Editor’s Note: An item from yesterday’s newsletter created a lot of questions and confusion among Pump Club app subscribers. In the newsletter, we wrote that a study found that 90 seconds of rest is superior for building muscle, and not every rest interval in Pump Club programs is 90 seconds. We wrote an exclusive article for all of the members and thought it was worth sharing with all of you.

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The best part of the Pump Club app is that you all feel connected to your health and want to get better, so you use every resource we have here to support your fitness, nutrition, habits, mindset, accountability, and overall health. 

The hardest part of the Pump Club app is that you consume what we put out, including what’s in the newsletter, and sometimes we don’t do a good enough job clarifying that it does not necessarily apply to everything you see in the app. 

This happened today with the “Number you won’t forget” in the newsletter. We discussed how scientists found that 90 seconds of rest is best for muscle building. 

And my mistake was not clarifying that while the research is great, getting married to 90 seconds of rest overlooks the reality of workout design.

Because you read the item, and a fair question came back: why doesn't every set have at least ninety seconds of rest? (We received MANY emails today; so many that I started writing this post 5 hours ago and felt it was necessary to get it done today.)

When we cover a study in the newsletter, we tell you what it found and keep the summary short. A summary teaches you a lot. It can't teach you everything, and it won't show you all the ways a single finding does and doesn't apply once you're building a real workout. 

We can do a better job filling in that context, and that's what this article is about. 

Our promise is that we do the thinking for you, and we do. And when you have questions, our approach isn’t “Just trust me.” We pull back the curtain so you can see how we build your workouts, and we give you evidence, reasons, and examples so you don’t have to second-guess it.

By the end of this post, I hope you'll better understand the role of rest, the art of workout design, and the science of rest, muscle, and other goals you might be trying to achieve with your workouts. 

A Number Is Not A Rule

First things first: The ninety-second guideline is a good one. It's a clean way to think about the trade-off between fatigue and intensity that drives muscle growth. 

And a good guideline isn't a universal law.

Ninety seconds is not the only rest interval that builds muscle, and when you're designing a workout, far more goes into the choice than a single number.

The urge to turn 90 seconds into a rule you can't break is worth understanding because it trips up many smart, motivated people. A specific number feels like control. Fitness is a place where many of us have felt out of control for years, trying things that didn't work and then blaming ourselves. 

A number promises certainty: follow it exactly, and you can't be doing it wrong. That promise is why the number takes hold, and it's also how a useful guide hardens into a cage. You stop training and start grading yourself.

I gave you a number. I did not give you a rule. (But the way I wrote the item made it seem that way, and for that, I apologize for not communicating better.)

The difference between those two things is most of what separates lifters who keep progressing from lifters who stall out. 

Muscles don't grow because you're tired. They grow because you've trained them to produce high force against a meaningful load. Tension is the signal. 

The old story was different. Short rest cranked up the burn and spiked growth hormone and testosterone right after training, and that spike was supposed to be what built you. The spike is real. It's mostly beside the point, though.

When researchers tracked it, the size of your post-workout hormone bump didn’t predict how much muscle or strength people gained.

Researchers had young men rest either one minute or five minutes between sets, then measured muscle protein synthesis (the process that drives muscle growth).

The short-rest group produced more testosterone and less of the muscle-building signal. Protein synthesis rose 76 percent after one minute of rest and 152 percent after five. The bigger hormone response came with about half the growth signal.

Rest is designed to protect your ability to bring as much force and tension as possible to the next set. Too little of it, and fatigue piles up faster than you can pay it down. 

By set three, the bar moves slowly, the reps fall apart, and the load you can challenge yourself with drops. You're working hard, but you're not building efficiently, paying in fatigue for a stimulus you're not getting back. 

When trained men rested three minutes between sets instead of one, they gained more strength and more muscle over eight weeks. Three minutes isn't magic. It let them keep training hard, set after set.

You also don't have to grind every rep to true failure to get there. 

Taking a set to within a rep or two of failure builds about as much muscle as taking it all the way, and it spares you a chunk of the fatigue you'd otherwise carry into the next set. Hard, not destroyed. That gap does a lot of the work in a good program.

A 2024 review found the benefit of longer rest is small, and that it comes mainly from letting you do more quality work over time.

