I use weights for resistance in my stretches. For example, I do a lot of Jefferson Curls and after that I can do a pike stretch with my hands on the ground. The next day, however, I feel that my muscles are stiff and I need to train my legs to be able to do a pike stretch again.
My question is how do I reach to a level that I'm able to do a pike stretch (and other stretches) whenever I want and without a warm-up or leg training?