Dr. Andy Galpin: The Art of Training Our Muscle Fibers (Podcast)

Dr. Andy Galpin is a tenured Professor in the Center for Sport Performance at CSU Fullerton. In 2011, he earned his PhD in Human Bioenergetics and has done incredible work in regard to muscle fibers and how we understand them. On top of being a tenured professor, Dr. Galpin co-authored the book Unplugged and works hand in hand with a variety of elite athletes. 

In today’s episode, I sit down with Dr. Galpin to chat about muscle fibers. We talk about what we know, what we don’t know, and everything in-between.

In this episode of the BarBend Podcast, BarBend’s Fitness Editor Jake Boly talks to Dr. Andy Galpin about:

  • 2:45 A brief background on muscle fibers and how we understand them
  • 5:45 The details of muscle fibers and how they change and adapt
  • 7:00 The idea “muscle fibers can’t change” is long gone
  • 8:40 Are their modifiable training variables that can influence muscle fibers more than others? Do we know this information yet?
  • 12:45 What Dr. Galpin’s lab is doing to close the gap between what we know and what we don’t know about muscle fibers and training variables
  • 14:45 Do timelines differ between the shift of fibers from slow to fast and fast to slow?
  • 18:40 Modifying variables to increase growth when an athlete is highly-specific with their training
  • 22:30 The case study that highlighted the elite powerlifter’s muscle fiber composition
  • 24:40 Do we have a real idea about the human potential when it comes to muscle fibers and long-term anabolic use?
  • 28:00 Type IIX fibers and how rare they actually are
  • 31:20 Do muscle fibers shift as rapidly when detraining versus adapting?
  • 34:00 Why we shouldn’t fear frequency completely when it comes to muscle fiber changes
  • 37:00 What Dr. Galpin prioritizes when it comes to influencing certain muscle fibers
  • 39:00 The importance of coaching philosophy and influencing adaptations
  • 43:00 Where to follow Dr. Andy Galpin (also see below!)

Relevant links and further reading:


Dr Andy GalpinDr Andy Galpin

 …from the athletes that I worked with. Typically, I work with fighters. Let’s imagine how an MMA fighter who is an unbelievable striker. You had Anderson Silva, Conor McGregor, man they’re just deadly striker.


Should that person work really hard on their grappling and wrestling so that they don’t have such a big gap in their overall skills or should they say, “Look, I can train for three years on my wrestling and I’m still not going to be competitive that these guys are wrestlers their entire life.”


I’m just not going to waste my ton of time on wrestling and I’m just going to make sure that my striking is always at the highest level possible and I’m just going to win that way.

Jake BolyJake Boly

Welcome to the “BarBend Podcast,” where we talk to the smartest athletes, coaches, and minds from around the world of strength. I’m your guest host Jake Boly and this podcast is presented by barbend.com.


Dr. Galpin is a tenured professor in the Center for Sport Performance at CSU Fullerton. In 2011, he earned his PhD in human bioenergetics and has done incredible work in regard to muscle fibers and how we understand them. On top of being a tenured professor, Dr. Galpin co-authored the book “Unplugged” in 2017 and works hand in hand with a variety of elite athletes.


In today’s episode, I sit down with Dr. Galpin to chat muscle fibers. We talk about what we know, what we don’t know and everything in between. As always, we’re incredibly thankful that you listen to this podcast.


Today on the BarBend podcast, I am joined by Dr. Andy Galpin. Who is arguably one of the front-runners of muscle fibers and how we understand them today. Dr. Galpin, it is a pleasure to have you on and chat. I always love our conversations. Thank you so much for coming on the podcast.


If you haven’t already, be sure to leave a rating and review of the BarBend Podcast in your app of choice. Every month, we give away a box full of BarBend swag to one of our listeners who leaves a rating and review.

Dr Andy GalpinDr Andy Galpin


It’s a pleasure to be here, man. I’ve enjoyed your work and in working with you and the times we’ve gotten to exchange just a tremendous amount. As well as the content you yourself put out. It’s a pleasure to talk to somebody who is fighting a good fight themselves.

Jake BolyJake Boly

First off, thank you so much. I really appreciate that. I know all the folks here at BarBend love having you. Featuring you in any form of content because of the great work you’ve done in this space. Without further ado, let’s dive into some of our questions for today’s podcast.


My first question for you is on a topic that we discussed last time we chatted and that was on the topic of hybrid muscle fibers. A lot of folks understand that there are three types of muscle fibers. We have Type I, Type IIa, and Type IIx but a lot of folks don’t understand that there are a lot of hybrid fibers in between.


Could you give us a little bit more information on those hybrid fibers and kind of the topical view of muscle fibers and how we understand them today?

Dr Andy GalpinDr Andy Galpin

In general, people are familiar with the concept that there are some fibers that are fast-twitch and some there are slow-twitch and like you said, some that are maybe in the field had a degree or their personal trainers that are trying to study what’s going on. They realize that there’s also a IIx fiber.


