this is world champion and gold medalist in 110 meter hurdles David Oliver running at 10.2 m/s on the SMU high-speed Force treadmill we simultaneously record ground reaction forces and video at 1,000 frames per second to run fast sprinters apply forces up to five times their body weight in less than 100 milliseconds on each leg here's distance Runner Ryan Hall the fastest American marathoner in history running at 5.7 m/s a 2hour and 3 minute marathon pace he has a different Force pattern lower in amplitude and longer in duration than a sprinter during a marathon Ryan will impact the ground 25,000 times with a peak force of three times his body weight for each footfall running ground reaction forces thus have fundamental physical and biological significance is there an underlying principle that relates the force to the motion of a Runner there is Newton's Laws of Motion we determined that the motion of the body behaves as a two Mass system when running Mass one consists of the lower contacting limb Mass two consists of the rest of the body an impulsive Force results from the vertical Collision of the lower limb with the running surface the magnitude and timing depend on the vertical acceleration of the ankle simultaneously an impulsive Force results from the vertical motion of the rest of the body the magnitude and timing depend on the contact and aerial time the forces add together to form the total vertical ground reaction force all Force patterns are determined by just three motion parameters contact Time aerial time and lower limb acceleration our model accurately predicted forces across running speeds from 3 to 11 m/s for 42 men and women with different footstrike mechanics applications of the model include gate analysis robotics Prosthetics Orthotics and shoewear design I'm Ken Clark further details of our research can be found in the Journal of experimental biology