Transcript Ground Reaction Forces in Running: A Reexamination

Ground Reaction Forces in
Running: A Reexamination
C F Munro, D I Miller & A J
Fuglevand
Methods
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20 male subjects ran at speeds 2.5 – 5.5 m/s
Kistler force plate interfaced to PDP 11/34 computer 1000 Hz
Photocells positioned 5 m apart to monitor average velocity
Subjects wore their own shoes
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
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
Impulses and Forces were normalized by dividing by body weight in
Newtons
Right and Left foot trials were averaged
Loading Rate Calculation
1800
1600
Loading Rate Calculation
Fz
Loading Rate
Vertical Force Fz (N)
1400
1200
Loading Rate = 1/(.028-.014)
Loading Rate = 71.4 BW/s
1000
800
time at BW+50 N =.028
600
400
200
time at 50 N = .014
0
0
50
100
150
Time (ms)
200
250
300
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