4x4 Climbing Training: The Complete Guide

Four boulder problems, climbed back to back, four times through. That's the whole workout.

It's also the most misused session in climbing. 4x4s get handed out as generic gym conditioning. Get pumped, get fit, feel like you did something. That is precisely why they mostly don't work. Power endurance is a specific adaptation with a specific stimulus. You either hit it or you spend forty minutes accumulating volume with deteriorating technique.

The difference between those two sessions comes down to a handful of numbers. Here they are.

Not the Norwegian 4x4

If you arrived here looking for the Norwegian 4x4, you're on the wrong page. That protocol is 4 × 4 minutes at 90–95% of max heart rate with 3 minutes of active recovery between efforts, and it's a running, cycling and rowing workout for raising VO2max.

Same name, completely unrelated training. Everything below is the climbing one.

What a 4x4 Actually Trains

Power endurance: the ability to keep producing near-maximal force once your forearms are already loaded.

That sits in a specific window. Each problem is a 20–40 second effort. A set of four runs 2–4 minutes of near-continuous climbing. Rest between sets is deliberately incomplete, so you start each set already partly occluded and never fully clear.

Compare that to what sits either side of it. Max strength work is seconds of effort with full recovery, because you want every attempt fresh. Aerobic capacity work is long, easy and high volume, well below the threshold where you'd pump. The 4x4 lives in the gap: hard enough to matter, long enough to hurt, repeated before you've recovered.

The failure mode it fixes is a familiar one. You fall off the back half of a boulder problem you can do move-for-move when fresh. You get to the last three bolts of a route with the moves dialled and nothing left in your arms. That's a power endurance problem, and it is one of the few climbing qualities that responds quickly to targeted work.

If your efforts routinely run past a minute, on long routes or sustained pitches, the 4x4 is the wrong length. Use a longer circuit protocol instead, like the one in One Power Endurance Workout to Rule Them All.

The Standard Protocol

4 problems, climbed back to back
4 sets, so 16 boulders total
Rest between problems within a set: walk to the next problem, that's it. 15–30 seconds. Cap it at 60 if your gym layout forces it
Rest between sets: 4 minutes. The workable range is 3–5
Problem length: 4–8 moves, 20–40 seconds of climbing
Total work: 25–35 minutes, not counting your warm-up

Sixteen boulders is not a lot of climbing. That's intentional. The stimulus comes from density, not volume.

Picking Your Problems

This is the section that decides whether the workout does anything. Get it wrong and nothing else in this guide can save the session.

Set the problems 2–4 V-grades below your flash grade. If you flash V6, your four problems live somewhere in V2–V4. If you flash V9, you're at V5–V7.

The test that matters more than the number: you should be able to flash all four on any given day, cold, without thinking about the sequence. If you need two goes to remember the beta, it's too hard for this workout. You are not solving problems here, you are executing known movement under fatigue.

A few more rules:

Vary the angle and style. Four steep crimp problems trains one tissue and one skill. Mix slab, vert, overhang, different grip types.
Keep them physically close. Walking 40 metres between problems is a different workout with different rest.
Use the same four problems for the whole block. If the problems change every session, nothing is comparable and you have no idea whether you improved.

Then calibrate by outcome. Sets 1–3 should go clean. Set 4 should be a genuine fight. If you fall off more than about two boulders across the whole session, your problems are too hard. If you finish all sixteen with clean movement and could comfortably run a fifth set, they're too easy.

Rest Is Part of the Prescription

Four minutes means four minutes.

Rest creep is the second fastest way to neutralise this session. You chat between sets, you check your phone, someone else is on your third problem, and a 4 minute rest quietly becomes 8. At 8 minutes you're recovered, and a recovered 4x4 is just easy volume with extra walking.

Start a timer at the moment you top the fourth problem. Be on the wall when it goes off.

Where It Fits

In the week: one to two sessions, never more than two, never on consecutive days. Leave 48 hours between a 4x4 and limit bouldering or a max hangboard session.

In the session: after a full warm-up, at the start of the hard work. Not bolted onto the end of two hours of projecting. A 4x4 done on an already-empty tank isn't power endurance training, it's fatigue.