From there, general consensus is just strong so there’s a lot of confusion past that because it’s honestly a misnomer the idea that there’s pure types anyways. If you go by the beginning, you realize there’s like a whole muscle and picture your quad or your bicep. The good analogy is a ponytail and you called the ponytail one thing. In this example your quad is a ponytail. A ponytail is just a composite of a whole bunch of individual hairs.


In this case, the muscle fibers themselves are the individual hairs and what’s different about muscle relative to hair is that the intrinsic properties of each one of those fibers can differ considerably from the other one.


One would maybe be a fast-twitch fiber and another would be a slow-twitch fiber but it’s not really that simple because the fiber themselves aren’t as fast or slow. They’re really on a different end of the spectrum. If you go to one end of the spectrum, an individual fiber might be, what we call purely slow-twitch, so a pure slow-twitch fiber.


Other end of the spectrum would be a pure IIx or the fastest fiber fibers we have. Everything else is really in between. Somewhere in the middle there, closer to the IIx side that would be a pure IIa or still the fast-twitch.


There’s a bunch of hybrids in between and so a fiber can be 95 percent slow-twitch and 5 percent fast-twitch. It could be 80 percent 20, it could be 59, 41, it could be any combination of these things. It could be 95 percent slow-twitch, 5 percent fast-twitch.


The opposite, the inverse, it could be 50 IIx, 50…so really any combination. In fact we see them fairly regularly that are some parts slow-twitch. Slow-twitch would be Type I, so I’ll use those interchangeably. Could be some part Type I, some part IIa, and some part IIx, and so it could be a triple hybrid.


Really, the example I would give would be if somebody paid you and said, “Hey, there’s tons of traffic in downtown LA. Let’s figure out why the hell there’s so much traffic.” The first thing we need to do is analyze what kind of automobiles are driving down the street there.


If you just wanted to get like a quick snapshot, you’d be like, “OK, it’s 50 percent cars and 50 percent trucks.” For most people that would probably be good enough. They’re fast-twitch and slow-twitch fibers fine, but if you really wanted to do a detailed analysis of that, you’d realize that there’s tons of automobiles that aren’t just cars or trucks.


In fact, you have things like an El Camino, that’s kind of a hybrid, right? You have an SUV and you have an electric one, and then you have like, is it a delivery truck or is it an F150? Are we talking of a school bus? Are we talking a motorcycle? A motorcycle is not the same as a car, like, what are we talking about here.


There’s just a lot of differentiation, and it’s really not that different. Where you decide to draw the line is somewhat arbitrary, so it just depends on how much detail you want to get into these things and what you’re trying to use the information for, that we can get there. That’s just a basic intro of the language that we’re talking about.

Jake BolyJake Boly

Got you. The last time we spoke, we talked about how training can actually influence muscle fibers and for — I can’t remember how you worded it — but for a long time, there was a misconception that fibers couldn’t change.


I remember going through my college exercise science program, and there were some parts of the textbook that were like, “Oh, fibers can change,” but more and more I think there’s more suggestion out there that fibers can change and more importantly…

Dr Andy GalpinDr Andy Galpin

Yeah, it’s beyond reproach at this point. Anyone that suggests the opposite is just massively misinformed, and they’ve been misinformed for 30-plus years. It’s not even close. Not only do we know that they change, but there have been, at this point now hundreds of studies that can explain the exact molecular mechanisms that cause the changes.


We know what happens upstream, downstream. Luckily, we know the genetics expression. It’s very well charted. There’s really no question at all that there’s a molecular possibility that the fibers have the ability to change. There are some questions about to what extent can this happen and what are the insults that are required to cause a change?


Is this is something that happens with normal physiology? Can exercise do it? If so, how much? How long does it take? Is this something that happens in a day? Does it take 10 years? Can food do it? Can other things? Those questions are reasonably valid, but whether or not they can actually change is just beyond reproach.

Jake BolyJake Boly

In terms of, let’s say exercise shifting fibers. Out of all the training variables, which variables do you think are worth considering maybe heaviest for getting a certain adaptation for a fiber shift? Let’s say I want to build more of top end strength and power. Would it correlate with traditional logic of like, “Oh, we need to focus on intensity,” “We need to focus on velocity,” things to that extent?

Dr Andy GalpinDr Andy Galpin

Yeah, this is a really good question. I actually think, the way you answered it is probably the most correct way. We do not understand which of the modifiable variables are the most important. With the exception of, of course, exercise selection.


If you’re performing an exercise that is say not necessarily activating your hamstrings, then be better not expecting your hamstring fiber to change to actually activating it. Outside of exercise choice though, volume intensity. I don’t really know my gut is, honestly.


It’s going to be driven mostly by volume in one direction, but perhaps intensity in the other. We don’t have any idea from that perspective. I would default right back to what you said, which is to say if you want to get more fast-twitch fibers, train simply like you would train to get more powerful, stronger and faster.


