Hammerblow
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Slow Twitch vs Fast Twitch Muscle Fibers: Know it and you will grow!
I'm sure some of you are aware that your muscles are composed of several different muscle types, but I’ll run through them here quick anyway.
Types of Muscle Fibers
Your muscles are composed of two types of muscle fibers. These are slow twitch and fast twitch fibers. On average the human body is split pretty even (50/50) between these two types of fibers, but this is not always the case. Look at your elite marathon/endurance athletes. It is has been shown that they can have up to 80% slow twitch fibers. On the other extreme are sprinters and I would also dare say bodybuilders. These individuals excel at what they do because of a preponderance of type 2 fibers. Is sprinting more your deal or are you more of an endurance athlete? Answering that should give you an indication of the predominant type of fibers you have. Here is more scientific method of determining your predominant muscle fibers. It is call the 80% test.
The 80% test for determining YOUR predominant muscle fiber makeup
First you need to find out the 1RM for which ever exercise you are doing. Want to test your pecs, do a bench press. Want to test your back, try a pulldown. After you have determined your 1 rep max, you then need to do a set with 80% of that 1RM. If you can do more than 8 reps with that weight, that muscle is more slow twitch than fast twitch fiber. If you do less than 8 reps, that muscle is more fast twitch than slow twitch. If you don’t want to max out (which I never do), keep reading and I’ll tell which muscle groups are primarily made up of what fibers.
Type 1 – Slow Twitch Fibers
The Type 1 slow twitch fibers are your classic endurance type fibers. They have a dense capillary structure which allows them to carry more oxygen and sustain aerobic activity. These fibers are able to contract for long periods of time but they produce relatively little force. These fibers produce little lactic acid which allows them to keep going without experiencing fatigue right away.
Type 2 – Fast Twitch Fibers
The fast twitch muscle fibers contract quickly and powerfully but they also fatigue very quickly. They are capable of sustaining only short, anaerobic bursts of activity before the muscle contractions actually become painful. They build up lactic acid (which is the burn you feel) very quickly which basically signals them to shut down and stop contracting. These fibers are what contribute most to muscle strength and have the greatest potential for hypertrophy. Let me repeat that again, your fast twitch fibers are actually the ones that are most capable of hypertrophy.
You also need to be aware that the Type II fibers have two main subtypes. These are Type IIa and IIb. These subtypes vary in both their contractile speed and the force they can generate and they need to be trained (stimulated) differently.
Type IIa Fibers
These fast twitch muscle fibers are also known as the intermediate fast-twitch fibers. I call them the inbetweeners. These fibers can use both aerobic and anaerobic metabolism almost equally to create energy. So in essence, they are a combination of Type I and Type II muscle fibers. These babies are pretty resistant to fatigue, but obviously not anywhere near the Type I fibers.
Type IIb Fibers
These puppies are the fast twitch fibers which use anaerobic metabolism to create energy and are the "classic" fast twitch muscle fibers you use when you need quick and powerful bursts . This fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types, and this is also why it has a much faster rate of fatigue. The quick buildup of lactic acid is a protection measure that shuts them down quick.
Applications for Bodybuilding
Here is the kicker. The different types of fibers respond best to the stimulus that is designed for them. Once you know the fiber type that the primary muscle groups are composed of, you can design your workout to maximize the potential and growth of those fibers. Factors such as rest periods, number of sets (volume), reps, frequency of training, weight used, etc. can all be adjusted for maximum growth of that muscle. I am now going to tell you what type of fibers your main muscle groups are primarily composed of.
Fast Twitch Dominant Muscle Groups (Type IIa)
Chest, triceps, biceps, hamstrings
Slow Twitch Dominant Muscle Groups (Type I)
Shoulders, forearms, calves
The In betweeners (Type IIb)
Quadriceps, back
Secret Insider Info
Here is how you can apply your new found knowledge about fiber types to maximize your gains.
Training the Fast Twitch Dominant Muscle Groups (Type IIa)
For the fast twitch dominant muscle groups, focus on lower reps like 4-6 and bump up the weight accordingly. These are the muscles that react better to high intensity (heavier weight), low volume, low frequency training. Since you are doing heavier weight, you could use rest periods up to two minutes between sets. Essentially you want to rest long enough so you are fully recovered before beginning your next set.
