[Image above] Lateral X-ray of a runner’s left foot in a carbon-fiber-plated running shoe. Red arrows outline the embedded plate. The green arrow shows the fulcrum point of the plate. Note the relation of the curvature of the plate to the metatarsophalangeal joints (toe knuckles). Credit: Tenforde et al., Sports Medicine (CC BY 4.0)
Even though some scientific studies suggest that, for most events, athletes have been operating at or near a plateau of human biological performance for years, new world records continue being made every year.
Part of those successes are due to advances in sports technology. The use of new materials, such as ceramic and glass fiber-reinforced composites, in sports equipment, apparel, and surfaces help athletes to enhance and extend their performance.
Carbon-fiber-plated running shoes are one example of how ceramics support enhanced athletic performance. In these shoes, a carbon fiber plate within the shoe’s midsole provides a runner with additional leverage, resulting in improved energy return while running. The video below provides more details on how carbon-fiber-plated running shoes work.
Sports science studies, such as here and here, have validated the performance benefits of carbon-fiber-plated running shoes. These results have been upheld in practice—since the introduction of carbon-fiber-plated running shoes into competition in 2016, every world record from the 5 km to the marathon has been eclipsed by competitors using this technology.
While the benefits of these shoes are well documented, little has been published about the potential injuries that can be sustained from using this technology.
“While I understand the excitement, we need to consider how to prevent injuries when athletes adopt this new footwear,” says Adam Tenforde, physician in Mass General Brigham’s Sports Medicine program and medical director of the Spaulding National Running Center, in a Mass General Brigham press release.
Tenforde is lead author of a recent open-access study that aims to raise awareness of possible health concerns around the use of carbon-fiber-plated footwear. To do so, he and his coauthors from the United States and Germany describe five case studies in which highly competitive running athletes experienced bone stress injuries after running in carbon-fiber-plated shoes.
Before describing the case studies, the authors note that the use of carbon-fiber-plated footwear is known to introduce novel biomechanical demands on the foot. Specifically, “No changes in knee or hip mechanics but differences in ankle and metatarsophalangeal joint [toe knuckle] mechanics were observed in runners using CFP [carbon-fiber-plated] footwear,” they write.
A 2018 study on these differences found more energy was stored in the midsole and less energy was stored in the muscles and tendons of the ankle. This significant change in the energy distribution may put runners at risk of novel bone stress injuries, such as in the navicular bone, the authors argue.
The navicular bone is located on the medial side of the foot. It is classified as a high-risk location for injury as some of these injuries may not effectively heal with nonsurgical measures.
In the five case studies, male and female runners in both their teens and 30s experienced navicular bone stress injuries after running in carbon-fiber-plated shoes. While for some it was their first time using such shoes, others had previously trained for months in the shoes with no issues. In all cases, after a period of convalescence, the runners were able to run again without pain.
Though the mechanism for injury in each case could not be determined due to limitations of the case report format, the authors emphasize their main goal was to simply raise awareness of potential associations between bone stress injuries and carbon-fiber-plated footwear.
“We hope this article helps to guide better recognition of medical issues related to CFP footwear, appropriate use of this new technology, and safety for our athletes,” they conclude in the paper.
The open-access paper, published in Sports Medicine, is “Bone stress injuries in runners using carbon fiber plate footwear” (DOI: 10.1007/s40279-023-01818-z).