We know that because when we have done those training studies, that is exactly what happens, and so we see that result fairly consistently. Or the opposite if you want to do and get more slow-twitch fibers, train more endurance base and probably more specifically, steady state longer duration, endurance to cause that shift.


You’re probably right in terms of what we know just for training is the best recommendation we can give. The one exception would be things like fiber type-specific alteration. An example of that would be what we would call fiber type-specific hypertrophy.


We know that, traditionally, strength training, it doesn’t even have to be the nuance sets of three, sets of five. It could be anything from heavy singles to sets of 10, 12, 15. That’s all lumped together. It’s still basically strength training.


It could be classic bodybuilding or it could even be a lower rep, high intensity, more pure strength training. It doesn’t really matter so far as we know. In both of those cases, they tend to selectively hypertrophy the fast-twitch fibers.


However, in recent years, very recently, there is some reasonable evidence, and it’s mounting, it’s beginning to collect that higher repetition ranges may selectively hypertrophy the slow-twitch fibers. We see this in a barrage of ways.


For years, our lab, and the stuff we’ve done, has shown very clearly that endurance-trained individuals often have their slow-twitch fibers larger than their fast-twitch fibers. We didn’t necessarily know if they performed well in endurance events because they already had that intrinsically, or if that was an adaptation to the training.


There is direct evidence this is OK. These endurance folks, their slow-twitch fibers are larger than their fast-twitch fibers, which we would typically teach as the opposite. Usually, fast-twitch fibers are “larger.”


Now, we’ve followed that up in recent years with studies showing that maybe repetition ranges, say 25, 30 reps per set. Specifically, hypertrophy both fibers, but the slow-twitch fibers will get larger in proportion than the relative change in the fast-twitch fibers.


More studies are coming out, which is specifically targeting that. We have some indirect evidence, and then some more direct evidence has spilled in where you could maybe get there.


That conflicts the issue of touch because, now, we’re not necessarily differentiating between fiber-type change and just simply changing the intrinsic properties of the fiber without changing our type. We can also see that as well.


We can see fast-twitch fibers gain a lot of endurance ability. We can see slow-twitch fibers gain a lot of speed and strength and size. It makes it really complicated to study because you have moving variables.


One, that it’s changed its type. That it goes from slow-twitch to a fast-twitch, or did it stay slow-twitch and simply get bigger. It makes it very complicated to study, but we’re making progress in those areas.

Jake BolyJake Boly

How are some of the ways you guys are making progress there? I know there’s a little bit of gap there in terms of nailing that logistics. What are some of the steps you guys are taking now to maybe more closely define what exactly is causing that?

Dr Andy GalpinDr Andy Galpin

There’s a whole bunch of things. There’s a lot of scientists, Mike Roberts at Auburn is doing a fantastic job. I don’t know if you’ve worked with Mike before, but just a really sharp guy. He’s done a lot of really good studies. He is doing a study or just completed a study, where one group will do sets of 5, or 8, or 10, or something like that, and the other group will do sets of 30.


Then, you take muscle biopsies before and after, and you look at how the muscle cells themselves increase size. If the fast-twitch fibers increase by 10 percent, and say the low training group, the groups that did sets of five, or eight, or whatever, their fast-twitch fibers went up 10 percent and their slow-twitch fibers went up 5 percent.


Then, you look at the group who did sets of 30, and their slow-twitch fibers went up 40 percent and their fast-twitch fibers went up 5 percent. There’s a pretty good indication that there was differential adaptation happening there. That’s one thing.


What we’re doing in our lab is trying to enhance the precision of the research. We’re using, [indecipherable 14:13] things your listeners probably don’t care about, but different laboratory techniques that allow us to study the muscle cells themselves, one by one, as opposed to throwing them all together, smashing them all up, and then trying to guess what happened.


We’ve had some breakthroughs in technology and some movements in the method side of this research where we can get a lot more precision. When we have that level of precision, we start to see clarity with what’s happening. There’s a lot of moving parts there.

Jake BolyJake Boly

With the adaptation that elicits the shifts in fiber types, with the research that’s been put out so far and with what you have observed, what is the normal timeline for seeing a shift in fiber type? Do timeline shift from, let’s say slow-to-fast to fast-to-slow?

Dr Andy GalpinDr Andy Galpin

Yes. That’s another good question. It depends on the level or the status of the muscle itself. Think about it this way. If somebody is very sedentary, and a muscle hasn’t been stimulated and challenged in a long time, do you all know this will work out? It doesn’t take much stimulus to cause adaptation because they have such a low baseline.


This is a similar way of saying, if you take somebody who is sedentary or fairly untrained, anything works. They see adaptations everywhere with the smallest dosage, but to somebody who’s more trained, they are going to require more of that.


