Amy Hudson and Dr. James Fisher explore the difference between type one and type two muscle fibers—why they matter, how they function, and how to train them effectively. They discuss why neglecting type two fibers can lead to rapid muscle loss and how simple strength exercises can make a huge difference in keeping you strong, mobile, and functional for life. 

Join us to hear ways a sedentary lifestyle weakens type two muscle fibers and how small changes in your workouts can have a huge impact on your long-term health.

• What are type one and type two muscle fibers, and why does it matter? Dr. Fisher explains that type one fibers are built for endurance, while type two fibers generate explosive power—think marathon runners versus sprinters or powerlifters.
• Dr. Fisher dives deeper into why we shouldn’t think of our bodies as purely type one or type two. While genetics play a role, the way we train determines how these fibers develop and function over time.
• The Size Principle explains how our bodies recruit muscle fibers based on demand. 
• If we only perform light movements, we activate type one fibers, but if we never lift heavy, we neglect type two—leading to faster muscle decline as we age.
• Amy asks whether someone could go decades only recruiting type one fibers. Dr. Fisher says this is a common issue, especially for sedentary individuals like office workers who don’t challenge their muscles regularly.
• According to Amy, the problem with neglecting type two muscle fibers is that they’re the ones that decline the fastest with age. 
• If we spend our 30s, 40s, and beyond avoiding high-effort exercise, we’ll lose strength rapidly, making everyday tasks harder over time.
• Amy points out that as we age, our exercise approach has to evolve. What worked in our 20s might not be enough to maintain type two muscle fibers in our 40s, 50s, and beyond.
• So how do we train type two fibers? Dr. Fisher emphasizes that you don’t need to lift extremely heavy weights. The key is engaging in strength training with sufficient intensity to activate those fibers.
• Having a personal trainer overseeing your workouts can go a long way in ensuring you’re training with sufficient enough intensity. 
• For Amy, the difference between recruiting type one and type two fibers comes down to duration and intensity. 
• For older adults who haven’t exercised in years, strength training is a game-changer. 
• Dr. Fisher explains that if the choice is between walking for 20 minutes or strength training for 10 minutes, the latter offers significantly more benefits for health and longevity.
• Resistance is your ally—when applied safely and at the right intensity, it triggers type two muscle fibers and helps us maintain strength as we age.
• Amy and Dr. Fisher agree that maintaining muscle is about more than just fitness—it’s about preserving independence and quality of life. 
• Dr. Fisher introduces the concept of concentric and eccentric muscle actions, explaining how both play a role in muscle development. The eccentric phase—where the muscle lengthens under tension—may be particularly effective for type two fiber recruitment.
• He highlights the benefits of exerbotic devices, like those used in The Exercise Coach, which provide more resistance during the eccentric phase.
• Amy talks about the future of fitness, and how embracing resistance training—especially with innovative tools—will be key to staying strong and functional for life.

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Resistance is our friend, especially if we can have that in a safe way.

Those type 1 muscle fibers will fatigue and I will need to recruit those type 2 muscle fibers.

As we age, we have to exercise differently to maintain our type 2 muscle fibers that we’re losing behind the scenes. Welcome to the Strength Changes Everything podcast, where we introduce you to the information, latest research, and tools that will enable you to live a strong, healthy life. On this podcast, we will also answer your questions about strength, health, and wellbeing.

I’m Amy Hudson. I own and operate three exercise coach studios. My co-hosts are Brian Saigon, co-founder and CEO of The Exercise Coach, and Dr. James Fisher, leading researcher in evidence-based strength training. And now for today’s episode.

Welcome back to the podcast. Today we are talking about muscle fibers. Did you know that you have two types, main types of muscle fibers, type 1 and type 2? Do you know the difference and what they mean for you and how training them impacts your mobility and your strength? Today we’re going to learn all about that and we’re going to learn why it’s important to pay attention to both of these types of muscle fibers for your everyday life. Dr. Fisher’s with me. How are you, Dr. Fisher? Dr. Fisher I’m doing great. Thank you, Amy. How are you doing? Dr. Amy Kendall I’m doing well. I’m doing well. All right. So type one and type two muscle fibers.

