Short VS Long Rest Periods For Muscle Growth (Science Explained)

Foreign. What's going on, everybody? And welcome back to the Built With Science podcast. You're here with your host, as always, of course, me, myself and I, that is Max Coleman, AKA A Coleman and all. And sitting in front of me, as always, as is tradition, is Daniel Plotkin, AKA I couldn't come up with anything creative this week, Plotkin, AKA Danny Boy. And today we're going to be talking about a hot button issue. Hot button issue. Forget states rights, forget anything that you've heard in the news lately. We're talking about rest periods for muscle growth. Today, a new meta analysis hot off the press, coming straight out of the AMDL lab out here in the boogie down Bronx looking at nine different studies analyzing breast periods effect on muscle growth. But before we get there, let's talk about why, for a long time it was kind of believed that shorter rest periods were ideal for muscle growth. So, Danny Boy, why do you think that for such a long time people thought that you rest for a shorter period of time if you want to get jacked and you rest for a longer period of time if you want to get strong?

Yeah. So I think part of it is just what bodybuilders typically did back in the day or what it seemed like a lot of bodybuilders typically did back in the day, which is use not as heavy loads, take shorter rests. And the reason why they did that is probably, probably just because the pump feels really nice and those metabolites just feel like you're really causing lots more muscle growth when you do that. So my guess is that the reason the bodybuilders did that so much is because sensation was just, you know, hard to ignore. And then I think hypotheses sort of arose from that lore, which mainly to my knowledge, revolved around hormones. So there were a few studies that showed that gh, testosterone and other hormones acutely were elevated after short rest periods compared to longer rest periods. So if one group did a bout of three exercises taking, let's say 30 seconds between sets and another did two minutes between sets, the 30 second group had higher elevations in testosterone and GH and a bunch of other hormones that were measured in a few early studies. Interestingly, later studies that measured it multiple times showed that sometimes it still held. But there was an amelioration of that effect where it seemed like if you continue to train with shorter rest periods, you wouldn't get that uptick in hormone. So even that hypothesis is on shaky ground in terms of the measurement itself, maintaining that higher level. So, yeah, I think that's a lot of the early history as to why a lot of people thought short rest would be better for growth. A combination of what bodybuilders did, the sensation and hormones.

Yeah, I think it's a charitable approach to say that a lot of people were like, well, because of the increase in insulin growth factor in response to shorter rest periods, I would pontificate that that's a much better way of going about growing muscle. I think it's much more like this makes my arms feel bigger, so I do it with shorter rest periods. It just feels good. And I think that that is like a really good example of why sensation during lifts isn't like necessarily a great indicator of the effectiveness of that exercise. Same as like, for instance, like if you do bicep curls in the shortened position with really, with really high intensities, like you're going to get the most gnarly skin splitting pump ever. But we have pretty good evidence to suggest that that's likely not ideal for growth. Right. And even though people thought that this was the case for a long time early on, one of the first studies, at least one of the most direct studies and one of the most popular studies that kind of first drew this into question. Well, this new question anyway caused just, wow, I'm really struggling to talk today. Uh, one of the first studies that basically was like, oh, maybe short periods aren't actually the way to go for muscle growth was one of Dr. Schoenfeld's study also out of the AMDL lab, looking at resting for one minute versus three minutes between exercises. And they found significantly more growth in those that rested for three minutes. Right. And that was kind of the first time that people were like, oh, longer rest periods is actually better for not only strength but, but, but for muscle growth as well. However, it's just one study doesn't really give us much insights at all into how we should go about things. And in fact, resting for three minutes as opposed to maybe one to two minutes might actually not be as ideal for muscle growth. And I think that leads us into talking about what we're actually here to talk about today, which is this new meta analysis by Singer et al. In which they analyzed nine different studies looking at rest periods effect on muscle growth. And in order to be included in this meta analysis, it had to be a study that was only comparing the rest period. So they had to equate volume. And they did that either through equating the number of sets that these participants were performing or volume load, blah, something we'll we'll get into here in a second. But Danny boy, why don't you go ahead and talk us through this meta analysis a little bit? What were the findings and is it going to affect how we go about training?

