Different Muscle Fibers Type I and II

Muscles contain various type of fibers, which can be grouped into “Type I” and “Type II”, predominantly, where Type II are known to be responsible for hypertrophy.

In reality, there’s always been some misconception in regards to which fibers we can grow via training and whether we could target Type I fibers with ultra-high volumes, yet, if we take a look at their own characteristics & metabolic properties, hypertrophy is most likely to occur on Type II muscle fibers.

In a new study conducted by Hatanaka and colleagues (2022), researchers tried to deveop a mathematical model that would estimate the mechanical activation of each muscle fiber (fast & slow twitch) during exercise, revealing that the highest determinant of the hypertrophic effect was related to the total mechanical activation of the fast twitch muscle fibers.