Muscles grow through protein synthesis. Despite what supplement companies will tell you, there is no magic formula that will supersede the basic science of protein synthesis.
Muscles grow by repairing small micro-tears that occur on a cellular level during exercise, making exercise a key component of muscle growth.
Resistance training is generally considered the best type of exercise to promote muscle growth. Acting as a light switch, this lasts for around 48 hours so if a muscle is trained 3-4 times a week it is fully optimised (so that 100kg monster on the gram who tells you to train ‘bro splits’ yeah... BS). When the muscle experiences small micro-tears, blood flow to the area increases, bringing with it the necessary components for repair through protein synthesis. In this specific case, the repaired muscle is then stronger and larger than it was before.
For protein synthesis and muscle growth to occur, a number of components must be present. First, the muscle must have exercise-induced micro-injury. Second, naturally occurring hormones, including testosterone and growth hormones produced by the pituitary, must be present.
Finally, you must have a diet containing sufficient protein. Protein is the basic building block of all of the body’s tissues, especially muscle. Proteins are made from amino acids, some of which the body can synthesize and some of which must be consumed in the diet.
Protein synthesis does not create new muscle cells. Instead, protein synthesis creates a state of hypertrophy. In hypertrophy, individual muscle cells increase in size. Bigger muscle cells are stronger and may give you a more aesthetically pleasing appearance.