Runners who heel strike may be at greater risk of hyperextended knee injury as compared with runners who forefoot strike. The reason for this is to begin the next step cycle in heel strike running, the swing leg is driven forward, like walking, which causes the knee to completely unbend.
Hyperextended Knee Injury Common in Heel Strike Runners
In heel strike running, driving the leg forward is accompanied by maximum knee extension and ankle dorsiflexion, allowing the foot to land on the heel and land a head of the center of mass.
Driving the leg forward is not only energy-intensive, but maximum extension of the knee at touchdown results in hyperextension of the knee.
- In this position at heel strike, the knee-joint is essentially locked into an inflexible position that is unstable, especially as the center of mass travels posteriorly to anteriorly to the support limb.
The net result is increased strain and loading within the knee-joint, putting the knee in hyperextension mode and is the reason heel strike running is associated with more trauma to the knee than forefoot running.
Preventing Hyperextended Knee Injury
Looking back at our evolutionary past as endurance runners, our ancestors on the hunt were not so different from habitually barefoot runners today: both groups are forefoot runners, they suffer less injury to the knee and use more knee flexion at touchdown.
In running, knee-joint health is perpetuated when the knees are more flexed. Flexed meaning soft and bent, knee flexion at touchdown is rewarding because it guides the foot to land more under the mass of the body at initial contact. The net result is the reduction in knee strain and a more responsive knee.
Researchers are beginning to recognize a trend in their collected data from studies that compared the mechanics of runners with knee injuries to runners with healthy knees and found that runners with healthy knees ran with both knees bent/flexed and not fully straightened.
What these data suggests to us is that softly bending the knees while running can completely halt or even prevent progressive degeneration of the knee-joint that lies at the heart of common running-related knee injuries.
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Romanov, N and Fletcher G. Runners do not push-off the ground but fall forwards via a gravitational torque. Sports Biomech, 2007; 6(3):434-452.
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.