In the block: power endurance is a peaking quality. It belongs after a strength or max phase, roughly 4–6 weeks out from the trip or the redpoint window you're building towards. It is not a year-round staple, and running it as one costs you the strength phase that raises the ceiling everything else operates under. If you haven't mapped where your peak actually sits, start with Plan Your Season, Not Your Week.

For what to fill the rest of the week with, Bouldering Workouts covers the other sessions worth building around.

How People Get This Wrong

1. The problems are too hard. By a distance the most common error. Hard problems mean falls. Falls mean unplanned rest. Unplanned rest destroys the density that produces the adaptation. You walk away with a bad limit session and a good story about how pumped you got.

2. Rest creep. See above. Untimed rest drifts long every single time.

3. Running them year-round as "conditioning." Power endurance decays in a few weeks and rebuilds in a few weeks. That's exactly why you shouldn't train it continuously. You're spending months on a quality you could rebuild in six sessions, at the cost of the strength work that actually moves your ceiling.

4. New problems every session. No baseline, no progression, no way to know whether any of it worked.

5. Four problems of one style. Usually the style you already like, on the angle you already prefer.

6. Treating the pump as the goal. The pump is a by-product. Density and movement quality are the targets. You can get a spectacular pump doing something useless.

Progressing It Over a Block

The 4x4 has exactly three levers: problem difficulty, rest length, and number of sets. Progressive overload means moving one of them, deliberately, and leaving the other two alone. Here's eight weeks:

Weeks 1–2, establish the baseline. Flash grade minus 3. Four sets, 4 minutes between. Note how set 4 felt and which boulders, if any, you dropped.
Weeks 3–4, compress the rest. Same problems, same four sets, inter-set rest down from 4 minutes to 3.
Weeks 5–6, raise the intensity. Rest back out to 4 minutes, problems up one notch to flash minus 2.
Weeks 7–8, pick one. Either cut the rest back to 3 minutes at the new grade, or add a fifth set. Not both.

One variable per two-week step. That's the whole method, and it's the same principle covered in Focus on One Variable at a Time.

Note that adding sets is the last lever, not the first. Most people reach for it immediately because more feels like progress. Extra sets add fatigue faster than they add stimulus.

Then drop 4x4s entirely in the week before a trip or a peak attempt. The adaptation is already banked; all another session does at that point is arrive on rock tired.

Who Should Not Be Doing 4x4s Yet

Plainly:

Under roughly a year of consistent climbing. Movement efficiency is your limiter, not fitness. General climbing volume buys you far more right now.
Anyone whose flash grade is low enough that flash-minus-3 is barely climbing. If you flash V2, there is no 4x4 intensity available to you. Build strength and mileage first.
Anyone whose real limiter is finger strength or technique. If you're falling off single hard moves when completely fresh, power endurance is not your problem and training it will not fix it.
Anyone carrying finger, elbow or shoulder niggles. High-density climbing on already-irritated tissue is the standard route from niggle to lay-off.
Anyone mid-season and close to a send. This is preparation work. Do it before the window, not during it.

None of that is permanent. It's a question of order.

4x4s Only Work If You Write Them Down

The protocol is progressive overload: grade, rest, sets. Three numbers that mean nothing individually and everything as a series.

"I think the rest was shorter last time" is not data. Neither is a vague sense that set 4 felt better.

Log four things every session: the four problems and their grades, your inter-set rest, sets completed, and which specific boulders you fell on. That last one is the most useful and the most commonly skipped. The fall pattern moves before anything else does. When set 3 stops costing you a boulder, it's time to raise the grade, and you'll see that in the log weeks before you'd feel it.

Eight weeks of 4x4s that you didn't record is eight weeks of guessing. Sequence tracks the workout structure and the climbs together, so grade, rest and sets sit in one place and the trend is visible without you reconstructing it from memory.

The 4x4 isn't complicated and it isn't magic. Pick problems that are genuinely easy for you, keep the clock honest, run it for a block at the right point in your season, and write down what you did.

Do that and it's one of the highest-return sessions in climbing. Skip any one of them and it's just a good way to get pumped.