Why Running Is Killing Your Strength Gains

Added: 2026-06-04

[00:00:00]Okay, Dr. Kramer, one of the first things that I wanted to ask you is actually based off of one of your earliest research papers. And it's where you were researching military cadets, if I remember correctly. And this is back in the late '80s, and I think it was released in the early '90s. I'm just jogging my memory right now, but we're going through this, and you're looking at cadets who were running and cadets that were also lifting and running at the same time. And my big thing is, somebody who does like to run and lift, what were the interference effects that you saw from this? What were all the big takeaways? What are things that we could apply? And how could we look at this paper? Can you walk us through this paper and and let us know exactly what you found out from this really, really cool research?

[00:00:45]Yeah, well, it's a great question. Uh we we were interested in that in the military, and I was utilizing uh soldiers from the 101st and and 82nd Airborne groups. So, they were fit uh fit uh men, and uh we we we were actually interested in it because there had been a study early on about uh you know, compatibility of exercise protocols that that that was done by uh hit Bob Hickson at University of Chicago, I believe, in the year 1980-81. And and there was by the certain period of time, the group that was doing both actually went down in their performance capabilities. So, we knew that the military at the time when we did this study, which was the early '80s, uh you know, we published it years later, but it was really in the early '80s that, you know, military training was predominantly running.

[00:01:43]And one of the roles I had as a captain in the US Army was to look at soldier fitness and help develop that whole phenomenon during my active duty uh work as a as a captain in the US Army.

[00:01:58]So, we we wanted to understand that. So, what we did was we kind of took the cue that Dr. Hickson had shown that that realistically many times it could be the fact that it's a type of overtraining.

[00:02:11]You just got too doing too much to really manage the uh the different stimuli, etc. So, what we did in this in this particular study is that we decided to use what would be a manageable uh program where we lifted you know we we we trained 4 days a week, Monday and Tuesday and then Thursday and Friday with a Wednesday rest day up at the USARIEM at the Natick Labs that I was stationed at.

[00:02:39]So, we had really an ideal uh situation cuz all of our all of our war fighters were there uh and they were stationed there, so we could pretty much control things to try to get a feel for it. So, essentially if I if I remember right, what we did was we typically would run in the morning and then and then lift in in the afternoon uh each day. And we we made we had different type of the different groups, too. So, we had one group that did the everything. They did the running and lifting they they did everything, the total programs on on the 4-day week. We had another group that just did the running portion.

[00:03:21]So, they did all the all the running and I'll get into that in a minute. All the running.

[00:03:26]And then we had an another group that just did you know upper body lifting and and and and and running. So, that it was very common for a lot of guys just to do upper body lifting and no no lifting on the bottom lower body and we we wanted to see that.

[00:03:43]And then we had another group that that did pure lifting, no running at all.

[00:03:48]Um you know, and that's really the kind of the the way we looked at it. So, what we did with the workouts is that on on Mondays, uh the the weight training workout was a strength training workout.

[00:04:01]So, those who basically they did heavy loading, you know, in the you know, three to five, eight, they were in the in the heavy loading uh with regard to the rep zone. Uh So, they were doing the heavy lifting on Mondays, and then on on Tuesdays, the the the lifting in the morning was really more of a a type of we called at the time a bodybuilding.

[00:04:24]Really, you kind of took it from what we did with bodybuilders in the cut phase, where you would do uh you know, moderate lifting, you know, eight to 10, and you would be then doing short rest, you know, two minutes or whatever between sets and uh you know, going from there.

[00:04:40]Whereas, you know, where So, you were really doing, you know, short rest type of workouts, and you had some supersets in there, etc. Wednesday they they rested, and then what happened on on on Thursday and Friday, we repeated the Monday and Tuesday workouts.

[00:04:55]The run training was done on on on on Monday, when they were doing the strength workout, the the morning uh running was in fact the very much of an interval training program. So, we did we did we went to the track uh in nearby Natick, and we did we did interval training. We did interval training on the track, you know, anywhere from 100 to 200 m.