What are they? What is the difference between these two types of muscle fibers?

Dr. Richard Diller Yeah. really think of type 1 and type 2. We can actually split them down a bit further than that but we generally think of type 1 and type 2. And probably the easiest way to think of them is somebody like an endurance athlete, like a marathon runner, might be more dominantly type 1. So type 1 muscle fibers are what’s called oxidative. They recover based on oxygen. So we use them when we’re doing aerobic exercise. as we breathe in and out those type one muscle fibers are effectively able to recover and be reused. They’re quite fatigue resistant so they’re able to contract and then recontract or sustain a prolonged contraction and so forth. So they’re pretty good, they’re pretty beneficial from that point of view. The downside is they can’t produce a huge amount of force. So then we’ve switched to type 2 muscle fibers and we should think about type 2 muscle fibers in context of our sprinter, our Usain Bolt kind of sprinter, who is very, very fast but only fast for less than 10 seconds, you know, nine and a half seconds. Or our powerlifter or our weightlifter who can lift a very heavy weight but can only lift it once and then needs a degree of time to recover. And type 2 muscle fibers are not very fatigue resistant. They will fatigue quickly but they can produce a high amount of force. Now we shouldn’t think of our body as being solely type 1 or type 2. Some people will be more dominantly type 1 and or type 2 and some muscles might even be more dominantly type 1 or type 2 depending on the muscles themselves. So for example our postural muscles like our lumbar extensors and the muscles of our trunk and our torso will be predominantly type 1 muscle fiber because they need to hold us up for prolonged periods but they don’t need to produce a huge amount of force. Whereas let’s say our gastrocnemius in the calf muscle, our major calf muscle, might be more dominantly type 2 or have a higher percentage of type two muscle fibers because they produce that force when we run or when we jump or things like that.

Okay.

So just to summarize type one muscle fibers are, they can produce a pretty low amount of, of force for a long period of time. One example we could give is type one muscle fibers are the ones responsible for us being able to stand up, walk around, you know, walk around the lake, get in and out of the car, everyday tasks. Type two muscle fibers are the type that are related to our strength and our ability to lift something heavy and run quickly. So stamina, force producing, but they can only do so for a shorter amount of time. Is that a good summary?

Yeah, that’s a great summary. And in fact, you transitioned into what we call the size principle. So when we first do any exercise, our body will only recruit the muscle fibers that it needs to do that exercise. So if, for example, I pick up a pen, then I won’t recruit type two muscle fibers to pick up that pen, then I won’t recruit type 2 muscle fibers to pick up that pen, I will recruit type 1 muscle fibers because the pen is very very light so it doesn’t require much force. So we kind of keep type 2 muscle fibers in reserve if we can. And this is a really interesting point because if we do generally low intensity activity, then we will recruit and re-recruit those type 1 muscle fibers, which is great. But if we never move into that higher end intensity, then we won’t recruit and we won’t retain those type 2 muscle fibers. And our big problem is that it’s the type two muscle fibers that are the ones that are characterized by a declining strength and functionality as we age.

So they’re the ones that we should be trying to look after. And they’re the ones that we lose. The earliest.

Okay.

So this is a really important point. Could somebody in theory spend decades of their life only or primarily recruiting type one muscle fibers because of the exercises that they’re doing?

Yeah, absolutely. So your typical, let’s say your typical couch potato who works a desk job, has very low intensity exercise. You know, they might not even have comorbidities. They might not be overweight or they might not even have comorbidities, they might not be overweight or they might not have diabetes, but they generally don’t do any heavy lifting or any hard exercise. They will only be recruiting and re-recruiting those type 1 muscle fibers and they will certainly have a low size and a low proportion of type 2 muscle fibers and that will be, that will be to their detriment as they age, because they will lose whatever type two muscle fibers they have as they age. Um, and that will, that will be a combined with a loss of strength and a loss of functionality and quality of life, to be honest.

