Braxton Gilbert Fitness

How to Target Certain Muscle Fibers


When it comes to the art of training, we tend to overlook some important variables that can contribute significantly to our potential success: Proper periodization, nutrition, and form. These are just a few of the variables that tend to get overlooked in daily workout routines. One specific detail I want to bring to the light to help people become better athletes or gym-goers, is to be cognizant of the repetition ranges, sets, and order of exercises you are doing in your workout routine. Repetition ranges, sets, and the order of exercise should fit your specific goals; there is no one size fits all for these things.  All of these variables depend specifically on the load or amount someone is able to lift, which is different person to person. 



Your personal goals for weight loss and muscle building are what will help to determine the type of muscle fiber we are aiming to recruit. There are three different types of muscle fibers: Type 1A or Slow twitch muscle fibers, Type 2A or Intermediate muscle fibers, and Type 2X or Fast Twitch Fibers. Before I go into all the details of each muscle fiber and how to target them, I want to clarify that, regardless of what your goals are, it is not ideal to only focus on one specific muscle fiber. However, it is recommended to spend a majority of your time in pursuit of the one of the three designated muscle fibers that will best meet your personal goal.  


Let us dive into our first muscle fiber: Type 1A or slow twitch muscle fibers. Type 1A muscle fibers are recognized by a few other names such as slow-oxidative fibers or slow twitch fibers. They are composed of large amounts of mitochondria and are surrounded by significantly more capillaries than fast-twitch muscle fibers. Additionally, slow-twitch fibers contain higher concentrations of myoglobin than both fast twitch and intermediate fibers. All these components allow the slow twitch fibers to excel in fatigue resistance and sustaining aerobic metabolism- the way your body creates energy through the combustion of carbohydrates, amino acids, and fats in the presence of oxygen. Just as the name suggests, slow twitch fibers contract slower than their close relatives. These muscle fibers are more effective in creating low force outputs. It is our goal to target these muscle fibers if we do not excel in long distances or drawn out activities such as running long distances, swimming, and biking. The best way to tax these muscles to respond effectively for our training goals is to provide a stimulus of a minimum of a 15-set repetition. It is imperative you do not rest any longer than thirty seconds between sets, unless specified otherwise. A few methods I love to use to enhance our quality of training sessions for the slow twitch fiber recruitment are the following: Compound sets, Super sets, Drop sets, Myo reps, circuit style training, AMRAPS, EMOMS, Giant sets, and complexes.


Type 2A or Intermediate are the next type of muscle fibers we will discuss. This muscle fiber also goes by fast-oxidative glycolytic fibers. They excel in being a sort of “middle ground” between the three types of muscle fibers, hence the term intermediate. They possess speed, fatigue resistance, and force- production, somewhere between both type 1A and type 2X fibers. These muscle fibers are also used greatly in strength and power activities but can sustain effort significantly longer (up to 3 minutes) than type 2X muscle fibers. These muscle fibers are highly adaptable and have been demonstrated to increase their oxidative capacity to levels similar to those observed in slow-twitch muscle fibers. The trainee that should be concerned with these muscle fibers is the one looking to train for hypertrophy– increasing the size of your muscle fibers. Some guidelines to properly train the type 2A fibers include training in the 8-12 repetition range, utilizing a minute to minute and thirty second rest, and working with an overall controlled tempo.


Last, but certainly not least (I am just biased because this is my personal favorite to train). The muscle fiber I will elaborate on now is the type 2X muscle fiber. This muscle fiber I commonly refer to as fast twitch or fast-glycolytic fibers. These muscle fibers are on the low end of mitochondria content; therefore, they struggle to tolerate aerobic metabolism. As a result of their struggle to tolerate aerobic metabolism, fatigue can happen much quicker than slow twitch fibers and even intermediate fibers.  Fast twitch fibers cannot sustain their efforts for more than a few seconds! They are composed of lots of glycolytic enzymes, which provide them with a considerable amount of anaerobic capacity. Type 2X muscle fibers are also the largest muscle fibers in cross- sectional areas, as well as the fastest, producing the most force out of all the skeletal muscle fibers. The athlete concerned with training these muscle fibers is that of powerlifters, sprinters, or anybody doing an explosive activity that relies on lots of force output and speed (power). It is ideal to train these muscle fibers in the 5 or less repetition range, rest for a minimum of 3 minutes between each set and perform the repetitions with the intent of training a movement rather than a certain part of your musculature, that is with maximal speed and power. I personally like training this type the most because I love to jump and dunk on 10-foot basketball goals. Being a couple inches under 6 feet, I had no choice but to focus on the development of these muscle fibers, to have my running vertical jump at 38 inches and be able to do the dunks I had always dreamed about doing when I was younger.


In conclusion, we want to be mindful of our goals and allow the muscle fibers we are targeting primarily be a result of that! As a reminder, we must train all 3 classes of muscle fibers no matter what, with an emphasis in the fiber specific to our personal goals.