Biomech of Cycling for BikeGeeks v4 · 1/19/2010 8. Knee Moment-40-30-20-10 0 10 20 30 1 5 9 13...
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1/19/2010 1 BIOMECHANICS OF CYCLING FOR BIKE-GEEKS W. Lee Childers PhD candidate Going from Zero to Hero with the turn of a Hex Key PhD candidate Robert Gregor PhD Introduction • General Overview • Human System • Performance • How to study Biomechanics • The Pedal Stroke • Effects of Position • Project 9 6 • Team Pursuit Team Pursuit Stone Mountain Velodrome designed using Fresnel Intregrals and Mathematica software • 4000m event • 4 min • Two teams/race • Elimination Ladder
Transcript of Biomech of Cycling for BikeGeeks v4 · 1/19/2010 8. Knee Moment-40-30-20-10 0 10 20 30 1 5 9 13...
1/19/2010
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BIOMECHANICS OF CYCLING FOR BIKE-GEEKS
W. Lee Childers PhD candidate
Going from Zero to Hero with the turn of a Hex Key
PhD candidateRobert Gregor PhD
Introduction• General Overview• Human System• Performance• How to study y
Biomechanics • The Pedal Stroke• Effects of Position• Project 96• Team Pursuit
Team Pursuit
Stone Mountain Velodrome designed using Fresnel Intregrals and Mathematica software
• 4000m event• 4 min• Two teams/race• Elimination
Ladder
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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.
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Cycling represents integration of man
and machine
Cycling represents integration of man
and machine
Cycling represents integration of man
and machine
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The human physiological system must work with the mechanical (Bicycle) system in order to perform.
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The saddle, handlebar and pedals create the contact points for the body
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That in turn determines the skeletal alignment and joint range of motion for the rider
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Neural Control
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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.
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Muscles produce different forces at different length and contraction velocities.
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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 system decides to activate a large thigh muscle to generate mechanical energy that will eventually turn the crank.
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The nervous system will then have to coordinate additional muscle activation to transfer that energy into the crank
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This resolves as a force (orange arrow) at the pedal that will turn the crank.
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Resistance to Overcome
• Aerodynamic Drag
• Gravity• Energy to gy
Accelerate• Rolling
Resistance• Drivetrain
Resistance
Resistance to Overcome
• Aerodynamic Drag
• 90% of the Resistance
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Another important thing to remember 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.
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The bicycle rider system must overcome resistance in order to move
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In our case of team pursuit, aerodynamic drag will be the largest force to overcome
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Resistance to Overcome
• Power Output– Subject Motivation– Commercial Products
vary +/- 5%• Heart Rate and
Measuring Human Performance
Heart Rate and Oxygen Consumption– Whole Body
Measurements• Joint Kinematics• Pedal/Joint Kinetics• Muscle Activation
• Power Output– Subject Motivation– Commercial Products
vary +/- 5%• Heart Rate and
Measuring Human Performance
Heart Rate and Oxygen Consumption– Whole Body
Measurements• Joint Kinematics• Pedal/Joint Kinetics• Muscle Activation
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To reduce drag, these riders adopt different positions. 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.
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Biomechanics study the last three variables trying to provide a detailed picture of how this person is performing a task.
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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.
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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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Knee Moment
-40
-30
-20
-10
0
10
20
30
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
% C C
Mom
ent (
Nm
)
- Figure from Ryan et. al., 1992. Sport Sci Rev. 2:69–80.
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We combine these data with Newtonian physics to solve the inverse dynamics problem and provides the researcher with information about the forces and moments (torques) at each joint.
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Example of a knee moment x-axis is from 0-360 degrees of crank rotation.
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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.
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What happens during the pedal
stroke
Childers et. al., 2009. Pros Orthot Int. 33:256-271.
You know, I am an Elite Bike Racer.Racer.
Being a Road Racing specialist,
I pedal in Perfect Circles!!
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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.
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This graph shows what some people believe would be an ideal pedal stroke.
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Please refer to Childers et al.,2009 for more detailed description of the pedal stroke
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The Pedal Stroke
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This is total crank power showing how people really pedal a bicycle.
