Stretching is supposed to be good for us, but if done before adequately warmed up, or done improperly, they can cause injury. Three popular stretches are the straight-leg toe touch, standing or seated on the floor, and the hurdler stretch, stretching one leg at a time. The problem with these stretches are that they “..can severely weaken the spine…” since they are pulling the “…spinal ligaments, not the hamstrings.”
Every time I try either of those stretches, my lower back hurts. If you still want to do these stretches, use a straight back, not a rounded back, don’t bounce, and just go to the level where you feel the stretch; a stretch should never be painful. Pain is a signal from your brain that you shouldn’t do that.
(1). Source: Hatfield PhD., Frederic. Fitness: the Complete Guide. Carpinteria: International Sports Sciences Association. 9th ed., 2018. Print. Pg. 349.