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7/28/2019 Rice Speed SymposiumTalk PDF Version for Casey
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From running mechanics to sprinting performance:
FORCING THE ISSUE
Peter Weyand
Locomotor Performance Laboratory
Southern Methodist University
Host and Organizer:Casey Thom
Rice Speed SymposiumFebruary 19, 2011
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From running mechanics to sprinting performance:
FORCING THE ISSUE
Speed is ~ entirelydetermined by what
happens on the ground
Physics Ground Force/ Body Weight SPEED
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Running speed is determined by:
1) The body weight of the runner.
2) The amount of force the limbs apply to the ground.
Force
WeightSPEEDis the key for
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Mass-specific force
Ground Force Applied
Body Weight
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Why is mass-specific forceso important?
Ground Force Applied
Body Weight
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Scientific Concept 1:
because FORCE DETERMINES MOTION:(no exceptions)
THE force-motion relationship
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The how of Mass-specific
force-speed relationship
Ground Force Applied
Body Weight
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Scientific Concept 2:
THE FORCE REQUIRED FOR SPEEDDEPENDS DIRECTLY ON BODY MASS:
true for runners across the continuum
of sprinting abilities
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Absolute
FORCE
into the ground(Newtons)
SPEED
Heavier Person
Lighter Person
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Relative
FORCE
into the ground(x Body Weight)
SPEED
Heavy andLight Person
Jog =
1.5 x Body Weight
(Everyone)
Sprint =
~ 2.0 x Body Weight
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The how of Mass-specific forceextends to sprinting speeds
Ground Force Applied
Body Weight
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Relative
FORCE
into the ground(x Body Weight)
SPEED
Sprinter
Jog =
1.5 x Body Weight
(Everyone)
Elite Sprint =
2.5 x Body Weight
[note: the forces above represent approximations of the average vertical forces applied during foot-ground contact]
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Ground Forces have:
1) magnitude, and 2) direction
1) Magnitude requirements set by body mass
2) What about direction requirements?
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Horizontal
Vertical
The forces that are important fortrack performance:
Vertical and Horizontal
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Horizontal
Vertical
The forces that are important fortrack performance:
Vertical and Horizontal
because a runners motion occurs
primarily along these two axes
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The motion of a runner in both thehorizontal and vertical directions is set by:
Force/Body Weight ratios
Can the vertical and horizontal forces needed forspeed be accurately measured?
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Horizontal (Y)
Vertical(Z)
YES, the both horizontal and vertical groundreaction forces can be measured very accurately:
FORCE PLATES, FORCE TREADMILLS
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Force plates and treadmills at SMUs LocomotorPerformance and Applied Physiology Laboratories
Force plates
(acceleration)
Force treadmills
(steady speed)
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The force-motion relationship
during sprint running
Phase 1 Acceleration
Phase 2 ~ Steady SpeedPhase 3 Slowing Down
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R t ti Elit 100 D h
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Representative Elite 100 m DashTime-Velocity Profiles
(1987 World Champs)
Velocity(m/s)
0
3
6
9
12
0 3 6 9 12
100 m World Champs Finalists
(n = 8 male; n = 8 female)
Men
Women
Time (s)
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The force-motion relationship
during sprint running
Phase 1 Acceleration (0 - 20 m)
Phase 2 ~ Steady Speed (20 - 80 m)Phase 3 Slowing Down (80 100 m)
R t ti Elit 100 D h
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Representative Elite 100 m DashTime-Velocity Profiles
(1987 World Champs)
Velocity(m/s)
0
3
6
9
12
0 3 6 9 12
100 m World Champs Finalists
(n = 8 male; n = 8 female)
Men
Women
Time (s)
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RACE PHASE I:
Acceleration Ground Forces
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Which forces are predominantlyimportant for speed while accelerating?
Horizontal (Fy/Wb ) - determines change in speed
Vertical (Fz/Wb) Body weight must be supported against gravity
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In space there is no need to support body weight:
The body is oriented horizontally to exert the force
needed for horizontal acceleration
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On earth there are two requirements duringacceleration:
1) Apply horizontal force to accelerate.2) Apply enough vertical force to support the body.
So, the body and limbs are oriented at an angle toapply both horizontal and vertical force to the groundin order to accelerate
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No gravity Gravity
Horizontal only Horizontal and vertical
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The only time during the stride that a runners speed canchange is when the foot is in contact with the ground
Speed in the air is constant
Scientific Concept 3:
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Small, but needed disclaimer
The frictional resistance of air (or wind) is being ignored
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If you want to speed up or accelerate, you can only do sowhen the foot is on contact with the ground
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How much ground force is necessary toaccelerate rapidly?
This depends directly on the body weightof the runner
Accelerating
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Accelerating
Force = mass accelerationForce/mass = acceleration
More massiverunners mustapply greater
ground forces toachieve the sameacceleration
h f / h ld
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How much force/mass shoulda good sprinter apply to the
ground while accelerating?
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How much force/mass should a good sprinterapply to the ground while accelerating?