Training the Slow Twitch Dominant Muscle Groups (Type I)
For the slow twitch dominant muscle groups, focus on higher reps like 12-15 or even up to 20. These muscle groups react better to your classic high volume, high frequency training using short rest periods. Keep rest periods under a minute, preferably around 40 seconds. You want these muscle groups to feel like they are on fire when you are done with the set, this is what they respond best to.
Training the Inbetweeners (Type IIb)
For these muscle groups you should focus on the medium rep range. Eight to 10 reps is a good range. Since these muscle groups contain both types of fibers (I and II) you must also mix in the training you use for the fast twitch and slow twitch fibers to be sure your are activating and maximizing all the types of muscle fibers.
Example of how knowing the predominant fiber type of the muscle benefited myself
Where I have really been able to put this into practice is for my leg development. I was suprised to learn that up to 83% of the fibers in the hammies are Type IIa. That is huge and what that told me is that I better start incorporating more heavy, low rep sets to really target those fibers. That is the type of stimulus they need. So I implented a lot more heavy stiff-legged deadlifts and more heavy work on the hamstring curl machine. I focused on banging out 6 quality reps. If I got more, I increased the weight. And what do you know, after doing that for only a couple of months I started noticing a significant improvement in my hammies. I still incorporate some 20+ rep sets, but knowing what the predominate fiber in my hammies is and gearing my training towards targeting those fibers has made a world of difference. It is kind of nice to know why certain muscles may respond better to different types of training.
So as you can see, there is more to muscle than just muscle. Use the knowledge of the fiber types to tailor your routine to target them the most effectively. The more effective your training, the more you will grow. Now, still keep in mind that even though a particular muscle group may be predominantly one type of fiber, it still has other types of fiber so you so you still need to add in some training to target those types as well...again if I've missed anything or anyone wants to add to this please please feel free. The day you stop learning is the day you stop improving. Peace.
I'm sure some of you are aware that your muscles are composed of several different muscle types, but I’ll run through them here quick anyway.
Types of Muscle Fibers
Your muscles are composed of two types of muscle fibers. These are slow twitch and fast twitch fibers. On average the human body is split pretty even (50/50) between these two types of fibers, but this is not always the case. Look at your elite marathon/endurance athletes. It is has been shown that they can have up to 80% slow twitch fibers. On the other extreme are sprinters and I would also dare say bodybuilders. These individuals excel at what they do because of a preponderance of type 2 fibers. Is sprinting more your deal or are you more of an endurance athlete? Answering that should give you an indication of the predominant type of fibers you have. Here is more scientific method of determining your predominant muscle fibers. It is call the 80% test.
The 80% test for determining YOUR predominant muscle fiber makeup
First you need to find out the 1RM for which ever exercise you are doing. Want to test your pecs, do a bench press. Want to test your back, try a pulldown. After you have determined your 1 rep max, you then need to do a set with 80% of that 1RM. If you can do more than 8 reps with that weight, that muscle is more slow twitch than fast twitch fiber. If you do less than 8 reps, that muscle is more fast twitch than slow twitch. If you don’t want to max out (which I never do), keep reading and I’ll tell which muscle groups are primarily made up of what fibers.
Type 1 – Slow Twitch Fibers
The Type 1 slow twitch fibers are your classic endurance type fibers. They have a dense capillary structure which allows them to carry more oxygen and sustain aerobic activity. These fibers are able to contract for long periods of time but they produce relatively little force. These fibers produce little lactic acid which allows them to keep going without experiencing fatigue right away.
Type 2 – Fast Twitch Fibers
The fast twitch muscle fibers contract quickly and powerfully but they also fatigue very quickly. They are capable of sustaining only short, anaerobic bursts of activity before the muscle contractions actually become painful. They build up lactic acid (which is the burn you feel) very quickly which basically signals them to shut down and stop contracting. These fibers are what contribute most to muscle strength and have the greatest potential for hypertrophy. Let me repeat that again, your fast twitch fibers are actually the ones that are most capable of hypertrophy.
