Biomechanical Principles in Sprint Running, Exercises of Biomechanics

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Biomechanical Principles in

Sprint Running

Basic Concepts

Iain Fletcher

Content

•^

Stride Length

-^

Stride Frequency

-^

Newton’s Laws

-^

Running Mechanics

-^

How to Run Faster!!

Running Speed

•^

Stride length x stride frequency

-^

At faster running speeds (above 7m

·s

) stride

frequency increases more then stride length^ – Up to 2.6m stride length & 5Hz frequency

-^

Force production increased with running speed^ – Up to 4.6 x body weight– NB 5.5 x body weight for a heel striker at 9.5m

·s

•^

Max speed ground contact 0.08- 0.1sec Mero

et al.

• increase in stride length, stride frequency,

force production or decrease in groundcontact will increase speed

• What is your training designed to change?

Impulse

• Linked to Newton’s 2

nd

Law

• Force x time applied = impulse to an

object

• r= 0.74 between propulsive force &

running velocity in 1

st

contact after the

blocks (Mero

et al.

Impulse- Momentum Relationship

• Need to exert a force to cause a change in

velocity

• Direction of force causes direction of

acceleration

• Increase force increases momentum• Or more precise increase impulse

increases momentum

Sprint Components

• Speed = stride length x stride frequency
  • 2m/stride x 4 strides/s = 8m

·s

• • Increase in either component should not

negatively effect the other

Stride Length

•^

Sum of

-^

Takeoff distance^ – Horizontal distance that C of G is forward of the take

off foot at the instant the latter leaves the ground

•^

Flight distance^ – Horizontal distance that the C of G travels while the

runner is in the air

•^

Landing distance^ – Horizontal distance that the toe of the lead foot is

forward of the C of G at the instant sprinter lands

Landing Distance (Support Phase) • Smallest of 3 contributions to total stride

length

• Arrests athletes downward motion

(acceleration due to gravity plus activedescent leg)^ – Triple flexion to absorb force– Prepare for driving phase

• Need as favourable ground reaction forces

as possible^ – Increasing landing distance can increase

breaking force so decrease running speed asstride frequency decreases

• Foot position under the C of G travelling

backwards

• Breaking phase less in faster sprinters (Mero

et al.

Foot Position

•^

Importance of dorsi flexed ankle^ – Store strain energy from stretch and recoil of calf

complex (achilles tendon)

• Pre stretch of calf complex helps promote Stretch

Shortening Cycle

• Decrease coupling time between eccentric and

concentric contraction

• Store mechanical work as elastic energy during

eccentric phase (Biewener & Roberts, 2000)

• Peak Achilles tendon force (12-13 x body wt.)

ActiveComponent

Sum Passive

Length (% resting length)

MuscleTension

50

100

150

Contraction Range

in vivo

Tension-Length Relationship

• Muscles, tendons & ligaments behave like

a spring^ – Higher stride frequencies associated with

increased spring (MTU) stiffness (Farley &Gonzalez, 1996)

• EMG in GA starts 100ms before ground

contact helps increase MTU stiffness (Mero &Komi, 1987)

Takeoff Distance (Driving Phase)

• Drive down and backwards through

forceful extension of the hip, knee andankles kinetic chain^ – Projects body upwards & forwards

• Importance of full extension to provide

greater impulse maximising forwardmomentum

• Peak power generated proximal to distal

sequence