Why Your Muscles Fatigue

There are different muscle types that contribute to their fatigue levels.

Obviously strength of each muscle plays a role in fatigue but knowing the fiber types of each muscle will make it more understandable in your training. If you seem more fatigued than you expected this could be why.

Here are the fiber types...

-Type I: Slow twitch, little fatigue. Less intensity, more endurance. Fatigues over time.

Long distance running

-Type IIa: Fast twitch, fatigue resistant. Active at moderate intensity. Continues until fatigue.

400-800m run

-Type IIx: Fast twitch, fast fatigue. Active during high intensity activity (about 80%).

Sprinting

The color of the muscle will also indicate fiber type. The darker the muscle, the more mitochondria. Let's go back to school for a second...

The mitochondria is the powerhouse of all cells. It is the powerhouse because it creates cellular respiration (energy (ATP), digestion, etc). ATP, or energy, is stored in those chemical bonds. Once these bonds break, the ATP, or energy, is then released.

The muscle with the most mitochondria, the darker in color, the more blood flow and the slowest to fatigue.

Type I Fibers: Large muscle groups that are slow to contract (red).

Type II Fibers: Small muscle groups that are quick to contract (white).