Opening scene
Come down to the floor. Get onto your hands and knees; hands under your shoulders, knees under your hips.
Now we're going to do something, and it will take ten seconds.
Push the floor away from you without ever bending your elbows. The upper part of your back will rise slightly.
Then release. Lower your chest between your arms. Again, without bending your elbows.
Up, down. Do it two more times.
Now notice: your arms never moved. Your elbows didn't bend, your hands didn't lift, the angle of your torso didn't change.
But something moved.
Your shoulder blades.
Most people have never done this movement knowingly in their life. And this is the movement sitting right at the center of everything we talked about in the last two lessons.
Today's topic is these ten seconds.
What this lesson covers
First we'll set up the all-fours position and you'll see why it's this section's laboratory. Then we'll look at the isolated scapular slide in detail. After that we'll get to the most common mistake: a lot of people think they're doing this movement while they're doing something completely different. Then we'll build the connection between the pressure the hand puts into the floor and the shoulder blade's movement; that's where the lesson's name comes from. After that we'll talk about the second mistake, the low back sagging. At the end I'll give you three exercises. We'll work through sixteen examples. By the end of the lesson, you'll be able to move your shoulder blade on purpose.
Starting point
Why is this position a laboratory?
There are three reasons.
The first is that the load share is small. From Y1.39; most of the weight is on your knees.
The second is that there's no balance problem. There are four points of contact; the fear of falling disappears, and attention stays on the movement.
The third, and most important: you can free up one hand. At the wall, both hands were on the wall, and you couldn't control your own shoulder blade. Here, you can stand on three points and bring one hand to your own back.
The cleanest application of the isolation principle from Y1.13 is possible in this position.
Mechanism
Isolated scapular slide
That's what you did in the opening.
Now let's look at what's happening mechanically.
In Y1.37 you learned that the shoulder blade isn't attached to the ribs by a joint; it glides over them. And you saw that when the arm moves, the shoulder blade follows it.
Here, the opposite happens.
The hand is fixed on the floor. The upper arm bone is fixed relative to the torso too. So the only thing that can move is the relationship between the shoulder blade and the torso.
When you push the floor away, your shoulder blades move apart and your torso rises slightly between them. When you release, they move closer and your torso lowers between them.
How large is the range? In most people, about a fist's width. You're not going to chase the amount; what you're after is being able to go in both directions on purpose.
And one more thing: we gave you this movement as an action instruction in Y1.38. "Push the floor away from you." Now you're seeing what that sentence actually does.
The false push
Now, the most common mistake.
What happens? When a person is told "push the floor," they bend and straighten their elbows. They do a small push-up.
The torso rises and lowers, so the result looks similar. But the shoulder blade doesn't move at all.
How do you tell the difference? There are three ways.
The first way is the elbow. Your elbows should stay visually straight throughout the movement. The moment you see them bend, you're doing the false push.
The second way is the hand. Move to three points of contact; bring one hand to the opposite shoulder blade and do the movement with the supporting arm. Do you feel the bone sliding under your hand?
The third way is a mirror or a phone camera. Viewed from the side, does the angle of your elbow stay fixed?
The second way is the most instructive, because it gives both a diagnosis and feedback.
The hand–scapula connection
Now we're getting to the lesson's name.
You'll see this through a comparison. The method from Y1.36.
First try: place your hand loosely on the floor, keep the weight at the heel of the palm, and do the scapular slide. How much movement did you find?
Second try: grip the floor lightly from the base of your fingers, create a small hollow in the center of your palm, and do the same movement. Now how much?
In most people, the second try produces noticeably more movement.
The reason is this: a loose hand absorbs part of the push. When the hand connects firmly to the floor, the force reaches the other end of the chain, the shoulder blade.
That's why the grip from Y1.39 isn't only a wrist matter; it's a shoulder matter too. The two lessons work together.
The second mistake: the low back sagging
When some people push the floor away on all fours, their low back sags down.
Why? Part of the push gets absorbed by dropping the hips down instead of lifting the torso up.
This isn't a disaster; a small change in the low back is normal. The criterion is this: can you control it?
The control test is simple. Remember the torso line from Y1.33. Put your hand over your low back, do the push, and watch whether the surface under your hand changes noticeably.
If it changes, the fix is to reduce the amount of push. You're not chasing the range; you're chasing control.
