Currently, the Physical Activity Lab at Colorado State University is
attempting to make a msculoskeletal model utilizing OpenSims simulation
software. We recently collected kinematic data using a motion capturing
system and I am trying to create a scaled model and motion file (.MOT) using
this information. We are new at this and need some guidance on the
following topics:

1. When scaling a current model (one that I've downloaded as an example),
where can I find the origin of that model in order to convert the lab
coordinates to the model coordinates?
2. Am I corrent when assuming that the location of each marker that I
specify in the MarkerSet.xml file needs to be scaled to the COM of its
respective segment?
3. Some models use "bodies" as bones and not actual segments (ie, instead of
using the foot as a "body", it will use the talus or calcaneous). How
should I scale the coordinates of different markers to these bones? Or
should I use a different segment?
4. Do you have any advice on what markers are crucial in obtaining
simulation of a walking lower extreminty? For instance, what markers on the
torso would you recommend? We currently have markers on the right and left
ASIS, T1, T10, and sternum. Would you recommend using all of these in our

Any input you could provide would be greatly appreciated and I will post a
summary of responses once I have everything figured out.

Robby Ketchell
Colorado State University
Department of Health and Exercise Science
Fort Collins, CO