ISBS 2015 Sprint Applied Session, Theoretical Part

A SIMPLE METHOD TO MEASURE EXTERNAL FORCE, POWER OUTPUT AND EFFECTIVENESS OF FORCE APPLICATION DURING SPRINT ACCELERATION

@jb_morin

J-B Morin

Professor University of Nice, France

jean-benoit.morin@unice.fr

Things as they are….

Work in progress…

2010

Field Field

Only  2  (im)possibilities        L  

SPRINT INSTRUMENTED TREADMILL St-Etienne, France Doha, Qatar

FORCE PLATES INSEP, Paris, France

2015,  a  simple  .ield  method  

1927

Archibald V. HILL

1950’s

Franklin Henry

Modern Devices

v(t) = vmax.(1-e(-t/τ))

vmax

di Prampero et al., J Exp biol, 2005 Furusawa et al., 1927

Henry, 1954 Volkov & Lapin, 1979

2015,  a  simple  .ield  method  

a(t) = (vmax/τ).e(-t/τ))

Fh(t) = m.a(t) + Fair Estimated from speed, mass and height

Ph(t) = Fh (t) . v(t)

v(t)

Ph(t) Fh(t)

Linear F-V relationship Polynomial 2 P-V relationship Validity ??

F0

V0

Pmax

2015,  a  simple  .ield  method  

2015,  a  simple  .ield  method  

•  INSEP-Paris: 3D GRF for 18 steps over 40-m sprints •  9 Elite and sub-elite sprinters (2 sub-10 s)

6.60m force plates 0 - 6.60 m

6.60m - 13.2 m

14m - 20.6 m

2 sprints

23.4m - 30 m

33.4m - 40 m

2 sprints 1 sprint

1 sprint

1 sprint

Very high reproducibility…

!

Comparison with force plates: Validity, Reproductibility J

2015,  a  simple  .ield  method  

Pierre  Samozino,  PhD  University  of  Savoy                

FORCE-­‐VELOCITY-­‐POWER  Pro1ile  of  Usain  Bolt’s  World  Record  Running  Speed  (m/s)  

Distance  (m)  

S(t) = Smax 1− e−t/τ( )

Field  Measurements  In  competition    conditions  

Computing  

Modeled  Speed-­‐time  curve  

Computed  Net  Horizontal  Force  output  

Max  Power  Output  of  30  W/kg  reached  after  about  1  s…  

Power  =  Force  x  Speed…  SpeciJic,  Field  Sprint  Force-­‐Velocity-­‐Power  proJile  

Jean-­‐Benoit  Morin,  PhD  University  of  Nice                  

“F0”  

“V0”  

Pmax  

Vopt  

F0  and  V0  are  the  theoretical  maximal  outputs  of  the  system  Vopt  is  the  speed  at  which  Pmax  is  produced  The  magnitude  of  the  slope  (F0/V0)  describes  the  Force-­‐Velocity  proJile  of  the  athlete  

DEVICES…  

Stalker ATS Pro II Speed-time curves

Timing Gates 5 split times

Appropriate trigger…

GPS Units ?? Speed-time curves

R. Nagahara 21 subjects, 5Hz GPS vs 100 Hz Laser Average data…

Category: Coaching

2011,  Concept  of  Effectiveness…  

For each step, averaged values of Horizontal, Vertical and Total Force

1. Concept of « Ratio of Force » RF

HZT

VTC TOT

2011,  Concept  of  Effectiveness…  

y = -0.0805x + 0.6584

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

2.0 3.0 4.0 5.0 6.0 7.0Vitesse (m/s)

Rat

io d

e fo

rces

Velocity

of

Step after step, the RF decreases…. for all athletes….

2. Decrease in the RF: Drf

Slope = index of the effectiveness of force application

onto the ground (Drf)

Step 1 Step 6

Very efficient

Not efficient

2011,  Concept  of  Effectiveness…  

We also compute the Ratio of Force !

After 50% of Vmax, Fv = m.g

2015,  a  simple  .ield  method  

Applications:  optimized  training  

Example: Season follow-up of C. Lemaitre

1st meeting…

Winter…

3 days before London…

Applications:  training  

Individual comparisons + Team Season Follow-up…

Applications:  training  

TYPICAL  EXAMPLE:  The  player  is  «  low  »  on  40m……But  has  high  velocity  skills!  

Applications:  training  

TYPICAL  EXAMPLE:  Same  30m  time,  but  different  capabilities….    

DIFFERENT  TRAINING  PROGRAMS  ?!  

PLAYER 1

T30: 4.9 sec 4.8 sec V0: 11.2 m/s 9.5 m/s F0: 5.15 N/kg 7.5 N/kg

PLAYER 2

Applications:  training  

Martin Buchheit PSG

Applications:  training  

Applications:  Injury  Management          (prevention  /  rehab)  

BETTER  TRAINING  PROGRAM  =  PREVENTION  !  

PLAYER 1

T30: 4.9 sec 4.8 sec V0: 11.2 m/s 9.5 m/s F0: 5.15 N/kg 7.5 N/kg

PLAYER 2

Applications:  injury  management  

Mendiguchia  et  al.  Int  J  Sports  Med,  2014  

Jurdan Mendiguchia Zentrum Center, Baranain

Applications:  injury  management  

Mendiguchia  et  al.  Int  J  Sports  Med,  2014  

At « Return to Sport » (post hamstring injury):

Ø Pmax and F0 (not V0) lower in injured group Ø 2 months later, values back to « normal » (non-injured)…

1/  what  objectvie/functional  tests  were  used  to  give  «  RTS  »  ?  2/  what  risks  during  this  2-­‐month  (or  less)  period!?  

Applications:  injury  management  

«  Case  study  »  

Elite  Soccer  player

Applications:  injury  management  

2-­‐season  cohort  follow-­‐up  study  (soccer,  rugby,  sprint…)  

1/  Is  F-­‐V-­‐P  pro.ile  related  to  a  higher  risk  of  injury?                  2/  Is  it  an  interesting  functional  variable  in  injury  management?    

       3/  Does  it  have  a  predictive  feature?  

Applications:  injury  management  

Collaborators: R. Nagahara, Japan - J. Mendiguchia, Spain - P. Samozino, France