Cycling Biomechanics: Science to take The purpose of this ... · 1/28/2013 2 Purpose...
Transcript of Cycling Biomechanics: Science to take The purpose of this ... · 1/28/2013 2 Purpose...
1/28/2013
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Cycling
Biomechanics:
Science to take
your performance
from zero to hero
W. Lee Childers PhD
• The purpose of this lecture is to introduce
myself to you
• Let you know what is happening at ASU
• Get the students of ASU and AUM
together to start collaborating on research
• Highlight research to help improve cycling
performance
Purpose
• Introduction • My background is mechanical engineering.
• My former career was an engineer on top
fuel dragsters. It was fun but they explode
a lot.
• The human machine is far more
interesting to me.
Purpose
• Introduction • My cycling experience begins designing
land speed bicycles during engineering
school, (not shown)
• I’ve ridden around Europe, New Zealand,
The US, and the Continental Divide
• Raced for Georgia Tech in Cross Country
mountain biking and Track
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Purpose
• Introduction
• At Georgia Tech, I built a lab to study
cycling biomechanics.
• Our research was focused on how to
improve the lives of people living with
amputation.
• However, since my advisor and I both love
performance, we did a lot of side projects
to understand cycling performance.
Purpose
• Introduction
• Collaboration
• I am new faculty here at ASU’s new
Prosthetics and Orthotics progrom
• We’re building a new lab here to study
human movement, especially those with
amputation.
• Students from ASU and AUM are here
Purpose
• Introduction
• Collaboration
• Future Symposia
• Meet the Community
• Research cannot be done without
community support.
• If you are interested in volunteering as
research subjects, email me
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• Cycling
Biomechanics
• The Pedal Stroke
• Effects of Position
• Project 96
• Modeling
Performance
Introduction
• I’m going to tell the story of the 1996 Olympic
Superbike program as an example of integrating
science into bicycle design.
• The “Superbikes” developed for the ‘96 Olympic
games were so advanced they were banned
from competition.
• Lessons learned and technology developed from
Project ‘96 are still applied today.
• Project ‘96 incorporated the same equipment we
have here at ASU.
• Dr. Jeff Broker was the biomechanist for Project
’96, he was a former student of my advisor, Dr.
Robert Gregor, and invented the force pedals in
our lab.
Bicycle/Rider System
• I think of the whole bicycle and rider as a
system.
• The human machine has all these different
muscles
• The position of the rider on the bicycle will
define the operating lengths of those
muscles
• This lab will study how and why people
move.
• We will focus our research on how people
use prosthetic and orthotic devices to
move.
• Additional research will be conducted to
study sport performance and mechanisms
of injury.
• It is being renovated and updated wit a
new Vicon motion capture system. This is
a special camera system used to track
how people move and can be used for
movie special effects
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• The heart of any cycling lab is a pedal
system
• There are only seven of these systems in
the world
– one of those is here at ASU
• This system can measure forces about 3-
axes and moments about 2 axes.
- Figure from Ryan et. al.,
1992. Sport Sci Rev. 2:69–80.
• The pedal information is combined with a
camera system to track motion and EMG
to measure when muscles are active
• This information is combined to give us a
picture of how the person uses their
muscles to energize the bicycle
• These techniques may also be used for
walking, running, any other motion.
What happens
during the pedal
stroke
Childers et. al., 2009. Pros Orthot Int. 33:256-271.
• Some light reading about cycling
• Millard-Stafford M., Childers W. L., Conger S. A., Kampfer A. J., Rahnert J. A. (2008) Recovery
Nutrition: Timing and Composition after Endurance Exercise. Current Sports Medicine Reports. 7
(4) pg 193 – 201.
• Childers W.L., Kistenberg R., Gregor R.J. (2009) Biomechanics of cyclists with transtibial
amputation: Recommendations for prosthetic design and direction for future research. Prosthetics
and Orthotics International. 33(3) 256-271.
• Childers W.L., Perell-Gerson K.L., Kistenberg R., Gregor R.J. (2009) Pedaling forces normalized
to body weight in intact and uni-lateral transtibial amputees during cycling. In: van der Woude,
L.H.V., Hoekstra, F., de Groot, S., Bijker, K.E., Dekker, R., van Aanholt, P.C.T., Hettinga, F.J.,
Janssen, T.W.J., Houdijk, J.H.P., editors. Rehabilitation: Mobility, Exercise & Sports: 4th
International State-of-the-Art Congress, Assistive Technology Series, Vol. 26. IOS Press,
Amsterdam, NL, 114 – 116.
