Ground Reaction Forces in Running: A Reexamination C F Munro, D I Miller & A J Fuglevand

Methods 20 male subjects ran at speeds 2.5 – 5.5 m/s 20 male subjects ran at speeds 2.5 – 5.5 m/s Kistler force plate interfaced to PDP 11/34 computer 1000 Hz Kistler force plate interfaced to PDP 11/34 computer 1000 Hz Photocells positioned 5 m apart to monitor average velocity Photocells positioned 5 m apart to monitor average velocity Subjects wore their own shoes Subjects wore their own shoes Trials where the change in Vy was greater than ±.10 m/s were rejected (Ant/Pos force was integrated) Trials where the change in Vy was greater than ±.10 m/s were rejected (Ant/Pos force was integrated) Stance time was defined as Fz > 16 N Stance time was defined as Fz > 16 N Loading rate was defined as the time to from 50 N to BW + 50 N Loading rate was defined as the time to from 50 N to BW + 50 N Decay rate was defined as the time from BW + 50 N to 50 N following Thrust Max Decay rate was defined as the time from BW + 50 N to 50 N following Thrust Max Impulses and Forces were normalized by dividing by body weight in Newtons Impulses and Forces were normalized by dividing by body weight in Newtons Right and Left foot trials were averaged Right and Left foot trials were averaged

Loading Rate Calculation

Anterior – Posterior Force Curves Increasing running speed increases the magnitude of A/P forces and decreases stance time.

Variability in Braking Patterns Rearfoot have a single peak braking pattern. Midfoot runners have two or more peaks during braking.

Vertical GRF as a function of running speed Increasing running speed: 1.Increases impact 2.Increases loading rate 3.Increases thrust max 4.Decreases stance time

Medial – Lateral Force Curves Stance time decreases and magnitude of peaks increases with increasing running speed.

Impulse Braking and Propulsion increases with increasing running speed.

Vertical Force Variables as a Function of Running Speed