BIOMECHANICS OF CYCLING FOR BIKE

1/19/2010
BIOMECHANICS OF CYCLING
FOR BIKE-GEEKS
Going from Zero to Hero with the turn of a Hex Key
W. Lee Childers
PhD candidate
Robert Gregor PhD
Introduction
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General Overview
Human System
Performance
How to study
y
Biomechanics
• The Pedal Stroke
• Effects of Position
• Project 96
• Team Pursuit
Team Pursuit
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4000m event
4 min
Two teams/race
Elimination
Ladder
Team Pursuit is the Olympic Event
We will Concentrate on because it
was optimized as part of project '96
Pursuit is a 4-man team
The lead rider will pull the team
later the lead rider will rotate to
the back.
Stone Mountain Velodrome designed using Fresnel Intregrals and Mathematica software
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The human physiological system
must work with the mechanical
(Bicycle) system in order to
perform.
Cycling represents
integration of man
and machine
The saddle, handlebar and pedals
create the contact points for the
body
Cycling represents
integration of man
and machine
That in turn determines the
skeletal alignment and joint
range of motion for the rider
Cycling represents
integration of man
and machine
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Muscles are attached to the
skeleton so position will affect
the length of these muscles as
they cross their respective joints.
Muscles produce different forces
at different length and
contraction velocities.
Neural Control
The brain and spinal cord needs to take
the properties and training state of
each muscle in order to figure out
how to coordinate these muscles to turn
the cranks.
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In this case, the nervous
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system decides to activate a large
thigh muscle to generate
mechanical energy that will
eventually turn the crank.
The nervous system will then have to
coordinate additional muscle activation
to transfer that energy into the crank
This resolves as a force (orange arrow)
at the pedal that will turn the crank.
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Another important thing to remember
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is the muscles and joints will
send information back to the nervous
system to help shape the next set of motor
commands and allow the person to adjust
to change in their environment whether
you're riding a bike or running, walking,
etc.
The bicycle rider system must overcome
resistance in order to move
Resistance to Overcome
• Aerodynamic
Drag
• Gravity
• Energy
gy to
Accelerate
• Rolling
Resistance
• Drivetrain
Resistance
In our case of team pursuit, aerodynamic
drag will be the largest force to overcome
Resistance to Overcome
• Aerodynamic
Drag
• 90% of the
Resistance
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Resistance to Overcome
To reduce drag, these riders adopt
different positions.
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However, these positions will affect
muscle lengths for muscles around the
hip joint, compromising the person's
ability to produce power.
Project '96 tried to find the best balance
between power output and aerodynamic drag.
Measuring Human Performance
• Power Output
– Subject Motivation
– Commercial Products
vary +/- 5%
• Heart Rate and
Oxygen Consumption
– Whole Body
Measurements
• Joint Kinematics
• Pedal/Joint Kinetics
• Muscle Activation
Biomechanics study the last three variables
trying to provide a detailed picture
of how this person is performing a task.
Measuring Human Performance
• Power Output
– Subject Motivation
– Commercial Products
vary +/- 5%
• Heart Rate and
Oxygen Consumption
– Whole Body
Measurements
• Joint Kinematics
• Pedal/Joint Kinetics
• Muscle Activation
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We use a special set of camera that
track markers on someone's joints,
providing the researcher with data on
how the person is moving.
We use a special set of pedals that
measure force designed by Jeff Broker
(project '96 and former student of
Dr. Gregor)
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We combine these data with
Newtonian physics to solve the 1/19/2010
inverse dynamics problem and provides
the researcher with information about
the forces and moments (torques) at each
joint.
Example of a knee moment
x-axis is from 0-360 degrees of
crank rotation.
Knee Moment
30
20
Moment (Nm)
10
0
1
5
9
13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97
-10
-20
-30
-40
%C
C
We also measure muscle activation that tells
us when a muscle is "on" or "off".
Combining all these data provides insight
into how the nervous, muscular, and skeletal
systems are working together to turn the
bicycle cranks.
- Figure from Ryan et. al.,
1992. Sport Sci Rev. 2:69–80.
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Please refer to Childers et al.,2009
for more detailed description of the
pedal stroke
What happens
during the pedal
stroke
Childers et. al., 2009. Pros Orthot Int. 33:256-271.
While riding one day, another rider told me
this... This idea of a perfectly circular
pedal stroke does not have any
scientific evidence supporting it.
You know, I am an Elite Bike
Racer.
Being a Road Racing specialist,
I pedal in Perfect Circles!!
This graph shows what some people
believe would be an ideal pedal stroke.
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This is total crank power showing1/19/2010
how people really pedal a bicycle.
This shows the power output for each leg.
Note the portions of negative power
production.
The following slides will break the pedal
stroke up into quadrants
The Pedal Stroke
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This shows the top of the pedal
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stroke. Lines in red
indicate muscles that are active
The Pedal Stroke
The power phase constitutes about 90-95%
of the total power output.