That's why a good program might have you rest 90 seconds on one set, forty-five on another, and three full minutes on a third, and every one of those can be the right call.

Now that we’ve established where the number comes from, it’s important to break down all the different reasons 90 seconds won’t show up for every set on every workout.

You Can Build Muscle With Less Rest

Ninety seconds isn't a switch that turns growth on. Muscle gets built across a wide range of rest, down to fairly short intervals, as long as your sets are hard enough. 

Shorter rest costs you some load and some clean volume, and you make up for it elsewhere. 

It's a trade, not a failure. 

The advice to rest at least ninety seconds is what you reach for when one goal, maximum muscle on a hard straight set, is the only thing on the table. Most workouts are juggling more than that.

Not Every Workout Is About Maximizing Muscle

Programs include all types of rest periods for a reason, and sometimes it seems to contradict science unless you think about it deeply (which we don’t want you to have to do). 

In Nic’s Workhorse program for Strongman prep, he uses 90 seconds of rest between your heaviest work, and sometimes less. If you just read the science here, you’d say, “That’s stupid! Strength requires three minutes.” 

But part of strongman is being strong while working a lot, often: “How many reps can you do in one minute?” The program builds work capacity, not just strength.

We have many different programs for many different goals. When we are trying to thread the needle to help you get the results you want, we blend rest periods to get the outcome you desire. 

Your Program Considers Your Schedule (Not a Lab-Controlled Scenario)

A study controls as many variables as possible so it can isolate one. 

Your life doesn't cooperate like that. You have a set number of days you can train, a set number of minutes before you have to leave, a body that recovers at its own rate, and a goal that might be muscle, or fat loss, or just staying strong and mobile enough to still be doing this at seventy. A program has to hold all of it at once.

Take pour program, “Rise of the Machines,” since so many of you asked about it. It’s Arnold’s current program, and it reflects where he’s at with his training.

Arnold rests less on purpose. He isn't chasing maximum muscle growth anymore, and he can't load a bar the way he did at thirty. That’s because of his heart valve replacements, not because age means you can’t lift heavy if you don’t have his exact limitations. 

What he wants now is high tension with efficient use of time, a session that does real work without eating two hours of his day. He’s building cardio, using progressive overload to maintain strength, doing higher reps to push him close to failure at lighter loads to maximize tension, and still chasing the pump because no one loves the pump more than Arnold. 

Shorter rest is the right tool for that. It would be the wrong tool for a powerlifter trying to add fifty pounds to a squat. Same variable, different job.

Fatigue Isn't A Constant (So Rest Can't Be Either)

Watch how a good session is built, and you'll notice the rest usually isn't uniform. Early sets, when you're fresh and the loads are heaviest, get more rest because that's where the highest-tension work happens, and it's worth protecting. 

Later sets, when fatigue is already banked and you've moved to smaller movements, can run on less because you're no longer trying to preserve a maximum effort you don't have anyway. 

Rest shifts through the session because your fatigue does.

Volume and Time Are Part Of The Equation, Too.

Muscle growth isn't a rest-interval problem. It's a total-stimulus problem, and volume -- the amount of hard, challenging work you do across a week -- is one of the biggest levers you have. 

A program's job is to get you enough of that work while managing fatigue and recovery, within a session length you'll finish. 

Stretch every set to three minutes and a good workout balloons past ninety minutes, and the version of you with a job and a family stops showing up. 

A workout you finish beats a perfect one you skip. Part of the craft is spending rest where it buys the most and saving it everywhere else.

Some Methods Appear To Break Rules (But They Work By Design)

Supersets and circuits run on different math. Pair two exercises that work opposing muscles, chest and back, say, and you can train one while the other recovers. 

You keep moving, the working muscle still gets its rest, and you save real time. The ninety-second number was built for a straight set. It was never meant to cover a superset in the first place. And research backs this up, as well. 

The exercises themselves change the answer too. 

A heavy set of squats taxes your whole system and needs real recovery before you can do it justice again. A set of lateral raises doesn't. If you use the same rest interval for both, you shortchange one while wasting time on the other.