Yeah, so I'd say given some of the limitations, I don't think it'll affect how we go about training, particularly because when you start subdividing and start talking about, oh, maybe is there a slight decrease in growth at above 3, then you were talking about a very small setup. So studies that were pointing in that direction. So I think that it did a good job of at least bringing attention toward the fact that just because there is a drop in performance doesn't necessarily mean that there will be a decrease in hypertrophy or a decrease in morphological outcomes instead of performance outcomes. So I think in general, it's fair to say that you want to keep performance up as high as possible, but there are definitely instances and potentially mechanisms that may or may not overlap where doing a combination of both might be a decent idea. So I think the benefits of the meta analysis is just shining light upon that and also shining light upon the fact that when you really subdivide between a lot of the different rest periods and sort of all of the exercises use upper body versus lower body and so on, there's just not a lot of studies to draw upon to have super strong feelings about this. So I think just to go over some of the actual conclusions from the meta analysis, it seems like for upper body exercises, longer rest periods are not necessary. So that kind of makes sense in terms of you can recover better set to set for upper body exercises, but for something like a squat, you know, you might need a little bit more time. So it seemed like lower body exercises needed a bit more rest and that one to two minutes of rest seem to have safely better outcomes than less than one minute. So that was, I think, the overarching findings of the meta, but the sort of meta findings were more about, okay, we need more studies, period. In terms of once you subdivide, it seems like we don't have that many studies to draw upon. And two, we may want to consider other factors like not using volume load and considering the specific exercise.

And yeah, just to quickly touch on that for those of you who don't know. So when we're saying equating volume, the best way to do that, generally speaking, is equating the number of sets in which the participants are performing. But this is like a somewhat new ideology in exercise, or at least within our field for a long time, they in order to equate volume, you equated what we called the volume load, which is just where you multiply the number of reps times sets times weight that the individuals are doing. However, Danny Boy and I at the very least are under the very strong conviction that volume load is not something that should be compared, especially when you're trying to match volume between groups for several reasons. One, it very much favors lower or higher rep ranges and makes it seem like you're doing much more work when you're doing sets of 20 versus sets of 5. Even though we have pretty good and direct literature showing that a sets of 20 don't cause any more growth than sets of 5. But so it's just probably not ideal. And yet this study, and a lot of studies do, compared volume load and used that to match volume. But there's a lot of reasons why that's probably not a good idea.

Sorry, I could touch upon that if you want. Like what could actually happen in the study. So, for example, you could equate volume load in two ways. You could have one group try to match the volume load by either doing less reps per set. So let's say I'm in the short rest period group and you're in the long rest period group from set to set. I'm going to have a larger drop in reps. So you could be pair matched to me and you would have to actually do less reps in order to get the same. So you could either be further away from failure or you could take those sets. And this is typically what's done. But actually one study did it in the way that I just mentioned. But typically what's done is that you still take your sets to failure, but you would do an extra set. So the group that does less volume load would do an extra set to make up for the lesser volume load. So either way there's issue. There's an issue there. You're either causing one group to be further away from failure the longer rest group in this case, or you're causing one group to have more set volume. So either way, that could substantively affect outcomes. So in my opinion probably shouldn't be used as a metric for quantifying volume and standardizing volume.

Well said. Now let's get back to what people are here to listen to, because we totally went off on a tangent there. But just to very briefly and kind of succinctly describe what this meta analysis found. Right. So when they. When you look at the Rest periods in a binary sense. Right. So short and long rest periods. And the way that they quantified this was either less than 60 seconds or more than 60 seconds. Right. And they found that there was substantially more muscle growth when you rested for longer than 60 seconds, as opposed to shorter than 60 seconds. And when you were looking at this meta analysis in general, the shortest time period that was analyzed across all nine studies was 20 seconds, which is insane. It's a very, very short rest, but essentially a drop set without or a myo rep set, I guess. And then the longest duration we saw was 240 seconds, so four minutes. Pretty long, especially for research. I'm sure that was a nightmare to conduct. Um, but still not. Not. It's a short rest period when you're looking at, like powerlifting standards. Right. Or something like that. Like strength standards especially. So just, just important to keep in mind that the largest range was about 220 seconds. Right. So the largest was 2:40. The shortest was 20 seconds. Right. So binarily much better growth when you rested for longer than 60 seconds versus much less growth when you rested less than 60 seconds. And when I say much more and much less, it's important to keep in mind that everyone grew, no matter what category they were in. You grew muscle even if you were resting for as short as 20 seconds. We're just talking about differences in growth here. Right. However, fortunately, this study didn't just look at things in a binary sense, which we shouldn't generally do, especially in exercise science, because time isn't binary. It's not just 60 seconds or more than 60 seconds, whatever. Right. So they broke it down into four categories. Right. Short, intermediate, long, and very long. To be quite honest, I had some trouble finding out what those quantifications were. Did you?

