A research team from the Chair of Biomechanics at the University of Bayreuth examined the soles of more than 100 running shoes. The results revealed that over a third of the heel areas were poorly designed and may therefore contribute to the risk of injury for runners. The researchers have published their findings in the journal Bioengineering.
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Why it matters
Sports are an important part of a healthy lifestyle and helps prevent chronic illnesses. Running is one of the physical activities recommended by the World Health Organization, which is particularly popular due to its ease of access: it requires no special sports facilities or equipment—apart from running shoes. However, these shoes must be designed to prevent injuries and chronic overuse syndromes. Yet the injury rate among recreational runners is around 45% per year. Running is supposed to be healthy—but in fact, it can be harmful. Studies like those conducted by the Bayreuth researchers help improve the design of running shoes and thus prevent sports-related injuries.
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The heel segments of running shoes are crucial for cushioning. Well-cushioned shoes absorb the impact energy generated when the foot strikes the ground, preventing the leg from having to absorb this energy. This helps prevent overloading of muscles and joints. If the heel material compresses only slightly, the shoes feel hard due to the minimal cushioning. But even excessively soft material can feel hard while running, as the heel “bottoms out” due to too much compression, causing the runner to feel the ground. Ideally, there should be an optimal point between these extremes where the heel is well-cushioned.
“The current standards for testing heel segments of running shoes are not optimal, as they test the shoes with an energy absorption of exactly five joules. But not everyone runs in the same way, so not everyone produces five joules of energy with every heel strike,” says Professor and Chairholder Franz Konstantin Fuss from the Chair of Biomechanics at the University of Bayreuth and lead author of the study. He therefore calls for improved methods that do not depend on preset measured values.
Together with doctoral researchers Tizian Scharl and Niko Nagengast, Fuss has developed a new testing system for measuring the properties of heel segments. This method calculates the ratio of absorbed energy to applied force and identifies the so-called “shoulder point”, where this ratio reaches its maximum—meaning the most energy is absorbed with the least possible force. This point represents optimal shock absorption for running.
Using four measurement parameters relating to the shoulder point, the Bayreuth researchers examined 112 shoes from various manufacturers and classified them into three categories: overdesigned (too little cushioning due to excessive hardness, i.e. a too high force would be needed to achieve optimal cushioning), well-designed (optimal cushioning), and underdesigned (too little cushioning due to excessive softness).
Using their new method, the researchers found that 38% of the 112 tested shoe models were either over- or underdesigned. “These design flaws are obviously unintentional on the part of the manufacturers, as no optimal testing method existed until now. However, this also highlights the need for design and manufacturing guidelines for heel segments to help prevent injuries,” says Fuss.
In addition, the study provides initial insights into 3D-printing of shoe soles, where the heel segments could be tailored to individual runners through simple and systematic design.
The study was conducted in collaboration with the Fraunhofer IPA – Applied Biomechanics Group and the sporting goods manufacturer Puma.
Prof. Dr. Franz Konstantin Fuss
Biomechanics
University of Bayreuth
Phone.: +49 (0)921 / 785 16 101
E-Mail: franzkonstantin.fuss@uni-bayreuth.de
A New Method and Set of Parameters for Evaluating the Cushioning Effect of Shoe Heels, Revealing the Inadvertent Design of Running Shoes. Franz Konstantin Fuss, Tizian Scharl, Niko Nagengast. Bioengineering (2025)
DOI: https://doi.org/10.3390/bioengineering12050467
One of the tested sports shoes in the testing machine while measuring the cushioning on the heel seg ...
Franz Konstantin Fuss
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One of the tested sports shoes in the testing machine while measuring the cushioning on the heel seg ...
Franz Konstantin Fuss
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