What Is Hypertrophy?

Muscle Cell Growth

Hypertrophy is defined as the increase in the size of cells, tissue, or organs in your body. Muscle hypertrophy can occur as a result of exercise, especially weight training exercise. Lifting weights and consistently (and safely) challenging muscle tissue can cause it to get bigger. Hypertrophy should not be confused with hyperplasia, which is an increase in the number of cells in your body. Here's how hypertrophy occurs in the body.

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Anatomy of a Muscle

All muscle tissue in your body is made up of cells called myocytes. There are three types of muscle tissue in your body. Those include:

  • Cardiac muscle: Cardiac muscle is the type of muscle cell in your heart.
  • Smooth muscle: This type of muscle is found in your intestinal tract and several other places in your body (like your lungs).
  • Skeletal muscle: Skeletal muscle is muscle tissue that attaches to bone and is used for movement of your limbs and torso.

Skeletal muscle cells are long and cylindrical in shape, and they contain many nuclei. The outer covering of muscle cells is called the sarcolemma, and the inner gel of the cell is called the sarcoplasm. Within the sarcoplasm, myoglobin molecules store oxygen, and glycogen molecules store glucose.

Oxygen and glucose provide energy for the muscle cell.

Also within the sarcoplasm, actin and myosin filaments form protein chains that can glide and slide past one another during muscle contractions.

How Does Hypertrophy Happen?

Hypertrophy is an increase in the size of muscle cells. When muscle tissue is placed under mechanical stress, myogenic stem cell activation occurs, which leads to repair of damaged muscle tissue and an increase in muscle cell size.

Those mechanisms include:

  • Cell swelling: During exercise, your muscle cells use energy from oxygen and glucose to power a contraction. This leads to an increase in blood flow to the contracting muscle, and temporary cell swelling occurs. Swelling of muscle cells causes a release of anabolic hormones (like growth hormone) that lead to myogenic stem cell activation.
  • Muscle cell damage: When you exercise, you cause slight damage to muscle cells, which activates myogenic stem cells.
  • Cell hypoxia: Hypoxia is a condition in which tissues of the body have inadequate oxygen. Resistance exercises can lead to temporary hypoxia due to increased oxygen demand, and compression of the muscle. Hypoxia signals the release of hormones that help modulate lactate and growth hormone within muscle cells.
  • Growth hormone: When you perform strength training exercises, growth hormone is released. This hormone is active during the muscle cell repair process, and it increases muscle strength. Growth hormone also decreases the effect of myostatin, a growth-inhibiting hormone within muscle cells. This shut down of myostatin allows muscle cell enlargement (hypertrophy) to occur.

So how do you safely put muscle tissue under stress to start the chain of events that lead to muscle hypertrophy? Exercise and movement.

Methods to Cause Hypertrophy

The single most effective way to induce muscle hypertrophy is through exercise.

High-intensity strength training exercises cause minor injury to skeletal muscle cells, and this sets in motion the release of anabolic hormones that create muscle hypertrophy.

Think of strength training as creating slight stress and injury to your muscles. Your body's repair of those muscles adapts to create tissue that is slightly stronger, preparing your muscles to effectively manage future stresses that could be placed upon them.

Heart Muscle

Performing aerobic exercise has a similar effect on cardiac muscle tissue. Stressing your heart muscle (within reason) helps your cardiac tissue grow in response to this stress.

Regular aerobic exercise improves the efficiency of your heart muscle.

Building Muscle When You Are Injured

You might not be able to perform high-intensity strength training at times, such as after an injury. But you may still want to create an environment where muscle growth and hypertrophy can occur.

Sometimes, this is accomplished through blood flow restriction training. This method of exercise therapy involves using specialized cuffs to restrict blood flow to muscles. Low intensity and high repetition exercises are performed, and the cuffs are then removed. This method has been shown to lead to muscle hypertrophy, even when high load training cannot be done.

Be sure to speak with your physician, physical therapist, or personal trainer before starting any exercise for muscle growth or hypertrophy.

Harmful Muscle Hypertrophy

Muscle growth is good. It signifies that you are getting stronger and exercising regularly. But hypertrophy can also be considered abnormal.

Sometimes your heart may become abnormally hypertrophied. This is called cardiac hypertrophy or left ventricular hypertrophy (LVH).

Causes of LVH may include:

Essentially, these problems cause your heart to work hard to continue to pump blood throughout your body each day. This excess work puts an unhealthy strain on your heart muscle tissue, leading to hypertrophy .

Symptoms of cardiac hypertrophy may include:

  • Shortness of breath
  • Fainting or dizziness
  • Fluttering sensations in your chest
  • Chest pain

If you have any of these symptoms or suspect any problems with your heart, see your physician right away. They can assess your condition and form a proper diagnosis, leading to the right treatment for you.

Pathological conditions involving skeletal muscle hypertrophy are very rare. One condition, called myostatin-related muscle hypertrophy, is a genetic disease characterized by low body fat and muscle hypertrophy. This condition is rare and typically doesn't cause other problems or impairments.

A Word From Verywell

Muscle hypertrophy is the growth of individual muscle cells. This causes your muscles to grow bigger in response to exercise, especially high-intensity weight training. Most of the time, muscle hypertrophy is a good thing; it signals that your muscles are growing normally or responding normally to resistance-training exercise. Occasionally, hypertrophy can be harmful, especially in diseases of the cardiac muscle tissue. Understanding how muscle hypertrophy works can help you decide on the best way to increase your muscle size and improve your overall muscular performance.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centner C, Wiegel P, Gollhofer A, König D. Effects of Blood Flow Restriction Training on Muscular Strength and Hypertrophy in Older Individuals: A Systematic Review and Meta-Analysis. Sports Med. 2019;49(1):95-108. http://doi.org/10.1007/s40279-018-0994-1

  2. Cuspidi C, Facchetti R, Quarti-trevano F, et al. Incident Left Ventricular Hypertrophy in Masked Hypertension. Hypertension. 2019;74(1):56-62. http://doi.org/10.1161/HYPERTENSIONAHA.119.12887

By Brett Sears, PT
Brett Sears, PT, MDT, is a physical therapist with over 20 years of experience in orthopedic and hospital-based therapy.