Physics of Fencing The Biomechanics of a Lunge

Physics of Fencing The Biomechanics of a Lunge William Goldhirsch Biology 438 Spring 2012

Weapons

The foil

What is fencing?

Physics of Fencing • The main motion in fencing is the lunge 1) Deconstruct the lunge, see if the analysis matches the conceptual understanding. 2) The goal of the lunge is to hit your opponent…how much force is in this foil? How safe is fencing? For example, it is known that to set off a foil, you must put a minimum force of 4. 9 newtons to press down the tip…how does this compare to the total force?

Video-Edited

Original Video

Lunge • A lunge is the primary, offensive technique in the sport of fencing. • It is an attack…and it is fast. • All weapons use it, and it is arguably the most important aspect in competitive fencing.

How do you lunge? • 1. The arm holding the foil begins to extend. • 2. The foot facing the opponent kicks forward. • 3. The back leg pushes forward by straightening – at the same time, the back arm is thrown back –the body is pushed forward. • 4. The foil reaches its target, and the front heel hits the floor. The foot lands and the leg bends until the knee is directly over the heel.

Start-before analysis

Video Analyzed - Finish

Which muscles are used? • In fencing…everything you can think of! • Focus on the lunge: • Quadriceps femoris muscle: the main worker of the lunge; provide much of the force (the back leg). • Calves: help the speed and explosiveness of the lunge, they help set up the lunge and then when recovering. • Anterior tibialis muscle: Body weight is put on this muscle when a fencer lunges (front shin). • Hamstrings: help speed and recovery • Gluteus muscles: Hold thighs and quads in place during lunge/recovery. • Shoulder/Biceps/Triceps/forearm – hold and extend/bend

Velocities (X) of muscles • Vi time is relative to the front arm, which starts at 0.

Velocities (Y) of Muscles (cm/s)

Do the results make sense? • Yes! • But, why? – Front arm starts first, followed by front leg and back leg/back arm. – Back leg has the highest Vmax. The front arm has the second fastest, and it’s over a longer period of time, whereas the back arm has a very fast velocity over a shorter period of time. – Body moves up and down together- want to move mostly in X direction.

Implications • Help fencers lunge better (better=more explosive and farther in x direction, less in y direction) • Need for fencing equipment to be elastic, form fitting (more on this later…)

Force • F=ma • Difficult to use, since: – Acceleration is different for different parts of the body – Hard to tell how much mass is truly accelerating, is it the whole body or just part? There must be another way!

Measure

Force of Foil-Measure 1

Force of Foil - Measure 2

Force of Foil -Calculations • Foil shortens 17. 49 cm (~6. 8 inches) • Using a scale, find force as the blade is bent and shortened 17. 49 cm • Scale = 8. 5 lbs • 8. 5 lbs * (4. 448 newtons/1 pound force)= 37. 80988 newtons

Calculations • …in an area of only ~0. 049087 in 2 or ~0. 31669 cm 2 (the tip of a foil is very small! It is a circle with diameter of about ¼ inch) • Pressure = force/area • Pressure=(37. 8098 newtons)/ (0. 31669 cm 2)= 119. 391 newtons/cm 2 • …that’s approximately 173 psi!

Force • • D=vi*t + ½ a *t 2 D=distance of lunge (known)=1. 778 m Velocity=0 m/s (initial) T=1. 1667 seconds – Therefore, a=2. 612 m/s 2 If F=ma, then 37. 89 newtons=m*2. 612 m= 14. 5 kg or about (14. 5/79. 5)=18. 2% of my bw (Around 2 -3 times bw -good thing we didn’t use f=ma right away! Probably not a great approximation)

Protection • For foil, you wear: – Lamé – Jacket – Plastron – Knickers – Socks/shoes/t-shirt/underwear – Mask – Chest plate

Kevlar • Fencing protection works like kevlar! Actually, the knickers, jackets, plastrons, and bibs of masks actually use kevlar as part of its fabric. -the high tensile strength of kevlar make it difficult to stretch, requiring a huge force to pierce…instead of letting a projectile go through, it spreads the force into stretching the fibers.

Protection • Masks come in 350 NW, 800 NW, (visor=1600 NW) • Jackets/Knickers/Plastrons come in 350 NW and 800 NW • FIE = All 800 NW and 1600 NW • US competition=not really regulated Range from 700 NW-1600 NW Foil force = about 40 newtons! You’re safe!. . . unless a blade breaks…

Conclusion • The physics of a lunge make it fast and explosive, thanks to the strong leg muscles. • The foil creates a decent amount of force, but much more pressure on the opponent. • Q&A- Has anyone ever been stabbed? – Yes, but always during times where the integrity of the material has been compromised.

About the Author

Works Cited • http: //www. ngfc. us/ • http: //www. tcnj. edu/~fencing/glossary. htmhttp: //www. howitworksdaily. com/technology/question-of-the-day-how-does-kevlar-stop-a-bullet/ • The Science of Fencing: Implications for Performance and Injury Prevention: www. adisonline. com

Q&A