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This shows the power output for each leg. Note the portions of negative power production.
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The following slides will break the pedal stroke up into quadrants
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The Pedal Stroke
The Pedal Stroke
The Pedal Stroke
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This shows the top of the pedal stroke. Lines in red indicate muscles that are active
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The power phase constitutes about 90-95% of the total power output.
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The Pedal Stroke
The Pedal Stroke• “Pulling Up” during
recovery not an efficient strategy
• Increase joint flexor EMG 1 1 – 3 4 times
-Figures from Korff et. al., 2007. Med Sci Sports Exerc 39:991–995.
EMG 1.1 3.4 times baseline - Mornieux et. al.,
2008
Pedaling Technique
-Figure from Broker, 2003. High Tech Cycling 119-146.
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The recovery phase does not have much muscle activity. Also the ascending limb cannot lift faster than the pedal being pushed up into it by the opposite descending limb.
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Recent research explored "pulling up" type pedal technique and showed this may not be an effective strategy for sub-maximal, steady-state cycling.
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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.
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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• STA has an effect on pedaling kinetics – Browning 1991
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Another important aspect of learning how to pedal is that it takes training
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Variability in muscle activation is less in trained cyclists.
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Seat Tube AnglePower vs. Crank Position
100
200
300
400
500
Pow
er (w
atts
67 deg
79 deg
-200
-100
0
100
0 18
32.4
46.8
61.2
75.6 90 104
119
133
148
162
176
191
205
220
234
248
263
277
292
306
320
335
349
Crank Postion (deg)
Cra
nk
Project 96; The US Olympic Superbike Program
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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Pictures are of the Obree and Superman positions that showed the importance of aerodynamics for time trial performance
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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
Project 96
Project 96
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Both positions were banned for competition and the subsequent rules provided additional challenge for the project '96 scientists
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A radical new and aerodynamic "superbike" was developed for the US cycling team
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Dr. Broker used force pedals to analyze the cyclist's pedaling technique in different positions to determine the best compromise between aerodynamic/legal positions and the cyclist's ability to produce power about the crank center
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Project 96
Project 96
Project 96
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This was combined with wind tunnel testing
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A saving of 2.3 seconds could mean the difference between medal or no medal
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Project 96
• P = Power (Watts)• K = Track Condition
• Kt = Aero Factor (Basset et al. 1999)
Constant (Basset et al. 1999)
• Mt = Total Mass (kg)• V = Velocity (kph)
• Af = Calculated Frontal Area
• H = Height (m)• M = Mass (kg)
Project 96• Team Pursuit
required drafting• What are the power
requirements forrequirements for drafting?
Project 96
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They developed equations to predict power requirements for individual pursuit
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But team pursuit was different and would require additional testing
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So they stuck the whole team in the wind tunnel.
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Project 96
-Figure from Broker et al. Med Sci Sport Exerc 31:1677-1685
Project 96• An extremely aerodynamic bike• Optimal Position• Knew the power requirementp q• Knew each rider’s endurance• Calculated the optimal order• Competed in Olympics
Project 96
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Then out to the track for field testing. With all of this data they were able to optimize rider order for the team pursuit
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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.
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But how did they actually do in the Olympics?
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Project 96Gold: France (4:05.930)
Silver: Russia (4:07.730)
Bronze: Australia (4:07.570)
USA 6th (4:12.510)
Project 96• The bikes were too
Aerodynamic• Athletes not
adjusted to bikesadjusted to bikes• Athletes were over-
trained
Project 96• The bikes were too
Aerodynamic• Athletes not
adjusted to bikesadjusted to bikes• Athletes were over-
trained
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We were beaten by the French.
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Why? Bikes so aerodynamics, the riders behind the lead couldn't get a good draft.
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And then the Superbikes were banned from future competitions
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Conclusion• Bicycle/Rider
Integration• Measuring
Performance • Project 96• Going from Zero
to Hero
Thank youHowie WeissTom Morley Jeff Broker
GRobert GregorBoris Prilutsky
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Position alone won't take you from zero to hero, it is a combination of several factors. Better performance also requires lots of training. If you want to get better riding you bike.... Ride your bike!
