Performing RRA on cycling data

[Adrian Lai]

Dear all,

I'm currently trying to run some experimental cycling data through RRA in preparation for CMC simulations.

However, because I'm using a lower-limb model without a torso or arms, I get large residual forces in the vertical direction roughly equally the weight of the subject. These large residual forces are a result of the subject being in the seated position on the ergometer. When I perform RRA (or CMC), the algorithm tries to reduce these large residual forces by translating the model vertically. To correct for this, I was thinking I could either lock the pelvis translation in the vertical direction thereby preventing the algorithm from shifting the model vertically or apply an external force at the pelvis COM roughly equal to the weight of the subject to account for the seated position.

Has anyone else been in this situation when performing RRA? What would be the best practice?

Thanks in advance!

Adrian

[Colin Smith]

Hi Adrian,

Since you have not measured the reaction forces at the seat or handle bars (nor have many other researchers) and applied them to your simulation, it is not surprising that the residuals are giving you troubles (even without the upper body masses included).

As far as I have seen, the majority of cycling simulations have fixed the pelvis in space (another option would be to prescribe the pelvis DOFs to the measured kinematics) to avoid having to measure these reaction forces and model the upper body.

Neptune, R. R., and M. L. Hull. "Evaluation of performance criteria for simulation of submaximal steady-state cycling using a forward dynamic model." Journal of Biomechanical Engineering 120.3 (1998): 334-341.

Thelen, Darryl G., Frank C. Anderson, and Scott L. Delp. "Generating dynamic simulations of movement using computed muscle control." Journal of biomechanics 36.3 (2003): 321-328.

This seems to be a fair assumption based on the bone pin study of hip joint center movement during pedaling.

Neptune, R. R., and M. L. Hull. "Accuracy assessment of methods for determining hip movement in seated cycling." Journal of biomechanics 28.4 (1995): 423-437.

[Adrian Lai]

Hi Colin,

Thanks for the reply! I also suspected that the high residual forces were a result of the reaction forces at the seat and/or handlebars.

Like you've suggested, I've decided to try and run my CMC simulations in two different ways, one with a fixed pelvis in space and another without running RRA and assuming the residual forces are due to the reaction forces at the seat and handlebars. If these two methods fail, I might try and prescribe the pelvis coordinates. Then I'll compare the results of the different methods to determine if the assumptions of each method are justified.

I'll let you know how the simulations go.

Adrian

[Emily Hubbard]

Hi Adrian,

I'm doing a similar study with cycling and using only pedal forces as input, not seat or handlebars.

What were your results from this comparison? We are examining different methods and hope to find one that has worked well for other studies.

Thanks,

Emily