Yeah, I mean, it was hard. Yeah. I mean, kind of like we're obvious there. Yeah.

Do you. Did you, like I'm telling in. In terms of. I wouldn't have known what these cutoffs were had I not watched Dr. Milo Wolf talk about what they were. But maybe I'm just not very good at reading scientific papers. Do you know, do you remember what they are?

I thought it was. So I. Full disclosure, did not read it today, so I'll let you take it over. But I thought it was 30 for, like, very short set.

I thought that it was that short was less than 60 seconds, intermediate was one to two, long was two to three, and very long was more.

Yeah, yeah, yeah, yeah. One less than one. Yeah, exactly.

Anyway, the differences between those were pretty small. But very interestingly, and this is, this is counter to what I generally recommend to individuals. I always say that, you know, there you can't really rest too long. Like there's that we have pretty convincing evidence the resting too short is probably going to hurt your gains, but you're probably not going to hurt yourself if you rest too long. But this, this meta analysis actually draws that into question. Right. They found that the largest effect size was in that long range. So somewhere between one to two minutes, or, sorry, in the intermediate, I believe somewhere between one and two minutes. Right. And going far above two minutes, you actually saw a reduction in the amount of growth that you're going to see. Not much. Again, we're talking about the largest discrepancy here is not much at all. But it's just if you're looking to build the most amount of muscle possible, you probably want to be resting somewhere between one and two minutes.

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Now, as Danny Boy and I have talked about and what we're about to talk about further, there are some limitations to this study and this just because we have a meta analysis now, I think because of the hierarchy of knowledge, people think that once you have a meta analysis, that means that we have all of the answers to the question that we're interested in. But just because this is a meta analysis does not mean that, okay, you have to rest for one to two minutes. And if you rest any longer or shorter, you're just, you're guaranteed not going to grow the most amount of muscle possible. So when you break it down, like Danny Boy was saying earlier a little further, these magnitudes seem to be even less important when you're talking about the upper body. So resting for a shorter period of time affected the upper body a little bit less than it did the lower body, which makes sense just from like an ecological standpoint. Like I know I personally need far longer to rest between sets of RDLs and squats than I do for like biceps, triceps or even compound movements as well like overhead pressing or bench pressing and stuff like that. Right. But again, the differences weren't very large at all. And then it's also important to note that we do have some preliminary evidence, like very, very new stages, suggesting that just resting until you feel ready to go again is good, at least in a performance standpoint. So, like, like I'm, like I said, these very preliminary. We cannot say this very confidently with respect to size, but full disclosure, our biggest takeaway from this meta, like, from this podcast, like, if you take nothing else from what either Danny Boy or I say, just rest until you feel ready to go again. And your body does a pretty good job of like regulating when that is right. I think a good general takeaway is once you feel as if the muscle intended that you're trying to target with that set is going to be the limiting factor of the set, you're probably good to go again. So let's say you finish a set of squats, you rest a minute, you're still kind of breathing heavily, and if you try to go again, you're going to be heaving for air and that's going to be the reason you cut off the set. It's probably worth resting a little longer, but after two minutes you feel good, your legs are ready to go again, your breathing is back to normal, and you're psychologically ready to hit the set hard again. You're probably good to go. Sorry, do you want to touch on some of the limitations as to why maybe this study doesn't paint the entire picture for how long we should be resting? I kind of went off on a tangent there.

