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Optimal Non-Circular Chain-Rings for Improved Cycling Performance

This journal club article discusses the use of non-circular chain-rings in cycling to optimize power output and minimize energy expenditure. The study investigates different shapes and orientations of chain-rings and their impact on muscular work. The results show that elliptical chain-rings with an eccentricity of 1.29 yield the greatest improvement in power output. The use of optimal chain-rings also reduces the potential for knee injuries during the pedal stroke.

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Optimal Non-Circular Chain-Rings for Improved Cycling Performance

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  1. Kevin Levi-Goerlich BAM Journal Club 9/26

  2. 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

  3. Introduction • Chainrings - Circular -Non-circular Why?

  4. Introduction

  5. Introduction • Is a non-circular chain-ring more efficient? • If so, what shape? • What offset?

  6. Methods • Forward dynamic muscle model simulation • Model • 9 segments • 10 muscle groups • Chain Ring Optimization • Circles • Ellipses • Rounded Squares • Orientation

  7. 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.

  8. Results

  9. 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

  10. Discussion

  11. 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.

  12. 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.

  13. Discussion Application • This study focuses on maximal force output, however the same optimized chain ring conditions could benefit submaximal cycling performance.

  14. Questions?

  15. References • Cycling Muscle Usage. (n.d.). Retrieved from http://www.bikejames.com/wp-content/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.

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