Separate GRF.mot into left and right foot data

[Han Xiang Lim]

Hi, I am currently working on running gait analysis with Bertec split belt treadmill. We let the subject to run on left belt to capture his habitual running gait.

However, we noticed there is a problem when we input the GRF data into OpenSim for analysis which requires separate left and right foot data. May I know are there any methods to further process the running GRF.mot into left and right data ? I have columns of vx, vy, vz, px, py, pz, mx, my, mz in recorded GRF.mot file, both left and right VGRF were recorded in column vy.

My current plan is send the data array into Matlab and replace data of another foot side to '0' and get the corresponding foot side data. For example, if I'm preparing right foot side VGRF data, I will replace all data value for left foot side to '0', finally save the array back to .mot file as right foot VGRF since no GRF peaks are overlapped in same period. Is it possible for me to process the data like this ?

Thank you =)

[Carmichael Ong]

If you are definitely sure only one leg could be on the treadmill/ground at any time, this plan should work. As you said, you'll just need to preprocess the data to format it in a way that looks like other walking/running examples.

[Aaron Fox]

Hi Han,

You could also check out a function within this projects downloads - https://simtk.org/projects/matlab_tools. There is a function called something like assign_forces.m which allows you to input markers that are on the left and right feet and a distance threshold to search from that marker for the forces centre of pressure. Effectively this process applies the force to the foot that is closest (and thus generating) the force vector. There are other functions that you can use around this to convert the data to the .mot and .xml formats starting from a .c3d file. These are a little dated now so might need some adapting for newer versions of OpenSim, but the general premise should hold.

Aaron