Download Optimal Chain Ring Shape to Optimize Crank Power

Kevin Levi-Goerlich
BAM Journal Club 9/26
Introduction
 Cycling
 Push down on pedal in order to go forward
 Maximal speed for minimal energy expenditure
 Pedaling mechanics
 Goal is to maximize the amount of power generated during
each stroke
 Emphasis on a smooth pedal stroke
Introduction
 Chainrings
- Circular
-Non-circular
Why?
Introduction
Introduction
 Is a non-circular chain-ring more efficient?
 If so, what shape?
 What offset?
Methods
 Forward dynamic muscle model simulation
 Model
 9 segments
 10 muscle groups
 Chain Ring Optimization
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Circles
Ellipses
Rounded Squares
Orientation
Methods
 Analysis
 Model was run at cadence of 60, 90, and 120rpm
 4 complete cycles were performed
 Data was extracted from the last cycle
 Muscular work was compared in each region to the
circular control model.
Results
Discussion
 Elliptical Chain Rings yielded the greatest improvement
in power
 Eccentricity of 1.29 yielded a 3% improvement at 90rpm
when compared to circular simulation
 Angular Velocity decreases
 Takes advantage of force-length-velocity properties of
muscles
Discussion
Discussion
Injury potential
 Most cycling overuse injuries are due to knee joint forces
 The increased duration in the “power phase” may increase
joint torques and increase knee injury potential.
 9.4%increase
 However
 45% reduction in the shear and normal force impulses in the
patellofemoral joint and shear forces in the tibiofemoral joint
when using optimal chaing ring.
 Reduced injury potential at the most vulnerable part of the
pedal stroke.
Discussion
Limitations
 Constraints from the Hill—Muscle model
 Force depression
 Muscle activation-deactivation changes
 Drive train characteristics
 Negligible
 Fixed hip position
 Used known circular chain ring position
 Hip movement is possible, but unlikely.
Discussion
Application
 This study focuses on maximal force output, however
the same optimized chain ring conditions could benefit
submaximal cycling performance.
Questions?
References
 Cycling Muscle Usage. (n.d.). Retrieved from
http://www.bikejames.com/wpcontent/uploads/2012/05/
20090505_032518_CyclingMusclesC.gif
 Rankin, J. W., & Neptune, R. R. (2008). A theoretical
analysis of an optimal chainring shape to maximize
crank power during isokinetic pedaling. Journal of
Biomechanics, 41(28), 1494-1502.