The science behind: Building muscle

You’ve probably heard before that you should eat protein if you want to build muscle. But has anyone ever told you why?

To be able to build muscle fast, all you need is an understanding of how muscles work. Exercise can be made far more effective by a better understanding of what is actually happening in your body when you do that bicep curl or run a few miles on the treadmill. To gain that foundational understanding and maximize your training efficiency, read on.

What are muscles?

Skeletal muscles are made of muscle cells, which are also called myocytes. Myocytes are made up of many tube-shaped myofibrils, which gives the cells their striped appearance. Myofibrils, in turn, are made up of long protein molecules called myofilaments. There is a thick type of myofilament composed of the protein myosin, and a thin type of myofilament composed of the protein actin. Muscle contractions occur when those actin and myosin filaments slide past each other in a series of repetitive interactions involving the body’s energy currency, ATP.

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Muscle contractions

Every time you use a muscle, you are contracting and releasing the muscle fibers. Each contraction involves the individual myosin filaments pulling along actin filaments within each muscle fiber, activated by energy in the form of ATP. The super-fast series of pulls causes the actin filaments to slide along the myosin filaments within the myofibrils in each muscle cell, contracting the muscle. You can imagine this like a tug-of-war, with the myosin representing the players pulling and releasing the actin, representing the rope, in synchronised repetitive motions. To relax the muscle, the filaments slide back over each other in the other direction.  

What happens when you exercise

Muscle contractions require lots and lots of ATP, which is created mainly in the mitochondria. In order to make ATP, the body needs oxygen. To understand why this is and exactly how ATP is made in the mitochondria, play the cellular respiration simulation.

When you put stress on your muscles during endurance or resistance training, the muscle cells are working harder and contracting more often, and so they require more ATP. Making more ATP means your muscle cells need a greater supply of oxygen. Without an adequate oxygen supply, muscles fatigue rapidly.

Accelerated heart rate and breathing

Muscles get oxygen from the oxygenated red blood cells. To get enough red blood cells to your working muscles, your heart has to pump blood through your body much faster. That’s why your heart rate increases when you’re working out.

Similarly, to make sure all the blood your heart is pumping to your muscles is oxygenated, your respiratory rate increases. In other words, you have to breathe harder to get enough oxygen in your bloodstream to allow your muscles to make ATP.

You might have noticed that the more you train, the longer it takes for your heart rate to increase and to start breathing hard. That’s because the more you work your muscles to fatigue, the more capillaries you develop for transferring oxygen into muscles cells, and the more efficient the whole process becomes. Endurance training also can increase the number of mitochondria in each muscle cell, which means each cell has more “factories” in which to create ATP.

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Muscle damage

Muscle strength is determined by number and size of muscle cells. The size of a given muscle cell or muscle fiber is limited by the number of filaments in each myofibril. When you exercise, whether you’re going for a run or lifting weights, you are asking your muscles to perform repetitive contractions that challenge their strength and endurance, which ultimately damages the existing actin and myosin filaments.

Have you ever felt sore after a workout? That soreness is your immune system’s reaction to damaged muscle fibers. As you rest, your body repairs the existing actin and myosin filaments, as well as creating new ones to deal with the increase in muscle stress during your workout. Your immune system also induces the creation of new muscle fibers.

In other words, muscle damage leads to muscle strengthening and growth by growing new muscle fibers as well as new filaments within each existing fiber.

Protein and muscle growth

The importance of protein in building stronger muscles is a hot topic, but it’s also essential to understand why you need that protein, and what exactly your body will do with it.

As explained above, when you exercise, you damage the myofilaments in your muscle cells. Myofilaments are long strings of actin proteins and myosin proteins. To repair myofilaments after a workout, muscle cells need to synthesize new actin and myosin proteins to add to the strings, or merge strings together to create new ones.

All proteins are made from amino acid building blocks. We get amino acids by eating protein. Whenever you eat protein, it gets broken down into its amino acid building blocks in the digestive tract, which can be absorbed into the bloodstream. All of the body’s cells are creating proteins constantly, and they all need a steady supply of amino acids to do so. Try the protein synthesis simulation to learn about exactly how your cells use amino acids to build the proteins that keep us alive and functioning day and night.

Since there is no way for the body to store amino acids, it’s important to consume protein steadily throughout the day to ensure that there are enough amino acids available for your cells. If there aren’t enough, your body will begin to break down its own muscle and other tissue to supply those amino acids.

Protein sources

There’s protein in almost everything, but a few foods to look for that are truly protein packed include:

  • Eggs
  • Yogurt, especially greek yogurt
  • Almonds, pistachios, and cashews
  • Chicken breast, turkey breast, and lean beef
  • Quinoa
  • Fish and shrimp

Build muscle fast

To repair myofilaments, muscle cells need access to amino acids. If you don’t eat enough protein and then do a rigorous workout, your body will actually feed on your muscle tissue, breaking it down to supply enough amino acids to repair the damaged myofilaments. If you’re trying to build muscle, this is the opposite of what you want. There is a window of about one hour after you finish exercising where your muscles will most readily use amino acids in the bloodstream, but it’s not enough to eat protein just in that window, as the protein won’t be broken down into amino acids in the bloodstream quickly enough to be useful.

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So what’s the secret to building muscle quickly? It’s simple. Work your muscles just to the point of fatigue, and then give them plenty of time to rest and repair. Increase protein intake on hard workout days to maximize muscle growth, and to avoid breakdown of existing muscle tissue. Follow those simple tips and you’ll be gaining muscle in no time.

For the science behind a healthy diet and reducing stress, check out our 3-step health guide.