If you take a highly trained person who has been strength training really hard and consistently for five years, it’s going to take a lot more training stimulus to cause adaptation.


The same thing would be true to fiber level. To directly answer, if we take somebody who’s untrained, and we exposed them to four days a week of hard training, we could probably see a change in fiber type in as little as a month. That would happen.


Conversely, when we take animals and we do extreme overload, like cut off one of their legs and make them walk 24/7 on one leg, we see those changes happen in fiber type in two weeks. That’s not like you couldn’t do that to your tissue.


Also, when we take people and send them up to space for 10 days, we’ve seen fiber-type changes in as little as 10 days. Again, that’s pretty extreme because you’re going from 24/7 gravity to zero gravity.


It really depends on the level of training and the level of stimulus. I guess the more specific realistic answer is, if somebody is really highly trained, it will take them a long time to see adaptation if they continue to train in the same way.


Let’s say, you’ve been powerlifting for five years. You have five years of adaptation already. There is just not much left to go. You’re at the diminishing return, so it might take you another year to see any additional change. You might only change by a few percent.


If you just started working out, and you haven’t worked out in five years, you would see changes in whatever way you’re training probably in a month. It depends on the training background.

Jake BolyJake Boly


That’s really interesting to think about with someone, let’s say, who’s at more of an accomplisher and elite-level trying to progress. What you mentioned is there needs to be a change of stimulus to obviously grow.

Dr Andy GalpinDr Andy Galpin

This would also be true in the opposite direction, say, somebody was powerlifting for five years. If you continue to try to power lift, you would see marginal changes, but if you immediately switch after five years of nothing but powerlifting, and you started doing endurance work, you would still see out of patience really quickly, because now it’s a totally different stimulus.


That way you would move really fast in the opposite direction. That’s an important piece to recognize as well. It’s not necessarily are you in shape or not, it is a like how specific of a training stimulus have you been giving yourself a long time? Are you doing something really different from that? That’s what matters. It’s not necessarily the trained versus untrained.

Jake BolyJake Boly

Got you. I was going to ask you about the training, but I’m going to hold off on that because I actually have another question.


Let’s say we’re working with a powerlifter who is been doing it for five to six years. They are pretty much capped on the strength level they can obtain for basically where they are now, but they want to stay in the specificity of the sport of powerlifting and progress at maybe a quicker rate.


What would be the logical thing to do as a coach, what would be the structure of their program going forward to get them to progress? I feel like to get rapid changes, they would almost need to do something completely non-specific to their approach, but they don’t want to veer away from the goal at hand.


As a coach, what would you do and what would your next call be for structuring a program that will get them an adaptation at their level, but not take them away from the specificity of their sport?

Dr Andy GalpinDr Andy Galpin

Yeah, it’s complicated. I can’t give you an honest answer there because it takes too many variables into account. However, I can give a bit of a framework.

Jake BolyJake Boly


Dr Andy GalpinDr Andy Galpin

One thing that we’ve kicked around with bodybuilders and stuff before and people that work in muscle hypertrophy, maybe if you stalled out like you’re saying and I don’t want to change career paths entirely here or our training paths, maybe you can vary the stimulus just at a smaller level.


Maybe, this might be if you’re traditionally used to doing sets of threes and sets of four, sets of fives, maybe it would help you to switch up entirely and do a four week long block of sets of 20 or sets of 50 or go nuts like sets of 100.


That’s not going to cause that significant of a change in your fiber type in just four weeks. Maybe what it’s doing is actually training some fibers that haven’t actually been used in a long time. That may then help you get past that plateau because you only have so many fibers in your muscle.


In order to do something like power lifting, you need as many of them activated as possible. If you have some chunk of them, say 10 percent of them that are just really not contributing to the pie, getting them back on board, may be what you need, because the ones you continue to train are already giving you all they’ve got.


The only way to get higher is to get the other ones on board. They’d be the same for our hypertrophy, so if you’ve only trained in like the 8, the 12 or the 15, that’s percent range, and you just continued to train there and you stopped seeing gains. It’s probably because or possibly because the fibers that respond to that type of training are maxed out already.


What you need to do is to introduce some variation and maybe go higher in your up-range or go a lot lower, because the fibers that are going to respond to heavy doubles and heavy triples. They are probably not being used a ton to do your sets of 8 to 10 or 12 or 15. You can see additional mass growth by training fibers that really again haven’t been asked to get to their size ceiling.


That is something that you can do, but just be variation without completely eliminating your dreams and hopes and goals, if you want.

Jake BolyJake Boly


Got you. What about taking it a step further and going outside of, let’s say, traditional variables? What about doing something like blood flow restriction. Would that be something that you can consider being different to facilitate a growth response?

Dr Andy GalpinDr Andy Galpin

Yeah, it could, certainly. You’re going after a different mechanism, but yeah, I don’t have any reason to think you couldn’t go there. That’s not going to necessarily help your strength a lot, but if you’re really at a place where you need some variation, it might be there. My honest gut with blood flow restriction though, is it’s probably more of just a mental refresher than it is anything else.


