thanks a lot everyone, i found an old post on cg society were noseman suggest the posemorph tag tecnique. but i am too lazy for that
i was curious to know if there was a parametric way to do it. but i dont know scene nodes or math. spline offset looks like one of those things that can be used in a lot of different ways to achieve interesting results in motion graphics.

for my specific case the best option i found is fit to circle capsule. with fit to circle i can expland my spline without intersections between points. its not ideal but it does the job in my animation.

@noseman hi noseman, thanks for the reply! i was thinking that may be there is a way to do it with scene nodes...unfortunately maxon is very moderate with info about scene nodes, so i have no idea how to use it!

I am sorry Dr Sassi i didnt explain myself very well!

This is what i want to achieve: https://youtube.com/shorts/IW1MkrRX0T8?feature=share

i used after effects to do this video (path + offeset).

I would like to be able to do the same with c4d splines but i dont know how.

thanks!

Inside the volume builder there is a very useful tool called erode and dilate.
is there any way i can achieve the same effect on a spline? can i dilate/erode a spline?

Thanks!