How Muscle Hypertrophy Happens

Muscle hypertrophy is a term for the growth and increase of the size of muscle cells. The most common type of muscular hypertrophy occurs as a result of physical exercise such as weightlifting, and the term is often associated with weight training.

Hypertrophy Process

When you start exercising a muscle, first there an increase in the nerve impulses that cause muscle contraction. This alone 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 two essential components necessary for the growth of muscles—stimulation and repair.


Stimulation occurs during the contraction of the muscle—during the actual exercising. Each time a muscle is exercised, it contracts. This repeated contraction during a workout causes damage to the internal muscle fibers. These muscle fibers are broken down throughout the course of a workout. Once damaged, these fibers are then ready to be repaired.


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.

Peripheral 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.

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
  • Speed of growth
  • Shape and appearance of muscle

Tendon Length

The shape of a muscle is determined by the length of the tendons of the muscle. Tendon length is a genetic factor. For bigger muscles, it is better to have shorter muscle tendons. Someone with extremely long muscle tendons may see less growth and shaping of their muscles than someone with much shorter tendons, 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. For example, lifting heavy weights targets slow twitch fibers and sprinting targets 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. That 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 have to work to the point of fatigue (muscular failure) to create the largest stimulus for muscle hypertrophy.

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  1. West DW, Burd NA, Staples AW, Phillips SM. Human exercise-mediated skeletal muscle hypertrophy is an intrinsic process. Int J Biochem Cell Biol. 2010;42(9):1371-5. doi:10.1016/j.biocel.2010.05.012

  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

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