Rest Intervals for Muscle Size: Your Complete Evidence-Based Guide

Maximizing muscle growth means manipulating your training variables to create the best stimulus possible.  These variables include volume, frequency, intensity, rest intervals, and others.  Scientific research helps give us an idea of how to manipulate these variables to get the best possible results.  One common question that people have is how long they should rest between sets when their goal is muscle hypertrophy.  In this article, I will go over all of the available research to date, and provide you with recommendations based on that research.  I want to note that I will only cover studies that directly look at changes in muscle size (such as muscle cross-sectional area or thickness using ultrasound).  Studies using body composition techniques like DEXA are not sensitive enough to differences in muscle size that might occur with different rest intervals.

Rest Intervals:  The Bro Days

In the early days of bro-dom, it was believed you needed to train with short rests if you wanted to get your muscles as big as possible.  This was mainly due to the massive pump you would get from short rest training, and the belief that the pump was related to muscle growth.  This belief was further cemented when scientists such as Bill Kraemer published research showing that short 1-minute rest intervals produced greater growth hormone and testosterone responses compared to longer 3-minute rest intervals.  This idea was based on the assumption that the elevation in anabolic hormones that you get in the 15-30 minutes after a training session were related to muscle growth.  We know now, however, that post-training hormone responses are not related to muscle growth.  Thus, the idea of "train with short rest = maximal growth hormone and testosterone stimulus = maximal hypertrophy" can safely be flushed down the broilet.

Rest Intervals and Muscle Size:  Early Research

At the time that Kraemer came out with his work, there wasn't any research directly investigating the impacts of rest intervals on muscle size, so it is understandable why one might assume that short rests were best based on the hormonal responses.  In fact, it took 15 years since Kraemer's work for investigations on the impacts of rest intervals on hypertrophy to be published.  In the first study to investigate the impacts of rest intervals on size, researchers compared 2 minute rest intervals to 5 minute rest intervals on quadriceps muscle size.  While the researchers tried to equate training volume (sets * reps * load), it was 7% higher in the short rest group (the short rest group did 9 total sets per session on legs, while the long rest group did 7 total sets as they could do more weight per set).  Gains in muscle size were identical.  The problem with this study, though, is that 2 minute rests are not really that short, and certainly not comparable to the 1 minute rests that produce dramatically greater hormonal responses.  Also, training was only partly supervised.

Four years later, a study was published that compared 1 minute rests to 2.5 minute rests.  The study involved untrained subjects, and loads were chosen so that subjects only hit failure on the last set.  Statistically, there were no differences in leg size gains between the groups, but the percentage gains favored the long rest group (6.6% versus 3.1%).  Gains were also statistically greater in the arms in the long rest group compared to the short rest group (12.3% versus 5.1%, respectively).  Essentially, gains were twice as high with 2.5 minute rests versus 1 minute rest, despite greater anabolic hormone responses in the short rest group (again falsifying the "hormone hypothesis" of muscle gain).  One major limitation of this study is that subjects were not supervised during training.

In another study, researchers compared constant 2 minute rest intervals to rest intervals that were progressively decreased by 15 seconds each week from 2 minutes down to 30 seconds.  The short rest training impaired load volume, but changes in arm and leg muscle size were similar.  A follow up study by the same group showed similar results; in fact, percentage gains favored the short rest group in that study.  However, one caveat in that study is that both groups were supplemented with creatine.

Schoenfeld Saves The Day

The Hypertrophy Specialist...look at that glow...

It's hard to draw conclusions from the earlier research due to limitations in the study designs, such as lack of training supervision.  Fortunately, Dr. Brad Schoenfeld saw the limitations in previous work, and carried out a well supervised study comparing 1 and 3 minute rest intervals in well-trained subjects; I ran the statistics on this study.  Subjects did 3 whole body workouts per week, doing 3 sets of 8-12 RM of 7 different exercises (mostly compound movements) each session.  One group had 3 minute rests and the other group had 1 minute rests.  Muscle gains favored the long rest group in all outcomes, with nearly twice the gains in the long rest group in some measurements.

