, your body will breakdown the target muscle’s glycogen and use the glucose to create energy in a process called glycolysis. To maximize growth potential (hypertrophy), you want to use as much of the target muscle’s glycogen as possible.

When you deplete the target muscle’s glycogen, your body will need to replenish it using the glucose (or other carbohydrates) you consume following your workout. Consuming carbohydrates immediately post-workout is valuable to replenish glycogen—and therefore, energy—but also to trigger an insulin-response.*

Ingesting carbohydrates will increase blood glucose and trigger the release of insulin. Insulin will then transport the glucose into the target muscle to refill its glycogen storage. In addition to transporting glucose into the muscle for glycogen storage, insulin will also aid in the transport of protein (amino acids) into the muscle which provides the building blocks of muscle cell growth.

Most people are familiar with the importance of ingesting protein following a workout; however, without carbohydrate ingestion, the protein will have a more difficult time transporting into the muscle because protein does not trigger the same insulin response.

For ingested macronutrients, insulin responds most intensely (in other words, largest insulin spike) to simple carbohydrates and sugars. Protein alone will still trigger an insulin response, but the response to protein is significantly lower. Therefore, post-exercise carbohydrates are important to increase insulin, thereby improving the delivery of protein (and the carbohydrates) into the target muscle.

Ultimately, depleting the target muscle’s glycogen will cause a demand for glucose (carbohydrates); post-exercise, consuming carbohydrates along with protein causes a larger spike in insulin, and that increase will help deliver more protein into the muscle.

Again, nutrition is not yet available through Art of Anatomy; however, here is a simple, yet important piece of nutritional advice for bodybuilders: limit your dietary fat intake in your first meal following your workout. Regardless of your daily macronutrient goals, limiting your post-workout fat intake will maximize protein absorption and mobilization in your body.

Promoting adaptation in the target muscle

There is a physiologic principle for nearly all body tissue called the SAID principle: specific adaptation to an imposed demand. For muscles, the specific adaptations are an increase in cell size (muscle fiber thickness) and the ability to tolerate more resistance (strength) and/or more loaded volume (endurance) without damage. However, these adaptations cannot occur without their imposed demand. The imposed demand here, of course, is resistance exercise.

Many people may still believe the primary reason for muscle cell growth following resistance exercise is due to a breakdown (low-level damage or micro-tearing) of the muscle cell structure—after which the muscle cells are healed to become thicker and stronger. As described above, recent research findings refute that theory.

Instead, research supports the notion that the mechanical tension, itself, is a more significant factor behind muscle growth. There is a cascade of physiologic responses in the muscle and its fascia (including the tendons) following periods of targeted mechanical tension. This appears to be particularly true in the eccentric, or muscle lengthening phase, of the exercise being performed.

This response is also seen in the bones. For example, you do not need to break your bones for them to become stronger. Instead, adding physical stress (e.g., simple weight-bearing activity, resistance exercise, or impact force such as walking or jogging) to your skeletal system will elicit a physiologic response to increase bone density to prevent damage.

Your body recognizes physical stress and attempts to adapt to protect itself from damage. If the stress is increased tension—such as resistance training for muscles—the adaptation is to make the tissue thicker and stronger to protect it. Without this adaptation, muscles and tendons would begin to tear under the overloaded and/or repeated resistance.

Increasing blood flow to the target muscle

Nutrients travel throughout the body via the blood. Therefore, to provide excessive feeding to a target cell, there needs to be a significant increase in blood perfusion. An appropriately designed and organized exercise routine will certainly increase blood perfusion and allow for the delivery of nutrients in high-volume. Perfusion can be influenced by training intensity, training volume, exercise selection and order, repetition performance, and rest-interval timing.

Specific to exercise selection, exercises performed in the target muscle’s lengthened and shortened positions tend to better increase blood perfusion. In bodybuilding, we call this high volume blood perfusion, as Arnold Schwarzenegger most famously described, “the pump.”

If you live in the Las Vegas area and are looking to maximize your pump, check out the “Pump” treatment offered by Art of Anatomy: Health and Wellness.