Understanding Fast-twitch and Slow-Twitch Muscle Fibers

We’ve all heard the terms “fast-twitch” and “slow-twitch” when referring to muscle types. From ultra-marathoners to Olympic sprinters and everyone in between, bodies are all made up of two main types of muscle fibers: slow-twitch (known as Type 1) and fast-twitch (known as Type 2).

Fast twitch is actually broken down into two types of muscle fibers that you can read more about in this article. For now, we’ll keep it simple and just call slow and fast twitch type 1 and type 2. While everyone is born with a finite number of slow and fast-twitch muscle fibers, knowing how to train both properly is important to maximize your endurance, speed and strength.

So what exactly are slow-twitch muscles and how are they different from their fast-twitch counterparts?

Slow-twitch muscle fibers are designed for endurance and are activated during aerobic activity (jogging, biking and other endurance activities) in order to prevent fatigue and provide energy. Slow-twitch muscles are more efficient at using oxygen to generate more fuel for continuous, extended muscle contractions over a long period. Slow-twitch muscle fibers rely on a rich supply of oxygenated blood. Within these muscles, there are a high density of capillaries, which help bring blood to the muscles.

They generate less power and strength than fast-twitch fibers but are slower to fatigue meaning they can sustain activity for much longer. This type of muscle fiber is what you use primarily during endurance activities. Whether you’re a recreational distance runner or aspiring to train for a marathon or Ironman (or even one of these ultras only a maniac would attempt), work on training you’re slow-twitch muscles.

You might also like this article about the importance of training fast-twitch muscle fibers

2 Ways To Train Your Slow-Twitch Muscle Fibers

1) Weight Training

Muscle fibers determine how much weight you can lift and how many reps you can complete. According to IDEA Health and Fitness Association, if you’re completing 12 reps or more, then you are engaging your slow-twitch muscle fibers for over 50% of the duration of the exercise.

Even if you’re a focused endurance trainer or training for an endurance event like a marathon or triathlon, we can’t stress enough the importance of weight training in your regimen. This will help to not only aid your performance but will help prevent injuries by improving muscular support of your joints. It’s also important to train slow-twitch muscle fibers through weight lifting so they can be as strong as possible during an endurance event. Here are some tips to training your slow-twitch muscle fibers when weight lifting.

When you’re lifting, focus on a higher number of reps (eight or more)

Focus on a slower tempo

Use shorter rest periods (30 seconds and under)

With resistance training, increase your time under tension

Every 2 weeks, train to failure of max reps and try and beat that each time

2) Cardio and Endurance Training

It goes without saying if you are training for an endurance event that you have to be diligent about getting your cardio in. Don’t dive in too soon and make sure you’re varying your cardio activity between various endurance sports like cycling, running, and swimming for a well-rounded regimen. This also helps prevent overuse injury. Incorporating high levels of cardio helps improve aerobic capacity and increase capillary density. The more capillaries you have in a muscle, the more aerobic energy you’ll have. This will keep you going for a longer period of time. Here are a couple of tips for your cardio training.

Start slowly and work your way up to larger goals

Build up your endurance activities to make slow-twitch muscle fibers more efficient and fatigue resistant

Incorporate long interval training

Always stick to a training plan that is spread over a long enough period of time to avoid injury and ensure you’re rested enough each time you train to perform your best

Even though genetic makeup accounts for slow and fast-twitch muscle fiber ratios, everyone can train both muscle fiber types to maximize their efficiency and improve performance. If you’re an endurance athlete, it doesn’t mean you can neglect training your fast-twitch muscles or visa-versa. If you want to learn more about training fast-twitch muscle fibers you can check out some more info here.

As always, don't neglect your mobility. Check out this series on quad and hip flexor mobility to make sure your training isn't going to waste. Injury prevention is just as important as your workout regimen!