[00:05:20]We were doing uh intervals, and uh high intensity intervals, you know, what's called hit training now, okay?

[00:05:27]And then on on that on that um Tuesday, the the morning was a long distance run at about 85%, you know, we would run for 30, 40 minutes at, you know, pretty much 85% of the max. So, it's a it was a it was a relatively high intensity run that they'd been used to from all the two-mile training they did because the army at the time was testing for two-mile run and this type of thing. And so that's what we had. So we had we had really kind of what I customized as a um uh a type of protocol that could be utilized if in fact whatever we learned from it. I didn't want to be random and it was very organized. Everything was um you know, actually um you know, validated and we had all of our training coaches there that I had in my in my group in my platoon and and and we ran a really probably one of the best studies that in my career uh that I've ever done.

[00:06:27]Unfortunately, there's a mistake in one of the in one of the tables in the publication but uh here and well, that's the study we did. So you know, there was a combination of uh people that were already, you know, probably aerobically fit. You don't get into the airborne groups unless you're aerobically fit. And they had, you know, some background uh but weren't highly weight trained at at that time because weight training wasn't some That's something that would my goal I was given the the role of having to uh promote resistance training in the military uh at that time and as a part of soldier fitness because there was a big need for that for a lot of different reasons uh for adaptations related to uh functionality etc. We know more about that today but at the time that's kind of what we had going on. So what was interesting was the compatibility question. What what happens, you know, when you do both types of training protocols together and you're doing everything.

[00:07:29]Remember, our podcast is sponsored by our own strength training app, Peak Strength. If you're a football player, a basketball player, a baseball player, click that first link in the description. Head over to peakstrength.app. Go to the Google Play Store or you can go to the Apple iOS Store. Download Peak Strength, put your email in, and then look for your specific sport. If you're tired of doing a lot of work and not really getting anywhere, we want you guys to get to the next level. All you have to do is download Peak Strength, and then submit your email, click on the specific sport, and when you sign up for 1 full year, you're going to get 38% off. And I'm going to challenge you right now. I'm going to give you this challenge. If you sign up for 1 year, imagine where you're going to be 1 year from today if you're training 3 to 4 days a week. Imagine where you'll be focusing on the things that actually matter. 1 year from today.

[00:08:20]All you have to do is head over to peakstrength.app, Google Play Store, or the Apple iOS Store. Start committing to yourself. Now, let's get back to the podcast. And we were doing it at relatively, you know, relatively high you know, demanding workouts. So, it wasn't like we we we were really We were resting on Wednesday and the weekend.

[00:08:40]So, that that wasn't a problem. You know, some athletes today, they don't know what a day of rest means.

[00:08:45]But, I think from the standpoint of what we found was the biggest discovery that we found was we did muscle biopsies, and we wanted to see well, what happens to the the the muscle fibers when in fact they are having to deal with recruitment to do the both types of things or just in singularity or both types of things.

[00:09:11]And what we found that had been, you know, at the time was a little controversial and then other people devalidated it with animal studies and everything else. It turned out we were we were really right. We had a great group, and I have I was very thankful for the late Digby Dudley at University was at University of Georgia and and basically at at Ohio University rather. And then also the my good friend Bob Staron who really put our histochemical technology and the assays in the highest level. And it was so the the the data from that was really amazing with regard to the people that we I worked with to make sure we had all the biopsy analysis and the histochemistry all done right.

[00:09:59]So what what we found was really we kind of fascinating. We found something that that people don't think about often but that if you remember that the it's the size principle that's so important to to functionality of mean Vladimir Zatsiorsky and I talked about this a lot.

