By Ofer Blutrich, MSc Physiotherapy, physiotherapist and elite climber with 100+ first ascents.
A 4x4 bouldering workout is four boulder problems climbed back to back for four rounds, resting only between rounds, never between problems. It is one of the most effective ways to build power-endurance, your ability to keep pulling hard moves without your forearms pumping out and forcing you to let go. If you've heard climbers talk about "doing 4x4s" but never gotten a straight answer on grade, rest, or how many rounds, this guide fixes that. I'll give you the exact protocol for your grade, how to progress it honestly, the mistakes that waste the session, and how to run 4x4s without tweaking a finger or a shoulder. I'm a physiotherapist and a climber with 100+ first ascents, so the injury guidance here is real clinical reasoning, not gym folklore.
What is a 4x4 bouldering workout (and what it trains)
A 4x4 bouldering workout works like this: you pick four boulder problems, climb all four back to back with no rest between them, then rest for a set block, and repeat that whole four-problem circuit for four rounds total. That's 16 climbs, but the number that matters most is four straight problems before you get to rest.
This drill sits in a specific box: power-endurance. Power is how hard a single move feels. Endurance is how long you can keep climbing at an easy intensity. Power-endurance is the space between them, your ability to keep pulling hard, near-limit moves back to back without your forearms flooding with the "pump," that swollen, seizing feeling in your forearms that eventually forces you to open your hands. A 4x4 bouldering workout is built specifically to train that middle ground.
Why does it work? Eric Hörst, one of the most established names in climbing-specific training, frames repeated near-limit efforts like this as a genuine, proven power-endurance protocol, one that trains your muscles to buffer and clear fatigue byproducts faster so you can link more hard moves before the pump forces you off the wall. In plain terms, you're teaching your forearms to keep recovering while you're still climbing, not just between attempts.
That is also why a 4x4 is neither a pure power drill nor a pure endurance drill. It sits deliberately in between, and that's the whole reason to run four rounds of four problems instead of one long easy lap or one single hard boulder.
How to do a 4x4 bouldering workout, step by step
Here is the exact protocol, in order.
- Warm up thoroughly. Spend 15 to 20 minutes on easy climbing and mobility work before you touch anything near your limit. A 4x4 done cold is how technique breaks down fast.
- Pick four problems, 2 to 4 grades below your hardest redpoint grade. Choose ones you already know well, short rather than long, and nothing with a move you're unsure of.
- Climb all four back to back with no rest between them. This is the core of the drill: four problems in a row, one continuous push.
- Rest between rounds only. Roughly 4 minutes if you're bouldering, closer to 10 minutes if you're doing this on routes, since routes take longer per attempt and generate more fatigue.
- Repeat for four rounds total, using the same four problems each round if you can manage it, or dropping to easier ones if your grip is fading.
- Don't top out. Climb to the last hold or a clear finish point, then step or hop off. Topping out wastes time and adds inconsistent rest between problems, which breaks the drill's timing.
- If you can't finish all four in a round, pick easier problems for the next round rather than grinding through repeated failures. Failing over and over turns a power-endurance drill into limit bouldering, a completely different stimulus.
That's the whole protocol: four problems, four rounds, rest only between rounds.
What grade should you pick for your 4x4 bouldering workout? (a graded table)
The right grade depends on your level, and getting it wrong is the single biggest reason people give up on 4x4s. Too hard and you'll fail the drill and end up doing limit bouldering by accident. Too easy and there's no real adaptation. Here's a graded starting point, in the same spirit as the progression logic our program engine uses, not a literal database extract.
| Level | Problem selection | Rest between rounds | Rounds |
|---|---|---|---|
| Beginner (V0-V2) | 4 problems well within your ability, prioritize clean movement over difficulty | ~4 min | 3-4 |
| Intermediate (V3-V5) | 4 problems 2-3 grades below your hardest redpoint | ~4 min | 4 |
| Advanced (V6+) | 4 problems near your limit minus 2, tighter rest as you adapt | 3-4 min | 4-5 |
One honest guardrail: if you're brand new to climbing, build a base of movement quality and general fitness first. Power-endurance training is most useful once you already have some strength and technique to protect, not as your very first training focus. If you want this dosing built into a full training block instead of a single session, an intermediate mesocycle runs this same progression logic across four weeks with a proper deload.
How to progress your 4x4 bouldering workouts
Once a 4x4 stops feeling hard, progress it in the right order. Gripped's coaching writeup on bouldering 4x4s lays out an honest sequence, and it's worth following exactly: increase the difficulty of your problems first, then reduce the rest between rounds, and only after that add more rounds (5x4, or eventually 6x4). Don't try to add "intensity" by climbing faster. Speeding up cuts your time under tension and actually reduces the training stimulus you're trying to build, the opposite of what you want.
Consistency matters more than any single hard session. Run 4x4s regularly, roughly 1 to 2 times a week within a training block, rather than as an occasional stunt session. That frequency lets the adaptation build without burying you in fatigue you can't recover from before the next attempt.
