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High Jumper Muscle Fiber Analysis: Type 1 & Type 2 Training
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Mar 27, 2025
If you want me to coach you personally to jump higher click here: If you want a FREE week of jump training click here: My name is Isaiah Rivera and I have the highest officially tested vertical on the planet at 50.5 inches and am the co-founder of THPstrength, a company that focuses on vertical jump training for athletes. What makes me a little different from most athletes that jump high is that I started with a pretty low vertical and documented my entire journey on this channel. Here is my journey in a nutshell: 14: Started working out to jump higher for basketball 16: Hit my first dunk and shortly after found out about the world of pro dunking 17: Trained like a madman and hit my first between the legs dunk 18: Entered my first professional dunk contest 19: Knee pain almost made me quit dunking 20: Met my coach John Evans, who helped me get rid of knee pain 21: Won my first international dunk contest 22: Tested a 48 inch vertical and started coaching full time 24: Tested a world record 50.5 inch vertical The reason I make so much free content about jumping higher now is because it’s a resource I wish I would’ve had when I was in high school that would’ve prevented a lot of unnecessary mistakes and injuries.
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0:00
Can you shift type 1 to type 2 muscle fibers to be a better athlete
0:05
Well, today we are going to discuss this topic. My name is John Evans. I coach the highest jumper in the world
0:10
This is Isaiah. He's the highest jumper in the world. And we are going to get into it. Before we do that, go to teachbestrength.com if you're looking to jump higher and be a better athlete
0:18
So let me ask you this, Isaiah. What do you think... Let me reword this
0:24
Do you think it's possible to shift your type 1 to type 2 fibers
0:28
I don't think it's fair to answer this because I was just looking at the studies
0:32
What do you think, though? Yeah. You can, okay, and because I also have looked at the study numerous times
0:40
We basically had a couple people in the last podcast that we did on type 2 fibers talk about how that's been debunked
0:45
and that it's actually possible to see a shift from type 1 to type 2X
0:49
And they've looked at it in tetrapelagics. Pelagics was one that they referenced
0:53
And then there was a S&C coach that also referenced, um, you know, athletes seeing more type two fibers, uh, over time
1:01
So there's a couple of limitations here. One is that you're looking at a population that basically it doesn't move, right
1:09
And, uh, there's no movement, there's no innervation. So basically if you cut innervation off to a muscle, it will shift towards type two X
1:20
If you're a bird and you've casted its wing and it doesn't move for 16 weeks, you look 16 weeks later, that bird will have more type 2 fibers
1:29
Part of the reason for this is that when we look at muscle fiber compositions, what essentially you do is you take the muscle, you slice it in half, cross-sectional area, and you look at it under a microscope
1:40
Then what they do is they look at the coloration of it, and based on that coloration, they say whether a muscle is going to be type 2 or type 1, etc., etc., etc
1:50
uh, basically what they look for is the amount of, I think it's red blood cells, what they're
1:55
actually looking at in there. Uh, it might be disgusting, but if you look at like birds
1:59
for example, or sorry, uh, like Turkey that you eat, if you are talking about dark meat versus
2:04
white meat, white meat is going to be the fast twitch fiber. Dark meat is going to be the slow
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twitch fiber. And typically you're going to see higher amounts of fat in the slow twitch fiber
2:14
because it will be fueled for slow twitch type activity or endurance activity. You have
2:20
anaerobic or aerobic pathways fueling that muscle. I'm not going to get too much into energy systems
2:27
here, but that's part of the reason why it looks like a dark meat. And then if you're, you know
2:33
lighter, if your fiber type or your fiber under a microscope is white, that is a fast twitch fiber
2:39
And so those fibers obviously have different contractile times. You'll hear people say like
2:45
oh, they're quick twitch or fast twitch. Now I think it's started to shift a little bit more for
2:49
me in terms of like tendon properties being a big determinant and more so your nervous system
2:54
because again, what you're seeing is, uh, you might have to cover the mic because of the wind
3:00
just cover that. What you're seeing is the fibers, the muscle fibers are changing because there's no
3:05
innervation. So if you're not doing anything, literally nothing, I'm talking, you sit on your
3:11
for 16 weeks straight, then yes, you will have a shift towards Type 2X fibers
3:18
That said, when you're looking at fiber type composition and you're saying, well this is Type 2A or Type 2B
3:24
or Type 2X or Type 1A or B or Type 1X, there tons of hybrid fiber types because it doesn fall perfectly into fast twitch and slow twitch If you remove the nerve right the fiber will shift towards type 2x Because it not
3:43
the muscle's not being innervated, it will naturally shift. Our body's propensity is to
3:48
shift towards type 2x, which is a fast twitch fiber. But as soon as that nerve is re-innervated
3:54
and you use that muscle regularly, you will automatically default back to your set genetic
4:02
predisposed fiber type. And that's determined by the nerve fiber. So you technically couldn't do
4:08
this because you're not going to remove innervation from your brain or to the muscle and then reattach
4:13
it. That doesn't happen. We see something happen in research where they de-innervate it, where they
4:20
remove the nerve fiber and then they can cross innervate it. So you have like alpha motor units
4:24
which are type two motor units. Those are the big, strong, thick motor units. You can think