[00:10:18]You know Henneman's whole lifetime was looking at how size principle recruitment on demands of the of the activity was really basing basically telling you what you get when you do a workout. And I I thought this is really interesting and we knew that the demands would be quite different but in some cases you'd have fibers that would be doing both. And if you look at if you look at size principle when you have a particular demand what happens is that activation of muscle is an electrical phenomenon and that's where you have the you know the the threshold for all or none recruitment of a particular motor unit. That's a hertz. That's that's an electrical signal that basically comes out. So the the higher you go in the from low to high in the array of motor units you have in your body the higher force production is a higher hertz versus lower force production like running maybe has a little bit lower hertz depending upon its intensity and and what your motor unit configuration is.

[00:11:26]So what we were very interested in was what happened to the fiber uh sizes because, you know, obviously hypertrophy of the fibers are one of the main objective of understanding, you know, adaptation size changes.

[00:11:43]And what we found was really interesting. Uh you know, it it was a fact that when we did the the guys who just ran alone, didn't do any lifting, all they did was just run.

[00:11:56]What we found was, if you think about it, they're not recruiting even with the interval training, which surprised us, they're not recruiting that many high threshold motor units and there's not in in in guys that are relatively fit to begin with, there's really no hypertrophy that occurs, you know, and you'll hear a lot of different people, you know, if you're out of shape and you're you're you're so out of shape, you're you know, we we call a couch potato, maybe you get some stimulus to change some of the constant the size, but in this group, what we found was interesting.

[00:12:29]The in that group, we were the first to show that heavy-duty oxidative challenges, the aerobic stress of intervals and high-intensity long-distance running, it really caused the type one fibers, the slow-twitch fibers early in the recruitment phase, to get smaller. And we go, wow, this you know, we did it we looked at it over and over and we you know, the the fibers are actually getting smaller.

[00:12:55]And and and and that we figured after a lot of thinking about it looking at the data for a long time and finally getting approval to publish it years later, we found out that oxidative stress, we knew from work that was done by Mike you know, Shane's later on, that there's really it's really obviously thing important that fact that the distance that oxygen has to travel, if you reduce the size of the type one fiber, all the transport distances for the mitochondria that worms now we know worms through the muscle is basically shorter. You have more you have more capillary capillarization of that of that fiber and it's made to produce, you know, it's made to produce optimal oxygenation of the of the fibers that are that are actually working primarily just to produce endurance capacity and that's that's what we now know happened.

[00:13:57]So, you got a you got a reduction in type one fiber size in the low threshold motor units, the type one fibers.

[00:14:05]Nothing happened to the type two fibers because they're just sitting around uh doing nothing, you know? So, if you just go out do running even sprinting, your high threshold muscle motor units and muscle fibers, the type two fibers, they don't do anything. So, they didn't decrease in size, they didn't increase in size. It's just the These are the vastus lateralis muscle we're talking about just to be specific. This is the leg muscle. So, they were they were basically doing really nothing and uh nothing happened. So, that that's what we found. Now, when we if we go to the other extreme and we say, "Okay, well, what about the guys that did all the lifting only?"

[00:14:45]Okay, they just lifted.

[00:14:47]And what we found there was kind of what we expected when you have that high hertz to get at those high threshold motor units with heavy loading, you got to go up the ladder, okay? You got to go up the ladder from low to high recruitment. And what happened was the the the the the muscle size increased across the board with regard to the type one and the type two muscle fibers.

[00:15:12]Everything got bigger and uh they increased in size and this is over uh you know, a three-month workout, three months of workout, 36 workouts. So, and you know, pretty like I said, pretty pretty well structured and intense volume-wise and everything we knew at the time.

[00:15:32]And so, it it basically they all got bigger. Okay, now that shows that hey, the type one fibers got bigger, too. And they don't like to get big. By the way, we learned often is that the type one fibers fight getting big for the same reason that they shrunk in the in the high-intensity endurance guys because they they want to optimize oxygen kinetics and and movement patterns and distances. So, they optimize oxygen capabilities. They they don't like to get big. But, they got they increased in size and that that's very regular and found and nothing surprises us there.

