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Pumped Thumbs When Jamming? Get the fix

by Pete Whittaker
Dec 30, 2025
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Hey Cracksters,

Ever look at a hand crack and think, "I'm doing the hand position right, but my thumb is getting too tired to stay in the jam"? When the pump clock is ticking, relying on brute strength is a losing battle. But there’s a sneaky, low-energy trick that can often buy you the few seconds you need to recover, even when your hands are exhausted.

The Forearm Brake: A Passive Trick for Exhausted Jams

The difference between falling off and hanging on often comes down to leveraging every available bit of friction—and for a well-placed hand jam, that means using your forearm.

Most climbers focus only on the hand itself (as we always say, this is where you should be putting your main attention). However, when you start to get tired and pumped, this focus can change. Here's a little trick to use, when those thumbs of yours are boxed!

 
 

The Trick: Get Greedy with Depth.

1. Insert and Push Deep: Insert your hand, and instead of keeping your wrist lined up with the crack edge, give it a final deliberate push deeper into the crack.

2. Initiate the Lock: Now you can initiate all the steps from start to finish of your hand jam. (If you’re unsure how to execute this correctly, you can join Global Crack School as it’s re-opened.)

The Magic: This happens when you start to get friction from the lower part of your forearm against the crack walls. This friction is low-energy and helps hold you in place by acting as a passive expansion jam. I.e. your forearm naturally wants to expand out against the crack wall with no effort from you.

On cupped hand cracks (which are slightly wider), the pump is going to be even worse, so use of the forearm is even more critical. (Again, if you are unsure of the techniques to execute a cupped hand jam to help minimize the initial pump, then Global Crack School will sort you out, we have a couple of tricks up our sleeve for you)

 

Want to learn more about crack climbing technique? join Global Crack School

 Join here

 
 

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