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These fibers are your friend for aerobic and endurance exercises
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.
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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.
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.
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“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.”
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:
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:
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.
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.”
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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.
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.
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.”
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.”
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