You get to do something different for a while. I don’t know if it’d provide any specific physiological advantage, but certainly, you could try it.

Jake BolyJake Boly

It was just an example of how nitty gritty we can go with variation and with different kind of training modalities. I want to ask you a question on one of the case studies that was published not too long ago on the elite power lifter, who had the muscle fiber that was greater than the size of the rhinoceros, right?

Dr Andy GalpinDr Andy Galpin



Jake BolyJake Boly


 I don’t know if we can say names of who it was, but that study blew my mind and honestly when I covered it, it blew up. It was really cool, because the Type A fiber composition that he had is insane for like a normal athlete?

Dr Andy GalpinDr Andy Galpin

Yeah, it was. He was, is a pretty unique fellow and of course, if you’re not familiar with this or you haven’t heard it, yes, definitely on antibiotic steroids and a lot of them for a long time. That was an interesting piece. Some of his fibers were fairly normal. Then, he had some that were so large, we had to search for a while. We’re trying to figure out, what the hell can we even compare this to? In all the literature, the closest we could find was a rhinoceros fiber size. It was there.


The individual has, 25 years, maybe more have really specific dedicated strength-training, in a lot of different fashions, powerlifting, bodybuilding, all over the place. The muscles really have been exposed to a lot of different stimuli fairly consistently, at a very high intensity and effort. In addition to a lot of focus on nutrition and lots of steroids.


Something like that is needed to get to that level. It’s not going to get there from an eight-week training cycle. We’d train pretty hard for a little bit and didn’t finish there. It was very interesting. I don’t know what we can draw from that per se, other than the fact that steroids work. [laughs] They work really well. Training really hard for a long time, also worked pretty well.

Jake BolyJake Boly


I actually do want to ask one question about using anabolics and muscle fiber-type composition. With anabolic specifically, is the type of training what indicates how the fibers will shift entirely? With that study, wasn’t there a mention that the fibers had more nuclei than what’s normal, or am I mis-speaking there?

Dr Andy GalpinDr Andy Galpin


Yes. That’s right.

Jake BolyJake Boly


With anabolics, my question is, do we have an idea of what the top capability even really is? Assuming that, they’re used correctly and training over time and intensity and effort is always there. Do we have any clue of the potential that the human body could even reach?

Dr Andy GalpinDr Andy Galpin

 I don’t think so. If you look at the bodybuilding community, it seems to be tapering off a bit now. If you look at Flex Wheeler, and everything prefects Flex Wheeler, or even Lee Haney, there was a difference between Columbu and these guys. There’s this generation that started, you’re just, “Whoa, these guys got really big.” They didn’t have that mass before.


Not that they were using steroids before that, but I’m not sure. I don’t know if we can get much larger than, what some of the folks in our community have already got to, I don’t think we understand what their capabilities are, no. The one thing that we’re trying to figure out though is, what is the true limiting factor? For a while we thought, OK, perhaps it was limited by the amount of nuclei.


If you’re unfamiliar with that, nuclei are the control-center of muscle fiber. Human muscles are really unique because we have thousands of these control centers, there is nuclei per cell.


Most of biology has one nuclei per cell. They take a lot of these control centers, these places hold your DNA. This is what’s telling your muscle fiber to grow, shrink, die, repair, whatever it needs to do. It is regulating that. What happens, is you can have satellite cells come into this, that are hanging out on, what’s called the basal lamina, the outside of the cell.


They will enter the middle of the cell, they’ll do, what’s called differentiation or they’ll turn into a nucleus. That will allow your muscle cell to grow because it’s limited by how many control centers you have.


The business example would be, if you own Mom and Pop’s coffee shop and you want to open up another shop in three states over, that’s fine. Then if you want to open up a third facility, a fourth facility, eventually, you have to start hiring other store managers. You can’t manage a store in Kentucky while the same time, you’re managing a store in Tennessee.


Especially, when you open one up in Texas and California and Washington. The amount of coffee shop you can open up is limited by the amount of managers you can hire. This is the same thing with muscle growth. This is what our current thinking is.


One of the things, anabolic steroids do, specifically testosterone, is it enhances the amount of those satellite cells that will go to muscle fiber and differentiate into a nuclei. That can help augment the process. At some point, you’re limited by the amount of satellite cells you have, and that’s where the science stops right now.


We’re trying to figure out, what there’s some relationship here, between satellite cells nuclei and potential hypertrophic growth of muscle cells, but we don’t know exactly what that means. We used a lot of animal models, not my lab, others like mice and things like that. Maybe there’s physiological differences there, maybe the signal is not right.


Like I said, we keep seeing folks that [laughs] break it down, and they break these barriers. You don’t really know.

