Lean in and fire one knee up.
Keep a straight line from heel to head, don't let your hips drop as you drive.
Leaning into the wall puts your body at the exact forward angle of sprint acceleration, and from there each rep is one violent knee drive at a time. The quads fire to punch the knee up to hip height while the glutes on the planted leg hold your hips high and your body line rigid. Working one side at a time makes it easy to spot a lazy leg, which is why sprint coaches lean on drills like this.
Acceleration mechanics. The lean recreates the body angle of a sprint start, and the drill grooves a fast, powerful knee punch while the rest of your body holds a rigid line.
Drive the knee up fast, return it with control. The speed is the point, but only inside a solid position. If your hips drop or your back arches, slow down and rebuild the line.
Enough that your body forms a clear straight line from heel to head, roughly the angle of pushing a car. Standing too upright turns it into a march and loses the acceleration carryover.