Mm-hmm.

Yeah.

So this is not what we want. We don’t want to spend our thirties,s, 50s, 60s only doing light exercise and never tapping into our type 2 muscle fibers because we’re going to be losing strength at did when we were younger in order to maintain our type two muscle fibers that we’re losing behind the scenes. Right. So how do we train type two muscle fibers and what does that mean for the way somebody needs to exercise to maintain fitness and strength after age 40?

Let’s say.

Yeah.

Well, so you, you raise a really interesting point that maybe we should change the way we train as we age. I would actually say that even when we’re younger, we can engage in this type of training because it helps to build up that reserve. Um, and of course, what we’re talking about here is strength training. We’re talking about high intensity exercise or higher intensity exercise.

So we talked about the size principle where I only recruit type 1 muscle fibers if the weight is light. Now it doesn’t mean that we need to lift a very heavy weight to recruit those type 2 muscle fibers but what generally happens is as I perform a certain number of repetitions with a weight, eventually those type 1 muscle fibers will fatigue and I will need to recruit those type 2 muscle fibers. So they’re often called low threshold and high threshold and what that means is it’s the stimulus that’s sent from our brain passing through our motor unit. So our motor unit is low threshold for type one muscle fibers. And that basically means that it can only be a small impulse sent from our brain. So if it feels easy, then it’s probably type one, it’s low threshold. But as the work gets harder, so maybe it’s now more repetitions with a weight, or maybe it’s a heavier weight. And it can be any weight. It can be lifting a dumbbell or a barbell or lifting a heavy bag of cat food or pet food out of the trunk of a car or lifting a grandkid. Then we’ve started to recruit those high threshold. We send a bigger impulse. It’s a high threshold to recruit those type two muscle fibers.

But of course, the easiest way to do this is through engaging in strength training. And you’ve said obviously changing the way we train in our 40s, 50s and 60s. But actually, if we begin our strength training earlier, then we build up this reserve of type 2 muscle fibers. And I would even go so far as to say that the type two muscle fibers are the ones that are most responsive to a change in muscle size. So actually anybody who’s young and looking to build bigger muscles or anybody who’s older and looking to build bigger muscles really wants to to be training a sufficiently high intensity that they’re recruiting and building those type 2 muscle fibers. Absolutely. Now if you’re 60 years old and it’s been two decades since you’ve really actively exercised, we just want to make the case that if you’re going to choose between walking a mile or engaging in strength training in terms of your muscles, what’s more beneficial. Strength training is going to be the way to get there, you know, much faster.

But one analogy about this too, Dr. Fisher, that we’ve used, especially in our studios, is even walking versus sprinting. You know, when we walk, we’re using type 1 muscle fibers, but we will not fatigue that fast. We can walk a long ways as human beings. I mean, our ancestors could walk hours and hours and hours all day. People hike across different, you know, like long paths and things like that in different parts of the world a whole day or more without really fatiguing and dropping to the ground. But if I asked you to sprint, there’s only so far you can sprint before you will fatigue. And that is the difference between recruiting type 1 and type 2 muscle. We’re not able to recruit type 2 as long, but it’s very effective because when we can recruit those type 2 muscles and activate them that’s where our strength builds up so fast and our stamina builds up so fast. So at an exercise coach studio in our concentrated cardio it’s short because it’s focused on interval training that is bursts of effort with resistance which is similar to sprinting versus a steady lower effort, cardiovascular that would take longer to fatigue you.

Right. Right.

