isb 2015_acceleration hip extensors

SPRINT  ACCELERATION  MECHANICS      

THE  ROLE  OF  HAMSTRING  MUSCLES  IN    HORIZONTAL  GROUND  REACTION  FORCE  PRODUCTION  

@jb_morin

Morin JB University of Nice, France Edouard P University of Saint-Etienne, France Gimenez P University of Franche-Comté, France Arnal P University of Saint-Etienne, France Jimenez-Reyes P Catholic University of San Antonio, Murcia, Spain Samozino P University of Savoy, France Mendiguchia J Zentrum Rehab Center, Baranian, Spain Brughelli M Auckland University of Technology, New-Zealand

jean-benoit.morin@unice.fr

Survival of the fastest?

Acceleration is the key…

2011  -­‐  2015  Sprint  acceleration:  importance  of  Horizontal  Force  Production  

Sprint  Instrumented  treadmill  Track-­‐Embedded  Force  Plates  Elite  Athletes    Med  Sci  Sport  Exerc  2011  Eur  J  Appl  Physiol  2012  Scand  J  Med  Sci  Sport  2015  J  Biomech  In  Press  

Horizontal  GRF  /  impulse    is  paramount      Vertical  /  resultant  GRF  is  not    «  Ratio  of  Forces  »  and  Hzt  Force    at  high  speed  higher  in  top  athletes    

Higher RF at high, not low speeds…

How to produce High net HZT Force At High running speed??

The  «  Hip  Extensors  »  hypothesis  

Synchronized EMG (2 kHz) and 3D GRF (1 kHz)

Treadmill Sprint Accelerations

2D Motion Knee and Foot

Knee Extensor Hip Extensor Isokinetic Torque

The  «  Hip  Extensors  »  hypothesis  

The  «  Hip  Extensors  »  hypothesis  

Preliminary results…. Paper  in  preparation  

Isokinetic Torque alone NOT correlated to GRF

Muscle activity (EMG) alone: NOT correlated to GRF

Multiple Regressions: FHZT entire acceleration correlated to : Eccentric Hamstring torque

EMG BF during end-of-swing phase FHZT initial acceleration correlated to : Eccentric Hamstring torque

EMG BF during end-of-swing phase

Concentric Glutei torque EMG Glut during end-of-swing phase

Quadriceps…. Contact phase: NS

2D Motion (speed, range of motion) of Knee and Foot: NS

«  Prepare  and  Repair  »  

Importance of Horizontal GRF (especially at high speed)

What balance between hip extensors and other groups in training?

Hamstring Eccentric Force and Activation: Performance AND Injury Prevention

Associated with: high hip extensors force (Glut in CONC and Ham in ECC) high end-of-swing EMG activity

MERCI !!