• Gregor R.J., Fowler E.G., Childers W. L. (2011) Biomechanics of Cycling. In: Magee D, Manske
R, Zachazewki J, Quillen W, editors. Athletic and Sports Issues in Musculoskeletal Rehabilitation.
Elsevier Saunders, 187 – 216.
• Gregor R.J. & Childers W. L. (2011) Neuromechanics of Cycling. In: Komi P.V., editors.
Neuromuscular Aspects of Sport Performace, The Encyclopedia of Sports Medicine, An IOC
Medical Commission Publication. Wiley-Blackwell Pub. West Sussex, UK, 52 – 77.
• Childers W.L., Gregor R.J. (2011) Effectiveness of force production in persons with unilateral
transtibial amputation during cycling. Prosthetics and Orthotics International. 35(4) 373-378.
• Childers W.L., Kistenberg R., Gregor R.J (2011) Pedaling asymmetry in cyclists with unilateral
transtibial amputation and the effect of prosthetic foot stiffness. Journal of Applied
Biomechanics.27(4) 314-321.
• Childers W.L., Perell-Gerson K., Gregor R.J. (2012) Measurement of Motion between the
Residual Limb and the Prosthetic Socket during cycling. Journal of Prosthetics and
Orthotics.24(1) 19-24.
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• A common misconception about cycling is
you should concentrate on the pedal
stroke and always direct forces
perpendicular to the crank arm
• This is a view I had as an engineer but it is
NOT correct
• The human machine has to account for all
of the muscles, what they can do and how
they can do it.
• This means work done at the crank is NOT
constant
• This is work done by both legs at the crank
• It is NOT constant
• The blue and magenta lines are power
output for the right and left limbs
throughout one pedaling cycle
• Note the large power impulse during the
downstroke and the negative power
produced by each limb during the upstroke
• This negative power production during the
upstroke is the focus of a lot of training
programs yet being negative isn’t
necessarily bad.
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The Pedal Stroke
-Figures from Korff et. al., 2007. Med Sci Sports Exerc 39:991–995.
• “Pulling Up” during
recovery not an
efficient strategy
• Increase joint flexor
EMG 1.1 – 3.4 times
baseline
- Mornieux et. al.,
2008
• Each leg weighs about 40 lbs and there is
a lot of inertia associated with the legs
spinning at 90 rpm.
• In order to “pull up” on the pedal, you have
to overcome inertial/gravitational forces
AND pull the pedal up faster than the
opposite leg is pushing down.
• The muscles used in pulling up the pedal
are smaller and not well designed for this.
• If you actively try to pull up, you will
drastically increase energetic demand and
fatigue these muscles very fast.
Pedaling Technique
-Figure from Broker, 2003. High Tech Cycling 119-146.
• Over time, training in a specific discipline
(like mountain biking) will change pedaling
technique a little.
• What is more important is to look at
pedaling as a motor skill.
• A motor skill is the ability to invariably
maintain task performance in a variable
environment. In other words, being able to
quickly react and adapt to changes during
a race.
• The more you train for a specific task, the
better you become. In other words, ride
your bicycle.
Pedaling Technique
-Figure from Chapman et. al., 2007. Exp Brain Res 181:503-518.
• This shows the difference in muscle
activation of highly trained triathletes,
cyclists and novice riders. Note the
cyclists have very little variability where as
the triathletes and novices have a lot of
variability.
• Triathletes train for multiple events and
become a “Jack of all trades, master of
none”
• Summary is variability is a key for
performance may be something to focus
on.
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Bicycle Positioning
• Project ‘96 had to find the best positions
for the cyclists to make power yet
minimize wind resistance for the 4km
Pursuit
• A key component of this is seat tube angle
(STA)
Seat Tube Angle
• Effects muscle
coordination
– Childers et al.,
2007
– Silder et al.,
2011
• The Rectus Femoris muscle has to
increase activity in steep STA because it is
shorter and short muscles have to work
harder.
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Project 96
• When you work harder, variability
increases.
• Project ‘96 was the first to identify this and
use it to develop the Superbikes.
• They varied position and looked at
variability in pedaling forces at the top of
the pedal stroke (when the rectus femoris
is active).
Project 96
• This is the US team and Dr. Jeff Broker at
the General Motors wind tunnel
• They went back and forth between the
wind tunnel and the Olympic Training
Center in Colorado Springs, CO to fine
tune the design.
• Then, each bicycle was made for each
specific rider.
