a question about filter kinematics

[Wang Xingyue]

hi,
I want to filter the kinematics because the curves are not smooth enough to get nice CMC results. I used two methods. One is using the lowpass function in Matlab2019a. The other is using the OpenSim own filter in CMC Tool interface. But I got different CMC results.
Hope someone can help explain it and give me some advice how to choose.
My code:
lateral=load('02lateral.mat');
fs=100;
t=lateral.data.time;
for i = 2:31
x(:,i)=lowpass(lateral.data{:,i},4,fs,'Steepness',0.999);
end
x(:,1)=t;

[Wang Xingyue]

In addition to this question, I want to limit the variation of the muscle fiber length to simulate damaged muscles. How can I do that?