Simplified Science of Muscle Growth - How Weight Training & Protein Builds Muscle

If you're in the gym, working out with weights, chances are you are trying to gain muscle mass.

During my initial years of weight-training, I never really understood the process by which my muscles would grow. But after being in the gym for over 30 years, and hanging around enough scientific conferences, I've gleaned a thing or two about biochemistry and human physiology. After learning how muscles "technically" grow, I've since put the process into a scientific, but simplified format, which is straightforward and easy to understand.

This brief article is meant to serve as an overview of the two primary cause and effects of muscle damage and repair to understand how muscles grow. Although there are several different types of muscles in our bodies, for purposes of this article, we are referencing skeletal muscle -- those muscles that make up the aesthetics of our physique.

How Do Muscles Grow?

#1 Break Down Muscle Tissue: Muscle Tension, Stress and Damage From Weight Training

Tension: In order to progress in strength, hypertrophy, or muscular endurance, you must increase your weight used, reps, sets, volume, or intensity performed over time. The ability to lift heavier weights or do more repetitions becomes possible with increased muscle mass.

Overload (Stress): Normally, beginner weight-lifters will see the greatest muscular gains while experienced lifters will see the least over the span of a few years of consistent, progressive lifting. This is because of the simple "law of diminishing returns," as the human body approaches its muscular genetic limit. This limit, however, can be overridden with drugs, and even some dietary supplements. The overload and stress of weight-training causes small, "micro-tears" in the muscle fibers.

Protein Synthesis: Muscle growth occurs whenever the rate of muscle protein synthesis is greater than the rate of muscle protein breakdown known as nitrogen balance. This adaption and rebuilding process, however, does not actually happen while you lift the weights. Instead, it occurs while you are at rest.

Damage Repair: After you work out with weights, your body repairs or replaces damaged muscle fibers through a cellular process called muscle protein synthesis (MPS) where it utilizes amino acids (see below for use of amino acids in muscle growth) where they fuse muscle fibers together to form new muscle protein strands or myofibrils.

These repaired myofibrils increase in thickness and number to create muscle hypertrophy. The result, when combined with #2 (next): new muscular size or growth.

#2  Build Up Muscle Tissue: Muscle Repair and Growth From Eating Protein (Foods) and Rest

Whether you consume your protein in the form of animal, plant or protein powders it doesn't really matter all that much. Your body breaks down all protein forms into amino acids (the building blocks of muscle tissue). However, there are advantages to protein powders, namely whey and caseins in terms of "bioavailability" and supply of amino acids, but we will not go into detail on those technical user benefits.

For muscle growth, most scientific evidence suggests that we should consume about 1.4 to 2.0 grams of protein per kilogram of bodyweight per day. This equates to roughly 112 to 160 grams of protein for 175-pound person.

• Ingestion/Digestion: Enzymes in your stomach and small intestines break the protein into peptides, which are combinations of at least two strands of amino acids. Then other enzymes further separate the peptides into individual amino acids. Amino acids are essential, non-essential and the most important to muscle repair are branch chain amino acids (BCAAs: leucine, isoleucine, and valine).
• Transport: The amino acids travel directly from your gastrointestinal tract to your liver, via the hepatic portal vein. While the liver's main job is to detoxify the blood, it also propels amino acids back into your bloodstream for delivery to your muscle cell satellite sites.
• Repair: Your muscles are essentially bundles of long fibers. Training with weights, and progressively causing an overload of stress on the muscle, causes "micro-tears" in the fibers. These tears signal your immune system to send out inflammatory molecules (called cytokines) to activate the immune system to repair the damaged muscle cells. This is what your muscles feel sore the next day or two after working out. Call them the work crew, ready to rebuild the muscle fibers.
• Construction: If these agents are the workers, then your DNA acts as a construction foreman, where it calls for (requests) specific amino acids, directs their deployment and assigns their roles. The muscle fibers use the fresh supply of amino acids to weave and reweave myofibrils; bundles of the protein filaments myosin and actin. A process called "protein synthesis." The greater you can influence the rate of protein synthesis, through increased amounts of amino acids or bio-active peptides, the faster and greater the muscles are rebuilt, bigger or stronger, depending on your training goals.
• Repair And Growth: The newly made myofibrils fuse with the damaged areas of your muscle fibers. Fortunately, "micro-tear" muscle repair is more than just a patch job; these myofibrils, in turn, help make the muscle bigger and stronger than it was before, dependent on your training goals.

How Muscles Grow: Conclusion

There you have it. Fairly simple and straightforward. Keep in mind though, muscle hypertrophy takes time and is a relatively slow process for the majority of weight-lifters.

There is no "magic cocktail" that can turn you into the Incredible Hulk overnight. Even so, most people will generally not see visible growth for several weeks or months of weight-training as most initial changes are due to the ability of your nervous system to activate your muscles.

However, with the right training techniques, sufficient nutritional proteins and even dietary supplements, you can make this process work to your advantage and grow new muscle at a relatively consistent pace. At least sufficient enough to be noticeable by you and your friends at the gym.

The best part is, the visible muscle growth and evident physical changes in your body's muscular structure can be highly motivational (and attractive) which is why understanding the science behind how muscles grow, and their primary mechanisms, is important.

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References

1) International Society of Sports Nutrition position stand: protein and exercise. Journal of the International Society of Sports Nutrition 2007, 4:8 doi:10.1186/1550-2783-4-8.
2) Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise. American College of Sports Medicine. American Dietetic Association. Dietitians of Canada. Joint Position Statement.
3) Protein Needs for Athletes. Bill Campbell, PhD, CSCS, FISSN. National Strength and Conditioning Association.
4) Kravitz, Len, PhD. Young, sub Kwon, M.S., CSCS. Paper: How do muscles grow?
5) Rasmussen, R.B., and Phillips, S.M. (2003). Contractile and Nutritional Regulation of Human Muscle Growth. Exercise and Sport Science Reviews. 31(3):127-131.