Three exercises
The first exercise is the isolated slide. On all fours, elbows straight, ten slow repetitions. Go both directions on every repetition. Criterion: the elbows don't bend and the low back doesn't go out of control.
The second exercise is one-hand control. Move to three points of contact; put your left hand on your right shoulder blade and do the slide with your right arm. Five repetitions, then switch sides. Criterion: you feel the movement under your hand.
The third exercise is weight transfer. On all fours, keeping the push, slowly shift your weight from one hand to the other. Ten times. This is the first exercise that puts more load on one side, and it's preparation for the plank family. Criterion: the push doesn't disappear during the transfer.
The three exercises take three to four minutes total. Do them right after the wrist preparation from Y1.39.
Reading the examples
Master layer
Now let's refine this a little.
First: the false push isn't always a mistake. The movement done by bending and straightening the elbows is a legitimate exercise in its own right; it has its own name, and it belongs to the push-up family. The problem is doing it while thinking you're training the scapular slide. The two movements build two different capacities, and both are usable. Telling them apart means being able to choose; the same logic as the hinge vs. folding distinction from Y1.30.
Second: I described the shoulder blade's movement in this position as "back and forth," and that's a simplification. In reality the bone rotates, tilts, and slides at the same time; the four directions from Y1.37 work together. A two-way axis is enough for learning, but you need to know that what you're seeing is a simplified reading of a complex movement.
Third: the hand–scapula connection works in both directions. A firm connection at the hand improves the shoulder-blade movement, and the right shoulder-blade position also distributes the hand's pressure better. So whichever one you fix, the other improves somewhat too. The practical conclusion: start with whichever one is easier for you to feel. Some people grip with the hand easily and can never find the shoulder blade; for others it's the reverse. Both are a door opening onto the same chain.
Fourth, and subtlest: this lesson is this section's quiet center. It has no recognizable pose and no result that shows up in a photo. Standing on all fours and moving your shoulder blade a fist's width isn't something you'd tell anyone about. And yet plank, Downward-Facing Dog, and the entire arm-support family are built on this single action. A section's most defining lesson is usually its least flashy one; you've already seen this pattern in this course, in Y1.34 and in Y1.36.
Common mistakes and misconceptions
Common mistakeFirst mistake: pushing the floor means straightening your elbows.
The movement done by bending and straightening the elbows doesn't involve the shoulder blade, and even though it looks similar from the outside, it's a completely different exercise. In the scapular slide, the elbows stay visually straight throughout the movement; the entire movement happens between the shoulder blade and the torso.
Common mistakeSecond mistake: the bigger the range in the scapular slide, the better.
In most people the range is about a fist's width, and trying to make it bigger usually brings the low back into play. The criterion isn't the range; it's being able to go in both directions on purpose and with control. The range increases somewhat as a result of that.
Common mistakeThird mistake: how the hand presses into the floor is a wrist matter and has nothing to do with the shoulder.
A loose hand absorbs part of the push, and the force doesn't reach the shoulder blade. Gripping from the base of the fingers noticeably increases the shoulder-blade movement; the hand and the shoulder blade are two ends of the same chain.
Common mistakeFourth mistake: these exercises are just preparation; the real work happens in plank.
In plank, the load share and the demand on the torso are high, and isolating the scapular slide there is nearly impossible. This position is where the action is learned; plank is the application of the action once it's learned.
Practice
Keep in mind
The all-fours position is this section's laboratory: the load share is small, there's no balance problem, and you can free up one hand to control your own shoulder blade.
The scapular slide is the shoulder blade sliding back and forth over the rib cage while the arm's position stays unchanged.
The false push is done by bending the elbows and never involves the shoulder blade; the criterion for telling them apart is the elbows staying visually straight.
The hand's pressure distribution determines the shoulder-blade movement; a loose hand absorbs the push, a gripping hand transmits the force.
What's chased is control, not range; if the low back goes out of control, the amount of push is reduced.
Bridge to the next lesson
You now have an action in hand, and you can do it on purpose.
Now it's time to increase the load.
In the next lesson, your knees will come off the floor, and your torso will become a single line. But not on the floor — on an inclined surface.
Incline plank is the lightest member of the plank family, and it gives you exactly as much load share as you choose. You'll carry the shoulder-blade action you've learned there, and this time your torso will have a job too.