4:28
about like a thick fire hose. They're really effective at sending action potentials down them
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and getting these muscle contractions to happen. And when you de-innervate that and you put
4:40
something else in there, like a smaller nerve tissue, that's what determines the fiber type
4:45
It's not necessarily your fiber, your muscle fiber has a set, uh, you know, type and, and
4:52
that's what determines it. It's the, the use of it and the adaptation that happens that the body does over time
4:58
from that set innervation. So if you have, you know, the, the smaller innervation, it's not an alpha motor unit
5:05
and you don't have these big, big, uh, nerve fibers connecting to it, then it's going to
5:11
be type one. But if you have the alpha motor unit and these big nerve fibers, it's going to be type 2X
5:17
And so over time, by not using it, right, you're going to adapt to the imposed demand
5:23
And if you're not using a muscle fiber, right, then, or maybe a better way to say it is
5:29
as humans, we predominantly are using our slow twitch fibers. And that's according to the size principle
5:35
We recruit smaller, more efficient motor units more frequently. So if I go on a walk, if I pick something up, I don't need to recruit large motor units
5:44
I don't need to recruit type two fibers. But if I'm walking to my car and I'm opening the door, I need slower rates of force development, right
5:52
I need less force. And so as a result, those are going to default towards type one fibers
5:59
Now, as an athlete who's trained, what actually happens is your type two X moves to type two A
6:05
Type two A is less explosive than type two B. what you're really weighing here is is type 2a or type 2b a better and more forceful contraction
6:15
where you can generate more impulse on the ground or your lever system is more effective
6:19
than being casted for 16 weeks right because if isaiah were to let's say i casted isaiah's body
6:26
right his whole body and i was like now we're gonna have a type 2x shift right what's gonna
6:31
happen as soon as you're uncasted what would happen to your body if i did that like get hurt
6:36
trying to... Oh, you can pull your mic back up now. Oh, shoot. I'd get hurt trying to
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train and jump and all that stuff. What would happen to the size of the muscle, too
6:44
It'd be weak. Yeah, you'd have way less force. Your rate of force development might be crazy
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but your force output, your peak force would go to, like, zero. And so what you'll see some athletes do or coaches
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do is something called an overshoot, where basically they'll have insane, insane amounts of training, right
7:00
And then they'll just cut all the volume and do nothing for, like, two, three weeks
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This is kind of what happened with Jonathan Edwards And then what they do is they go back to their competition and you know they have these crazy performances You could do that technically And some coaches have tried to do it I tried to do it However what typically happens is they
7:20
pull a muscle or they'll get hurt, right? That's super common because the muscle's detrained at
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that point. It hasn't done anything. The connective tissue is now incredibly stiff and the muscle's
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weak. So when the connective tissue, your tendon's stiffer than the muscle, the muscle's going to pull
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or tear, the tendon will actually soften over time and its function drops as you don't use it
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That's why doing nothing when you're an athlete is really, or you have jumpers knee or Achilles
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tendonopathy is really bad because that weakens the tendon and your coordination is going to drop
7:48
right? You're not doing the activity you want to get better at. Let's say it is 16 weeks. I mean, even two weeks could be, you know, kind of a detriment, but we don't even know what the
7:57
timelines are. And we haven't really looked at long-term research and elite athletes to
8:02
to see because most athletes aren't going to sign up to have, you know, their body put in a full
8:06
body cast or cast it and then go out and compete. That's just not going to happen. We know that this
8:11
happens in rats. We see it happen in birds. Um, they've seen it happen in paraplegics or
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tetraplegics. They have more type two fiber than anyone else. Right. But their muscles are
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incredibly atrophied. The, the peak force they can generate is way less. Right. And so, yeah
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maybe hypothetically it is really twitchy, but there's a lot of other implications that come
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along with that. So when I said on the podcast the other day, you can't change the amount or
8:35
number, or you can't see a fiber type shift. That's because the fiber type is determined by
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your nervous system and your nervous system is going to be determined by largely your genetics
8:45
You're not going to change the number of type one or type two fibers, uh, or sorry, the motor
8:51
the type of motor unit that you have that's genetically predisposed. So you can train the
8:56
muscle by taking advantage of something like the size principle or rate coding where your nervous
9:01
system is upregulated to a high degree and you're doing a lot of explosive movements and you can
9:05
train the muscle to act more like a type 2 fiber you can train a type 1 fiber to act more like a
9:11
