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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

• lchilders@alasu.edu

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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