|Variability of Ground Reaction Force Characteristics for Slow Running Speeds (Abstract). G. A. Smith, FACSM and J. B. Fewster. Oregon State University.||"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
|If the Shoe Fits …. Jazzercise, Inc.||"our feet bare the brunt of nearly 1,000 tons of force a day"||9 × 106 N
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.
- At the University of Oregon, G. A. Smith and J. E. Fewster did a study on the variability of the ground reaction force for slow running speeds. Nine subjects ran a series of five speeds ranging from 1.6–2.4 meters per second. The force exerted on the ground ranged from 1,038 to 1,314 newtons at a speed of 2.4 meters per second.
- The Saucony shoe company reports that a force of up to three times body weight can be exerted on the human foot while running. For example, a person weighing 670 newtons (150 pounds) can experience forces of up to seven times their body weight or 4700 newtons (1000 pounds). The greatest force is experienced on the forefoot phase of a stride when the whole width of the forefoot absorbs the surge of power that propels the foot off the ground.
- A similar report done by the Z-Tech shoe company states that the maximum force can equal up to three-and-a-half times body weight. Therefore, a person weighing 670 newtons (150 pounds) would experience a force of up to 2300 newtons (525 pounds).
Over the course of the day, these forces can accumulate to millions of newtons (hundred or thousands of tons).
Sara Birnbaum -- 1999