Learn compression in bouldering: press two opposing holds or volumes toward each other with arms and body tension. With milestones and safety notes.
In compression you press two opposing surfaces, holds or volumes toward each other and hold yourself through pressure and body tension. The honest answer to "Isn't that just holding on?": no, because the hold itself carries hardly anything; the counter-pressure between the surfaces does. Whoever understands compression can hold positions that would never work with finger strength alone.
Sports science describes the principle like this: body parts should establish optimal wall contact. This can arise through form-fit, but also through force-fit via friction or clamping [1]. That is exactly what happens in compression: you generate pressure that builds friction and a clamping effect. At the same time, the same principle says the applied force should only be as high as necessary ("soft gripping") [1]. If you press too hard all the time, you lose the strength for the next moves. A detail from the same systematization comes on top: to increase tension in rotated techniques, two footholds are pressed apart [1]. That is also a form of counter-pressure.
Compression typically shows up on arêtes, on volumes that face each other and at wall corners where two surfaces meet at an angle. There often is no hold in the classic sense that you could pull. Instead, hold arises because you use hands, chest and feet as a pair of tongs. This feels unfamiliar at first because you are not looking for holds but for counter-pressure.
Expect it to take several sessions until you find the right pressure (an experience value, not a measurement).
Entry criteria (practice standard):
Find two holds, volumes or edges that face each other. Place palms or sides against them. No pressure yet, just position.
Milestone: You stand between the surfaces for ten seconds.
Tense chest, back and core and press the surfaces toward each other. The pressure comes from the body, not the fingers. Imagine hugging a big tree trunk: the arms close, but the power sits in chest and back.
Milestone: You hold the pressure for five seconds without your hands moving.
Place your feet so they support the pressure and the hip stays close to the wall. Feet and hands work together.
Milestone: You hold pressure with hands and feet for ten seconds.
Release one hand and reach on while the rest of the body holds the pressure. The pressure must not break off. Move only one contact point at a time and keep the others under pressure. If you notice the pressure fading, go back to the last stable position.
Milestone: Three moves in a row under pressure.
Climb a medium boulder with a compression section. Start at low height before you practice the same movement higher.
Milestone: One calm run at low height.
Compression strains arms, shoulders and core. In a prospective study of 507 boulderers, 63 percent of all injuries affected the upper extremity [2]. A systematic review found that a strength training intervention prevented shoulder and elbow injuries [3]. Compression can fail abruptly when the pressure drops, and then you are suddenly in free fall. The DAV advises route setters not to place the main difficulty of a boulder in hard-to-control moves at maximum height [4]. So practice compression at low height, warm up shoulders and core and stop if your shoulder or chest pinches. This guide explains and motivates but does not replace supervised training.
Imagine you want to squeeze an orange between the surfaces without crushing it: firm enough that it holds, but not so firm that you cramp. This is practical experience and not proven, but the image helps you dose the pressure.
Compression means pressing two opposing surfaces, holds or volumes toward each other with arms and body tension. The hold comes from counter-pressure, not from a single hold. The principle of force-fit describes friction and clamping as a form of wall contact [1].
Find two opposing surfaces, build tension through chest and back, involve the feet and keep the pressure only as high as necessary. Release a hand only when the pressure is stable.
Usually you press too hard or only with your arms. Use chest, back and core, support with the feet and dose the pressure.
On arêtes, on volumes that face each other and at wall corners. There often is no hold in the classic sense, but hold through counter-pressure. If in doubt, ask the gym staff for boulders with compression sections.
It can fail abruptly when the pressure drops. Practice it low, warm up shoulders and core and don't move hard-to-control moves to great height [4].
Full Crimp: Maximum Hold at a High Price