Ground Reaction Forces

Ground reaction force (GRF) is the force exerted by the ground on a body in contact with it. For example, a person standing on the ground exerts a contact force on it (equal to the person’s weight) and at the same time an equal and opposite ground reaction force is exerted by the ground on the person.

The ground reaction force is related to Newton’s 3rd Law of Motion, which basically state, “For every action there is an equal and opposite reaction.”

Remember that GRF is a non-propulsive force.  However, it can provide the body great feedback to the running form.  Does your foot slap on the ground?  Do you feel your footstrike too much?  Most runner can decrease ground reaction forces by decreasing stride length and increasing stride rate.  An easy way to measure this is count your strides for a given distance (think 100 yards/meters).  What that count is, try increasing it by 5-10% each week for over a few weeks to see if it makes you “feel” better with your running.

Contact the Fitness Staff Office at the MHFC at 406 994 6309 if you have further questions.  Thanks.  Enjoy the day!

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