Ground Reaction Forces in Ground Reaction Forces in Running: A ReexaminationRunning: A Reexamination

C F Munro, D I Miller & A J C F Munro, D I Miller & A J FuglevandFuglevand

MethodsMethods 20 male subjects ran at speeds 2.5 – 5.5 m/s20 male subjects ran at speeds 2.5 – 5.5 m/s Kistler force plate interfaced to PDP 11/34 computer 1000 Kistler force plate interfaced to PDP 11/34 computer 1000

HzHz Photocells positioned 5 m apart to monitor average velocityPhotocells positioned 5 m apart to monitor average velocity Subjects wore their own shoesSubjects wore their own shoes Trials where the change in Vy was greater than Trials where the change in Vy was greater than ±± .10 m/s .10 m/s

were rejected (Ant/Pos force was integrated)were rejected (Ant/Pos force was integrated) Stance time was defined as Fz > 16 NStance time was defined as Fz > 16 N Loading rate was defined as the time to from 50 N to BW + Loading rate was defined as the time to from 50 N to BW +

50 N50 N Decay rate was defined as the time from BW + 50 N to 50 N Decay rate was defined as the time from BW + 50 N to 50 N

following Thrust Maxfollowing Thrust Max Impulses and Forces were normalized by dividing by body Impulses and Forces were normalized by dividing by body

weight in Newtonsweight in Newtons Right and Left foot trials were averagedRight and Left foot trials were averaged

Loading Rate CalculationLoading Rate CalculationLoading Rate Calculation

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0 50 100 150 200 250 300Time (ms)

Ve

rtic

al F

orc

e F

z (N

)

Fz

Loading Rate

time at 50 N = .014

time at BW+50 N =.028

Loading Rate = 1/(.028-.014)Loading Rate = 71.4 BW/s

Anterior – Posterior Anterior – Posterior Force CurvesForce Curves

Increasing running speed increases the magnitude of A/P forces and decreases stance time.

Variability in Variability in Braking PatternsBraking Patterns

Rearfoot have a single peak braking pattern.

Midfoot runners have two or more peaks during braking.

Vertical GRF Vertical GRF as a function as a function

of running of running speedspeed

Increasing running speed:

1. Increases impact

2. Increases loading rate

3. Increases thrust max

4. Decreases stance time

Medial – Medial – Lateral Force Lateral Force

CurvesCurves

Stance time decreases and magnitude of peaks increases with increasing running speed.

ImpulseImpulse

Braking and Propulsion increases with increasing running speed.

Vertical Force Variables as a Function of Running SpeedVertical Force Variables as a Function of Running Speed