The Biomechanics of a Javelin Throw

Biomechanical Concepts

Impulse

• Impulse = change in momentum
• Impulse = force x time
• Impulse used to generate more velocity
• Applying force over a long period of time = ^ impulse
• Eg. Hold Jav as far back as possible in run up with straight arm
• = force on release applied for longest amount of time possible

Jav VS Shot-put:

• Top javelin throwers do not have the same maximum strength as shot-putters but they are successful because their technique maximizes the duration of the force they exert

(Darren McPartland, 2016)

Momentum

• p= m x v
• Cannot increase mass, must increase velocity
• Done through a faster run up

(Robert Wood, 2000)

All about Javelin

What is it?

• Track and field event
• Thrower gains momentum by running within a predetermined area
• Javelin thrown directly forward with an over-the-shoulder motion into a 29° sector marked on the field.

Rules:

• It must land point first
• The thrower’s body may not rotate a full turn (360°) before javelin released
• May not step on or beyond line at the end of the runway.

(Britannica, 2016)

Angle of release

Demonstration of skill

• Optimal angle of release = between 32º and 36º
• Angle of attack = difference in:
• angle of attitude: the orientation of the javelin to the ground
• angle of velocity vector: the flight path of the javelin’s centre of mass (not the tip).
• The ideal angle of attack is zero degrees.
• A common cue from coaches is to “throw through the tip” to help throwers control the release angle of the javelin.

Checklist for Jav

(WAlittleathletics, 2016)

Carry + Grip

History of Jav

• Era of Mycenaean times and Roman Empire --> Jav = commonly used offensive weapon
• Thrown rather than thrust = long distance attacks against enemy.
• Diff between Jav (ancient games) and Jav (now) = leather thong, called ankyle = wound around the middle of shaft.
• Athletes hold javelin by thong
• When released = thong unwound giving the javelin spiraled flight.

• The aim is to carry the javelin so as to allow the muscles of the right shoulder, arm and wrist to relax and also to allow an easy running action.

American Grip:

• Needs proper flexibility --> prevent injury
• Strongest grip -->deliver a high amount of rotation upon release
• Javelin lightly held across palm, with index finger wrapped around top of cord + thumb pressing against top of cord as well

Finnish Grip:

• Harder to master
• Good rotation
• Middle finger rests closer to top of cord and index finger wraps higher along shaft.

Did you know?! x2

• The ancient Olympics had two forms of the javelin event, one measuring distance thrown and another to hit a specific target.

Did you know?!

• 1986 men's javelin redesigned C.O.G moved forward by 4 cm = shortened throwing distances by approx 10 % = bringing nose down earlier + more steeply.
• Reason? following world record of 104.80m (East Germany's Uwe Hohn) in 1984- people in danger in stadiums.
• 1999, the women's javelin similarly redesigned.

Levers

theconversation.com, 2015

Lift

• Force created by air flow over javelin = upwards effect
• Lift = greater air pressure below the javelin than above it.
• Javelins- There is no flat surface for air to build-up pressure behind
• Some lift created by throwing javelin with tip up, problems with this =iIncreased drag
• The only lift given to the spear comes from the thrower's body

Drag

World Champs 2015- Beijing (final)

• A force pulling an object backwards due to a low pressure air pocket

• Cause of air resistance = air compressing on the nose of the javelin as it gets pushed out of the way

• Smallest surface area facing into the direction of the throw + the smallest possible vibration= reduce the amount of drag on a javelin.

• The amount of drag will be greater when the object is moving quickly than when it is flying slowly.

The BIomechanics of a Javelin Throw