Locations:
Search IconSearch

Slow-Twitch Muscle Fibers: What They Are and How To Work Them

These fibers are your friend for aerobic and endurance exercises

Person wearing goggles doing the back stroke in a pool

You might not think you’re working your muscles when walking to your car, pushing a grocery cart or sweeping the floor. But every time you do one of these low-intensity activities, you engage your slow-twitch muscle fibers.

Advertisement

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

These muscle cells, also called type I muscle fibers, keep you going during everyday movements and longer workout routines. Exercise physiologist Katie Lawton, MEd, explains slow-twitch muscle fibers and how to keep them healthy and strong.

Do you need slow-twitch muscle fibers?

Absolutely! “Your slow-twitch fibers are necessary for everyday life and endurance,” says Lawton. “Every time you sit, stand, walk or do moderate-intensity exercise, you use your slow-twitch fibers.”

But if you follow fitness experts and trends, you’ve probably heard more about fast-twitch muscle fibers, also known as type II muscle fibers. Your fast-twitch muscle fibers are muscle cells that produce a lot of power very quickly, allowing you to do explosive movements and intense weight training.

As the name suggests, slow-twitch muscle fibers utilize energy more slowly than fast-twitch muscle fibers. But that doesn’t mean they’re second best. In fact, slow-twitch muscles are actually used first and more often in everyday activities.

Plus, they last much longer. “Fast-twitch muscles fatigue after a few seconds or a couple of minutes,” says Lawton. “Slow-twitch muscle fibers, on the other hand, keep going for extended periods.”

Why do slow-twitch fibers punch the clock for more hours than their fast-twitch counterparts? The main reason is fuel.

Advertisement

“Your slow-twitch muscle fibers are aerobic, meaning they use oxygen for fuel,” she continues. “You replenish this oxygen as you breathe so your slow-twitch muscles can keep going. Fast-twitch fibers use glucose and lactic acid, which take longer to regenerate as fuel.”

How many slow-twitch muscle fibers do you have?

You’re born with a mix of fast-twitch and slow-twitch muscle fibers, says Lawton. But everyone has a different ratio of these fibers. The numbers depend on:

  • Age: In general, older people have more slow-twitch fibers. “As we age, many people lose muscle mass through sarcopenia,” says Lawton. “Sarcopenia affects your fast-twitch muscle fibers more, so your slow-to-fast-twitch ratio increases. However, you can avoid or slow this process by doing high-intensity exercises and strength training.”
  • Exercise habits: A long-distance runner will have more slow-twitch fibers than a sprinter. Doing a mix of longer, moderate-intensity and short, high-intensity exercise will help you keep a healthy amount of both types of muscle fibers.
  • Genetics: Like eye color, hair color and many other traits, your genes play a role in your muscle composition. “But how you train and the stimulus you place on muscles can also have an impact on muscle fibers,” notes Lawton.

How to build type I muscle fibers

Training and building slow-twitch muscle fibers requires moderate-intensity exercise. If your intensity gets too high, like with high-intensity interval training or weightlifting to your maximum, your fast-twitch fibers will take over.

“Slow-twitch muscle fiber exercises are aerobic exercises,” says Lawton. “These activities are great for your cardiovascular health. Slow-twitch fiber exercises also burn fat, which can help with weight loss.”

Slow-twitch muscle exercise examples include:

Walking

This tried-and-true exercise is widely recommended for a reason. “Walking has mental health benefits and improves cardiovascular and metabolic health,” says Lawton. “Every time you walk, you work your slow-twitch muscle fibers.”

Plus, you don’t need special equipment and it’s great exercise for beginners and seasoned athletes alike.

Swimming

Got sore joints? Swimming will work your slow-twitch muscle fibers and has practically zero impact, thanks to the buoyancy of water.

“Water exercises offer moderate resistance and engage your slow-twitch fibers,” says Lawton. “Swimming is often a good choice for people with reduced mobility, arthritis, fibromyalgia or obesity. But even hard-core athletes can get a great full-body workout with swimming.”

Advertisement

Jogging

Like to run longer distances? You’re using your slow-twitch muscle fibers when you do. “Fast-twitch fibers are necessary for sprinting, but your slow-twitch fibers carry you through a longer, slower run,” explains Lawton.

Primal movement workouts

A primal movement workout involves movements we use every day, like bending, twisting and lunging. It’s a moderate-intensity exercise and targets muscle groups you need to stay mobile and active, which makes it a good way to target slow-twitch muscle fibers.

Don’t ignore your fast-twitch muscle fibers

It’s easy to assume that you don’t need fast-twitch muscle fibers unless you’re a powerlifter, but that’s not the case.

“Everyone needs fast-twitch muscle fibers because they improve reaction time,” clarifies Lawton. “If you’ve ever tripped and caught yourself before you fell, you can thank your fast-twitch fibers. Many older adults are prone to falls due to declining amounts of fast-twitch fibers.”

Finding the right routine

Creating a workout routine that works all of your muscle fibers can be overwhelming. If you’re not sure where to start, consider getting help from a pro.

“Many people are surprised to find out they’re only working one muscle fiber type,” says Lawton. “That’s why it’s helpful to consult a personal trainer or exercise specialist to evaluate your routine. They can help you find activities that are best for your fitness goals and personal preferences.”

Advertisement

Advertisement

Learn more about our editorial process.

Related Articles

Runner sprinting from starting line on track
August 23, 2024/Orthopaedics
Fast-Twitch Muscle Fibers: What They Are and How To Build Them

Strength training and HIIT exercises can keep these vital muscle fibers strong

Person doing a Bulgarian-split squat outside
June 17, 2024/Exercise & Fitness
10 Squat Variations To Add to Your Workout

Bulgarian split squats, hack squats and goblet squats are just a few of the moves you can try

Person in a deep squat
June 13, 2024/Exercise & Fitness
Here’s the Right Way To Do a Squat

Squat smart with proper technique, including a neutral spine, wide knees and an engaged core

Person contemplating healthy food choices with protein
June 7, 2024/Nutrition
How Much Protein Do You Need? And How To Get It

The general rule is 0.8 to 1 gram of protein per kilogram of body weight — but that may not be right for you

Person on scale, questioning muscle weight vs. fat weight
April 12, 2024/Exercise & Fitness
The Difference Between Muscle Weight vs. Fat Weight

Both are needed for a healthy body

woman using hand weights
August 6, 2020/Exercise & Fitness
Want To Lose Weight? Build Muscle

Strength training has many benefits for any age

Performing an ultrasound on a man
September 6, 2019/Orthopaedics
When Is Ultrasound Used vs. an MRI for Bone, Muscle and Joint Problems?

Understand how these imaging tests differ

Bare feet of person standing on exercise mat, with one foot rolling on a roller
November 18, 2024/Orthopaedics
How To Stop Foot Pain From Standing All Day

Try stretching, massage, elevation and a supportive pair of shoes to help relieve foot aches and pains

Trending Topics

Person touching aching ear, with home remedies floating around
Home Remedies for an Ear Infection: What To Try and What To Avoid

Not all ear infections need antibiotics — cold and warm compresses and changing up your sleep position can help

Infographic of foods high in iron, including shrimp, oysters, peas, cream of wheat, prunes, eggs, broccoli, beef and chicken
52 Foods High In Iron

Pump up your iron intake with foods like tuna, tofu and turkey

Person squeezing half a lemon into a glass of water
Is Starting Your Day With Lemon Water Healthy?

A glass of lemon water in the morning can help with digestion and boost vitamin C levels, and may even help get you into a better routine

Ad