The Biology of Muscle Growth

The sheer number of articles, opinions, magazines and experts on fitness and muscle growth makes the field of weight lifting appear more like the practice of medicine in the 16th century than a concrete science. Every day new theories, approaches and miracle workouts appear, contradicting each other and proclaiming that they have the truth, and that by following their advice you will achieve the body of your dreams. Clearly, some of them are on the right track and some are not, but how to tell the difference between them all? The answer lies in understanding the basics of the biological process of muscle growth. Once you know some key principles, you will be better equipped to evaluate whether a new exercise routine is based on sound physical principles-or completely bogus.

The most basic principle to understand is that your muscles adapt to whatever stress they are subjected to. If you spend all day on the couch, then you will be in possession of a fine set of muscles equipped for couch sitting. If you jog forty minutes each day, than your body will adapt to that. If you always follow the same number of reps and sets and routine when weight lifting, then your body will adapt to that too. And once you've adapted, your system will stop growing, and simply rest at this new plateau, having achieved the bare minimum required to function at that level. Therefore the basic idea is that if you want growth, you need to continuously overload your system.

The result of progressively overloading your muscles is called muscular hypertrophy, and that is the increase in muscle mass and cross-sectional area. Note that the number of muscle cells does not increase ( a phenomenon called muscular hyperplasia), but rather the size increases. As you work out, your muscles are subjected to microtrauma, where small tears appear in the muscle tissue. These tears signal what are called the 'satellite cells' on the surface of your muscle to activate and multiply and go to the damaged sites where they fuse with the existing muscle fiber, helping them regenerate.

While the satellite cells are multiplying and fusing with the damaged areas, your immune system kicks in with a complex series of reactions that ultimately lead to inflammation meant to contain and repair the damage as well as clean up the area of waste products. This process if key not only to the health of the muscle, but its growth, as numerous hormones and cytokines are released which stimulate muscle hypertrophy. Among these are hormones like insulin-like growth factor (IGF), fibroblast growth factor (FGF) and hepatocyte growth factor (HGF). Growth hormone (GH) is also released, and is key to promoting satellite cell division and the release of IGF.

What is important to understand is that this entire process (microtrauma resulting in the complex interaction of satellite cells, the immune system, growth factors and hormones) is dependent not only on exercise, but also receiving the appropriate amount of rest and nutrition to optimize the healing process. Muscular hypertrophy occurs when the muscle heals itself, not when you are working out. Furthermore, your muscles will only adapt as much as they need to, resulting in a 'plateau' effect if you don't change things up and challenge them in new ways. This is why it is a good idea to switch up your exercise routines like they do in P90X, and always keep your body guessing as to what comes next.