The Science behind Muscle Growth

mus·cle (msl) n : A contractile organ consisting of a special bundle of muscle tissue, which moves a particular bone, part, or substance of the body.

While many magazines, TV shows, websites, and people are full of fitness advice, how much of this is actually credible? The fact is that scientists still don’t have the human body 100% figured out, but they do believe that they have a good understanding of how muscles work and grow. In this article, I will discuss the science behind how muscles function and grow, as well as what they are composed of.

Although the word muscle evokes thoughts of biceps and pectorals, in reality there are three different types of muscles.

1. Skeletal Muscle: this is what we normally think of when we think of muscle. Anchored by tendons to bone, this type of muscle is used to affect skeletal movement such as locomotion and in maintaining posture.

2. Smooth Muscle: this type of muscle is found within the walls of organs and structures such as the esophagus, stomach, intestines, bronchi, uterus, urethra, bladder, blood vessels, and even the skin (in which it controls erection of body hair). Unlike skeletal muscle, smooth muscle is not under conscious control.

3. Cardiac Muscle: Muscle found within the heart is cardiac muscle, which is not under conscious control but is much more akin to skeletal muscle otherwise.

For this article, I will only be discussing the first type of muscle, skeletal muscle, but you should be aware that there are three types of muscle, not just one.

The only logical place to begin an article about muscles is with the beginning. So just how do muscles form? Primarily, muscles are composed of thousands muscle fibers, which come in two varieties, fast-twitch and slow twitch. Both of these types of muscle fibers are composed of protein, which is why protein supplements can benefit muscle growth. Amino acids are the building blocks of protein, which is why they also play an essential part in muscle growth.

1. Slow-Twitch Muscle Fibers: Without getting into too much detail, slow-twitch fibers contract less powerfully and are related to endurance. But since I know you want to know the details, here we go. According to wikipedia (an extremely reliable source), Slow-twitch, or type I, fibers (sometimes referred to as “Red”) have more mitochondria, store oxygen in myoglobin, rely on aerobic metabolism, have a greater capillary to volume ratio and are associated with endurance; these produce ATP more slowly. Marathon runners tend to have more type I fibers, generally through a combination of genetics and training.

2. Fast-Twitch Muscle Fibers: These fibers are very powerful but cannot contract for long periods of time. From wikipedia: Fast-twitch, or type II, fibers (sometimes referred to as “White”) have fewer mitochondria, are capable of more powerful (but shorter) contractions, metabolize ATP more quickly, have a lower capillary to volume ratio, and are more likely to accumulate lactic acid. Weightlifters and sprinters tend to have more type II fibers.

 Okay, so just how do muscles function (contract)? The process is long and complicated, but it all begins with an electrical impulse sent from the brain. Once the muscle receives this signal, it knows to contract. But to understand how this contraction is possible, one must first understand two structures inside muscles, myosin and actin. Myosin is a think filament made of protein, where as actin is a thin filament, also made of protein. During contraction, the myosin thick filaments grab on to the actin thin filaments by forming crossbridges. The thick filaments pull the thin filaments past them, making the sarcomere shorter. In a muscle fiber, the signal for contraction is synchronized over the entire fiber so that all of the myofibrils that make up the sarcomere shorten simultaneously. For even more details about how muscles contract, please visit this great article on howstuffworks.

Now that you have a basic understanding of muscle structure, we will move on to the part that you’ve all been waiting for: how do muscles grow? Well, its simple: muscular hypertrophy.

Muscular hypertrophy is a scientific term for the growth and increase of the size of muscle cells. So therefore, in order to get bigger and stronger, you MUST trigger muscular hypertrophy. How is this done? With simple weight training, which is why body builders are so built and people who sit around all day are not. But not all forms of muscular hypertrophy are created equal. There are, in fact, two different kinds of muscle growth: sarcoplasmic hypertrophy and myofibrillar hypertrophy.

1. Sarcoplasmic Hypertrophy: an increase in the volume of the non-contractile muscle cell fluid, sarcoplasm. This type of hypertrophy greatly increases the volume of muscles, but since sarcoplasm cannot contract, it leads to little actual strength gains. Performing high repetitions with fairly low weight causes this type of hypertrophy, which is why professional bodybuilders workout with high reps (10-15). The science behind sarcoplasmic hypertrophy also explains why bodybuilders are not the best athletes or the strongest people.

2. Myofibrillar Hypertrophy: an enlargement of the muscle fiber as it gains more myofibrils, which contract and generate tension in the muscle. In sharp contrast to sarcoplasmic hypertrophy, this type of muscle growth leads to great increases in strength and moderate gains in size. To cause this type of hypertrophy, one must lift heavy weights with limited reps. This type of hypertrophy greatly benefits athletes and powerlifters, as it actually increases strength and performance.

So you have a decision to make when you workout. Do you want to gain size, or do you want to gain strength?If you are an athlete or otherwise need strength and performance benefits from weight lifting, I highly recommend following a 5 sets of 3 repetitions philosophy instead of the most commonly practiced 3 sets of 8-12 repetitions. But while each type of hypertrophy specializes in boosting either size or strength, both types will ultimately improve both your size and strength, just at different rates. So if you are just an average guy who likes to occasionally hit the gym, here’s what I recommend: mix it up. Some days you should lift the standard 3×8-12, but other days it would be beneficial to mix in the 5×3 for significantly faster strength gains.