Why Cushioned Running Shoes And Heel Inserts Are Bad for the Achilles Tendon

One of the reasons cushioned running shoes is bad for the Achilles tendon is the elevated heel creates a large heel-to-toe offset which is a major mechanical disruptor that causes a runner to mistakenly strike harder heel-first. This loads more forms of impact at higher magnitudes and intensities through the Achilles as compared with running barefoot or in barefoot-like shoes, which encourages a low-impact, forefoot strike landing.

Cushioned Running Shoes is Bad for Achilles Tendon
The higher the heel relative to the toe-box of a running shoe, the more mechanically reckless you will be when you run because when your foot sits on an incline, like it does in a heeled running shoe, the greater the mechanical displacements like heel striking with an over-stride as compared with running in flatter shoes.

Heel inserts have the same injurious effects too because like cushioned heeled running shoes, heel inserts also results in a large heel-to-toe offset which, again, facilitates mechanics that work against you, mechanics that counter gravity, causing you to pound the pavement harder on your heel (heel strike) accompanied with a long over-stride stride.

How Do You Treat an Achilles Injury When Running?
To date, no evidence has found that impact on the Achilles is successfully reducible with a heel lift.

In principal, heel inserts (shown above) are used to treat Achilles tendon injuries by reducing impact on the Achilles via increasing shock absorption under the heel. However, studies have found that heel inserts actually increase stress and strain on the Achilles, and can therefore, clearly  holds a runner back from making progress in resolving an Achilles injury.


For instance, a  study in the Journal Applied Biomechanics revealed that heel strike runners who wore a 15 mm heel lift had significant increases in maximum ankle moments and maximum Achilles tendon force compared with the barefoot runners.

The heel strike runners wearing 1- mm heel lifts also had greater ankle moment at the time of maximum Achilles tendon force which resulted from the increase in the ground reaction force.

Worse still, the higher the heel, the smaller the length of the Achilles tendon moment arm, meaning the Achilles is always shortened when a heel lift is worn. This not only negatively alters the anatomy of the Achilles, it also limits the space for the Achilles to stretch and recoil to store and release elastic energy during running. This  explains why the evidence-based benefits of a heel lift are always mixed, at best, because what’s most problematic about heel lifts is they counter the structure and function of the Achilles, and from that alone, Achilles injuries will always be on the rise.

The take home message is runners have been  treating Achilles injuries the wrong way with heel inserts! In too many places do cushioned heeled shoes or heel inserts negatively impact a runner. For one, a heel insert abnormally shortens the Achilles which hinders the efficient use of the tendon as an energy-saving spring.

Secondly, heel inserts leads to misaligned mechanical exchanges when running, causing a runner to ram harder heel-first, resulting in dangerous rises in peak impact on the tendon. Therefore, impact reduction cannot happen on the Achilles with heel inserts or in running shoes with thicker cushioned heels, it must happen by adjusting your foot strike to a forefoot strike.

Its not just the Achilles tendon that is at less risk of injury in forefoot running, the heel, the IT Band, knees, hips and lower back are all unburden from damaging impacts, too!

If you’ve enjoyed my post, you’ll love my YouTube Channel, here, where I talk more about why forefoot running is better than heel strike running as well as how running barefoot can make you a better shod runner!


References:

Dixon S and Kerwin G. The influence of heel lift manipulation on Achilles tendon loading in runners. J Appl Biomech, 1998; 14, 374-89.

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Bretta Riches

"I believe the forefoot strike is the engine of endurance running..."

BSc Neurobiology; MSc Biomechanics candidate, ultra minimalist runner & founder of RunForefoot. I was a heel striker, always injured. I was inspired by the great Tirunesh Dibaba to try forefoot running. Now, I'm injury free. This is why I launched Run Forefoot, to advocate the health & performance benefits of forefoot running and to raise awareness on the dangers of heel striking, because the world needs to know.
Bretta Riches

P.S. Don't forget to check out the Run Forefoot Facebook Page, it's a terrific place to ask questions about forefoot running, barefoot running and injury. I'm always happy to help!