Running Angles

Running technique has a lot to do with the angles at which the runner’s legs and feet strike and push off the ground. When your foot lands on and pushes off the ground, it applies a force to the ground. As Isaac Newton taught you in high school physics class, for every action there is an equal and opposite reaction. The ground applies a force to your foot when it lands on the ground, throughout the stance phase, and when the foot pushes off the ground that is equal in magnitude and opposite in direction to the force applied by your foot. This is called the “ground reaction force.”

Running is about optimizing the ground reaction forces upon both landing and push-off to absorb shock effectively upon landing and optimize propulsive force at push-off to move forward.

When your foot lands out in front of your body, a brake is created, which quickly decelerates your leg. The magnitude of this brake depends on the angle of your leg’s shank (the part of your leg from your knee to your foot). The greater the shank angle, the greater the braking force.

With a large shank angle, your foot pushes down and forward on the ground, resulting in a ground reaction force that pushes up and back on your body.

“But, wait!” you exclaim. “I want to run forward.” That’s right, you do. But when your leg lands sharply on your heel and extended in front of your body, the ground reaction force pushes your leg back instead of forward — the exact opposite of what you want!

A large shank angle may also increase risk of injury, because it produces greater impact forces and greater loading rate of the impact force (how quickly the impact force is transmitted through your leg).

To maximize propulsive forces from the ground reaction force and reduce injury risk, land on the ground with a small shank angle. The shank angle at touchdown of average runners is about 16 degrees, compared to 6-10 degrees of proficient runners, who land with their foot close to underneath their hips.

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