type 2 fiber but as soon as you detrain or you go the other direction like let's say uh i stopped
9:18
training completely and i was a normal human not casted i'm gonna go back to my type 1 fiber
9:23
activity if I'm sedentary. And actually Ben Moxness posted about this. Werner Gunther was
9:28
a shot put thrower. They saw this happen with him. He had more cross-sectional area of type 2 fibers
9:34
but as soon as he reverted back to his everyday life, and he had a brother actually as well that
9:39
they looked at, they found that, hey, he just has type 1 fiber again. Like he goes back to the same
9:45
cross-sectional area of type 1 fiber. So you detrain back to homeostasis, like your baseline
9:49
right? Or I guess it would be homeostasis. The training over years and years and years is what
9:54
allows you to be a better athlete. That's what allows you to improve your output. So can you have
10:02
a fiber type shift? Yes. Can you have a fiber type shift and improve your athleticism over time
10:09
No, you would have more cross-sectional area of those bigger type two fibers, right? But you're
10:15
not going to have your type 1 fibers turn into type 2 fibers because you're not a paraplegic
10:21
basically right or a tetraplegic you're using those muscles regularly so that's kind of the
10:26
maybe more of an explanation to what i said the other day i know again a lot of not a lot of people
10:32
but some people were bringing up kind of counter arguments so what do you what is your lens on that
10:36
do you have any anything you'd like to share anything you'd like to say about that i mean i think that at the end of the day it comes down to you know what makes you jump higher That true And doing nothing does doing nothing make you jump higher No
10:50
Doing nothing does not make you jump higher. And it also makes you have a higher intensity to get hurt
10:56
I mean, there was a period of time you didn't jump or you didn't lift at all, right
11:00
Yeah. So you really didn't do anything other than jump. And what happened? Yeah, I was jumping like three times a week on average for a whole year without training
11:07
and I jumped lower and got more injured. Right. And I think this is also something interesting
11:13
I probably had higher fast. You might have had more fast-rich fibers
11:18
Yeah, because I wasn't doing anything aside from – I mean, I was actually – I was working. I was on my feet all day, so maybe I didn't
11:23
But I've had periods of time where I've done nothing and I don't jump as high as when I do stuff
11:31
Yeah, yeah. I will say there was one interesting scenario where I had a high ankle sprain in high school
11:35
and I didn't do anything for like three or four weeks after training for like six months. I think I took a month off and I jumped high as shit, like really, really high
11:44
That was like when I PR'd my high jump. But it's safe. Didn't it happen to Donovan Hawkins too
11:49
Donovan has it happen too. Yeah, he takes off like a month or two months at a time
11:54
His vertical goes to shit during the year and then he just trains like once every seven days or something like that in the weight room
12:00
Or no, maybe it's one week out of every four or five weeks he trains and then his vertical is sustained basically it can sustain the vertical and health um so it is
12:09
possible to maybe take advantage of some of those mechanisms but typically you have to be working
12:15
with someone that knows from experience how their body responds right they know that if they don't
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jump for a period of time or sorry don't lift for a period of time that they will maybe have this
12:27
overshoot mechanism happen i don't think it happens for everyone i remember before dunk league season
12:32
two chris stable said he had to dunk for like two weeks straight or something like that he went off
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right he went off yeah highest i've ever seen a jump so it's it's possible these genetic genetic
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freaks they have these fiber type shifts towards type 2 a or whatever and then if they don't do a
12:48
lit like their volume drops a little bit they're not necessarily in a cast that or they're not
12:52
lifting or anything they start to see more of a shift towards their default which is type 2 x right
12:59
But if you're not a genetic freak and you're more type one like me, like if I'm living my everyday life, I'm going to default to type type one
13:07
You know, and I think at the time I'd been training for a lot, a lot, a lot
13:11
It's possible it was just I don't have as much fatigue. Right. My body feels better. You know, I had other issues pop up as a result from not training because my body was detrained at that point
13:22
Right. Even if my rate of force development was higher, et cetera, there were other issues that arise
13:26
And maybe that's another another point. Right. Your transmission's not good. Your engine might be big, but you can't handle that power anymore
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Your wheels can't put the power down. You can't steer. You can't whatever the issue is as an athlete from doing nothing
13:41
Maybe you're fat. Maybe you just get fat, and that's also another thing
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Also, I heard you're a big proponent on athletes not being fat
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What did you tell the people the other day? If you can't see your abs, you're leaving gains on the table
13:56
I can't see. Well, you're leaving vertical jump inches. Yeah. Yeah. Anyways, yeah, that's pretty much
14:03
Do you have any other anecdotes? Anything else you wanted to mention? I don't know. I think that's pretty good
14:07
Yeah, let's go train. I've had a day. He's had a day
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He's dying. You want some caffeine? I can't drink caffeine. How about a trap slap
14:16
No. I'll be fine. All right. See you guys
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