PodOBlog #5
28 November 2025
Hiya Dad,
I’ve probably gone overboard on colour coordination today, my orange gym top matching my Hokas makes me look like I’ve been tangoed. Do you remember that ad? These trainers give me all-day comfort, but they don’t suit everyone. I’ve been considering how trainer design affects hips, pronation and overall running form.
A paper published by Kettner, Stetter and Stein (2025) examined the effects of running shoe stack height on running style and stability. Thicker-soled “super shoes” do change how people run and can make certain movements slightly less stable, but this study did not find that they are inherently dangerous.
The researchers tested 17 experienced runners on a treadmill at two speeds (10 and 15 km/h), using three very similar shoes differing only in sole height: low (27 mm), medium (35 mm), and high (50 mm). They used 3D motion cameras and clever analyses to measure how long each foot stayed on the ground, how bouncy the runners were, how their joints moved and how consistent key body parts—such as the hips—were from step to step.
In the thickest shoe, each foot stayed on the ground for a slightly larger portion of each stride, showing that sole height alone can subtly change running style. At the faster speed (15 km/h), the higher shoes (medium and high) were associated with a lower step rate relative to leg length, typically resulting in slightly longer steps than with the low shoe. In other words, longer strides but slower. As the soles got thicker, the runners’ bodies moved up and down more with each step. The lowest shoe behaved most like a firm spring, with the highest measured vertical stiffness.
The thickest shoe also led to more time spent in eversion (often called pronation) during stance compared with the medium shoe. Some of my patients worry about pronation, but it’s a natural foot motion; likewise, supination. I tell them that pronation itself isn’t bad, but in extremes, it can make the ankle less stable.
Overall, the study supports the idea that simply changing the sole's thickness can meaningfully alter how someone runs, even when the shoes are otherwise very similar. The tallest sole (50 mm) produced a combination of longer ground contact, more vertical movement, more time with the foot rolled outward and slightly less stable hip motion. These changes could affect performance or injury risk if repeated over long distances or at high training volumes.
Importantly, the study didn’t measure joint loads, energy cost or actual injury rates, so it can’t say that tall soles cause injury. Instead, it reasonably concluded that very tall soles come with movement patterns worth monitoring, while moderate stack heights may offer the best balance of cushioning, hip control and stability.
Dad, you can probably tell I enjoyed this paper, and I’ve prattled on a bit and definitely enjoyed it more than the one about Nordic skiers, which made me want to ball up A4 paper and hurl it at the window like snowballs.
If you made it this far, I think you deserve a slug of London Pride and a dose of Sibelius.
Thinking of you,
Pen xx