[00:16:10]And and that's the two extremes. So, then we said, "Well, what about the the group that that did uh what about the group that just lifted upper body?" I'll take that one next. They They didn't do any uh lower body uh you know, lifting at all.

[00:16:28]And what happened there? Well, obviously, you know, we did all strength tests. Obviously, if you trained a muscle, it got stronger, more more, you know, this type of thing. But, what happened there was the fact that that that those leg muscles did something interesting because when you do upper body exercise, you stabilize yourself a lot, right? You're sitting there and you're using your your thighs, you're doing isometric holds, you know.

[00:16:54]So, nothing happened to the type to the type one fibers or the type two fibers except the fact that they they basically in the in the thighs, they didn't see any decrease due to the aerobic endurance factors that that went on. So, they they basically that that isometric stabilization and the different things you do when you're doing a variety of upper body lifts, you know, cause the them it to nullify the reduction in the size of the fibers when you're just doing pure high-intensity aerobic training.

[00:17:29]And and it went from there. So then we finally got to the uh we finally got to the the combination group that did that did everything. And we we just review we just remembered we we we we saw the different responses. So well what what's going to happen? Well, what happened is that the the the the dual training in our study found that in these relatively fit guys, they found that the type one fibers didn't get big at all.

[00:18:01]Remember in the weight training only group the type one fibers got big. They increased in size. They had increase in mass. The type two fibers got big. So, you know, it it basically what we found is compatibility goes to those fibers especially the aerobic fibers that are trying to do both because they have to they have to be recruited for both. So, we now know that that basically if you're trying to gain size and you're doing a lot of a lot of high-intensity aerobic running uh simultaneously and you're you're kind of going to nullify size gains gains in in size for your for a lot of your motor units that are the type one in the lower threshold.

[00:18:47]So, that that was the interesting thing we found.

[00:18:52]You know, we we found also that that power output in the combined group was also not as good as as it was in the only lifting group. So, it you know, power can be and and Gary Dudley the late Gary Dudley found that with his isokinetic work, you know, later and and basically um we found that. Now, if you look at John McCarthy, who was at Wisconsin at the time, did a similar study with kind of average, you know, people that were just going for fitness things. He didn't have the same He went with a 3-day week program, and he didn't find any incompatibility uh because of the fact that he backed off on the prescriptions, where we were going with full bore, you know, maximum strength, power, size, and full bore sprinting, and everything else together.

[00:19:42]And you know, so basically, backing off the prescription you know, basically was was showed that the compatibility maybe goes back to what Bob Hickson said, the late Bob Hickson, that that said that hey, it it really gets to be in overtraining. My My Our study of our group showed that the overtraining is really a function of those lower threshold motor units that got to try to adapt to high hertz and low hertz, and they got to get good at both, and it's it's difficult. And basically, if you're trying to get size, uh you you basically if you if you don't back off your aerobic or periodize that properly, you're you're you're going to you're going to get size of certain muscle fibers, but not others, just because of this this battle that's going on when you have to do both. So, that's kind of what that study was all about, and I I think it it showed some unique physiological adaptation aspects of muscle fibers and motor units, and and it tells you that you got to be careful as you know, now decades later, you got to be careful on how you periodize and how you wide wide rest, and that basically know what your targeted workout is for. I mean, if it's targeted for what phase you're what you're trying to do, and you you don't want to you don't want to you know, offset a target by doing something with what we call now non-functional overreaching because you did something that was just stupid on top of something. So, the body is very careful to try to optimize what it does best at the each level of the motor unit recruitment for the primary muscles.

[00:21:27]And you know, strength testing are you know, if you trained it they got they got a little bit stronger.

[00:21:34]You know, we also saw that that if you when you when you test certain exercises, it it it basically are going to if you train them properly, you're going to get stronger. But but the but how it all works with regard to the total programs integrating are different. So, that's that's in a nutshell of what that study did at that point in history.