It sounds like you want to do simulation-based predictions where you keep the muscle controls constant and experiment with the mechanical system or environment. Yes, that is only possible for shorter simulations. I have done a lot of research like that on ACL injuries and the simulations were only 2...

Matthias, If you get a good agreement for almost a second, that is actually quite good and you can conclude that Moco and forward integration are in agreement. This is typically what I have seen when I validate my optimal control solutions. When balancing against gravity, the system is unstable. Sma...

I have attached my Matlab implementation of the SVD method.

Also a Fortran code for the eigenvalue method. I have once (a long time ago) verified that both give the same result unless the marker configuration is almost on a line.

Ton

Yes, absolutely it will be the same result in all respects. You could verify this with some simple test data (one frame, one bone with 3 markers). Let me know if you need code for the SVD and eigenvalue methods. SVD and eigenvalue methods also give the same answer, but the eigenvalue method is somew...

When you have 6-dof joints, OpenSim's inverse kinematics will give you exactly the same solution as those algorithms you mention. They all use a least-squares fit of marker positions.

Ton van den Bogert

Force-measuring horse shoes were developed in the 1980s by several labs. Some of those produced accurate 3D ground reaction force data. An interesting idea is to use strain gauges on the hoof and calibrate against a force platform. Then there is nothing between the foot and the ground. This was done...

Is it the "exo_back" joint that you changed from free to ball? The type of joint can be very important if there are fewer than 3 markers on each body segment. In general, it is good to remove as many degrees of freedom as possible, to make the IK solution more robust against errors in marker data an...

Vahid, I would suggest using a 2-dimensional model. A 2-D model for hopping could assume symmetry and have only one leg (with mass properties and muscle strength values doubled). If you use a 2-legged model, it can also be done by dividing the force plate data equally between the two legs. You shoul...

I support Edward's suggestion. Although the SimmSpline can be differentiated to give velocities and accelerations, I would not recommend this. Interpolating splines are sensitive to noise and will give unreliable derivatives. To see an example, run my test code with these knots: x = 0:10; y = x + ra...

You're welcome! I am not sure it's a bug. The extrapolation always looks correct in my tests with SimmSpline. I have not thoroughly analyzed the code, but keep in mind that an array in C++ starts with index 0. With n knots, there are n-1 knot intervals, indexed from 0 to n-2. The polynomial with ind...