Learn smearing in bouldering: press the shoe flat into the wall, stack your weight over the foot and stand on slabs with no edge. Step by step, no shortcuts.
Smearing means pressing the shoe flat against the wall or a volume without any edge and standing on friction alone. The honest answer to "Does that really hold?": yes, but only if you actively push into the wall. The shoe does not hold because it hooks onto something. It holds because you press it against the surface.
Why bother? In a study of eleven female climbers, the more experienced climbers loaded the footholds harder than the novices and got through the same route with a lower heart rate and lower oxygen uptake. Load on the feet was highest on the flattest wall (85°, just under vertical) and dropped as the wall got steeper (85°, 90° and 98° were tested) [1]. Slab climbing is pure footwork, and smearing is its foundation. It fits one of the five climbing principles from sports science: movement starts from the legs [2].
Honest warning: smearing feels wrong at first. Everything in you wants to put the foot on an edge. Expect a few sessions before you trust the shoe (an experience value, not a measurement). There is hardly any solid bouldering data on shoe rubber friction against the wall, so everything below about foot technique is coaching consensus, not study evidence.
Entry criteria (practice standard):
On a vertical wall, find a flat surface at knee height. Place the ball and front of the shoe flat, heel slightly lower than the ball. Hands on big holds, arms long. Then push the shoe into the wall as if you wanted to push the wall away.
Milestone: you stand on a smear for ten seconds without the shoe slipping.
Slipping happens when your weight hangs beside the foot. Bring the hip over the standing foot, keep the torso upright and do not glue your chest to the wall. Your weight should press the shoe into the wall, not pull past it.
Milestone: you stand on the smear for ten seconds and release one hand for three seconds.
Place the foot, build pressure, only then stand up. Once placed, the shoe does not move: a shoe that slides has already lost. Move slowly and evenly, because any jerk can break the grip.
Milestone: five steps in a row on an easy slab, every smear holds on the first try.
In a real boulder the smear is often the in-between step and the edge the resting point. Decide anew on every move: is there a real foothold? Use it. If the edge is tiny or sloping, a flat smear is often the better choice.
Milestone: you climb an easy slab boulder and use at least three smears on purpose.
Down-climbing is the most honest drill: you barely see the foothold and must trust the shoe. Practice it just above the mat first.
Milestone: you climb an easy slab all the way down without jumping off.
A smear can slip without warning. On a slab you often slide down the wall instead of falling: scrapes on hands and knees are the result. The landing is the bigger risk. In a prospective study of 507 boulderers, 44 percent got injured within twelve months. Lower-limb injuries made up only 23 percent but were more often severe and more often caused by falls and jumping off [4]. In climbing in general, almost half of all acute injuries involve the leg and foot [3].
So: practise smearing at jump-down height first, keep the landing zone clear and land feet first with soft knees, then roll back. This does not replace supervised training. Beginners should have a coach show them falling technique and mat rules.
Think of your shoe as a palm: you would not tap a smooth stone with fingertips, you would lay your hand flat and press. Give the shoe a second to press on before you give it weight. This trick is practical experience, not proven, but for most people it changes the feel immediately. Set it, then load it.
Smearing is a foothold without an edge: you press the sole flat against the wall or a volume and stand on friction alone. That is why it only works with pressure into the wall and weight over the foot. It is typical on slabs and vertical walls where no real foothold is available.
Place the ball and front of the shoe flat, heel slightly lower. Bring the hip over the standing foot, keep the torso upright and push the shoe into the wall. After that, do not move the foot. Step up slowly and evenly, because a jerk can break the grip.
Usually it is one of three things: your weight hangs beside the foot (chest at the wall, bum out), the heel is pulled up, or the foot is shoved after placing. On top of that, many people start too steep. Begin on an easy slab and focus on pressure, not strength.
When the edge is tiny, sloping or round and your shoe does not sit securely on it, a flat smear is often more reliable. If there is a real, large enough foothold, use it. Decide anew on every move.
Half Crimp: Holding Small Edges the Right Way