FAST-TWITCH VS. SLOW-TWITCH MUSCLE FIBER TYPES + TRAINING TIPS

Looking to build endurance? What about power? Do dreams of being an all-star hitter or marathon runner need to be dashed if twitch ratios aren’t ideal? Not necessarily. The types of muscle fibers targeted in different types of training programs can impact sports performance training goals.

• WHAT ARE MUSCLE FIBERS?

Skeletal muscles are made up of individual muscle fibers. And like muscles themselves, not all muscle fibers are the same. There are two types of skeletal muscle fibers, fast-twitch and slow-twitch, and they each have different functions that are important to understand when it comes to movement and exercise programming.

Slow-twitch muscle fibers are fatigue resistant, and focused on sustained, smaller movements and postural control. They contain more mitochondria and myoglobin, and are aerobic in nature compared to fast-twitch fibers. Slow-twitch fibers are also sometimes called type I or red fibers because of their blood supply. Fast-twitch muscle fibers provide bigger and more powerful forces, but for shorter durations and fatigue quickly. They are more anaerobic with less blood supply, hence they are sometimes referred to as white fibers or type II. Skeletal muscles contain both types of fibers, but the ratios can differ depending on a variety of factors including muscle function, age and training.

Skeletal muscles contain both types of fibers, but the ratios can differ depending on a variety of factors, including muscle function, age and training.

SLOW TWITCH VS. FAST TWITCH MUSCLE FIBER TYPES

The two types of skeletal muscle fibers are slow-twitch (type I) and fast-twitch (type II). Slow-twitch muscle fibers support long distance endurance activities like marathon running, while fast-twitch muscle fibers support quick, powerful movements such as sprinting or weightlifting.

MUSCLE FIBER TYPE COMPARISON CHART