Yeah, I think there's potentially multiple limitations that they touched upon in the matter. So I think one really big one is when you compare groups that had rest periods that weren't standardized throughout the study, then you have less of an ability to say whether rest periods are meeting that, mediating that effect. If there's actually a threshold at which you're not going to get better gains, then you're spending less of the time during the study at that suboptimal rest. So, for example, two studies in the meta analysis started at, I believe two minutes of rest between sets and then week by week they went down by 30 seconds. And so it could be that the threshold is one minute. So half the study was spent above that threshold and half the study was spent underneath the threshold. So now you have, instead of an eight week study looking at rest periods, now you have potentially a four week study that was below the threshold or the theoretical threshold. Then you have pretty big issue of some of the ways that muscle growth was measured in many of these studies. So BIA is probably, I don't want to crap on it too much. It's probably not the best way to measure muscle growth. We also have straight up circumference measures like taking a tape measure and putting it around the eye and the arm. And some interesting outcomes on that front for I want to say two of the studies in the med, definitely one, but I want to say potentially two of the studies in the meta. So, yeah, there's definitely stronger studies that you can lean on that wouldn't necessarily be captured in a meta because they'll be treated similarly. Like, you can't specify in the mathematical model that this study didn't use a metric that we would consider to be the gold standard. You would just take the standardized mean difference regardless of what that metric is. That's what the utility of the standardization actually does. It takes different types of measures, whether it's mri, ultrasound, thickness, circumference, or two compartment models like the DEXA and the bia, all of which were used in the studies.

And you're right, it's two that had the circumference.

Yeah, exactly. So like we were saying in the beginning, I wouldn't take this literature and say, oh, for sure. Once you get past this 2 minute mark, higher rest periods are going to.

Be.

More detrimental for gains. I'd say tentatively that I think we have good evidence that resting for longer than a minute is a good idea, particularly on exercises that are taxing above that. I'd be very surprised if resting too long was a thing. As long as it's a reasonable, you.

Know, I rest 24 hours between sets of squats.

Exactly. Like you could rest an hour in between. Then I can guarantee you that's going to be more negative considering you won't have enough, you know, time in the day.

But that's a really interesting question though, just from like a, like a. Let's pretend like we're in the hyperbolic chamber time chamber in Dragon Ball Z. Right. For all my fellow nerds out there who've never actually watched anime like myself, but like, do you think that, like, let's say you had unlimited time, like, and you rested 20 minutes between sets of squats, do you think that there would be a difference?

I think that there's probably a threshold on both directions. So I think resting too little is, is a bad idea. So like we were saying, like one, one minute, you'd have to do more sets to make up for that. But resting for too Long.

I'm hard pressed to think of a logical reason why that would interfere with growth.

I think that you would want to have a stimulus of animalism that wasn't spread out so much that. I mean, this is obviously completely speculative.

And it doesn't matter either because we're.

Yeah, exactly. I mean practically. Practically it wouldn't make any sense too. But you could imagine something similar to protein thresholds, like a leucine threshold, where consuming 5 grams of protein in two, you know, reaching the same amount of protein, but consuming 5 grams once every hour compared to consuming, you know, 30. 30 I think would be worse if, if we could do a study that was super well controlled because there's threshold of anabolism that the body's like, all right, we're getting a stressor that's really well above what. And we need to adapt to that stressor. Obviously. Complete speculation, but yeah, I'm inclined to say that I think having an acute stressor that's a bit more stressful than just doing a set, waiting a super long time doing another set would be better. So there's a point there where it would be. And it might not even be a point that somebody could reach practically. But yeah, big tangent for super.

I've just genuine curiosity on my end. I can't imagine anyone actually.

You don't think he would matter? Think.

It's hard to say. I think that. So really interestingly, I was listening to Dr. Israel, Dr. Mike Isretel with a Renaissance periodization talk about this study and he was wondering, or at least suggesting or like even just bringing it into question, the idea that if these longer rest periods, let's say greater than two minutes, are causing less growth than that one to two minutes range could in some ways be an argument for metabolized sequestration being like a, A lever for. For growth. Right. Which I thought was an interesting theory. I'm skeptical obviously, because again, the. I'm not even very convinced that you can still rest too long based on the findings from these studies or from. From this meta analysis. But I do think that's interesting and I'm curious as to your thoughts. Like, do you think it's an argument for, or at least in the potential of metabolite sequestration being one of the drivers of hypertrophy?

