Type I Muscle Fibers

Fitness / 15 November 2022

Let’s talk about type I muscle fibers!

You’ve probably heard me say these things regarding fitness sessions:

“Sweating doesn’t necessarily indicate a successful workout.”

“The intensity of your fitness session isn’t what matters most.”

“Muscle soreness in the days following your workout isn’t the indicator of success.”

Here’s what does count: targeting the various muscle fibers! This is what will get you visible results, efficiently.

Muscle is not just a simple mass. For starters, there are different types of muscles, i.e. heart muscle, skeletal muscle and smooth muscle. In this post, we’re focusing on skeletal muscle: abs, calves, glutes, biceps, etc.

There are also different types of fiber found in skeletal muscles: Type I, IIA, IIB or IIX.

Every fiber behaves differently. Some contract slowly, others quickly. This is called slow-twitch (type I) and fast-twitch (type II).

Type I muscle fiber is a slow contraction fiber, which is activated during the following types of activities:

Marathons
Long distance running
Swimming
Cycling
Fast walking
Endurance training

Type I muscle fibers are quite small and have a high concentration of capillaries. In trained muscles, these fibers contribute to that muscular look which bodybuilders love :).

These fibers produce little strength but can stay engaged longer than others, and also tire more slowly than types IIA and IIB/IIX.