Jake BolyJake Boly


Interesting. Speaking of things that we’re still trying to figure out, I know you mentioned earlier that you don’t really see a lot of individuals of pure Type IIx fibers. I think the last time we talked…

Dr Andy GalpinDr Andy Galpin


No, almost never.

Jake BolyJake Boly


I think the last time we talked is, you brought up that, sometimes though, you’ll see them. Let’s say, somebody who’s maybe been in a coma, their lower or half of their body was paralyzed for quite some time, sometimes you’ll see Type IIx fibers there. Am I remembering this correctly?

Dr Andy GalpinDr Andy Galpin

Yeah, you’re dead on. Going to take you back in the beginning, there’s Type I, slow-twitch, Type IIa or fast-twitch, and Type IIx, incredibly fast-twitch.


If you look across the literature, you’ll see a combination of mistakes that the scientists have made in this stuff, but you just have to trust me that, when done properly, the amount of individual muscle cells that are purely IIx or close, like 95 percent or higher, is just extraordinarily rare.


We never see this IIx fiber in its state. The only time we will see the IIx being expressed is when there’s a IIa-IIx hybrids, and those tend to be very, very highly concentrated in people that are untrained. I have biopsied, I don’t even know, 400 people, probably something like that, maybe more.


We have analyzed hundreds of thousands of individual muscle fibers. I don’t know if I’ve ever seen anybody with more than, gosh, like half a percent of their fibers being pure IIx.


The vast majority of time, I would probably say if we biopsy a 100 people, 99 will have as literally zero IIx fibers. It is very, very, very rare, and the one that has it might have two percent or something like that. It’s super, super small.


The only difference being, you mentioned, people that have nerve denervation, or they’re paraplegic, or something like that, and the muscle hasn’t been activated for years. They can start to buildup, not only a measurable amount to this IIx fibers, but the number can get extraordinarily high, like 50, 60, 70 percent of their fibers, will be the pure IIxs.


We don’t really see that anywhere else. When we hear this as a side note, if you look at felines, like at tigers and anything in that category, they tend to have a huge percentages IIx fibers, and of course, they’re not unfit. That’s one of the reasons why they’re so much faster than we are. They have these things.


They also have an either even faster fiber Type IIb, which humans don’t even have. Yeah, it is complicated. We don’t understand exactly what the point of the IIx fibers are. They go up when we don’t work out. When we work out at all, it doesn’t really matter what type of training you do, those IIx fibers would generally transition away into being IIa to go down.

Jake BolyJake Boly

Interesting. To go off that fibers going away, we talked about a loose timeline for adaptations for certain levels of athletes. What about detraining? Do you see as fast of a shift or as much of a shift when somebody goes from very active to not active?


I’m guessing that like anything, once you’re at the elite level, it’s going to probably progress quicker, but if you guys noticed any or observed anything that would suggest a timeline for folks who are active and then stop for a while, whether that be because of a job or so forth, and they are level of detrained.

Dr Andy GalpinDr Andy Galpin

Yeah. Again, it will come down to how big of a difference the stimulus is. If you’re going from, “Twice a week, I’ll kind of like it,” they love to go for 30 minutes, and you go from that to not exercising? It’s not really that much of a change.


If you go from, “Now, I’m hitting, I’m doing spinning class twice a week,” “I’m lifting heavy circuits for both,” and you get all this training, and then you go to nothing? Then that change is going to happen very fast. I would expect to be, if you take somebody who’s very active five days a week, and all of a sudden, they go to none, I would say, within a month, you would see changes in fiber type.

Jake BolyJake Boly

Interesting. What about somebody who’s, let’s say, prepping for a meet, and they’re lifting four or five days a week, and then after the meet, they shifted two in three days, what would you guess the shift in fibers would be?


To the extent, because I know, it’s a bigger question there. It’s like, “What are they doing?” “How much?” “How intense?” My question is, would you see a shift? If so, would it be rapid because it’s not as specific in the nature of their training? Or, what would you guess what would happen?

Dr Andy GalpinDr Andy Galpin

My guess in that situation is you would not, because if you go down to training twice a week, there’s probably still enough of a stimulus to keep those things live. You’re probably OK there. One thing I can talk about is taper.


We’ve done a study years ago where we looked at taper. This was in cross-country runners, collegiate cross-country runners. We looked at them before and at the end of a three-week taper.


In this particular case, their taper result was a 50 percent reduction in training mileage. I think they’re running something like 65 miles per week before taper. By the third week of taper, they were down to 30 miles per week, or something like that, just mileage.


This model is nice because running is extremely quantifiable. Lifting is a lot harder to quantify, but this one is just like, how many miles you run. Then, of course, we tracked heart rate, and we’re able to capture intensity and all that stuff.


One of the things we saw was there was no change in real to max, pre to post. There was no change in the amount of enzymes in the muscle fibers that regulate anaerobic glycolysis or aerobic glycolysis. Metabolically, nothing happened there.


