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 in2 or ~0.31669
cm2 (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 cm2)=
119.391 newtons/cm2
• …that’s approximately 173 psi!
Force
•
•
•
•
D=vi*t + ½ a *t2
D=distance of lunge (known)=1.778 m
Velocity=0 m/s (initial)
T=1.1667 seconds
– Therefore, a=2.612 m/s2
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 350NW, 800NW, (visor=1600NW)
• Jackets/Knickers/Plastrons come in 350NW and
800NW
• FIE = All 800NW and 1600NW
• US competition=not really regulated
Range from 700NW-1600NW
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.c
om/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