Biomechanics of skeletal muscle

Structural factors:

Muscle fiber type: Not all muscle fibers function the same.  As shown below, there are two distinctly different types of fibers with many other types in between. There are different methods for assessing fiber function such as histochemical staining (Type I, IIA, IIB), metabolic activity (SO, FOG, FG), and mechanical velocity.  We will use the mechanical classification; fast twitch (FT) and slow twitch (ST). (See interesting Fact # 1).

 

The relative percentage of FT and ST fibers in your body varies between muscles and between people. Generally, a person with a greater percentage of ST fibers will excel at endurance sports and people with a greater percentage of FT fibers will excel at short duration high intensity events.  Where are you in the spectrum?

Notice to that if you have a high percentage of ST fibers composing your body that you will probably not hypertrophy to the same extent than if you had a lower percentage.  Again, where do you fit in the spectrum?

The differences in fiber diameter also dictate the order of fiber recruitment.  That is, ST fibers are recruited first during development of tension followed by FT.  This observation is called the size principle of motor unit recruitment.