What we did see though is the fast-twitch fibers exploded. There was about around a 10 to 15 percent improvement in fast-twitch muscle fiber strength. You can imagine we take biopsies, we isolate the individual muscle cells, and you tie it to a pole, if you will.


Then you put a little force transducer at the other end of the pole. You can measure how hard that muscle can contract maximum, so that the individual cell exerts maximum force production, its speed, and even its size. We saw about a 10 percent increase in fast-twitch fiber size by just taking three weeks and doing little bit less training.


This is when you said like, “Oh, I go from five days a week to two days a week is a bad one, might actually be a good thing.” We think probably happened in this folks, is that high mileage was probably fatiguing and compromising that muscle.


When they backed off, it was sort of allowed to return to baseline. It was not necessarily that I really grew, but it probably grew back to where its default setting was because it was being hammered so much by all the training.


It really depends. Like I said, on how hard, did you train hard for four weeks for that meet to back off? Or, is this a four-year training cycle, where you’re really putting throttle down because you’re getting ready for the Olympics, or something? It depends on how much training went into it beforehand.

Jake BolyJake Boly


Wow, that is insane. I feel like that only complicates it further when you think about the central and peripheral nervous system too, and how much those are probably at play with the taper and everything else, right?

Dr Andy GalpinDr Andy Galpin

Yeah, of course. The signal from the nerve is what’s going to tell the muscle fiber to do what it’s going to do. It’s always a component to it, John. Then, if you just think about human performance. I’m a muscle guy, obviously, so I default to muscle. That’s what I like. Human performance is really a function, movement-wise, of three things.


Number one, there has to be some kind of neurological input to tell something what to do. That nerve has to force a muscle to contract. That muscle, the contraction of it has to pull on some sort of connective tissue, which inserts to the bone and moves the ball. That’s how human movement happens.


If you want to look at human performance, even just from the movement perspective, you have potential contributions and changes and adaptations at any and all three of those levels. If you’re only taking one into account — you don’t know what happened with the other two — you really don’t know exactly what happened. Scientifically it’s really hard to do all three at once. We virtually stick to one.

Jake BolyJake Boly

Before we cut this podcast off, because I know we are a little bit pressed on time. I do want to ask you a couple more questions that are a little bit more applicable to training specific fibers.


I think one of the most powerful things that I’ve learned from you, is when you said that muscle fibers the way to look at them, is structure equals function. Pretty much how a muscle on the body performs on a daily basis for that matter, is probably a good suggestion of the fiber composition that comes along with them.


My question for you is, as a coach, as an athlete who wants to strengthen my quads. We can guess that there’s going to be a little bit more fast-twitch there, especially if I’ve been training strategically over the last few years working on my strength.


My question for you is, when you’re structuring variables off of that logic for a training program, what do you prioritize first and last? I know it’s a very loaded question, because it’s going to vary based on goals, needs and where somebody’s at.


Just as a guideline for folks who might be trying to structure their training a little more strategically, which exercise variables are most important for influencing certain types of fibers? If I want to influence, let’s say a more predominantly what’s suggested to be a fast-twitch muscle.


What variables should I look to train a little bit more of, versus let’s say a more slow-twitch like the soleus? How would I improve that to perform better? Should I use higher reps, lower reps? Should I do a little bit of both? How should I approach that?

Dr Andy GalpinDr Andy Galpin

I don’t think I have a great answer for you. At this point it’s mostly guessing. I will guess for you based on what I know now. I’ll give you my best guess.


If you are trying to train fast-twitch fibers, you probably should stick to things at higher intensity. This could be speed or load, so percentage of your max. You’re probably going to see a better response by doing that, so either heavy or fast, at minimum.


You want to train slow-twitch fibers, it’s probably going to be the opposite which is something to lot of fatigue. It really depends on what you are training them to do, what you are trying to get them to accomplish. That’s the best guess of what I would say now. Again, I don’t know if that is entirely fully true but that’s as far as we can go so far.

Jake BolyJake Boly

Interesting. I guess where my head goes next is, so train the muscles in a way that is best suggested based on how they perform and how they are designed to perform. If we went with the logic that let’s say my quads are at a level where there’s not much strength I’m actually putting on them at a point, would it pay off to train them in the reverse fashion?


So training them with…

Dr Andy GalpinDr Andy Galpin

This is why the question is so damn hard because it’s a coaching philosophy question. The example I can give you is, from the athletes I work with, typically I work with fighters. Let’s imagine you had a MMA fighter who was an unbelievable striker. You had Anderson Silva, Conor McGregor, man they’re just deadly striker.


Should that person work really hard on their grappling and their wrestling so they don’t have such a big gap in their overall skills?


Or should they say, “Look, I can train for three years on my wrestling and I’m still not going to be competitive with these guys who are wrestlers their entire life so I’m just not going to waste a ton of time on wrestling and I’m going to make sure that my striking is always at the highest level possible. I’m just going to win that way.”