You also need to be aware that the Type II fibers have two main subtypes. These are Type IIa and IIb. These subtypes vary in both their contractile speed and the force they can generate and they need to be trained (stimulated) differently.
Type IIa Fibers
These fast twitch muscle fibers are also known as the intermediate fast-twitch fibers. I call them the inbetweeners. These fibers can use both aerobic and anaerobic metabolism almost equally to create energy. So in essence, they are a combination of Type I and Type II muscle fibers. These babies are pretty resistant to fatigue, but obviously not anywhere near the Type I fibers.
Type IIb Fibers
These puppies are the fast twitch fibers which use anaerobic metabolism to create energy and are the "classic" fast twitch muscle fibers you use when you need quick and powerful bursts . This fiber has the highest rate of contraction (rapid firing) of all the muscle fiber types, and this is also why it has a much faster rate of fatigue. The quick buildup of lactic acid is a protection measure that shuts them down quick.
Applications for Bodybuilding
Here is the kicker. The different types of fibers respond best to the stimulus that is designed for them. Once you know the fiber type that the primary muscle groups are composed of, you can design your workout to maximize the potential and growth of those fibers. Factors such as rest periods, number of sets (volume), reps, frequency of training, weight used, etc. can all be adjusted for maximum growth of that muscle. I am now going to tell you what type of fibers your main muscle groups are primarily composed of.
Fast Twitch Dominant Muscle Groups (Type IIa)
Chest, triceps, biceps, hamstrings
Slow Twitch Dominant Muscle Groups (Type I)
Shoulders, forearms, calves
The In betweeners (Type IIb)
Quadriceps, back
Secret Insider Info
Here is how you can apply your new found knowledge about fiber types to maximize your gains.
Training the Fast Twitch Dominant Muscle Groups (Type IIa)
For the fast twitch dominant muscle groups, focus on lower reps like 4-6 and bump up the weight accordingly. These are the muscles that react better to high intensity (heavier weight), low volume, low frequency training. Since you are doing heavier weight, you could use rest periods up to two minutes between sets. Essentially you want to rest long enough so you are fully recovered before beginning your next set.
Training the Slow Twitch Dominant Muscle Groups (Type I)
For the slow twitch dominant muscle groups, focus on higher reps like 12-15 or even up to 20. These muscle groups react better to your classic high volume, high frequency training using short rest periods. Keep rest periods under a minute, preferably around 40 seconds. You want these muscle groups to feel like they are on fire when you are done with the set, this is what they respond best to.
Training the Inbetweeners (Type IIb)
For these muscle groups you should focus on the medium rep range. Eight to 10 reps is a good range. Since these muscle groups contain both types of fibers (I and II) you must also mix in the training you use for the fast twitch and slow twitch fibers to be sure your are activating and maximizing all the types of muscle fibers.
Example of how knowing the predominant fiber type of the muscle benefited myself
Where I have really been able to put this into practice is for my leg development. I was suprised to learn that up to 83% of the fibers in the hammies are Type IIa. That is huge and what that told me is that I better start incorporating more heavy, low rep sets to really target those fibers. That is the type of stimulus they need. So I implented a lot more heavy stiff-legged deadlifts and more heavy work on the hamstring curl machine. I focused on banging out 6 quality reps. If I got more, I increased the weight. And what do you know, after doing that for only a couple of months I started noticing a significant improvement in my hammies. I still incorporate some 20+ rep sets, but knowing what the predominate fiber in my hammies is and gearing my training towards targeting those fibers has made a world of difference. It is kind of nice to know why certain muscles may respond better to different types of training.
So as you can see, there is more to muscle than just muscle. Use the knowledge of the fiber types to tailor your routine to target them the most effectively. The more effective your training, the more you will grow. Now, still keep in mind that even though a particular muscle group may be predominantly one type of fiber, it still has other types of fiber so you so you still need to add in some training to target those types as well...again if I've missed anything or anyone wants to add to this please please feel free. The day you stop learning is the day you stop improving. Peace.