And those are great examples. And, and it’s, and it’s, it’s even pragmatic to think about the duration of the exercise and even the intensity might be whether I can continue a conversation. So if you go for a light run and you can continue a conversation with the person next to you, then you’re only working aerobically. So you’re working with oxygen coming into the body and carbon dioxide being breathed out. But if you’re working aerobically, then you’re probably dominantly recruiting type one muscle fibers. There will be some type two involved. It’s not a switch. It doesn’t just suddenly happen that you are only type one or type two. Um, in recruitment, there can be a higher proportion of one or the other.

Um, but certainly if your exercise is a prolonged duration or is of a low enough intensity, then you’re only really using the type one. You’re certainly not doing enough to recruit and retain those type two. And therefore, yeah, absolutely. For an older person who’s maybe not engaged in strength training for 20 years or high effort exercise, then yeah, the choice between walking for 20 minutes, strength training for 10 minutes is a real no brainer. Strength training for 10 minutes is going to do infinitely more for their health and their quality of life and their functionality than walking for 10 minutes. One of the things that I often see is people engaging in aqua aerobics classes. And I don’t want to discourage people from doing different modalities of exercise. And I love the social element of these older people going in the pool and doing these aquaerobics kind of dance moves and so forth. But one of the big problems is that they’ve unloaded their bones and their muscles.

So there’s actually lower recruitment than there would be if they were doing it on dry land. So if you’re on dry land dancing or moving around, at least there’s a higher degree of recruitment and a higher degree of loading in the skeletal structure. And they’ve got in a pool and they’re unloading their bones and their muscles even more.

So it’s even more concerning for me watching these people doing this activity, that’s great from a social perspective, but certainly not as beneficial as it could be from a strength and a wellbeing perspective.

Absolutely.

Yeah. So the key is, is resistance is our friend, especially if we can have that in a safe way to load our muscles and resist at the appropriate level of intensity so that we can activate those type two muscle fibers and get stronger. And so if we’re aging, we really do need to care about these type 2 muscle fibers because they are the ones responsible for our strength. And this podcast, and Dr. Fisher just mentioned, is called Strength Changes Everything, right? Because there are so many implications of maintaining our strength as we get older, more than we can even cover on this one episode. Yeah, and so let’s move on a little bit because there’s something else really interesting when we talk about different muscle fibers. And when we consider just a normal exercise in strength training, there’s typically two types of muscle action. There’s a concentric muscle action where we lift the weight or an eccentric muscle action when we lower the weight. So if you’re in a traditional gym and you do a chest press then the pressing away of the weight or when your arms straighten that would be the concentric phase and then when your arms come back towards you and you’re lowering the weight back down that’s the eccentric phase or the eccentric muscle action. A lot of muscles shorten in the concentric and they lengthen in the eccentric phases respectively. Now, one of the great things about the exerbotics devices within the exercise coach is there’s the capacity to overload the eccentric phase of the exercise. So that means that the motor can actually give you more resistance in lowering the weight compared to lifting the weight. Now obviously there isn’t a weight stack on the exerbotics devices. But the reason that this is important is because recently the researchers started to suggest that there’s actually preferential recruitment of type 2 muscle fibers in that eccentric phase. So when we’re lowering the weight and when we’re pressing against resistance that’s coming down on us, whether it’s a leg press coming back towards us or a chest press coming back towards us, then we can use more dominantly our type 2 muscle fibers in that phase of the exercise. And of course, exerbotics where that extra resistance can be added, that’s even more beneficial. So a good way to think about this is when you go into a traditional gym and you lift a hundred pounds in an exercise, the weight stack shows a traditional gym and you lift 100 pounds in an exercise, the weight stack shows 100 pounds and you lift it and it’s at best 100 pounds on the way up, but it’s still 100 pounds on the way down. Whereas when you get on an exerbotics device, it will match your force on the way out, on the concentric phase.

