The Physics
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Force on a Runner's Foot

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Smith, G.A., and J.B. Fewster. "Variability of Ground Reaction Force Characteristics for Slow Running Speeds 517" Medicine & Science in Sports & Exercise, vol. 28, no. 5, May 1996, pp. 87. "Midstance VGRF [vertical ground reaction force] also consistently increased with running speed (r = .97) from 1083 to 1314 N at 2.4 m/s." 1083–1314 N
The Science Behind the Shoes - Biomechanics. Saucony, Inc. "The Rearfoot Phase… The actual shock of heel contact creates an impact of up to three times body weight." 2000 N
"The Forefoot Phase… the force exerted actually increased to between four and seven times body weight. (That means the foot of a 150 pound runner can be called upon to support a weight of a thousand pounds or more!!)" 2700–4700 N
The History. Z-Coil Shoes for Pain Relief. Z-Tech, Inc. "The Recoil shoe is meant to lessen the impact every time a runner's foot slams into the ground with the force of three to three-and-a-half times his or her body weight." 2000–2300 N
Foot Facts - How Foot Smart Are You? Footcare Direct. "During a typical day, the feet endure a cumulative force of several hundred tons." 106 N
(per day)
If the Shoe Fits…. Jazzercise, Inc. "our feet bare the brunt of nearly 1,000 tons of force a day" 8.9 × 106 N
(per day)

A force is a push or a pull acting between two objects. It is a vector quantity that has both magnitude and direction. A category of forces known as contact forces affect us in our every day lives. The basis for the contact force is the electromagnetic force between atoms. The contact force is also known as the normal or reaction force. You experience these forces every day when you walk or run. As your foot pushes against the ground, the ground pushes back, propelling you forward.

To answer the question, "What is the normal force on a human foot while running?" we turn to of biomechanics: the study of how the body moves.

Over the course of the day, these forces can accumulate to millions of newtons (hundred or thousands of tons).

Sara Birnbaum -- 1999