When it comes to increasing muscle size or definition, you’ve probably been told that lifting weights breaks down a muscle, which then becomes stronger or bigger as a result of the repair process. But is this really true or simply another one of the common gym myths that is passed along from more seasoned veterans to newbies?

Well, unlike many common gym myths, this claim is actually based in fact because resistance training to the point of fatigue does indeed cause muscle damage. Specifically, that damage occurs to the proteins that comprise muscle fibers. Muscles are bundles of individual fibers wrapped in fascia and connective tissue. The smallest components of muscle fibers are the actin and myosin protein microfilaments. The sliding filament theory suggests that actin and myosin overlap, and that when they receive the signal from the central nervous system to contract, they slide across one another to create a force-producing, muscle-shortening action.

There are two types of overload that can stimulate muscle growth: metabolic and mechanical. Metabolic overload refers to the amount of work that a muscle performs that depletes it of its available supply of energy. As a muscle is repeatedly exercised to the point of fatigue, the muscle cells adapt to hold more glycogen for fuel. Because 1 gram of glycogen can hold on to 3 grams of water, when a muscle stores more glycogen it can increase in size due to the extra glycogen and attached water.

Mechanical overload refers to the structural damage that occurs to the actin-myosin protein filaments as a result of strenuous exercise like weightlifting or explosive plyometrics. The muscle damage initiates a repair process in which certain hormones, along with the macronutrient protein, synthesize new satellite cells, which are used to repair the damaged muscle fibers. In other words, the role of protein is to help repair tissues damaged by exercise.

Read on to learn nine things about the role that protein plays to support the body during and after exercise.

1. In the human body, proteins are the primary structural components of cells and perform a few different duties. The primary function of the protein consumed in the diet is to build and repair cells, including the muscle cells damaged when exercising to the point of momentary fatigue. (Note: Failure is not completing a repetition; fatigue is not being able to perform another repetition.) Additional roles that dietary proteins play in the body include transporting cells, serving as enzymes to support various physiological functions and acting as hormones.
2. While the primary role of protein is to repair damaged tissues, it can also be used to produce energy for muscle contractions when other sources of adenosine triphosphate (ATP, the cellular form of energy), namely fats and carbohydrates, are not available. Gluconeogenesis is the term that describes how protein is converted to glycogen for ATP. However, this only occurs as the result of moderate-to-high intensity for an extended period of time. Sport drinks contain sugar and sodium, which helps to maintain glycogen levels to avoid gluconeogenesis, sparing proteins so they can be used to repair tissues after exercise. Another option is to limit high-intensity activity to no more than 45-50 minutes to ensure an adequate supply of glycogen during exercise.
3. Amino acids are the building blocks of protein. (Note: For the record, “amino” means “containing nitrogen.”) There are 20 amino acids. Four are considered non-essential because the body can produce them, and nine are essential because they cannot be produced in the body and must be consumed in the diet. Eight amino acids are considered conditional, because they can become essential and must be consumed in the diet. Taking amino acids before and during a workout, combined with a post-exercise recovery snack or meal containing protein, can increase muscle protein synthesis. Applying various post-exercise recovery strategies could allow your clients to train at a higher volume to reach a specific strength or performance goal.
4. Protein provides about 4 calories of energy per gram, and when protein is consumed as part of a well-balanced diet it can help provide feeling of satiety or being full. This, in turn, can reduce feelings of hunger that could lead to consuming too many calories. In addition, protein is more energy expensive, which means that it requires more energy during the digestive process compared to carbohydrates and fats.
5. The body is constantly building new cells to replace old ones, and amino acids consumed in the diet support this process. The nutrition guidelines for protein consumption for the average, healthy adult are 0.8-0 grams of protein per kilogram of bodyweight (0.4-0.5 grams per pound). The recommended daily intake for a person who performs a lot of aerobic endurance training is 1.0-1.6 grams/kilogram of bodyweight (0.5-0.7 grams/pound). For those who do a lot of strength training, consuming 1.4-1.7 grams/kilogram of bodyweight (0.6-0.8 grams/pound) will support muscle protein synthesis. For example, an active 170-pound male who exercises at a moderate-to-vigorous intensity most days of the week should consume approximately 70-170 grams of protein per day.
6. Protein should comprise 15-30% of an individual’s daily caloric intake, depending on activity levels. More protein should be consumed on days that include higher-intensity activity.
7. For individuals interested in muscle growth, it’s a good idea to consume foods that are high in protein, such as lean meats, fish, eggs, chicken or milk. Soy is the only form of plant-based protein that contains all eight essential amino acids. While consuming protein is important for muscle growth, eating too much protein, while not necessarily dangerous, will simply result in the body excreting it in urine.
8. Protein should be consumed throughout the day rather than at a single meal. For example, the aforementioned 170-pound active male would be wise to consume 20-40 grams of protein at a time, distributed among three meals and two snacks.
9. Of the protein stored in the body, almost half is stored in skeletal muscle, up to 15% is used for structural tissues such as skin and bone, and the remaining proteins are in tissues and organs including the kidneys and liver.

Interested in learning more? Read about a few hidden sources of protein here.