You may have noticed that elite marathon runners look a lot different than track and field stars. Marathoners are thin and willowy while sprinters possess massive thighs, glutes, and calves that help them explode down a short stretch of track. This difference in appearance has a lot to do with the type of muscles these different sports require. You’ve probably heard of slow-twitch muscles and fast-twitch muscles, but what are they and how can they affect the way you move and the way you look? Let’s explore fast- vs. slow-twitch muscle fibers, and then review ways you can cultivate your big and explosive fast-twitch muscles.
Understanding Fast- vs. Slow-Twitch Muscle Fibers
If you want to get nitpicky, the body is actually made up of muscles that fall into a variety of sub-categories. However, for simplicity’s sake, it’s easier to divide muscles into two main groups: slow-twitch muscles and fast-twitch muscles.
Introducing Slow-Twitch Muscles
Slow-twitch muscles possess their own mitochondria, which lets them use oxygen to create energy. This ability to power themselves up (using a chemical called adenosine triphosphate, or ATP) means that slow-twitch muscles are all about endurance. They can keep going and going, like the Energizer Bunny (or your neighbor’s yappy dog).
Endurance athletes, like long-distance runners, swimmers, and cyclists rely on their slow-twitch muscles to help them make it from the start line all the way to the finish. You may also notice that these endurance athletes tend to be trim rather than heavily muscled. Slow-twitch muscles are not big or bulky.
Introducing Fast-Twitch Muscles
Slow-twitch muscles have a low activation threshold. That means when you go out for a walk or jog, the first muscles your body recruits to get your legs moving and arms swinging are, that’s right, your slow-twitch muscles. It’s only when those muscles grow weary or they don’t have the power to generate a big, explosive movement that fast-twitch muscles enter the picture.
Fast-twitch muscles are all about force and power. If you want to jump, sprint, lift a heavy barbell, or tackle that linebacker, you’ll need some help from your fast-twitch muscles. These muscles are also primarily responsible for your body’s muscular definition and your overall strength. As Active.com reports, “…if you’re looking to increase muscle mass and improve strength, using fast-twitch fibers is the only way to do it.”
Endurance work is great for improving your cardio, but sculpting comes down to fast-twitch training. That means focusing on movements that incorporate power and explosiveness. Remember, your body wants to use slow-twitch muscles if it can, so you need to add weight and intensity to your workouts to give your fast-twitch muscles a good workout.
A Quick Note About Genetics
Research indicates that your genes play a role in the amount of fast- vs slow-twitch muscle fibers you possess in your body. (You can’t turn slow-twitch muscle fibers into fast-twitch muscle fibers or vice versa.) Some of us are born with more slow-twitch muscle fibers while others enjoy a higher ratio of fast-twitch muscle fibers. That may explain why some people can jog five miles without breaking a sweat while others look like they have rockets strapped to their feet when they sprint down a straightaway.
Don’t let your genetic predisposition get you down. Unless you plan to be a professional football player or a cross-country skier, it doesn’t really matter whether your body favors fast-twitch or slow-twitch muscle fibers. You still have both kinds, and you can still train your fast-twitch muscles. If you fall on the slow-twitch muscle side, you may need to work a little harder for your results and you may never be as swoll as Arnold Schwarzenegger was in his day, but you’ll still see impressive results if you train the right way.
How to Train Your Fast-Twitch Muscles
The name of the game is power, speed, and explosiveness when it comes to training your fast-twitch muscles. To engage your fast-twitch muscles, you’ll need to go big and hard in your workouts. Just remember to always warm up your muscles before putting them through big movements. If you plan to throw around big weights, make sure you feel comfortable with the movements and ideally have a workout buddy to keep an eye on you.
Lift Heavy Weights
Lifting light or moderate weights will not be enough to wake up your fast-twitch muscles. According to ACE Fitness, “Resistance training with heavy weight stimulate muscle motor units to activate more muscle fibers. The heavier the weight, the greater the number of fast-twitch fibers will be recruited.” Build up in weight and then, when it gets heavy, focus on short sets of only a few reps.
Muscle & Fitness suggests using 55-82.5% of your 1RM on your lifts and to “perform each rep as explosively as possible through the full range of motion.” (Your “1RM “or one rep max is the heaviest weight you can do for that movement). Keep in mind that your fast-twitch muscles deplete quickly. Make sure you add 60 to 90 seconds of rest between sets.
It is crucially important that you focus on maintaining good form when lifting heavy weight, or you risk injury. If you are just starting your fitness journey, consider using resistance machines at your local gym. When you feel more comfortable with the movements, transition to dumbbells and barbells.
You don’t necessarily need weights to work your fast twitch muscles. You can activate your fast-twitch muscle fibers using only body movements as long as those movements are explosive. One of the easiest ways to do this is to add sprints to your workout routine. Head over to the local high school or college track or find a flat stretch of sidewalk near your home (if your joints are healthy). Then put yourself through sprints.
This is all about power, so keep your sprints short and intense. You should try to maintain at least 80 percent of your fastest speed throughout the sprint.
On a track, consider sprinting the straights and walking the curves for four laps with a rest between each lap if necessary. If you’re not on a track, you can always use a stopwatch (or stopwatch app) to sprint for 20 seconds followed by 40 seconds of walking. Repeat that 10 times and you’ll get an excellent workout.
Another way to invite your fast-twitch muscles to the party is to perform a plyometric workout. Plyometrics is all about jumping. As long as you perform these jumps explosively (no slow and easy jumping jacks, unless that’s your warmup), you’ll recruit your fast-twitch muscle fibers. Plyometrics also helps you engage a wide range of muscles, as well as improve your coordination and body awareness. Just make sure your joints are in good shape. Plyometrics can put a strain on ankles, knees, and hips.
A simple plyometrics workout could include three sets of five box jumps, five broad jumps, and single leg cone jumps (five on each leg). You may also want to see if your local gym offers a plyometrics class.
Combining power, explosiveness, and heavy weight, Olympic lifting is the fast-twitch muscle trifecta. It’s also an advanced form of fitness that requires guidance and practice, especially as you learn the movements. Olympic lifting is comprised of two primary movements (with nearly endless derivatives): the clean and jerk, and the snatch. Both movements require you to lift a heavy barbell overhead. The snatch movement entails getting the bar from the ground to overhead in a single movement. The clean and jerk includes moving the bar to the chest (front rack) and then jerking it overhead.
Again, these movements are complex. You should not attempt them without instruction and guidance from a trained lifter.
Slow-Twitch Muscles and Fast Twitch Muscles
If you only perform moderate or easy workouts, you’ll never truly engage your fast-twitch muscles, which could be a reason why you aren’t seeing the results you want in the mirror. If you dream of well-defined muscles or want to lose weight (more muscles burn more calories throughout the day), it’s time to get your fast-twitch muscles into the game by adding power, speed, and explosiveness into your workouts.
Not sure how to do that? Consider hiring a personal trainer to put together a customized fitness plan for you. We also encourage you to keep reading our informative fitness blog, where you’ll get great advice on how to incorporate different fitness modalities and how to design a nutritious diet.