Kevin Levi-GoerlichBAM Journal Club 9/26

Introduction

CyclingPush down on pedal in order to go forwardMaximal speed for minimal energy expenditure

Pedaling mechanicsGoal is to maximize the amount of power generated

during each strokeEmphasis on a smooth pedal stroke

IntroductionChainrings

- Circular

-Non-circular

Why?

Introduction

IntroductionIs a non-circular chain-ring more efficient?

If so, what shape?

What offset?

MethodsForward dynamic muscle model simulation

Model9 segments10 muscle groups

Chain Ring OptimizationCirclesEllipsesRounded SquaresOrientation

MethodsAnalysis

Model was run at cadence of 60, 90, and 120rpm4 complete cycles were performed

Data was extracted from the last cycleMuscular work was compared in each region to the

circular control model.

Results

Discussion

Elliptical Chain Rings yielded the greatest improvement in powerEccentricity of 1.29 yielded a 3% improvement at

90rpm when compared to circular simulationAngular Velocity decreases

Takes advantage of force-length-velocity properties of muscles

Discussion

DiscussionInjury potential

Most cycling overuse injuries are due to knee joint forcesThe increased duration in the “power phase” may

increase joint torques and increase knee injury potential. 9.4%increase

However45% 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.

DiscussionLimitations

Constraints from the Hill—Muscle modelForce depressionMuscle activation-deactivation changes

Drive train characteristicsNegligible

Fixed hip positionUsed known circular chain ring positionHip movement is possible, but unlikely.

DiscussionApplication

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

Questions?

ReferencesCycling 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.