Fast twitch muscles help with sudden bursts of energy involved in activities like sprinting and jumping.

Twitch muscles are skeletal muscles that help support your movement. They’re especially important for working out.

There are two main types of twitch muscles:

  • Fast twitch muscles. These muscles help with sudden bursts of energy involved in activities like sprinting and jumping.
  • Slow twitch muscles. These muscles help with endurance and long-term activities like running or bicycling.

Let’s go deeper into what exactly fast twitch muscles are and how you can benefit from training them. We’ll also show how you can use both fast and slow twitch muscles for an optimal fitness level.

Fast twitch muscles support short, quick bursts of energy, such as sprinting or powerlifting. You can see how they’re meant to function when you compare their design and structure to slow twitch muscles.

Fast twitch muscles have very few blood vessels and mitochondria (unlike slow twitch muscles) because they don’t need to fuel quick, intense activities.

This is because fast twitch muscles are anaerobic. They use sources of energy that are already present inside your body, such as glucose, to make adenosine triphosphate (ATP).

Here’s a breakdown of the different types of fast twitch muscles.

Type IIa

Type IIa is the first type of fast twitch muscle. (Keep in mind that Type I muscles are slow twitch. More on that later).

They’re known as oxidative-glycolytic muscles because they can use oxygen and glucose for energy.

These fast twitch muscles have a higher number of mitochondria than the other type, Type IIb. This makes them similar to slow twitch muscles in their ability to use oxygen along with glucose and fat to burn for energy.

And like slow twitch muscles, Type IIa fast twitch muscles are not easily exhausted and can recover from a short, intense workout relatively quickly.

Some research has also found a link between Type IIa muscles and how big your muscles are.

Type IIb

Type IIb is the second type of fast twitch muscle. They’re known as nonoxidative muscles because they don’t use any oxygen for energy. Instead, they rely on glucose to produce the energy needed for activity.

Type IIb muscles also have a much lower number of mitochondria because they don’t need them to produce energy from oxygen like Type I and Type IIa muscles do.

They’re also much larger around than other muscles and become worn out much faster than the other types of muscles despite their capacity for feats of strength.

Fast twitch muscles are optimized for short, intense activities, such as:

  • sprinting
  • powerlifting
  • jumping
  • strength training
  • agility training
  • high-intensity cycling
  • high-intensity interval training (HIIT)

Here are some exercises you can do to improve your fast twitch muscle speed.

All-out sprint training

Here’s an example of an exercise based on a 1990 study that increased the number of Type IIa muscles from 32 percent to 38 percent:

  1. Get on a stationary bicycle or similar pedaling machine.
  2. Set the resistance on the machine to a level you’re comfortable with — you don’t want to injure yourself.
  3. Pedal as fast as you can for 30 seconds without stopping.
  4. Stop pedaling and get off the machine.
  5. Take a 20-minute break and do other exercises (if you’d like).
  6. Return to the machine and do another 30-second pedaling session.
  7. Take another 20-minute break.
  8. Repeat 2–3 times in a single workout session. You’ll probably start to notice results after about 4 to 6 weeks.

Hang clean

This is a common upper body workout for fast twitch muscles:

  1. Get a bar with an amount of weight you feel comfortable with.
  2. Hold the bar in front of you with your arms fully extended and about shoulder-width apart, gripping with your hands over the bar.
  3. Squat a little bit (not all the way down).
  4. Shift your weight back to your heels and launch yourself up, pulling the bar up with you up to chest level and moving your hands backward to rest the bar on your chest.
  5. Hold this position for a few moments.
  6. Slowly return the bar back to the position you started in.

Slow twitch muscles have tons of blood vessels and energy-producing mini cells called mitochondria to help keep them going for long periods of time.

They’re your body’s first choice for muscle use before tapping into fast twitch muscles for shorter, more extreme bursts of energy.

Slow twitch muscles are aerobic muscles, This means that they use oxygen to generate energy in the form of ATP from their high concentration of mitochondria. They can keep you going as long as you get enough oxygen.

Slow twitch muscles are great for endurance exercises such as:

  • long-distance running (marathons or 5Ks)
  • cycling
  • swimming

Slow twitch “aerobic” exercises are usually called “cardio” exercises because they’re good for heart health. They’re also good for toning muscles.

Here are some exercises that can increase your slow twitch muscle speed.

Jumping rope

This is a good, basic exercise you can do almost anywhere:

  1. Get a jump rope that’s long enough for you to jump over without hitting the ground too much.
  2. Begin by swinging your rope forward above your head and under your feet for about 15 seconds.
  3. Pause briefly, then swing the rope in the other direction, back behind you and under your feet. Do this for 15 seconds.
  4. Take a 15-second rest.
  5. Repeat the process about 18 times to start seeing results.

Aerobic strength circuit

This aerobic circuit is designed to get your heart rate up.

First, do each of these exercises for 1 minute each:

Next, lightly march or jog for 1 minute for the stage called “active rest.” You’ve now completed a full circuit.

Repeat each exercise and your active rest 2 to 3 times. Don’t rest any longer than 5 minutes between each circuit to make sure you get the best results.

Fast twitch muscles are optimal for short, quick bursts of energy. Slow twitch muscles are better for long-term endurance activities and can improve your heart health.

Working out both can give you a wide variety of activities to choose from and increase your overall health and strength.