At the same 44.5mm stack, where the foam sits changes the ride
In short
On a running shoe spec sheet, stack height tells you how thick the foam under your foot is and nothing about where that foam sits. One recently reviewed high-stack trainer runs 44.5mm of stack with a 7mm drop, but puts 25mm of supercritical ATPU foam into the insole rather than the midsole as a drop-in — one of the largest drop-in midsoles in any production running shoe. The reviewer described it as feeling more connected to the ground than other max-cushion shoes, without the squishiness the category is known for.
See 44.5mm of stack on a spec sheet and you file the shoe under max cushion. Yet this one looks like an ordinary daily trainer from the outside. The difference is not how much foam there is but where it went — the shoe uses a drop-in midsole that places 25mm of foam where the insole would normally sit. The visible midsole gets thinner by that much; the total foam underfoot does not change at all.
What does a drop-in midsole actually change?
Normally foam is stacked up as the whole midsole beneath your foot. A drop-in sets a block of foam into the insole cavity, closing the distance between foam and foot. Functionally your foot sits down into the foam rather than perching on top of it. Same thickness, but with the compression happening closer to your foot, what the ground did reaches your sole faster. At 25mm, this shoe's drop-in is among the largest on the market.
Why does a high stack not feel squishy here?
What makes tall shoes feel unstable has less to do with foam thickness than with how well your foot is held over the platform. This model widens the platform and uses an engineered woven upper with suede overlays to keep the foot centred on it, while a rockered chassis carries you through the transition from landing to toe-off. The reviewer's verdict: none of the jelly-like sensation that max-cushion trainers often develop.
So how should you read the spec sheet?
Stack, drop and weight are still the fastest way to read a running shoe. Just remember that stack is a measure of quantity, not of position. Two shoes at 44.5mm — one with all the foam in the outer midsole, one with more than half of it raised into the insole — are not the same shoe. When reviews of similarly specced shoes contradict each other, this structural difference is usually what they are describing.
What does this mean for a lifter?
One conclusion changes and one does not. What changes: if you run as well as lift, do not screen shoes on the stack number alone — look at the construction. What does not: 44.5mm is 44.5mm wherever it sits. Close to your foot or close to the floor, it still compresses under a maximum, and in the deadlift it still adds distance to the pull. A drop-in makes a running shoe a better running shoe; it does not turn a running shoe into a lifting shoe.
Because a drop-in sits in the insole cavity, it usually lifts out. Swapping it for an off-the-shelf insole removes more than half the shoe's cushioning along with it. Check the thickness of what you are taking out before you replace it.
Frequently asked questions
What is a drop-in midsole?
Instead of stacking all the foam as the midsole, a block of foam sits in the insole cavity, reducing the distance between the foam and your foot. The reviewed model uses 25mm of supercritical ATPU foam this way, among the largest drop-ins in a production running shoe.
Can I choose a running shoe on stack height alone?
Not reliably. Stack tells you how thick the foam is but not where it sits. At the same 44.5mm total, a shoe with all its foam in the outer midsole rides differently from one with more than half raised into the insole.
Why do high-stack shoes feel unstable?
It is less about foam thickness than about how well your foot is held over the platform. A wide platform and an upper that keeps the foot centred reduce the jelly-like feeling even at a tall stack.
Does a drop-in midsole make a shoe suitable for lifting?
No. Moving the foam does not reduce the total thickness, so it still compresses under a maximal load and still lengthens the deadlift pull. Barbell work wants a flat sole that resists compression.
Can I replace the insole in a drop-in midsole shoe?
It is a bad idea. That foam block provides more than half the shoe's cushioning, so a standard replacement insole removes the ride the shoe was designed around. Check the original's thickness before swapping anything in.
Source: Men's Health