rice speed symposiumtalk pdf version for casey

7/28/2019 Rice Speed SymposiumTalk PDF Version for Casey

1/68

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


2/68

From running mechanics to sprinting performance:

FORCING THE ISSUE

Speed is ~ entirelydetermined by what

happens on the ground

Physics Ground Force/ Body Weight SPEED


3/68

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


4/68

Mass-specific force

Ground Force Applied

Body Weight


5/68

Why is mass-specific forceso important?


Body Weight


6/68

Scientific Concept 1:

because FORCE DETERMINES MOTION:(no exceptions)

THE force-motion relationship


7/68

The how of Mass-specific

force-speed relationship


Body Weight


8/68


THE FORCE REQUIRED FOR SPEEDDEPENDS DIRECTLY ON BODY MASS:

true for runners across the continuum

of sprinting abilities


9/68

Absolute

FORCE

into the ground(Newtons)

SPEED

Heavier Person

Lighter Person


10/68

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


11/68

The how of Mass-specific forceextends to sprinting speeds


Body Weight


12/68

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]


13/68

Ground Forces have:

1) magnitude, and 2) direction

1) Magnitude requirements set by body mass

2) What about direction requirements?


14/68

Horizontal

Vertical

The forces that are important fortrack performance:

Vertical and Horizontal


15/68

Horizontal

Vertical

The forces that are important fortrack performance:

Vertical and Horizontal

because a runners motion occurs

primarily along these two axes


16/68

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?


17/68

Horizontal (Y)

Vertical(Z)

YES, the both horizontal and vertical groundreaction forces can be measured very accurately:

FORCE PLATES, FORCE TREADMILLS


18/68

Force plates and treadmills at SMUs LocomotorPerformance and Applied Physiology Laboratories

Force plates

(acceleration)

Force treadmills

(steady speed)


19/68

The force-motion relationship

during sprint running

Phase 1 Acceleration

Phase 2 ~ Steady SpeedPhase 3 Slowing Down


20/68

R t ti Elit 100 D h


21/68

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)


22/68



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


23/68


(1987 World Champs)

Velocity(m/s)

0

3

6

9

12

0 3 6 9 12



Men

Women

Time (s)


24/68

RACE PHASE I:

Acceleration Ground Forces


25/68

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


26/68

In space there is no need to support body weight:

The body is oriented horizontally to exert the force

needed for horizontal acceleration


27/68

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


28/68

No gravity Gravity

Horizontal only Horizontal and vertical


29/68

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



30/68

Small, but needed disclaimer

The frictional resistance of air (or wind) is being ignored


31/68

If you want to speed up or accelerate, you can only do sowhen the foot is on contact with the ground
http://sportsillustrated.cnn.com/vault/gallery/featured/GAL1144172/2/10/index.htm


32/68

How much ground force is necessary toaccelerate rapidly?

This depends directly on the body weightof the runner

Accelerating


33/68

Accelerating

Force = mass accelerationForce/mass = acceleration

More massiverunners mustapply greater

ground forces toachieve the sameacceleration

h f / h ld


34/68

How much force/mass shoulda good sprinter apply to the

ground while accelerating?


35/68

How much force/mass should a good sprinterapply to the ground while accelerating?

No single answer is available at present


36/68

Acceleration and Impulse-momentum approaches can both beused to understand step to step changes in running velocity


37/68

Acceleration

F = ma

Instantaneous only


38/68

from acceleration to impulse-momentum

Impulse - Momentuman informative approach for considering the mass-

specific forces required for sprint accelerations


39/68

Impulse

Average force time force is applied

determines the net

change in velocity


40/68

Acceleration

F = maForce = mass acceleration

acceleration = velocity/time

= m/s per second

= ( m/s)/s

l l


41/68

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


42/68

The change in the horizontal velocity of the bodymust equal:

speed = Time of force Average horizontal force applied (Fy/Wb)


43/68

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


44/68

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)


45/68

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


46/68

RACE PHASE II:

~ Steady-speed Sprinting


47/68

The how of the mass specific force-speed relationshipduring steady-speed running


Body Weight

Representative Elite 100 m Dash


48/68


(1987 World Champs)

Velocity(m/s)

0

3

6

9

12

0 3 6 9 12



Men

Women

Time (s)


49/68






50/68

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]


51/68

Runners keep the speed they

already have

Need to push down, not backwardonce up to speed


52/68

Runners are like bouncing balls

Need to push down, not backward


53/68

Skipping stones

Momentum moves the stone forward after the initial push

PART II


54/68

PART IIMechanics of steady-speed running:

scientific basics

Very Basic Running Mechanics:


55/68

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.


56/68

VERTICAL

FORCE

Body

Weight

Synchronized Force-motion video


57/68

[force and video data acquisition at 1000 Hz]

SMUs Locomotor Performance Laboratory

Vertical Force vs Foot ground Contact Time across Running Speed


58/68

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


59/68

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;


60/68

-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


61/68

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


62/68





Representative Elite 100 m Dash


63/68


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


64/68

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.


65/68

CONCLUSIONS and Wrap-Up:

ALL RACE PHASES

SINGLE CONCLUSION:


66/68

Sprint running performance:

Speed is ~ entirelydetermined by theMASS-SPECIFIC

FORCE APPLIED TO

the ground

Physics Ground Force/ Body Weight SPEED

SCIENTIFIC TAKE-HOME MESSAGES


67/68

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


68/68

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

rice speed symposiumtalk pdf version for casey

Documents