August 1, 2011
By Ashley Yeager
. . . 158 . . . 159 . . . 160.
In the first minute of my morning run, my feet strike the ground 160 times, 80 times each foot.
Yes, I count. But not for the whole run. I cheat and do the math.
It's pretty astounding to calculate that in a short, 30-minute jog through Duke Forest, each foot hits the dirt 2,400 times.
While that's not much that compared to the pounding American marathoner Ryan Hall or former Duke runner Bo Waggoner give their feet (and shoes), thinking about the thousands of impacts made me curious about the science that could reduce the stress on my soles.
Unfortunately, "there's a lot we don't know about how our feet strike the ground when we run," Waggoner says.
He researched the topic for his senior thesis and found that while many scientists had done experiments to test the impacts of running, few had tried to model them.
The experiments show that, even on hard surfaces, runners without shoes who hit the ground with their forefoot made smaller collision forces with the ground than shoe-clad runners landing on their heels.
But, the tests can't measure the internal impacts between bones at the ankle or knee.
"And, there are a lot of simple, unanswered questions about what physics goes on when our foot hits the ground and pushes back off, like where the force is going and coming from and why," Waggoner says.
In other words, scientists don’t really know how, mechanically, a foot strike in running actually occurs.
Drawing of the tendons and muscles of the foot. Image courtesy of Runner's World.
To take strides in that direction, Waggoner turned human feet, ankles and legs into rods and springs. He simulated impacts between the rods and springs and a network of dots representing the ground.
Surprisingly, the "very basic" model began to show that impact forces were higher when hitting the ground with the heel. Hitting with the front of the foot created less stress.
With better models, which are "still an if at this point," scientists may learn where the stress and forces are going during different foot strike patterns and how and why runners get overuse injuries, Waggoner says.
The simulations could also alter shoe design. When Waggoner put mock shoes on his simulated feet, the sneakers with more padding at the front made less impact with the ground during a forefoot strike. Most real running shoes have more padding in the heel.
I know my shoes do, or they did, so I think the models are telling me to stay on my toes.