I can’t tell you one way is better than the other one. All I have to say is those are philosophies, right? Whether or not you say, “No, let’s just play to our strengths.” In this case you want to train fast-twitch fibers, train heavy, train fast.


Or do you want to shore up your weaknesses? You’ve got a slow-twitch quad. Let’s give it the opposite stimulus to make it come up and match a little bit.


I can’t answer those questions because there is no right answer to them. It depends on what do you think you should go after. I can give you direction about what to do once you make that decision. Which decision to make is just really tough.

Jake BolyJake Boly

Got you. I feel like it also comes down to sport too and what…

Dr Andy GalpinDr Andy Galpin


Most definitely. I agree. What are you, a bodybuilder? Well, the answer’s a little more obvious. Are you a sport athlete? Well, that’s a little trickier.

Jake BolyJake Boly

I recently went to the Under Armour Human Performance Summit, and I was talking to James Newbury and his logic to training because CrossFit is such a diverse sport. His logic was kind of what you just said.


He’s like, “Look, I could either train my weaknesses and never really be as competitive as the guys who are at the top of the game in those, or I could keep those at maintenance but really double down on my strengths and really try to get those event wins because that’s going to help me out in the long run.”


I guess the better question is then looking at it from a bigger picture as to your competition, the sport you’re in, and then structuring training around that, right?

Dr Andy GalpinDr Andy Galpin

Yeah, exactly. Do you want to be Rich Froning or not? Do you want to win because you’re just pretty good at everything, and by the end of the weekend you just have enough build up points, and no one can catch you because you just don’t have any holes?


Or do you want to be the opposite and just be like, “Well, I’m going to lose this event and so I’m just not going to waste any gas on it, but I’m going to make sure I get first in these other five events and hope that total gives me enough to win.” It’s tough to say. It’s up to you to decide.


That’s funny because right before we got on here I was working on my class lecture where I’m actually changing my entire program, the design class. The first thing I’m going to do at the beginning of the year, because I kind of break it down into two components. Quality program design, so designing your workouts to get the thing you want, is really only two things.


It’s being really clear with what you want to train for and then being clear with how to train for, and I feel like the vast majority of people only talk about number two, which is how to train. What intensity should I use? Should I use a barbell? Which order should I do my exercises in?


Those are all questions about how to train, but the more important too is that you’ve got to understand what you’re training for in the first place. What are you really going after?


Spending more time on the front end of “what should I be really targeting” once you make that decision, your execution of how to actually do it is not that complicated, and I don’t think we have that many disagreements in that area, but typically why people don’t hit their goal is because they don’t spend enough time really addressing what goal they should be going after in the first place.

Jake BolyJake Boly

I love that. That’s beautifully said. Man, every time we talk, it just makes me wish I could go back to grad school and then enroll at Fullerton even more, literally, because of the constant “we’re not sure just yet.” It just makes you actually think about what you’ve experienced versus what we’ve seen versus where it could go based off of pulling all the suggestions there.


I appreciate the time. Unfortunately, we are coming to a close. We’re definitely going to have to have you on for a part two. I want to really pick your brain about periodization a little bit more and structuring training variables for certain adaptations, so we’ll definitely have you back on in a couple months, for sure.


Before we head out, man, I would love for you to give the listeners an idea of where to follow you, where they can learn more about you, and so forth.

Dr Andy GalpinDr Andy Galpin

Yeah, sure. Twitter and Instagram are the best place. Twitter is nice because I can directly link to things if you’re the type of person who wants to see the study that I’m talking about or something. I don’t put my link in my bio every damn time I make a post on Instagram. It’s just too much pain in the ass, but there’s more action on Instagram usually.


It’s just my name. It’s Dr. Andy Galpin on both of those. If you are the real nerd type or you really want to actually spend some time learning, my YouTube page is basically just all of my class lectures. You can really get a big chunk of my class material for free there without having to come all the way to Fullerton and actually enroll. I put those up in 5-minute videos, 25-minute videos, and even 55-minute videos.


If you’re super interested in your own training or you’re a personal trainer but maybe you switched career fields and you were in accounting before, you don’t have an undergrad degree, you can get pretty close to finishing that damn thing by just watching these videos. That was the intent. It’s not meant to just drive a ton of YouTube views. Who’s going to watch an hour long video on exercise selection? I don’t care. If you do, that’s great.

Jake BolyJake Boly


That’s for sure. You’ve got to be a special type of loving it to watch a full hour on that. Listeners too, I will drop all the links below in the description of this podcast for those who want to follow along and find Dr. Galpin on all these different mediums.

Dr. Galpin, thank you again for the time. It’s always a pleasure talking. You’re one of my idols in this industry, and I really do appreciate the time and the effort that you put into all walks of life in trying to help out the field progress.

Dr Andy GalpinDr Andy Galpin


You’re far too kind, man, far too kind.