I just posted here from Intro, but here say [ Yesterday, i did stretched before rode on the bike, and i felt my leg and half ass like electric, then Today just rode on bike, just little electric on half ass. i did really fully the stretch, it seem not enough to have a stretch warm up?]

Usually better to ride for a while, then stretch, then ride some more. Not good to stretch before riding.

OKay, why is not good to stretch before riding?

Your muscles are cold. When they are cold, the muscle fibers don't slide past each other easily. So you can tear and injure your muscles by stretching them cold. After you have ridden long enough to start sweating, it is usually OK to stretch.

I'f follow this guide.

https://www.mayoclinic.com/health/stretching/HQ01447

https://www.mayoclinic.com/health/stretching/SM00043

In the last two years I can no longer do my hamstring stretch because it gives me very bad lower back pain the next day. Still trying to figure out why this is.

I take a pilates class and the instructor has us do a toe-touch stretch at the end. She says if you straighten your knees, you stretch more hamstrings. If you bend your knees a bit, you stretch more of your lower back. Are you doing something like this?