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Slow-Twitch vs. Fast-Twitch Muscle Fibers and How to Target Them (Top 12 Training Tips)

man flexing back muscles holding dumbbells

Your skeletal muscles are made of fast-twitch and slow-twitch muscle fibers. The other muscle fiber types are involuntary, such as your cardiac muscle fibers and the smooth muscles that exist throughout your digestive tract and circulatory system. The marvel of slow-twitch and fast-twitch fibers are that you can influence and improve them, and this article tells you how.

The Difference Between Fast-Twitch and Slow-Twitch Fibers

Let's quickly break down the difference between the types of skeletal muscle fibers. Hint: it has everything to do with types of muscle contractions.

  • Slow-twitch (type I): Type I muscle fibers are known as "red" muscles due to their blood supply—slow-twitch muscle fibers contain capillaries full of myoglobin, the oxygen-carrying heme protein. This oxygen supply makes slow-twitch muscles essential for triathlon trainers, marathoners, and other athletes who engage in Olympic levels of endurance training.
  • Fast-twitch (type II): Type II muscle fibers are those which contract in short, powerful bursts and are useful for weight-training endeavors. There are three subcategories of fast-twitch muscle fibers.
    • Type IIa fibers: These quick-firing fibers are indispensable in activities like sprinting and weight lifting.
    • Type IIx fibers: More powerful and less energy-efficient than type IIa fibers, type IIx fibers are the ones that don't need training—they kick in for short emergency uses, such as during a fight-or-flight reaction.
    • Type IIb fibers: Known as "white" muscle, these fibers have the lowest amount of myoglobin, and so function anaerobically, without oxygen.

Slow-twitch fibers are fatigue-resistant, long-haul muscles that are aerobic (oxygen-reliant).

Fast-twitch fibers reach exhaustion more quickly but are also the muscles that could hulk you out of a dangerous situation.

The ratio between slow-twitch red fibers and fast-twitch white fibers in your body varies depending on your age and fitness level. If you want to increase the size and strength of one or both of these muscle types, read on for training tips.

The Difference Between Fast-Twitch and Slow-Twitch Fibers

How to Train Fast-Twitch vs. Slow-Twitch Muscle Fibers: Top 12 Tips

Here are the activities that directly help target specific muscle types, and a dozen tips for how to max out your training and fitness potential.

Slow-Twitch Training

These endurance muscles are best targeted with marathon training and activities like long-distance running. Here are our best tips for all you endurance athletes out there.

1. Start Slow

Distance runners aren't out there pacing the globe on day one. Endurance training involves a slow and steady buildup of capacity throughout the cardiovascular system just to supply your slow-twitch muscles with efficient oxygen turnover. Set your goals in terms of weeks and months, and care for your body as it changes.

2. Warm-up

The best way to make sure your goals aren't thwarted by cramps or injury is to warm up properly. While many endurance athletes begin with light jogging or biking, it's important to include bodyweight exercises like push-ups, squats, jumping jacks, and lunges to get all of your muscles limber and engaged.

3. Suit Up

Appropriate footwear during endurance activities and sports can help prevent even more injuries, those like muscle sprains, tears, and ligament and tendon damage. The right shoe helps stabilize your gait and reduces the impact felt by your joints all the way up.

4. Stay Hydrated

Proper hydration helps reduce the risk of muscle cramps, muscle fatigue, and feelings of faintness. We're talking about 16 to 24 ounces of water before your workout, and electrolyte replenishment afterward.

5. Include Strength and Resistance Training

There is more information on strength training in the fast-twitch section, but even for endurance athletes who aren't trying to bulk up, it's important to pepper in at least three strength-training workouts each week so you don't end up with a muscle imbalance in the body.

6. Supply Your Muscles

Eating more protein is important, as the amino acid content of protein foods is essential for building and maintaining new muscle. Shoot for about 1 gram of protein per pound of bodyweight. We also recommend taking a fully balanced amino acid supplement developed specifically to meet the amino acid and nutrient needs of professional athletes.

Fast-Twitch Training

Running isn't solely a slow-twitch activity. Sprinters fall into the fast-twitch training arena. That being said, the development of the fast-twitch type of muscle fiber is more often associated with bodybuilding, because fast-twitch muscle can expand and provide the sort of visible muscles you can take to a competition. Here are tips for fast-twitch lifting and training activities.

7. Amino Acids

While the essential amino acids are important for anyone working on their muscles, they're especially vital for bodybuilders. The demands that weightlifting puts on new muscle creation needs to be met with a complete supply of EAAs, otherwise, the body will turn to catabolism (a form of molecular cannibalism) to take what it needs from the muscles you've already got.

8. Lift Heavy

The heavier you can lift, the more efficiently you're engaging your fast-twitch muscle fibers. The goal is to lift as much as you can as fast as safely possible.

9. Train Eccentrically

There are concentric and eccentric muscle contractions. In a concentric contraction, the muscle tension remains stable against the resistance (push-ups, barbell curls, squats). In an eccentric contraction, the resistance becomes greater than the force of the muscle (the downward motion of a push-up, depth jumps, and the downward motion of a squat). We can handle more weight eccentrically, so to accelerate the growth of fast-twitch fibers, emphasize eccentric contractions in your workout.

10. Dress Your Joints

When it comes to heavy lifting, it's important to protect your joints as your muscles explode. Consider using a weight belt for the lumbar portion of the spine, neoprene knee sleeves to protect those ligaments like the ACL and MCL, and stable footwear.

11. Plyometric Training

Plyos, otherwise known as jump training, are exercises that throw maximum force into extremely short time intervals. This kind of training requires healthy joints and (if you have access) professional training to ensure you have the right form to avoid injury.

12. Train Fast

Compensatory acceleration training involves working to move the weight as fast as possible throughout a lift. It's a basic component of physics class: the equation "force = mass x acceleration." The more acceleration you have, the more force you can fit into your movements.

How to Train Fast-Twitch vs. Slow-Twitch Muscle Fibers: Top 12 Tips

Mixed-Muscle Training

Your skeletal muscles all work together to get your body moving, and while some exercise activities can specifically target one or the other, there are a few sports and training practices that target both types, including the following.

  • Rock climbing: While training for rock climbing focuses on fast-twitch muscles to allow climbers to lift their entire body weight over uneven terrain (sometimes using the strength of just one limb), no one can pretend that climbing a mountain isn't a feat of endurance.
  • Soccer: The near-constant movement and jogging in soccer combined with the fast-twitch force of moving the ball make it a sport that requires comprehensive muscle training.
  • Gymnastics: While this is a large umbrella and many gymnastic routines favor aerobic slow-twitch over anaerobic fast-twitch needs, gymnastics is such a mixed-bag area of sporting that those who participate in multiple gymnastic events also require training for both kinds of skeletal muscle fibers.

The Types of Muscle Fibers You Can Control

You can personally control and influence skeletal muscles, unlike the involuntary muscles of the intestines, the heart, and even the tiny muscles that make each of your hairs stand on end when there's a chill. The ability to influence your fast- and slow-twitch muscles is both a privilege and a responsibility, so when you go to train up these different muscle types, do so as safely and with as much support as possible with the proper gear, professional techniques, and amino acid supplements.

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