The Grip Your Hangboard Can't Train

Most climbers train one grip. Some variation of half-crimp, on a flat edge, maybe a drag day mixed in. The edge doesn't move. The load is predictable. Progress is a number on a loading pin.

That's fine. It also leaves a gap.

Rolling edges and claw grips close it. Not by replacing what you already do, but by loading your fingers in positions a flat edge lets you skip.

What "Training Weird" Actually Means

Training weird is grip geometry that forces engagement and strict form. That's the whole definition. The tool isn't weird because it looks unusual. It's weird because you can't cheat it.

A flat 20mm edge is generous. The surface is predictable, your skin has time to settle, and friction does a surprising amount of the holding. Under maximal load, friction between the flexor tendons and the A2 pulley can account for up to 18% of grip force (Schweizer, 2008). Almost a fifth of the work, handled by something that isn't strength.

A rolling edge removes the stability. A claw grip removes the mechanical assist your half-crimp quietly relies on. Both shift the stimulus from "how much can you hang" to "can you actually hold this position under load."

Rolling Edges: Rotational Instability as a Training Variable

The rolling edge block rotates. It wants to spin out of your grip, and the only thing stopping it is the pressure you apply through your fingertips. That's the mechanism.

Two things happen under load that don't happen on a flat edge:

  • You can't rely on skin friction. If the hold is rotating, skin contact alone won't hold it. You have to actively squeeze. The 18% assist Schweizer described disappears the moment the edge starts to move.
  • You can't sag into the position. Passive hanging requires a stable surface. A rotating edge requires continuous active engagement, which is what climbing actually demands on the wall.

Lower peak loads than a flat edge, higher engagement cost per rep. That's the tradeoff. You won't hit max hang numbers on a rolling edge, and you shouldn't try. It's a different stimulus for a different problem.

Claw Grips: FDP Isolation Without the Half-Crimp Assist

Your fingers are powered by two main flexor tendons. The flexor digitorum profundus (FDP) runs to the fingertip and controls the distal joint. The flexor digitorum superficialis (FDS) runs to the middle bone and controls the PIP joint. Both pull. They pull differently depending on what your fingers are doing.

Biomechanical work by Vigouroux and Schweizer mapped out how grip geometry changes which tendon carries the load. Crimp positions load the FDP heavily. Slope positions shift more work onto the FDS (Vigouroux et al., 2006; Schweizer and Hudek, 2011). Half-crimp sits in the middle and lets both contribute, which is part of why it feels so stable.

A claw grip changes that. The DIP stays flexed, the fingertip pulp is the contact point, and FDP has to do the work without the usual mechanical split. You're not adding a new muscle to the job. You're taking away the help.

If your open-hand sloper feels disconnected from your crimp strength, this is part of why. The grip positions you train determine which tendons get stronger. Specificity is boring but brutal: you get strong at what you train, in the positions you train it. Fingerboarding works well because it's the closest thing to the actual demand, and the closer the stimulus matches the position, the better the transfer (Langer et al., 2023; Hermans et al., 2022).

The On-The-Wall Payoff

You'll feel it first on the holds your usual training doesn't prepare you for. The hold on your project that feels weirdly blank. The sloper that should feel easier for how big it is. The shouldery crimp that collapses the second you load it wrong.

That's the real outcome. Not a bigger 20mm number. A smaller gap between your strong grip and your weak ones. You stop being surprised by positions that used to feel bad, because you've been loading them on purpose instead of hoping climbing would handle it.

How to Use It

Rolling edges and claw grip work are not max hang tools. Running a rolling edge like a max hang day is a good way to frustrate yourself and learn nothing. Use them alongside your normal training, not as a replacement.

Two ways to fit them in without overhauling your cycle:

  • As a second finger day at lower intensity. If you're already doing one max hang session a week, add a rolling edge or claw session two to three days later. Keep the load submaximal. Focus on clean engagement, not peak force. Think 4-6 reps of 6-10 second holds per grip, with long rests.
  • As warmup before climbing. Short pulls on a rolling edge before a bouldering session wake up active grip pressure in a way a passive warmup hang doesn't. Two or three sets at low intensity is plenty.

Track it loosely. Progress on these tools isn't a clean loading-pin number, and trying to force that framework onto them will miss the point. The question is whether you can hold the position with clean form under a load that challenges you. If yes, it's working.

The Skeptic's Pushback

The honest objection: if a rolling edge produces lower peak loads than a flat edge, and max force correlates with climbing grade, isn't this a waste of training time?

No, and the reason is that peak force on a 20mm isn't the only thing that carries a send. Grip-specific strength does. Active engagement does. The ability to hold a rotating, low-friction, or geometrically awkward hold without collapsing does. A rolling edge trains all of that. A flat 20mm trains one variable extremely well and leaves the others to chance.

You still need your max hangs. You still need your flat edges. Training weird isn't a replacement. It's the part of the stimulus your normal training was quietly leaving out.

Sources

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