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The Acce

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by

Mari Walsh

on 25 February 2014

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Transcript of The Acce

The Acceleration Phase of Sprinting
Outline:
Acceleration and Power
What causes acceleration in sprinting?

Orientation of GRF
Braking vs. Propulsive phase
Impulse
Muscular power
Contact vs. flight phase


Define acceleration and power

Discuss variables that influence acceleration during sprinting

Apply this knowledge to train for optimal acceleration

Acceleration
measures changes in velocity:

(Vf-Vi)/T or stride length X stride rate
Muscular power
is the rate of torque production at a joint:

muscular force X velocity of muscle shortening


Muscular Power is Affected
by Muscular Strength and Movement Speed
Hall, 2012
GRF
External Forces:
1. GRF 2. Gravity 3. Wind resistance
Horizontal vs. vertical (Shepherd, 2008)
Blocks (projection angle & incline trunk), weight distribution & "active touchdown"
"The athlete actively attempts to move the foot backward as fast as he or she is moving forward."
(Hunter et al., 2005)
Horizontal Velocity?
Total Body Center of Gravity (TBCG)
In a study examining the start of a world class sprinter, the average vertical rise in TBCG in the first three meters was
0.67 m.
Coh et al., 2006

Impulse
Magnitude and duration of GRF
Block impulse
GRF X Time (Ground contact time)
GRF impulse (expressed relative to body mass) reflects the change in velocity of an athlete
(Hunter et al., 2005)
Therefore, changes in relative GRF impulse help to explain acceleration







Braking vs. Propulsion
Belief that sprinters should
minimize
braking GRF and
maximize
propulsive GRF
Minimize braking
: "Active touchdown"
Small touchdown distance

Maximize propulsion
: Greater hip joint extension
velocity during stance
Hunter et al, 2005
Muscular Power
= muscular force X velocity of muscle shortening
Fast twitch vs. slow twitch
Muscle-tendon stiffness
Muscular strength
http://breakingmuscle.com/running/mechanics-more-important-than-metabolic-power-in-sprinting
Brechue, 2011
http://www.telegraph.co.uk
Contact vs. Flight Phase
Stride Rate x Stride Length = Velocity
Both stride rate and stride length increase to
cause acceleration
"Negative interaction" - leg length, height and vertical velocity of take off (Hunter et al., 2004)


Brechue, 2011
As velocity changes from almost maximum to maximum, stride length remains constant and stride rate increases
Training Methods
Concentric training
Plyometric training
Weighted sled
Overspeed

Shepherd, 2008
(Debaere et al., 2012; Hall 2012; Harrison 2010)


Brechue, W. F. (2011). Structure-function relationships that determine sprint performance and running speed in sport.
International Journal of Applied Sports Sciences, 23(2), 313-350.

Coh, M., & Bracic, M. (2010). Kinematic, dynamic and EMG factors of a sprint start. Track Coach(193), 6172-6176.

Čoh, M., Jost, B., Skof, B., Tomazin, K. & Dolenec, K. (1998). Kinematic and kinetic parameters of the sprint start and
start acceleration model of top sprinters. Gymnica, 28, 33-42.

Čoh, M., Tomažin, K., & Štuhec, S. (2006). The biomechanical model of the sprint start and block acceleration.
Biomehanicki Model Sprinterskog Starta I Blok Ubrzanja. Facta Universitatis: Series Physical Education & Sport, 4(2),
103-114.

Debaere, S., Jonkers, I., Aerenhouts, D., Hagman, F., van Gheluwe, B., & Delecluse, C. (2010). Performance determining
factors in elite sprinters during sprint start and two following successive supports. International Symposium on
Biomechanics in Sports: Conference Proceedings Archive, 28, 1-2.

Hall, S. (2012). Basic Biomechanics (M. Ryan Ed. 6th ed.). New York, NY: McGraw-Hill.

Harrison, A. J. (2010). Biomechanical factors in sprint training- where science meets coaching. International
Symposium on Biomechanics in Sports: Conference Proceedings Archive, 28, 36-41.

Hay, J. Cycle rate, length, and speed of progression in human locomotion. J. Appl. Biomech. 18:257–270, 2002.

Hunter, J. P., Marchall, R. N., & McNair, P. J. (2005). Interaction of step length and and step rate during sprint running.
Medicine & Science in Sports and Exercise, 261-271.

Hunter, J. P., Marshall, R. N., & McNair, P. J. (2005). Relationships between ground reaction Force Impulse and
Kinematics of Sprint-Running Acceleration. Journal of Applied Biomechanics, 21(1), 31-43.

Pitsiladis, Y., Davis, A., & Johnson, D. (2011). The Science of Speed: Determinants of Performance in the 100 m Sprint.
International Journal of Sports Science & Coaching, 6(3), 495-498.

Shepherd, J. (2010). Conditioning Sprint Acceleration: Recent Research. Track Coach(193), 6177-6180.


References
Summary
Acceleration is influenced by the magnitude, direction, and duration of the GRF
Muscular power should be targeted for maximizing acceleration
Training methods used for sprint acceleration should closely mimic the kinematics desired during racing
Conclusion
Concentric Training
Multijoint exercises with emphasis on concentric phase
Shepherd et al. (2008)
Essential for first 10 m of race (during accleration), stretch-shorten cycle then becomes increasingly active
Plyometric Training
Loaded jump squats: 30% RM vs. 80% RM

Lighter loads = greater acceleration in 20 m sprint
Heavier loads - slower ground contact times and reactive forces
Muscular power - 1/3 RM (Hall, 2012)
Shepherd, 2008
Weighted Sled
Low drive position
Heavy loads =
stride rate and stride length
ground contact time
Overspeed training
External devices force runner to increase speed
Similar to heavy sled towing, shown to alter sprint kinematics
Shepherd, 2008
Impulse = Changes in momentum
Summary
-Maximize horizontal velocity
(blocks, projection angle, incline trunk)
-Stride length = short to long
-Stride rate = increases

-Ground contact time = long to short
-Velocity = slow to fast
Hay, 2002
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