No single answer is available at present
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Acceleration and Impulse-momentum approaches can both beused to understand step to step changes in running velocity
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Acceleration
F = ma
Instantaneous only
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from acceleration to impulse-momentum
Impulse - Momentuman informative approach for considering the mass-
specific forces required for sprint accelerations
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Impulse
Average force time force is applied
determines the net
change in velocity
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Acceleration
F = maForce = mass acceleration
acceleration = velocity/time
= m/s per second
= ( m/s)/s
l l
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From Acceleration to Impulse
F = maF = m (v)/t
multiply through by t
Force t = m v*
Force time = mass velocity*
Change in velocity
*Change in velocity during thetime of force application
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The change in the horizontal velocity of the bodymust equal:
speed = Time of force Average horizontal force applied (Fy/Wb)
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The change in the velocity of the body must equal:
speed = Time ofcontact Average force exerted (Fy/Wb)
If you know the change in the horizontal velocity of the
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If you know the change in the horizontal velocity of thebody and the contact time,
you can determine the horizontal force applied during
contact:
(speed Wb)/contact time = Average force (Fy)
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Practical Acceleration Messages
1) No extra time in the air
2) Train to enhance force delivered to theground (relative to Body weight):
- Strength, power, running mechanics
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RACE PHASE II:
~ Steady-speed Sprinting
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The how of the mass specific force-speed relationshipduring steady-speed running
Ground Force Applied
Body Weight
Representative Elite 100 m Dash
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Representative Elite 100 m DashTime-Velocity Profiles
(1987 World Champs)
Velocity(m/s)
0
3
6
9
12
0 3 6 9 12
100 m World Champs Finalists
(n = 8 male; n = 8 female)
Men
Women
Time (s)
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The force-motion relationship
during sprint running
Phase 1 Acceleration (0 - 20 m)
Phase 2 ~ Steady Speed (20 - 80 m)Phase 3 Slowing Down (80 100 m)
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Understanding running speed interms of ground force application:
steady-speed running
Speed = Force/Wb Freqstr Lc
where:
Force stance-averaged vertical force
Wbthe force of the bodys weight
Freqstr Stride frequency
Lc - length of contact*
*forward distance the body travels while the foot is in contact with the
ground [illustrated as step length above]
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Runners keep the speed they
already have
Need to push down, not backwardonce up to speed
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Runners are like bouncing balls
Need to push down, not backward
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Skipping stones
Momentum moves the stone forward after the initial push
PART II
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PART IIMechanics of steady-speed running:
scientific basics
Very Basic Running Mechanics:
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e y as c u g ec a cssteady-speed running
The average vertical ground reaction force must equal the bodysweight over time.
Horizontal forces are relatively small and have relatively littleeffect on a runners motion.
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VERTICAL
FORCE
Body
Weight
Synchronized Force-motion video
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[force and video data acquisition at 1000 Hz]
SMUs Locomotor Performance Laboratory
Vertical Force vs Foot ground Contact Time across Running Speed
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Vertical Force vs. Foot-ground Contact Time across Running Speed
0
500
1000
1500
2000
2500
3000
111
21
31
41
51
61
71
81
91
101
111
121
131
141
151
161
171
181
191
201
211
Fz (N)
Tc (ms)
Vertical Force-Time Across Speed - AVERAGES
3.03 m/s
4.02 m/s
5.01 m/s
6.04 m/s
8.05 m/s
10.83 m/s
note: the waveforms at each speed represent an average of 8-20 footfalls for an individual runner
Horizontal Force vs Foot ground Contact Time across Running Speed
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Horizontal Force vs. Foot-ground Contact Time across Running Speed
note: the waveforms at each speed represent an average of 8-20 footfalls for an individual runner
Vertical (yellow) and Horizontal (red) Ground Rx Forces for three consecutive steps at 10 m/s;
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-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
126
51
76
101
126
151
176
201
226
251
276
301
326
351
376
401
426
451
476
501
526
551
576
601
Force(BW)
Time (ms)
Vertical (yellow) and Horizontal (red) Ground Rx. Forces for three consecutive steps at 10 m/s;
Time
Force
Practical Top Speed Messages
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Practical Top Speed Messages
1) Maximize time in the air
2) Minimize time on the ground
3) Train to enhance force delivered to theground (relative to Body weight):
- Strength, power, running mechanics
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The force-motion relationship
during sprint running
Phase 1 Acceleration (0 - 20 m)
Phase 2 ~ Steady Speed (20 - 80 m)Phase 3 Slowing Down (80 100 m)
Representative Elite 100 m Dash
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Representative Elite 100 m DashTime-Velocity Profiles
Velocity(m/s)
0
3
6
9
12
0 3 6 9 12
100 m World Champs Finalists(n = 8 male; n = 8 female)
Men
Women
Time (s)
Phase III Fatigue
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Phase III FatigueScience and Application
1) Late race speed is compromised by muscular
force impairment.
2) Fatigue is minimal in a 100 m race.
3) Training should focus on enhancing topspeed rather than enhancing speed-endurance.
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CONCLUSIONS and Wrap-Up:
ALL RACE PHASES
SINGLE CONCLUSION:
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Sprint running performance:
Speed is ~ entirelydetermined by theMASS-SPECIFIC
FORCE APPLIED TO
the ground
Physics Ground Force/ Body Weight SPEED
SCIENTIFIC TAKE-HOME MESSAGES
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SCIENTIFIC TAKE-HOME MESSAGES
1. Sprinting speeds depend directly on the amount ofground force applied in relation to the bodys weight(mass-specific).
2. The above is true during all phases of a sprint race:
acceleration, steady-speed, fatiguing.
3. Acceleration: relatively longer ground times, shorteraerial times.
4. Maximum velocities: relatively short ground timeslong aerial times.
Southern Methodist University
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y
Locomotor Performance Laboratory
(http://www.smu.edu/locomotor)
5538 Dyer Street
Dallas, TX 75206
http://www.smu.edu/locomotorhttp://www.smu.edu/locomotorhttp://www.smu.edu/locomotor