Being aware of your muscle anatomy

To be able to develop one's musculature, it is important to know its anatomy and specificities. Pushing, pulling, or lifting are functions that activate different muscle groups with varying hypertrophy potentials. Knowing the function of each muscle group is essential for the harmonious and balanced development of muscle mass (Frontera & Ochala, 2015).

Skeletal muscles

are the muscles under voluntary control of the central nervous system. The human body has over 600, including 125 pairs of major muscles that ensure major postures and movements. Their names are generally related to their location (dorsal, pectoral, brachial, abdominal, for example), but we can certainly classify them according to their functions and the type of movements that activate them.

In bodybuilding, movements can be summarized into 3 main functions:

• Push
• Pull
• Lift

In general, when performing a given movement, several agonist muscle groups are activated simultaneously: a major muscle group associated with a small supporting group. For example, when pulling a load, the back muscles are activated, but also the biceps and the rear shoulders (posterior deltoids) secondarily. Pushing, pulling, and lifting are 3 major multi-joint movements that activate many muscle groups simultaneously. In this sense, they constitute the basis of muscle development and strength (Paoli et al., 2017).

Muscle anatomy does not stop there. It goes even further within the fibers that compose it. Skeletal muscles are made up of a large number of cells, muscle fibers. Depending on their type, some will be adapted to respond to a long and low-intensity effort, while others will be involved in short but intense efforts.

Slow fibers:

These are type 1 fibers. They are called red because they benefit from a very dense network of blood capillaries and are rich in mitochondria (the energy centers of our cells). They are small in diameter and are involved in low-intensity endurance efforts (of long duration). These slow-twitch fibers use the aerobic process to obtain energy. Slow fibers have a very limited hypertrophy potential but are very useful for endurance efforts (Scott et al., 2001).

Slow fibers respond to muscular endurance-type efforts (long sets, light loads 20 to 40% of the 1RM, short rest periods).

Fast fibers:

These are type 2 fibers. They are called white because they are poorly irrigated. However, they have a significant glycogen reserve. They are large in diameter and are involved in fast and intense efforts (strength and resistance). These fast-twitch fibers use the anaerobic process to extract energy. Fast fibers have a very high hypertrophy potential (Fry, 2004). These are the ones that will be primarily developed in bodybuilders. They respond to short but intense efforts (short to medium sets, heavy loads 60 to 90% of the 1RM, long rest periods).

There is a third type of muscle fibers, the so-called "intermediate" fibers (Type IIa). Their characteristic is a mix between slow and fast fibers. Depending on the environment or physical activity, they can adapt their energy efficiency in an aerobic or anaerobic direction and behave like slow or fast fibers (Wilson et al., 2012).

The distribution between these 2 fiber types within the same organism is genetically defined (Simoneau & Bouchard, 1995). This ratio explains why some people are very skilled in endurance sports like marathon or cycling, and others have explosive but limited strength like sprinters and a muscle volume like bodybuilders.

This same ratio explains why some muscles develop more easily than others. For example, the calf muscles: a ratio in favor of slow fibers (as in the soleus muscle, composed of ~80% type I fibers) will greatly limit the volume gain for this muscle (Edgerton et al., 1975). Therefore, the type of work for this muscle will have to be adapted, opting for endurance-type efforts (long sets, light loads and short rest periods).

As you have well understood, knowing your muscle anatomy is essential for the effectiveness of your training sessions. By properly mastering the subject, you will be able to define your own training programs by choosing the right movements and adapting the type of work you will perform.