Brad was involved in more work on rest intervals, this time comparing 30 second to 150 second rest while using light weights (40% 1-RM) to failure.  The exercises were squat and bench press.  Muscle gains favored the long rest group for legs, but gains were similar in triceps.  One limitation of this study is that the subjects were untrained.

There's also the study comparing sets of 8 RM and 3 minute rests to sets of 20 RM and 30 second rest that I reviewed recently in the Weightology.  This study showed twice the gains in the arm muscles with the short rest/high rep training compared to the long rest/moderate rep training, which is in the opposite direction of what some of the other research has shown.  One limitation was that there was different rep ranges used for each rest interval (8 RM for the 3 minute rests and 20 RM for the 30 second rests).

Finally, there's research out there on drop sets.  Drop sets are essentially the ultimate in short rest training...they are "no-rest" sets.  I discussed a couple drop set studies in a recent research review in Weightology.  When training volume is high, drop sets don't provide any advantage over regular training, as long as training volume is the same (at least in the legs).  However, there is some data to suggest that drop set training might be effective for small upper body muscle groups (like the triceps) when training volume is low.

Making Muscle - Effects of Rest Intervals on Muscle Protein Synthesis

One final piece of data that we can look at is the impact of rest intervals on muscle protein synthesis.  In the hours after a training session, muscle protein synthesis is elevated, meaning your muscles are already building new protein and going through the process of hypertrophy.  One study looked at the impacts of 1 minute versus 5 minute rests on muscle protein synthesis in the legs.  The subjects did 4 sets of leg press and 4 sets of leg extensions at 75% 1-RM to failure.  Muscle protein synthesis at 4 hours was elevated by 152% in the long rest group and 76% in the short rest group.  Intracellular anabolic signaling was increased by 4.2 fold in the long rest group but was not elevated in the short rest group.  Total load volume was 13% lower in the short rest group.  This study indicates that long rest training is superior for inducing muscle protein synthesis and anabolic signaling, at least when it comes to leg training.  The better anabolic response from the long rest training may be partly due to the greater load volume achieved.

Putting It All Together

The following table summarizes all of the evidence I have discussed.  Grey rows represent no difference between short and long rests, orange rows represent outcomes that favor long rest, and blue rows represent outcomes that favor short rest.

Overall, most of the data favors long rest training.  The primary benefit of long rest training appears to be that it allows for higher load volumes.  However, short rest training may have its place in certain instances.  Looking over the table, some trends emerge:

  • Long rest training (2 minutes or more) appears superior for heavier loads (like your typical 8-12 RM), large muscle groups like legs, and compound movements
  • Short rest training (30 sec) may have some benefits with small, upper body muscle groups trained using isolation movements and high repetitions (like 20 RM)

Practical Application

  • Most of your training should involve longer rest intervals of 2 minutes or more between sets.  This is especially true when training with moderate to heavy loads, large muscle groups, and compound movements.
  • There doesn't appear to be any advantage in to doing short rest training on legs, so you can breathe a sigh of relief that you don't need to be puking your guts out from short rest leg training.
  • Follow up your typical moderate-to-heavy work with some high-rep, very short rest "pump" isolation movements for the very small upper body muscle groups, like arms and shoulders.

 

 

3 Responses to “Rest Intervals for Muscle Size: Your Complete Evidence-Based Guide

  • Travis McKinstry
    1 year ago

    Ohhhhhh the type of $hit I’d get if I referenced the conclusions this article draws… science is science!… but sometimes bro-science is more convincing for some dumb reason…

    Thanks for this!

  • erwin maasbach
    1 year ago

    I’m on a full body schedule including 8 different exercises for 3 sets. I Usually take 1 minute rest as described by one of my bros. Increasing rest from 1 to 2 minutes would mean a training time increase of 24 minutes, nearly 50%. This means my time spent in the gym would need to go up considerably. Would combining exercises in supersets help offset the amount of additional resting time, or would this negatively impact my training in another way?

    • Yes, combining exercises in supersets can help offset the additional rest time. It shouldn’t have any significant negative impact on your training, except for that some people can have trouble pushing themselves if the supersets are too close together and they are “huffing and puffing” too much and feeling too fatigued.

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