• Kilo
• Silver • Erin Hartwell
• Individual
Pursuit
• 9th
• Team Pursuit
• 6th
Project 96 • The results, the US team managed a
Silver medal and although lacking in the
4km individual and team Pursuits, it was
enough to scare the IOC so…
• If you can’t beat it, ban it.
• The bicycles are illegal to this day and
now hang in museums.
• One of the many technologies developed
via Project ‘96 was advancements in
computer modeling of cycling
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Money = Speed;
How fast do you
want to go?
• We developed our own computer model of
cycling (based off the original work of Project
‘96) to investigate how to best spend our
(college student budget) money to go faster.
• Turns out it is just like Drag Racing, cost goes
up with speed.
• A lot of the baseline conditions for this model are
presented in the article;
• Jeukendrup AE & Martin J. (2001). Improving
Cycling Performance. How should we spend our
time and money. Sports Medicine 31 (7): 559-
569.
Aerodynamic Drag
• Aerodynamic
Drag
• 30 mph
• 92%*
• 77%**
* Wood velodrome ** Dick Lane velodrome
• Aerodynamic drag is the major resistance
to cycling.
• At 30 mph (typical Pursuit speeds) this is
92% of the resistance on a wood
velodrome.
• On a rough, outdoor concrete velodrome,
the rolling resistance of the tires is much
larger so aerodynamics plays a smaller
but significant role.
Pursuit Model
Corner radius
P Edr = ½ ρ CDA V3 +
μ V Fn + ∆PE/∆t + ∆KE/∆t
• We built a model based of this
equation.
• The model is being reviewed now for
publication in Medicine and Science in
Sports and Exercise.
• More details about the model may be
found here; – http://www.dicklanevelodrome.com/node/1037
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Pursuit Model Kph of model compared to experimental data
30
35
40
45
50
55
1 101 201 301
time point (0.126 sec)
km
/hr
Model Output
Experimental Data
• The model does an incredible job of
predicting speed based on power. The
model output is in blue and the
magenta is what actually happened at
the track.
• The model is calibrated to a standard
error of +/- 0.14 m/s and can predict
4km Pursuit performance within +/- 3.7
seconds
• You can use this model to predict
performance based on doing different
things.
The cost of going faster
• Internal factors
• Interval training
• Altitude training
• “Sleep high, race low”
• Caffeine
• Doping
• EPO or blood doping
• One way to go faster is through “internal factors” that would increase
the cyclist’s ability to produce more power.
• Interval training (Jeukendrup & Martin, 2001)
• Power increase of 5%
• Cost assumed to be one month of coaching at $200/month
• Altitude training (Jeukendrup & Martin, 2001)
• Power increase of 2%
• Cost for an altitude tent = $2400
• Caffeine (Jeukendrup & Martin, 2001)
• Power increase of 5% with 400 mg an hour before competition
• Cost = $4.50 at Starbucks
• Doping (Eichner, 2007)
• EPO
• Power increase of 6% for one month regimen
• Cost of EPO treatment for renal failure = $5000 per year
• Assumed cost = $5000/12 or $417
The cost of going faster
• External factors
• Shoe Covers
• Aero helmet
• Aero wheels
• Aero frameset
• Aerobars
• Wind tunnel
• Gruber Motor
• “Mechanical Doping”
• Another way to go faster is to reduce aerodynamic drag
• Shoe Covers (adjusted from data in Kyle, 2003)
• Reduction of ~150 grams in drag savings
• Converts to a CDA reduction of 0.0073 m2
• Cost = $30.00
• Aero helmet (adapted from Sidelko, 2007)
• Reduces power requirement by 3.8%
• Cost = $140.00
• Aero wheels compared to std. rim, 36 round spokes (Kyle, 2003)
• HED jet 9 used for aero front wheel (data from HED website)
• CDA reduction of 0.0056 m2
• Cost = $900
• Carbon flat disc used for rear wheel
• CDA reduction of 0.0068 m2
• However, the rear wheel is blocked by the frame and is
adjusted by 0.5 to compensate (Jeukendrup & Martin, 2001)
• Cost = $1100
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• Aero frameset compared to round, steel tube bike
• Assumed to be Felt and similar drag reduction to a Cervelo or
Lotus (Jeukendrup & Martin, 2001)
• CDA reduced 0.020 m2
• Cost = $4440
• Aerobars
• The modeled rider was already in an “aero” position so CDA
was increased to 0.307 m2 (Jeukendrup & Martin, 2001)
• Cost = $180
• Wind tunnel
• “Optimizing” position in a wind tunnel should reduce CDA by
0.029 m2 (Jeukendrup & Martin, 2001)
• Cost = $1000 for 2 hours in the A2 tunnel plus travel to NC
• Gruber Motor
• This is the Motor assist system Cancellara was accused of
using.
