Running shoes have grown considerably thicker over the last decade, and the change alters more than cushioning. Increasing the distance between the foot and the ground changes the mechanics of the ankle in ways that follow directly from leverage.
Height creates a lever at the edge of the shoe
When a foot lands slightly off centre, the shoe contacts the ground at its edge rather than flat. The ground pushes upward at that edge while the ankle sits above the midline of the shoe.
The horizontal distance between those two points, combined with the height of the stack, determines the twisting force applied to the ankle. A taller shoe lengthens that lever arm.
The same landing error therefore produces a larger rotational demand in a thicker shoe, which is the mechanical basis for concerns about ankle stability in high-stack footwear.
Wider bases counteract part of the effect
Manufacturers have widened the base of tall shoes, particularly at the midfoot and heel, which increases the range of foot positions that still produce ground contact under the joint.
A wider platform means a greater sideways displacement is required before the shoe begins to tip. Within that range the leverage problem does not arise.
The trade-off is mass and the freedom of the foot to move naturally, since a wide, tall platform constrains how the foot behaves during the transition from landing to push-off.
Soft material adds its own instability
Compliant foam compresses unevenly under an off-centre load, so the platform itself tilts. That tilt occurs after contact and is not something the runner can anticipate.
The softer the material, the more it deforms, which is why perceived instability tends to accompany the softest and thickest constructions rather than height alone.
Some designs address this with firmer material at the edges or with structural elements that resist compression asymmetrically.
Sensory information from the foot is reduced
A thick, soft layer between the foot and the ground reduces the mechanical information reaching the sole, where dense sensory receptors normally report surface texture and pressure distribution.
Less information means the corrective responses that stabilise a landing are triggered later, which matters most on uneven ground and in low light.
Adaptation takes time and varies by runner
Changing stack height changes which tissues are loaded, so a transition redistributes work between the ankle, the calf and the knee rather than reducing load overall.
This is why abrupt changes in footwear are associated with new complaints, and why any change is introduced gradually alongside advice from a qualified practitioner where symptoms exist.
