Forefoot strikers, including barefoot runners, run safer on pavement than heel strikers because forefoot running eliminates the impact transient.
Why No Impact Transient in Forefoot Striking
In forefoot striking, the foot ‘swoops’ down to the ground, making initial contact on the balls of the foot, then the rest of the foot is lowered down. The movement path of the foot in a forefoot strike (shown below), reduces braking and lowers the rapid force of impact regardless of surface hardness.
Therefore, it is not the surface that causes injury, its how the foot initially interacts with the surface that determines injury during running.
Need more convincing? A 2012 Harvard study compared the nature of the ground reaction force in heel strikers and forefoot strikers and found that foot strike, not surface type, determined the peak element of the ground reaction force. The peak element being the impact transient that was produced in a heel strike, not a forefoot strike landing.
Below shows the figures from the study comparing the impact transient in heel striking and lack-thereof in a forefoot strike:
This figure shows how heel striking (A), generates an impact transient compared to a forefoot strike (B), which does not. The difference between (A) and (B) is that (A), the heel striker generates the impact transient because the body comes to a dead stop at heel strike where the mass of the body collides with the leg. In (B), a forefoot strike, the foot strike position of the forefoot with the ground is under or close to the knee where the knee is slightly bent and compliant, allowing the lower leg to act as a spring and cushion. The foot strike position in a forefoot strike is much closer to the body which contributes to the reduction of the impact transient, allowing for a smoother, softer interaction with the ground regardless of surface hardness.
Evolution Designed Humans to Run Safely
Since the impact transient is eliminated in a forefoot strike, forefoot runners tend to land lightly and gently as other mammals who also do not generate ground reaction forces during running -mammals don’t ‘heel strike’ when they run, just watch your dog or cat run to see, they land on the more anterior part of the foot, or paw, hoof, etc.
The Harvard study suggested that since the forefoot runners ran with less impact and no peak force production, cushioned shoes may not be needed to dampen impact even on hard surfaces such as a steel plate.
The Take Home Message
These findings may imply that running on harder surfaces, such as the road, may not be the main culprit in causing your injuries. It is most likely how your foot strikes the ground that determines impact and thus injury.
The key point to always remember is that heel striking produces a peak impact force which forefoot striking does not. As I always say, I would like to run with the foot-strike that produces the least amount of force. Therefore, in theory, forefoot runners may virtually run anywhere without having to experience the physical trauma related to the peak impact force.
Bobbert, M. F., Schamhardt, H. C. & Nigg, B. M. Calculation of vertical ground reaction force estimates during running from positional data. J. Biomech 1991; 24, 1095–1105.
Lieberman et al. Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 2009; 463, 531-535.
Run Forefoot Because You’re Faster Than You Think
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.