So it might vary between 90 and 110 pounds depending on how strong you are throughout the movement but now it can jump up in the eccentric phase and we’re actually 40% stronger in the eccentric phase compared to the concentric phase. So now the weight can suddenly jump up to 150 pounds on the way back and we can press against it and that’s serving to really recruit those type 2 muscle fibers that we want to recruit for our longevity, for our health, our well-being and they’re the ones that we lose as we age. So they’re the ones that we want to recruit more favorably and as I said there’s a preferential recruitment in that eccentric muscle action.

And this is so great. And one thing we love to see when we we can point this out to clients in that example, you just described is after an exercise set with our robotics technology. I can see what I did and my performance on the screen in front of me and it will actually break down my concentric average effort and my eccentric average effort and it’s really cool to to see some of those exercises where I was almost 40% stronger let’s say in my eccentric my concentric graph is this high but then my eccentric is up here because I was really able to give more and what that simply means is I’m accomplishing so much more faster by giving what I can every single second of that exercise, which is why the results that come, come so quickly when we’re able to do this so effectively and maximize what we’re giving every single second.

Yeah.

Yeah.

So of course, and this, this improves the efficiency of the exercise because the concentric component is optimized because of the resistance, the exercise because the concentric component is optimized because of the resistance. The resistance matches your effort level. So you don’t have to worry that you’ve put on a hundred pounds, but today you’re having a great day, so a hundred pounds feels really light.

Or you don’t have to worry that you’ve put on a hundred pounds and a hundred pounds feels really hard, so today I can only get one or two reps with it. We know that the resistance matches your strength. So there’s this incredible efficiency in what’s happening with the exobotics devices. And it’s something that I could really go on about from a biomechanical perspective. But the other thing that we can think about is that the eccentric component of a muscle action, and I’m going to labor the point with this now, Amy, so bear with me, but the eccentric component of a muscle action, or the eccentric muscle action I should say, is also linked to different myokine release. So in the podcast previously, we’ve talked about myokines, and we’ve had a couple of questions about these, so we’re going to do a full podcast that’s going to talk in detail about myokines. But we know that in different muscle actions, the muscle sends off these signaling proteins around the body. And we know that in the eccentric muscle action or in a forced eccentric muscle action, so the weight’s coming down and you’re pushing against it, then you release what’s called interleukin 6 or IL-6. And this is one of the main myokines that we know about. So it’s an anti-inflammatory myokine. So we talk about inflammation around the whole body and this can obviously serve to combat that but it can also enhance insulin sensitivity and then it also plays a key role in what’s called satellite cell multiplication and that’s for muscular growth and muscular hypertrophy. So there’s just a win-win-win from this point of view. So you train in this way, you get this eccentric component which helps you recruit type 2 muscle fibers more favorably and they help you age better and have a better strength and a better functionality and quality of life as you age. But then they also, this muscle action also serves to release interleukin-6 which is a myokine that can really positively impact our insulin sensitivity and anti-inflammatory properties. But it also stimulates greater muscle growth as well. So if you’re young looking to get bigger muscles it’s great and if you’re just looking for the health benefit in myokines then it’s great and if you’re older and looking to hang on to every type 2 muscle fiber you can and retain or recover any strength that you might have lost then it’s great as well. So we just can’t undersell the benefit and the importance of this kind of eccentric training with exerbotics devices and that’s really the differentiator compared to a traditional weight stack machine. It is super cool. We call it the future of fitness. It is truly remarkable and it is the best way to experience all of the benefits that Dr. Fisher just mentioned. It’s very exciting and it’s only available at the exercise coach. If you’ve never tried it, you have to try it. You have to come experience it. While you’ve made a compelling case, Dr. Fisher, for the E-Centered training and all of the ways that it’s benefiting us and tapping into those type 2s.

Do you have any other closing thoughts that you want to leave us with?

No, not at all. I would love to see more people engaging in strength training however they do that, but I definitely think there’s a greater benefit and efficiency with the use of the exerbotics devices at the exercise coach. Couldn’t agree more. All right, we will see you next week.

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