One of the main criticisms of conventional running shoes raised over the last few years has been that they encourage “hard” landings that increase the impact forces of running, especially on initial contact with the ground. Minimalist shoes, some advocates say, can help reduce impact forces, in part by encouraging a “softer” foot strike and more of a midfoot landing.
For one of the 10-minute runs, the men wore the Nike Pegasus, which the researchers classified as a standard running shoe. On another 10-minute run, the men wore the Nike Free 3.0, which the researchers classified as a minimalist running shoe. According to the researchers’ measurements, the Pegasus’ heel height was 36.3 millimeters, compared to 17.6 millimeters for the Free. On the basis of compression tests, the Pegasus provided 31% more cushioning, the researchers said.
While the men ran, Willy and Davis recorded impact forces, stride length and other biomechanical data. They took measurements at the 1-minute mark of the run, and again at the 10-minute mark, to see if impact forces, joint angles, etc. changed during the short run.
The results were the opposite of what Willy and Davis had expected. As they wrote, when in the Free “runners struck the ground with a more dorsiflexed foot [toes pointing toward the shin, meaning more of a heel strike], in more knee flexion, and with higher vertical impact peak and higher average vertical loading rate.”
These differences remained consistent throughout the run. That is, as the men–who, again, weren’t used to running in a shoe like the Free–continued to run in the Free, they didn’t adjust their form to compensate for being in the Free. Their stride length and stride rate remained comparable to when they ran in the Pegasus, and their impact forces remained greater than in the Pegasus.
“We expected that impacts would initially be higher in the minimalist shoe than the standard shoe in the first minute of running. After 10 minutes of running, we expected the reduced cushioning of the minimalist shoe would cause heel discomfort, resulting in a less inclined foot at foot strike, perhaps even a midfoot strike pattern. We then expected a likewise reduction in impact forces. Obviously, our results were completely counter to what we hypothesized.”
Willy said that he and Davis used the Free instead of a more barefoot-style shoe, such as the Vibram Fivefingers, because of the popularity of the Free and its positioning as a transitional shoe for runners looking to switch from conventional trainers to barefoot-style running.