• Claims increase in 130 watts, I used 130 watts in the model but
my feeling is the actual benefit may be less.
• Cost = $2400
The cost of going faster Item
Seconds saved in
3k
Everything 30.8
Gruber Motor 24.1
Wind Tunnel 18.2
Caffeine and Training 11
Aerobars 10.1
Caffeine 7.6
Interval Training 6.2
EPO 6.1
Aero Frame 5.5
Skinsuit 2.8
Aero Helmet 2.7
Aero/Disc Wheelset 2.5
Altitude Tent 2.3
Shoe Covers 1.9
Aero Front Wheel 1.5
Disc Rear Wheel 0.9
The cost of going faster
Note – If simply summed, everything
would be a 53 second time savings
• You can’t simply add the seconds saved because
things interact.
• The item “everything” represents what would
happen if you combined everything in the red box.
• If you simply added everything, you’d “save” 53
seconds. Yet when you adjust for everything in the
model, it calculates a time savings of 30.8 seconds.
This is due to how all the variables interact within
the model.
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The cost of going faster
Note – The cost of Everything is
~$11,000
• Just because the wind tunnel
may shave 18.2 seconds, it
does cost $1000 for the
service. For those of us on a
budget, it may be a good
idea to look at things from a
cost/benefit perspective or $
spent per second saved.
Low number = good
Item $/sec
saved in a 3k
Caffeine 0.592
Shoe Covers 15.79
Aerobars 17.82
Caffeine and Training 18.59
Interval Training 32.26
Aero Helmet 51.85
Skinsuit 53.57
Wind Tunnel 54.95
Gruber Motor 102.6
Everything 355.9
EPO 416.7
Aero Front Wheel 600
Aero/Disc Wheelset 800
Aero Frame 807.3
Altitude Tent 1044
Disc Rear Wheel 1222
Modeling Cycling
with and without
and amputation
Lee Childers1
Tim Gallagher2
Chad Duncan1
Douglas Taylor3
1Alabama State University, Prosthetics and Orthotics
2Georgia Institute of Technology, Aerospace Engineering
3Southeast Community Research Center
• A person with a transtibial amputation cannot make
as much power as someone with intact limbs
• BUT, the prosthesis is more aerodynamic
• Could the aerodynamics of the prosthesis actually
provide Parathletes an advantage during the
Pursuit?
Modeling Cycling
with and without
and amputation
Jack Bobridge Holds the World Record for the 4km Pursuit at 4:10.5
What if he was given an amputation?
• We modeled a world record Pursuit and then reran
the model as if Bobridge had an amputation.
• We used lots of experimental data from my prior
research to adjust the power output of Bobridge.
• Childers W.L., Kistenberg R., Gregor R.J (2011)
Pedaling asymmetry in cyclists with unilateral
transtibial amputation and the effect of
prosthetic foot stiffness. Journal of Applied
Biomechanics.27(4) 314-321.
Table 2 - CDA and asymmetry corrections for conditions with an intact limb (baseline) a generic cycling
prosthesis (GP), an aerodynamically optimized prosthesis (OP), and a cosmetically covered prosthesis (OP).
Condition
Abbreviation
Type
of
limb
Frontal
Area
(m2)
CDA
correctio
n factor CDA
Cyclist
Asymmetry
Power
Factor
Baseline baseline 0.053 1.0 0.215 0.0% 1.0
TTA GP 0.027 0.906 0.195 21.4% 0.824
TTA-ASYM GP 0.027 0.906 0.195 7.0% 0.935
TTA-AERO OP 0.024 0.893 0.192 21.4% 0.824
TTA-CC CC 0.053 1.0 0.215 21.4% 0.824
TTA-OPT OP 0.024 0.893 0.192 7.0% 0.935
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Used Experimental data from Childers et al., 2011 to adjust for power loss
Used 3-D models of cycling prostheses to adjust CDA
Using a prosthesis will
NOT provide you an
advantage.
Used Experimental data from Childers et al., 2011 to adjust for power loss
Used 3-D models of cycling prostheses to adjust CDA
Brian Hicks is just that
much faster than you.
Questions? Thank You • Cindy Laporte
• Hank Williford
• Arletha Willis
• Regina Adams
• Jesse Adams
• Brenda Dawson
• Dan Gulde
• Chad Duncan
• Dean Chesbro
• Lindsey, the Vicon Commander