Yeah, I mean, that's what I'm saying. That's what I was saying early in the conversation, that there's a theoretical argument to be made. But it is very theoretical because obviously it's super hard to have evidence of those kind of mechanisms because they're overlapping in such a way that it's pretty much impossible to disentangle. But just based on the fact that there's no downside in things like drop sets and short rests could actually be efficient from a time standpoint, not a per set standpoint, I think not dipping into those waters, at least sometimes would probably be, you know, a bad idea for, for, for some. Do I think it would matter that much? No, but I definitely like to use those techniques for the theoretical mechanistic benefit, but also some of the time saving and novelty and so on.

So, yeah, I think that that's a really good segue into us adding even further complexity to this conversation with respect to rest periods. Because in the, in the research that we have comparing just rest periods and making sure that everything else is equal, we see a slight benefit to resting longer according to this metadata analysis, not too long than shorter. Right. So just looking at the binary sense, like I said earlier, this meta analysis showed more growth from resting for more than 60 seconds as opposed to resting less than 60 seconds.

Right.

But when you add some further complexities to that, like the very, very limited superset research we have, the drop set research we have, the MYOREP research we have, the BFR research we have even that throws kind of further complexity to this because those, though not directly and though not exclusively comparing rest intervals show basically no difference with respect to something like BFR or something like drop sets. Even though you're theoretically resting for a much shorter period of time, you're getting the same amount of growth, Right? So are there ways to potentially negate the detriments of doing shorter rest periods? Probably. In fact, one of the studies was, drew that into question, one of the studies analyzed in this meta analysis, where they basically did extra sets to equate volume load between those resting shorter and those resting longer. And once you did that, they actually showed no difference as well between, between groups. So from a time standpoint, if you're just someone who's pressed for time and you just want to make sure that you're getting all of the, you're not worried or sorry, you're pressed for time, but you want to make sure that you're doing all you can to get the same gains as if you were someone with a completely open schedule, right. You could rest for a shorter period of time and maybe, maybe that in of itself wouldn't make a huge difference. Especially if you're resting for like around a minute, you're probably fine. But if you really wanted to edge your bets, you could probably tack on an additional set to make up for any potential losses that you would see from shorter rest periods. And then of course, you could also use certain intensity techniques like bfr, like supersets, like drop sets, like Myorep sets, to like just be a more time efficient person. And that was something that I heard milo Wolf talking, Dr. Milo Wolf talking about with respect to this study, is that it's kind of just great news, kind of just further adds to the idea that you can still build muscle on a time crunch. Like you don't have to be resting. Because I know me myself, like I would rest a good three minutes sometime, especially earlier in my like lifting career, if I felt ready to go, I would kind of force myself to rest even LONGER Just because Dr. Schoenfeld's study showed better growth in three minutes versus one minute. So I have to rest all the way. Right. But now it's. And granted I stopped doing that a long time ago, but now I can be a little bit more confident that I don't have to rest for an extended period of time. And in some instances that might actually be negative. Though again, I'm not super convinced of that. Okay. Is there anything else you want to say? Sorry, I kind of, I've been going on tangent after tangent. I apologize. Is there anything else you'd like to add with respect to maybe practical takeaways, how you would recommend going about resting between sets?

Yeah, so I think a lot of the science sort of sometimes can make things seem complicated when they're really not. So resting when you feel ready is probably a really good idea. And typically people feel ready much more quickly for isolation exercises, upper body exercises in general. The research sort of fleshes that out as well. So a calf raise, you know, you can recover very, very quickly from a calf raise. And so I think going when you're ready is probably a really good idea. And I think you, you summarize the how to know when you're ready pretty well. All of the feeling, all of the feelings that are related to both neurologically and just psychologically, usually with some decent amount of training, you kind of know when you're ready. So I'm not too worried about people undershooting from that front. But practically speaking, let's say you're not so sure and you're at the minute, 22nd mark veer on the side of slightly longer and then you'll be good. It's not that big of a deal. So I think that's One thing I want her to cover just from a practical standpoint, then from what you mentioned about drop sets and some intensity techniques, they do more sets, quote unquote, in, in all of those conditions. So like, there's more drops than com.

In like in most studies? In most.

Yeah, exactly.

