Whether your goal is to PR a marathon, climb a mountain, or crush your coworkers in the annual office plank competition, you need to understand type 1 muscle fibers and how to build them.
Of the two main types of skeletal muscle fibers, type 1 muscle fibers (known as “twitch” muscle fibers) are the most endurance-oriented and are essential for steady-state exercise, strength training sets with high repetitions high and isometric holds.
But before we get into the specifics of how to target type 1 fibers in your workouts, let’s take a closer look at what they are and how they work.
What are type 1 muscle fibers?
Compared to type 2 (fast-twitch) muscle fibers, which are larger and more powerful, type 1 muscle fibers have long contraction times (hence their “slow-twitch” designation). As a result, they generate less force but are more resistant to fatigue.
That’s why they’re the fibers your body needs for longer-duration, steady-state activities like running and cycling, and for sustained-strength, higher-repetition exercise like circuit training.
How to train type 1 muscle fibers
Every muscle contains both type 1 and type 2 muscle fibers, and everyone is born with their own unique ratio, says Breanne Celiberti, MS, former adjunct instructor in the Human Performance department at the University of Tampa. But with targeted training, you can favor and build one type of thread over another.
To develop type 1 muscle fibers, focus on aerobic and endurance-oriented activities and training modalities:
1. Steady state training
Maintaining a steady pace for longer distances will hit your type 1 fibers (as opposed to sprinting and interval training, which target type 2 fibers).
2. Resistance training
Incorporate light-weight, high-rep sets into your routine to target your type 1 fibers. Research also shows that performing both light-weight/high-rep and heavy/low-rep sets can help maximize hypertrophy (muscle building) by working both major types of muscle fibers.
3. Circular training
Sets of back-to-back plyometric, bodyweight, and weightlifting exercises will hit your cardiorespiratory system and your muscles—especially your type 1 fibers.
What do type 1 muscle fibers look like?
Type 1 muscle fibers require more oxygen to produce energy than type 2 muscle fibers, so they are red. Their counterparts, type 2 muscle fibers, which are more anaerobic (oxygen independent), are white.
“Type 1 fibers are also slightly smaller,” says Celiberti. “Upon close examination, type 1 muscle fibers have higher capillary density and oxidative capacity, as well as a smaller diameter than type 2 fibers.”
