Why Climbers Keep Blowing Pulleys and the Training Variable Most People Ignore

Nearly half of recreational climbers have hurt a pulley. A 2025 study published in BMJ Open Sport & Exercise Medicine surveyed 745 recreational climbers and found 47% reported a pulley injury, 47% reported joint pain or swelling, and 14% had a flexor tendon injury. Seventy-seven percent had been injured at least once, with fingers and hands accounting for most of it.

Most climbers file that kind of injury under bad luck. A bad move on a bad hold on a bad day. But the distribution isn't random. It follows from how pulleys work, how crimp loads them, and one specific thing most climbers never train.

Why Pulleys Take the Most Damage

Finger flexor tendons don't run freely through the finger. They're held against the bone by annular pulleys — five per finger, A1 through A5 — that act as ligamentous loops keeping tendons in contact with bone during flexion. A2 and A4 carry most of the load during climbing, with A2 doing the bulk of the work.

In a full crimp — knuckles high, DIP slightly hyperextended — the force through A2 can reach several times bodyweight. Vigouroux et al. modeled this and found the middle and ring fingers show consistently higher pulley load than the index or little finger during sport climbing. The ring finger is the most common site for A2 pulley rupture. If you've torn one, it was probably that finger.

Half-crimp reduces pulley load. Open hand reduces it more. But that's not an argument for ditching the crimp — it's an argument for building fingers that can actually handle crimp forces without something giving way.

What the BMJ Data Actually Says About Hangboarding

The 2025 study also found that injury odds were higher among climbers who used a fingerboard. This gets misread constantly. It doesn't mean hangboarding causes injury. It almost certainly means climbers who train harder are exposed to more load — and load without structure is where injury accumulates.

Saeterbakken et al. (2024), in a review published in Sports Medicine Open, put it plainly: structured low-volume, high-resistance finger training is a feasible injury prevention approach, but fingerboard and campus board training should be limited in lower-graded climbers due to high mechanical stress on the flexor system. Load without a base to absorb it isn't training. It's just exposure.

And then there's the thing almost nobody addresses: climbers don't train the back of their fingers.

The Flexor-Extensor Problem

Devise et al. (2023) tested 78 experienced climbers and found a significantly higher flexor-to-extensor strength ratio in climbers compared to non-climbers. Years of pulling-dominant training will do that. The researchers flagged it as potentially detrimental to finger strength and a possible contributor to injury risk.

The same group then ran a training study with 52 experienced climbers split into four groups: flexor-only, extensor-only, paired, and control. Only the extensor-only group significantly improved finger extensor strength. Training extensors alongside flexors in the same session didn't shift the ratio the same way. If you want to close the gap, extensors need their own work.

The connection to pulleys is mechanical. Finger extensors help stabilize the finger during gripping. When they're weak relative to the flexors, more load on hard moves — especially crimps — routes directly through the pulley system without that muscular check. Not a guarantee of injury. Just how the conditions get set.

What the Training Should Actually Look Like

Two things change your odds: real flexor strength built through a protocol, and extensor work you're probably not doing.

Hermans et al. (2022) followed 35 intermediate-to-advanced climbers through 10 weeks of hangboard training and found meaningful gains in finger force, explosive strength, and endurance. The protocol mattered — not just the hanging. Load, edge depth, grip position, rest intervals. These are actual variables, not background details.

Gilmore et al. (2024), in a retrospective study in Sports Medicine Open, analyzed climbers using the Crimpd app who logged Max Hangs, Abrahangs (a low-intensity protocol), or both. Frequent low-intensity loading produced grip strength gains comparable to max-intensity work. Combining both produced the best results. If you haven't built connective tissue tolerance yet, high-intensity loading isn't where you start — and the data backs that up.

On the extensor side: rubber band extensions, isolated finger lifts, open-hand reverse hangs. The 2023 Devise study used 4 weeks of twice-weekly extensor training to produce a 41.4% increase in maximum extensor strength in the TExt group. Four weeks. Twice a week. Most climbers skip this because it doesn't feel like training. That's kind of the point.

The Crimp Position Question

Full crimp puts the most force through A2. That's manageable if you've built the capacity for it. It becomes a problem when you're crimping at your limit every session with no variation in grip position.

Training open-hand on a board isn't a consolation prize for people who can't crimp hard. It's a different load distribution, a different adaptation, and it happens to reduce what's going through your pulleys on the wall. Climbers who train all three positions — crimp, half-crimp, open hand — tend to stay healthier than climbers who only train the one they reach for when a move gets hard. The research doesn't have a clean RCT on this yet, but the biomechanics aren't complicated.

The Short Version

  • Fingerboard twice per week. Saeterbakken et al. (2024) describe twice-weekly sessions as the feasible frequency. More volume before your connective tissue has adapted isn't a faster route to strength.
  • Train all three grip positions. Crimp, half-crimp, open hand. Not just the one you use on hard moves.
  • Add extensor work every session. Rubber bands. Five minutes. Devise et al. (2023) showed a 41.4% extensor strength gain in four weeks with targeted training. Most climbers have never done a single set of this.
  • Progress load before volume. Add weight as the fingers adapt. Stacking more sessions or sets without adding load is how you accumulate fatigue without building capacity.
  • Vary edge depth deliberately. Smaller edges increase pulley stress. Train on edges that are hard but not desperate. The difference between a training stimulus and a pulley incident is sometimes a few millimeters.

The 47% pulley injury rate isn't something that just happens to climbers. It follows from how climbers train — a lot of flexor work, essentially no extensor work, no load progression, no grip position variation. Those are all changeable variables.

The Zodiac edge system covers multiple grip positions and depths because that's what the injury distribution points toward — not as a product angle, but because training only what you're already good at is how you end up on the injured list. Whether you use our edges or something else, the question is whether your protocol is actually built around where climbers get hurt.

Sources

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