What Is Muscle Hypertrophy?

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Muscle hypertrophy refers to the increase of the size of muscle cells and is often associated with weight training. The most common type of muscular hypertrophy occurs as a result of physical exercise, such as weightlifting, but genetics play a role as well.

What Is Hypertrophy?

When you start exercising a muscle, first there an increase in the nerve impulses that cause muscle contraction. This often results in strength gains without any noticeable change in muscle size.

As you continue to exercise, there is a complex interaction of nervous system responses that result in an increase in protein synthesis. Over months, the muscle cells begin to grow larger and stronger.

There are three essential components necessary for the growth of muscles—stimulation, repair, and peripheral fatigue.


Stimulation occurs during the contraction of the muscle (during the actual exercising). A repeated contraction during a workout causes damage to the cells that exist in internal muscle fibers. This triggers an inflammation response.

Although excess or chronic inflammation is not generally healthy, the body naturally uses inflammation to help it heal after being injured or damaged.

At the same time, stressing the muscle leads to an increase in hormones connected with muscular growth. These hormones include testosterone, growth hormone, and insulin-like growth factor-1.


Muscle fiber repair occurs after the workout, while the muscles are resting. New muscle fibers are produced to help replace and repair the damaged ones. More fibers are produced to make up for the damaged ones and this is where the actual muscle growth takes place.

Peripherhal Fatigue

Researchers are beginning to identify a third component to muscle hypertrophy: peripheral fatigue. Peripheral fatigue occurs when you are unable to complete exercises, such as at the end of strenuous activity.

Studies are ongoing, but scientists believe that the more peripheral fatigue you can induce, the harder the muscles have to work. The more the muscle is stimulated, the more hypertrophy occurs.

Types of Muscular Hypertrophy

There are two basic types of muscular hypertrophy:

  • Myofibrillar hypertrophy: This refers to the increase in the number of myofibrils, which are the long strands in the muscle that help it contract. When the myofibrils increase, the muscle gets stronger and more dense.
  • Sarcoplasmic hypertrophy: This type of hypertrophy refers to the muscles increasing their volume of sarcoplasmic fluid, or the fluid that is filled with a variety of energy-containing substances.

Research shows that just six weeks of high-volume resistance training can increase skeletal muscle fiber by as much as 23%, thanks largely to sarcoplasmic hypertrophy.

How Genes Affect Hypertrophy

Although the process of hypertrophy is the same for everyone, the results are likely to be different, even in people doing the same workouts. This variance in results is due to the genetic make-up of each individual person's muscles.

Genetics can affect muscle growth in several ways:

  • Degree of growth, or how big the muscles can get
  • Speed of growth, or how quickly they can increase in size
  • Shape and appearance of the muscle, or what the muscle looks like

Tendon Length

The shape of a muscle is determined by the length of the tendons of the muscle. Tendon length is a genetic factor. Shorter muscle tendons lead to bigger muscles while longer muscle tendons lead to smaller muscles.

Someone with extremely long muscle tendons may see less growth and shaping of their muscles than someone with much shorter tendons. This is despite doing the same amount of (or more) weight lifting.

Muscle Fiber Types

Muscles are made up of different muscle fibers: type 1, or slow-twitch, and type 2, or fast-twitch. Different muscles have different ratios of type 1 and type 2 fibers, and these are affected by genetics. For maximum hypertrophy, you need to train each muscle fiber type with different exercises.

This is why athletes in sports like football have large muscles. Their training involves different types of activities that target both fast and slow twitch fibers. Lifting heavy weights, for example, targets their slow twitch fibers and sprinting targets their fast twitch fibers.

If you won the genetic lottery, you may grow bigger muscles or see results sooner than others at your gym. Unfortunately, the opposite may also be true.

Exercises for Muscle Hypertrophy

Exercises that build muscle are those that contract the muscle against resistance repeatedly. This usually means weight training using free weights, exercise machines, resistance bands, or bodyweight exercises.

There are many suggested training regimens that vary the load weight, the number of repetitions, and the rest intervals between sets. While each has its proponents, the end results may depend more on your dedication to your workouts and your body type.

Regardless of the plan that you choose, you want to work to the point of fatigue (muscular failure) as this creates the largest stimulus for muscle hypertrophy. This means lifting until you cannot lift any more, but without sacrificing proper form.

How Often Should You Lift?

The American College of Sports Medicine recommends that most people strength train two to three times per week. Training on non-consecutive days gives the muscle fibers time to relax and repair, thus growing bigger in size.

If this feels overwhelming, research has found that doing one strength training session per week is as effective as doing three sessions per week; that is, as long as you do the same exercises and same number of repetitions that you'd do in the three separate sessions.

If you are new to weight training, start with one session per week and work up from there. If you have been strength training for some time, three sessions weekly may fit into your workout schedule more easily.

A Word From Verywell

Weight training can help you increase your muscle size, but genes play a role as well. Listen to your body when trying to increase your muscle mass. Push your muscles hard enough to grow, but avoid pushing them too far as this can cause injury.

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  1. Fink J, Schoenfeld BJ, Nakazato K. The role of hormones in muscle hypertrophy. Phys Sportsmed. 2017;46(1):129-34. doi:10.1080/00913847.2018.1406778

  2. Cè E, Longo S, Limonta E, Coratella G, Rampichini S, Esposito F. Peripheral fatigue: New mechanistic insights from recent technologiesEur J Appl Physiol. 2020;120(1):17-39. doi:10.1007/s00421-019-04264-w

  3. Taber C, Vigotsky A, Nuckols G, Haun C. Exercise-induced myofibrillar hypertrophy is a contributory cause of gains in muscle strength. Sports Med. 2019;49:993-7. doi:10.1007/s40279-019-01107-8

  4. Haun C, Vann C, Osburn S, et al. Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy. PLoS One. 2019;14(6):e0215267. doi:10.1371/journal.pone.0215267

  5. Dankel S, Jessee M, Mattocks K, et al. Training to fatigue: the answer for standardization when assessing muscle hypertrophy? Sports Med. 2017;47:1021-7. doi:10.1007/s40279-016-0633-7

  6. American College of Sports Medicine. ACSM guidelines for strength training. Published Jul 31, 2019.

  7. Thomas M, Burns S. Increasing lean mass and strength: a comparison of high frequency strength training to lower frequency strength training. Intl J Exerc Sci. 2016;9(2):159-67.

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