What It Might Look Like In A Workout

Picture an upper body day. You open with a few heavy sets of bench press supersetted with rows. You might rest 1 minute between exercises, then another minute after you do both. That means you get 2-3 minutes between working the same muscle (after bench press, it’ll be 2-3 minutes before you hit bench press again, because your back is working during rows).

Next comes an incline press and pull-ups. This time, you’re doing straight sets with 90 seconds of rest. Do the press, rest 90 seconds, and repeat. Once you’ve done all sets, you move to pull-ups, same approach. Straight sets replace the superset, since fatigue is already building from the first two exercises. 

Then you move to lateral raises, biceps curls, and triceps. You might see only 45 seconds of rest. At this point, fatigue has already kicked in, and you’re also working against the clock while training smaller muscles that don’t build fatigue in the same way as those earlier chest and back movements. 

Same workout, three different rest periods (2-3 minutes, 90 seconds, and 45 seconds), none of them a mistake and none of them a contradiction of the ninety-second idea. Each plays a role where it does the most good.

The Rest On Rest (And Other Training Variables)

That's a lot of legitimate reasons for a program not to abuse or overuse the exact number I told you was best, and they all point to one larger idea:

All of these principles work together to create programs that work. 

Focusing on rest without considering exercise selection, training time, volume, or intensity means you’re missing the elements that make a workout effective and drive month-over-month results.

Science is a guiding principle. It is not the only kind of evidence, and it was never built to answer every question you'll face standing in front of a rack.

A study is designed to isolate one variable and hold the rest of the world still. That's its power and its limit. It can tell you, cleanly, that longer rest tends to beat very short rest for muscle on a straight set.

It cannot tell you how to weigh that against your schedule, your training age, your recovery, the other eleven exercises in the session, and what you're trying to accomplish. No single study can, because no single study was asked to.

Program design is its own body of evidence. 

It's what you learn from watching thousands of real people train, seeing what they can sustain, what breaks them, and what keeps working over months in a way no eight-week trial can capture. 

Arnold has been gathering that evidence for more than 60 years. I've been at it for 26 years. 

And our “evidence” is a combination of the science, the real-life trials and tests of the programs, and the undeniable results of the tens of thousands of people who have transformed with the app. 

When we build a workout, we combine the science the research shows with the craft that holds up in real life. Neither one alone gets you a program that works.

Forcing one clean data point onto every set, every goal, and every person isn't rigor. It's a misreading of what the data was ever for. The researchers who ran those rest studies would tell you the same.

The whole job that number was doing comes down to one thing. Rest long enough to bring your effort close to your best effort for the next set. On a heavy compound early in your workout, it might take two or three minutes to get there. On a smaller movement late in the session, it might take forty-five seconds, because you're not protecting a true maximum effort anymore. You're now giving the most you can given the fatigue that has accumulated. 

When the app suggests a rest period, we factor in all of these variables: Your goal, your fatigue, the exercise, the volume it's aiming for, and the fact that you'd like to be done before dinner. 

The number in your program isn't a compromise on the science. It's the science applied to your real life by people who have done this for a very long time.

It also helps to remember all the variables that build muscle. 

Showing up regularly, whether your hard sets get close to failure, and whether you're getting enough total work across the week. You also need to progress and add weight or reps as you get stronger. Then there's rest, which lets everything happen well.

It matters, and it’s not the end-all, be-all. 

Ultimately, your results depend on showing up, following a good program, and training hard. 

Rest a little short on a busy day, and you lose a sliver. Skip the workout because you couldn't find a clean ninety-minute block, and you lose the whole thing. One of those is worth worrying about. It isn't the sliver.

The details matter. Doing the work matters more.

Chase the hard reps. Follow the rest. Stay consistent. The program balances fatigue, volume, and time, so let it do its job. That's the thinking we promised you.

If you'd like to get a personalized Pump Club program — with, yes, variable rest periods, depending on your goals, age, gender, and experience — then give our 7-day free trial a go. We want to make sure it's right for you, which is why we also offer a 30-day money-back guarantee. Pump Club is the product of Arnold's six decades of experience, combined with the latest science — and our collective observations of working with tens of thousands of regular people across many millions of workouts. If that sounds like something you might be interested in, join us.

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Publisher: Arnold Schwarzenegger​

Editors-in-chief: Adam Bornstein and Daniel Ketchell