Want a way to track this as you progress? Enter your email and we'll send you the 4x4 Progression Tracker, a free printable PDF for logging your grades, rounds, and rest across a full training block.
5 mistakes that ruin your 4x4 bouldering workouts
These are the same mistakes that show up again and again in climber forums and comment sections whenever this drill comes up.
- Speeding up to "make it harder." Climbing faster doesn't add intensity, it just cuts your time on the wall and weakens the stimulus you're trying to build.
- Picking the wrong grade. Too hard and you fail the drill, turning it into limit bouldering by accident. Too easy and your forearms never get taxed enough to adapt.
- Topping out or wasting time between problems. Every extra second between climbs breaks the work-to-rest ratio the drill depends on.
- Letting technique fall apart under the pump. Sloppy feet and over-gripping when you're tired aren't just wasted reps, they're exactly how tweaks happen.
- Doing 4x4s too often, including back to back days. This is a high-fatigue drill. Running it daily doesn't speed up progress, it usually just buries you in fatigue you can't recover from.
The physio lens: fatigue, technique, and staying injury-free
This is the part most 4x4 guides skip entirely, and it matters. A 4x4 bouldering workout is done pumped, tired, and with degrading technique by design, which is exactly the state your fingers and shoulders are most vulnerable in.
The guardrail is simple: when your technique visibly breaks down, feet start cutting loose, you're over-gripping holds that don't need it, or your latches turn sloppy, that's your body's signal to stop the round. It is not a cue to grit through for one more problem. Learn to autoregulate by feel (your rate of perceived exertion, or RPE) rather than forcing a fixed number of rounds regardless of how you feel that day. Avoid running 4x4s on back-to-back days for the same reason, your connective tissue needs real recovery between high-fatigue sessions like this one.
To be clear, normal pump and muscle fatigue are expected and part of the point. Pain that changes how you move, or soreness that lingers well past a day or two, is different, and that's a signal to see a professional rather than to self-diagnose. Nothing here is a diagnosis or a substitute for that.
Not sure power-endurance is even your actual limiter? Take the free 5-minute assessment before you build a whole session around a guess.
When to use a 4x4 bouldering workout (and where it fits in your week)
Run 4x4s about 1 to 2 times a week within a training block, not every session. Substr8 Climbing makes a fair point in their comparison of 4x4s versus interval training: 4x4s are a great tool early in a training cycle to build a power-endurance base, and later on they work well as an occasional "topper" session during a performance or redpoint phase. They are not meant to be your only tool, every single week, indefinitely.
They're also not always the right priority. If your actual limiter is finger strength or technique rather than power-endurance, a 4x4 is the wrong place to spend your limited training time, use the free 5-minute assessment to find out before you guess. If you're only training a 2-day training week, a 4x4 bouldering workout is an ideal Day 2 session, since your first day can carry strength and power while this one covers volume and power-endurance.
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Frequently Asked Questions
What is a 4x4 in bouldering?
A 4x4 bouldering workout is a drill where you climb four boulder problems back to back with no rest between them, then rest, and repeat for four rounds total. It's used to build power-endurance, your resistance to the forearm pump.
How do you do a 4x4 climbing workout?
Warm up, pick four problems 2 to 4 grades below your max, climb all four with no rest between them, then rest about 4 minutes (or around 10 minutes if you're doing it on routes), and repeat for four rounds.
What grade should I pick for a 4x4 bouldering workout?
Beginners should pick problems well within their ability, intermediate climbers should go 2-3 grades below their max, and advanced climbers can go closer to their limit minus 2. The graded table above gives a full starting point by level.
How often should I do 4x4 bouldering workouts?
About 1 to 2 times a week within a training block, not every session. This is a high-fatigue drill, and running it too often usually causes more harm than benefit.
Are 4x4 bouldering workouts good for beginners?
Yes, at an easier grade, well within your ability, with a focus on clean movement rather than difficulty. Brand-new climbers should build a base of movement and general fitness first before making power-endurance a primary focus.
Do 4x4 bouldering workouts build power or endurance?
Neither, exactly. They sit deliberately in between and train power-endurance, your ability to keep pulling hard moves back to back without the pump forcing you to let go.
Should I top out on 4x4 boulder problems?
No. Climb to the last hold or a clear finish point and step or hop off instead. Topping out wastes time and adds inconsistent rest between problems, which breaks the drill's timing.
What is the rest time for a 4x4 (bouldering vs routes)?
For bouldering, rest around 4 minutes between rounds. For routes, rest closer to 10 minutes, since each route attempt takes longer and generates more fatigue than a single boulder problem.
A 4x4 bouldering workout is a simple drill that's easy to run wrong. Get the grade, rest, and technique right, progress it honestly in the correct order, and respect your recovery, and it becomes one of the most effective tools you have for building power-endurance. If you're also working on a specific grade ceiling rather than just power-endurance, our V5 plateau guide walks through how to diagnose and train your actual limiter.
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