Understanding Muscle Hypertrophy: The Science Behind Muscle Growth

Muscle hypertrophy refers to an increase in 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 exercises, such as weightlifting, but genetics play a role as well. Learn how muscle hypertrophy works and how to maximize your gains during your strength training workouts.

Hypertrophy: How Do Muscles Grow?

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

But, as you continue to exercise, there is a complex interaction of nervous system responses that results in an increase in protein synthesis. Over months, the muscle cells begin to grow larger and stronger. This is a three-step process.

What You Need to Know About Strength Training for Muscle Growth

  1. Stimulation: Stimulation occurs during the contraction of the muscle (during the actual exercising). A repeated contraction during a workout causes damage to the cells that make up internal muscle fibers.This cellular damage triggers an inflammation response, which the body actually utilizes to promote recovery. Stressing a muscle leads to an increase in hormones connected with muscular growth, such as testosterone, human growth hormone, and insulin-like growth factor-1.1
  2. Repair: 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.
  3. Peripheral Fatigue: Researchers have begun to identify another component of muscle hypertrophy.2 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.3 Therefore, the more the muscle that becomes stimulated, the more hypertrophy occurs.

Types of Muscle Hypertrophy

There are three basic types of muscular hypertrophy:

  • Myofibrillar hypertrophy is 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 denser.4
  • Sarcoplasmic hypertrophy refers to the muscles increasing their volume of sarcoplasmic fluid, or the fluid that is filled with a variety of energy-containing substances.5
  • Myostatin-related muscle hypertrophy is a rare condition that involves a significant reduction in body fat and an increase in muscle size—up to twice the normal amount of muscle mass. Those with this condition also tend to have increased muscular strength compared to the average person.6

Research shows that just six weeks of high-volume resistance training can increase skeletal muscle fiber by as much as 23% due to sarcoplasmic hypertrophy.5

How Genes Affect Hypertrophy

Although the process of hypertrophy

Muscle Hypertrophy Nutrition and Supplementation Proper nutrition plays an essential role in muscle hypertrophy. Consuming enough calories, proteins, carbohydrates, and fats can help optimize your muscle growth.

  1. Calories: To build muscle, you need to consume more calories than you burn. A caloric surplus helps provide your body with the energy required for muscle growth. Aim for an additional 250 to 500 calories per day above your maintenance level, depending on your goals and activity level.12
  2. Protein: Protein provides the building blocks for muscle growth. Aim for 1.6 to 2.2 grams of protein per kilogram of body weight daily.13 High-quality protein sources include lean meats, poultry, fish, dairy, eggs, legumes, and plant-based protein powders.
  3. Carbohydrates: Carbohydrates provide energy for your workouts and help replenish glycogen stores in your muscles. Aim for 5 to 7 grams of carbohydrates per kilogram of body weight daily, focusing on complex carbohydrates like whole grains, fruits, and vegetables.14
  4. Fats: Fats are necessary for hormone production, which plays a role in muscle growth. Aim for 20 to 35% of your daily caloric intake to come from healthy fats such as avocados, nuts, seeds, and olive oil.15

In addition to a balanced diet, some supplements may help support muscle hypertrophy:

  1. Creatine: Creatine has been shown to increase muscle strength, power, and size. It's one of the most researched and effective supplements for muscle growth.16 Aim for 3 to 5 grams of creatine per day, either pre- or post-workout.
  2. Branched-Chain Amino Acids (BCAAs): BCAAs, including leucine, isoleucine, and valine, can help support muscle protein synthesis and reduce muscle soreness.17 Consider taking 5 to 10 grams of BCAAs per day, particularly around your workouts.
  3. Beta-Alanine: Beta-alanine is an amino acid that can help increase muscle carnosine levels, which may delay muscle fatigue and enhance endurance.18 Aim for 2 to 5 grams of beta-alanine per day, either pre- or post-workout.
  4. Protein powder: A protein powder supplement, such as whey or plant-based protein, can help meet your daily protein needs and support muscle growth. Use protein powder as needed to help reach your daily protein goal.

Remember, supplements should not replace a well-balanced diet but can complement your efforts to optimize muscle hypertrophy.

The Importance of Rest and Recovery

Adequate rest and recovery are crucial components of a successful muscle hypertrophy plan. During rest periods, your muscles repair and rebuild, leading to growth. Ensure you get enough sleep each night (7 to 9 hours for most adults), as sleep is essential for muscle recovery and growth.19

Incorporate active recovery days into your workout routine, where you perform light, low-impact activities such as walking or yoga to help promote blood flow and reduce muscle soreness.

Listen to your body and take rest days when needed. Overtraining can lead to decreased performance, increased injury risk, and even hinder muscle growth.20

Muscle hypertrophy involves various factors such as exercise, genetics, nutrition, and rest. To optimize muscle growth, focus on compound exercises, follow a well-balanced diet, and ensure adequate rest and recovery. Keep in mind that everyone's journey will be different, and progress may vary depending on your genetics and other factors. Stay consistent, challenge yourself, and seek guidance from fitness professionals to help you achieve your muscle-building goals.

William H. McDaniel, MD

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School.

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