A shoes’ age really DOES affect performance

Footwear ⋅ October 18, 2023

A new study throws a bit of light on this, and I found it really interesting reading.

The influence of shoe aging on children running biomechanics
Alexis Herbaut, Pascale Chavet, Maxime Roux, Nils Guéguen, Franck Barbier, Emilie Simoneau-Buessinger
Gait and Posture, Article in Press

Abstract

Athletic children are prone to overuse injuries, especially at the heel and knee. Since footwear is an extrinsic factor of lower limb injury risk, the aim of this study was to assess the influence of shoe aging on children running biomechanics. Fourteen children active in sports participated in a laboratory biomechanical evaluation. A new pair of shoes was provided to each participant at an inclusion visit. Four months later, the participants performed a running task and their kinematics and kinetics were assessed both with their used shoes and with a new pair of shoes identical to the first. Furthermore, mechanical cushioning properties of shoes were evaluated before and after in-vivo aging. After 4 months of use, the sole stiffness increased by 16% and the energy loss capacity decreased by 18% (p < 0.001). No ankle or knee kinematic adjustment was found at foot strike in used shoes but changes were observed later during stance. Running with used shoes produced a higher loading rate of the vertical ground reaction force (+23%, p = 0.016), suggesting higher compressive forces under the heel and placing children at risk to experience impact-related injuries. Nevertheless, the decreased peak ankle and knee power absorption in used shoes (−11%, p = 0.010 and −12%, p = 0.029, respectively) suggests a lower ankle and knee joints loading during the absorption phase that may be beneficial regarding stretch-related injuries.

Highlights

• 14 children performed a running task with new shoes and used shoes.
• GRF loading rate increased by 23% in used shoes compared to new shoes.
• Peak ankle and knee power absorptions decreased by 11% and 12% in used shoes

Commentary

So there are a couple of things jump out at us here, not the least of which is that the ageing of the footwear is based on time elapsed rather than distance covered. This means we have no idea how much the shoe has been used from subject to subject, and no way of titrating the actual ageing of the shoe. This is also quite a small sample for a study like this.

That said, let’s take a look at the AVERAGE results across the study after four months of wear:

1. sole stiffness increased by 16%, a big change
2. energy loss capacity decreased by 18%, a big change
3. running in the used shoes resulted in an average increase in the loading rate of the vGRF by 23%, a very big change
4. conversely, there was a reduction in ankle and knee joint loading, most likely due to altered lower limb stiffness (possibly due to increased knee flexion and STJ pronation), as the brain processes the fact that there is greater midsole stiffness that needs to be accounted for.

Even taking into account the study limitations, this provides fairly compelling evidence that the biomechanical properties of footwear change in a detrimental manner after even a fairly short period of ageing.