Also called kneebar, knee scum, knee clamp · Feet and legs
You wedge your leg between a foothold and a surface above the knee, with the toe pushing one way and the thigh the other. Your hands can then rest or move. A knee scum is the light version: the knee presses lightly and takes a little weight [116].
Grade Rare, because it needs exactly the right gap [117]. Indoors it shows up on steep V5+ problems with big volumes (judgement). Learn the drop knee first [118].
How to do it
Find a foothold and a flat surface about one shin length from it. That is the distance from the top of your knee to your big toe [118].
Place the foot first. Then wedge the knee in and load it [113].
Press with the lower thigh, just above the kneecap. Never use the kneecap itself [118].
Dig the big toe into the foothold. Lift the heel towards the knee surface, like a calf raise [118].
Push only as hard as you need to stay in [116]. Let your weight sink in slowly [117].
Press the free leg against the wall. Knee, toe and free foot form a tripod [116, 118].
Gap too short? Rock onto the foot and angle the shin. Gap too long? Point the toes [116].
To leave, tighten your middle and plan where the feet go. Toe in hard and pull down with the hands. Walk the feet up first, so you swing less [116].
Kneepads: strap-on pads are easiest for bouldering. Wear them on bare skin, just above the knee. Tape them if they slip [116]. A pad grips better than trousers or bare skin [118].
Figure 26 Side view of a 40° overhang. The right toe digs into the foothold. The thigh just above the knee presses up under the volume. The left foot presses on the wall below. The right hand is free.
Common mistakes
Letting the pad slip. A slip of a few millimetres makes a tight bar fail [116].
Having no exit plan. Your whole body swings out [116].
Wedging the leg where it could stay stuck in a fall [118].