There is. I think there's one or two where they do the same number of sets and you still see similar growth. So, but again, if you want to like, really hedge your bets and you're, you're on a time crunch, hacking more into a shorter period of time is probably your best exact.

Yeah, so, yeah, so I just wanted to mention that a lot of the studies obviously do more sets for, for the drop condition. And I think you mentioned. What was it? Oh yeah, time saving. So I think one thing that people really sort of sometimes don't mention when they talk about time saving in this case is you really don't need to do the same muscle group. So that just takes that out of the equation completely. If you're really pressed for time and you're at least somewhat convinced that, you know, resting a little longer is a good idea and that muscle should be, you know, a little bit more fresh than, than it would be if you were waiting less than a minute, just do an exercise for a muscle group that is unrelated or the antagonist, and you've just saved a ton of time right there and pretty much lost nothing, as long as it's not a super fatiguing exercise. So anytime people say or are really, really angry about the rest period literature in terms of it leaning toward more rest, I'm like, if you're really worried about people saving time, they could save time just by doing a different exercise that is unrelated to the muscle group. And then you'd be super hard pressed to say that there's much of a downside in that case. So, yeah, I'm generally not gonna. Unless I'm specifically doing an intensity technique, I'm generally not gonna try to save time by taking shorter rests for the same exercise because of the fact that other exercises exist that are not fatiguing, like doing a lateral raise in between leg extensions. Like, I don't think that my lateral raise is really negatively affecting my, my leg extension.

Yeah, I think if you're someone who's pressed for time, just resting shorter between sets is fine. But there are probably better way. One, there's probably better ways to do it from a time saving standpoint, like literally from a time saving standpoint. And there's probably better ways to do it from A balancing time saving with optimal muscle growth. Optimal muscle growth. So yeah, I would say if you're trying to save as much time as possible, antagonist paired super sets and drop sets are like your, like for your isolation movements. Maybe some drop sets, though I don't think that there's any reason to do like you need to do drop sets for isolations and antagonist supersets for compounds or anything like that. But that's usually just the, the go to recommendation. I think it's a good recommendation, but. Okay. Anything else you want to say before I, before I summarize this, before I recapitulate the findings?

I like it.

Cool. All right, so not a whole lot to say here. For a long time, people thought that you needed to rest a shorter period of time for muscle growth and a longer period of time for strength. And then we had some evidence coming out in the early stages suggesting, oh wow, maybe we should be resting a bit longer for optimal muscle growth. But then this meta analysis came out, kind of even drawing that into question, suggesting that resting longer than 60 seconds is certainly better than resting less than 60 seconds. But there might be a potential in resting for too long. Maybe above three minutes is not a good idea. However, like Danny Boy and I said, there is some. There are several limitations to this meta analysis that may make us question whether or not it's actually detrimental to rest far longer than two or three minutes between sets. Right. That being said, if you're someone who's pressed for time and you're looking to still get as jacked as possible, you can rest for a pretty short period of time without and, and change nothing else without worrying that it's going to affect your muscle growth too much. But if you're concerned and you want to make sure you're doing everything you can, you can always tack on an extra set or two to kind of like continue saving time while also maximizing muscle growth. But in our personal and humble opinions, you're probably better off doing intensity techniques if you're looking to save time while optimizing growth. So using things like supersets, drop sets, bfr, MYO reps, all that, rather than just doing more sets and resting for a shorter period of time. Yeah. Anything else?

Especially because of the fact that if you were trying to rest longer, you could use antagonist supersets. That's why, that's why put them into two different categories. Yeah, exactly.

Oh, and biggest takeaway, just rest until you've already to go again. It's probably going to serve you well. It's unlikely that. And, and the kind of cool thing about that is that like, like Danny Boy was saying, the evidence kind of corroborates that actual finding. Where, like, generally you feel like you need longer for legs, and it seems like longer rest periods are probably better for legs, at least according to this meta analysis. Right? So rest until you feel ready to go, and you're probably doing all you need to do as far as rest periods are concerned. Cool. As always, everyone, thank you so much for listening to the Built With Science podcast. If there's something that we haven't covered yet that you'd like us to talk about, feel please feel free to reach out to us at Built With Science on Instagram. And as always, thank you so much for listening. Peace.