The Pedal Stroke
The Pedal Stroke
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The recovery phase does not have
much muscle activity. Also the 1/19/2010
ascending limb cannot lift faster than
the pedal being pushed up into it by the
opposite descending limb.
The Pedal Stroke
The Pedal Stroke
Recent research explored "pulling up" type
pedal technique and showed this may not be
an effective strategy for sub-maximal,
steady-state cycling.
• “Pulling Up” during
recovery not an
efficient strategy
• Increase joint flexor
EMG 1.1
1 1 – 3.4
3 4 times
baseline - Mornieux et. al.,
2008
-Figures from Korff et. al., 2007. Med Sci Sports Exerc 39:991–995.
Pedaling Technique
There are slightly different pedal
techniques for each cycling discipline.
Mountain bikers have the smoothest, possibly
due to the loose environment they must
perform in.
-Figure from Broker, 2003. High Tech Cycling 119-146.
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Another important aspect of learning
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how to pedal is that it takes
training
Variability in muscle activation is less
in trained cyclists.
Pedaling Technique
-Figure from Chapman et. al., 2007. Exp Brain Res 181:503-518.
Bicycle Positioning
Seat Tube Angle
• Studies on energy expenditure conflict
– Heil et al., 1997
– Price & Donne 1997
• STA has an effect on pedaling kinetics
– Browning 1991
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Seat Tube Angle
Power vs. Crank Position
500
67 deg
79 deg
300
200
349
335
320
306
292
277
263
248
234
220
205
191
176
162
148
133
90
119
104
75.6
61.2
18
46.8
0
32.4
100
0
Crank Power (watts
400
-100
-200
Crank Postion (deg)
Project 96; The US Olympic
Superbike Program
Pictures are of the Obree and Superman
positions that showed the importance of
aerodynamics for time trial performance
Project 96
• Began in 1992
• Key Figures
– Chester Kyle PhD
– Jeff Broker PhD
– Edmund Burke PhD
• Combine Science with
Cycling to create a
Bike/Rider Combination
for the ’96 Olympics
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Both positions were banned for
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competition and the subsequent
rules provided additional challenge for
the project '96 scientists
Project 96
• Began in 1992
• Key Figures
– Chester Kyle PhD
– Jeff Broker PhD
– Edmund Burke PhD
• Combine Science with
Cycling to create a
Bike/Rider Combination
for the ’96 Olympics
A radical new and aerodynamic
"superbike" was developed for the US
cycling team
Project 96
Dr. Broker used force pedals to analyze
the cyclist's pedaling technique in
different positions to determine the
best compromise between aerodynamic/legal
Project 96
positions and the cyclist's ability to
produce power about the crank center
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This was combined with wind
tunnel testing
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Project 96
A saving of 2.3 seconds could mean the
difference between medal or no medal
Project 96
Project 96
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They developed equations to predict
power requirements for individual
pursuit
Project 96
• P = Power (Watts)
• K = Track Condition
Constant (Basset et al.
1999)
• Mt = Total Mass (kg)
• V = Velocity (kph)
• Kt = Aero Factor
(Basset et al. 1999)
• Af = Calculated Frontal
Area
• H = Height (m)
• M = Mass (kg)
But team pursuit was different and would
require additional testing
Project 96
• Team Pursuit
required drafting
• What are the power
requirements for
drafting?
So they stuck the whole team in the wind
tunnel.
Project 96
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Then out to the track for field
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testing. With all of this data
they were able to optimize rider order
for the team pursuit
Project 96
-Figure from Broker et al. Med Sci Sport Exerc 31:1677-1685
Project 96
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After 4 years of work, they accomplished
a lot and much of their work still
influences bicycle design and performance
evaluation.
An extremely aerodynamic bike
Optimal Position
Knew the p
power requirement
q
Knew each rider’s endurance
Calculated the optimal order
Competed in Olympics
But how did they actually do in the
Olympics?
Project 96
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We were beaten by the French.
Project 96
Gold: France (4:05.930)
Silver: Russia (4:07.730)
Bronze: Australia (4:07.570)
USA 6th (4:12.510)
Why? Bikes so aerodynamics, the riders
behind the lead couldn't get a good draft.
Project 96
• The bikes were too
Aerodynamic
• Athletes not
adjusted to bikes
• Athletes were overtrained
And then the Superbikes were banned from
future competitions
Project 96
• The bikes were too
Aerodynamic
• Athletes not
adjusted to bikes
• Athletes were overtrained
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Position alone won't take you from
zero to hero, it is a combination 1/19/2010
of several factors. Better performance
also requires lots of training. If you want
to get better riding you bike.... Ride your
bike!
Conclusion
• Bicycle/Rider
Integration
• Measuring
Performance
• Project 96
• Going from Zero
to Hero
Thank you
Howie Weiss
Tom Morley
Jeff Broker
Robert Gregor
G
Boris Prilutsky
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