select your global control curve, then shift select the root JOINT not character group or anything else, just the root joint, then go
Contraints > point constraint....then
Constraints > Scale constraint.
Make sure this curve has deleted history, freeze your transformations, and centre pivot
Works for me...??????? hmmm, what am i advising you wrongly (baffled)
those who succeed are only the failures that never gave up.
https://www.vimeo.com/7080130