The Nike Free is not minimalist enough for forefoot running and may cause knee injury, because like regular running shoes, the Free’s have an elevated cushioned heel which encourages heel striking and greater knee-loads.
For example, Sinclair et al. investigated the influence of regular running shoes and minimalist shoes, such as the Nike Free, the Vibram Five Fingers, and the Inov-8 Evoskin, on knee and ankle loading in runners. However, their data showed that the aspect that was most troubling for the Nike Free was it’s cushioned heel which resulted in greater knee-loads similar to regular running shoes.
Nike Free Not Minimalist Enough for Forefoot Running
The researchers found that runners in regular running shoes and the Nike Free had greater patellofemoral joint force and pressure than runners in barefoot-inspired footwear (Vibram Five Fingers and Inov-8). Thus, the biggest pay-off of the Vibrams and the Inov-8s was their ability to prevent heel strike, thereby reduce knee-loads.
How did the barefoot-inspired footwear reduce knee loads?
- Runners in barefoot-inspired footwear had less knee extensor moments which is indicative of a shorter stride, thereby knee-joint torque is reduced.
- A shorter stride typically corresponds to the stance limb being close to the center of mass, which reduces the moment arm of the quadriceps and knee-joint torque.
Cushioned Heel Causes Heel Strike
Because runners in the Nike Free had greater knee loads, suggests that these runners were heel striking. The researchers also found that Achilles tendon force was lower in the Nike Free runners as compared to runners in barefoot-inspired footwear –lower Achilles tendon force is indicative of a heel strike running style.
- Heel strike runners tend to have less Achilles tendon force than forefoot strike runners because the elastic properties of the Achilles tendon is underutilized in a heel strike landing.
In forefoot running, greater Achilles tendon force is a good thing as it allows greater storage of elastic energy during the loading phase of running and reduces muscular demands, thereby saving energy.
The Take Home Message
In all, knee injuries stem from biomechanical abnormalities evoked by cushioned heeled footwear, like the Nike Free. These shoes increase knee-stress because they provoke greater knee extension at touchdown and increase heel strike potential.
Since Nike Free strongly favors heel strike mechanics, they should not be marketed as minimalist. Minimalist shoes are supposed to extinguish adaptive problems, such as heel strike, not create them.
More From Run Forefoot:
- Sock Thickness Affects Forefoot Strike
- Avoid Forceful Toe-Push Off
- Puff Up Your Chest to Accelerate
- Look Down While Running
Daoud et al. Foot strike and injury rates in endurance runners: a retrospective study. Med Sci Sports Exerc, 2012; 44(7): 1325-34.
Sinclair, J. Effects of barefoot and barefoot inspired footwear on knee and ankle loading during running. Clin Biomech, 2014; 29:395-99.
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.