@john146 When most people do toe touches, they arch their lower back a great deal, so called "leading with the head." This can aggravate the sciatic nerve and or put some undue pressure on your discs, ligaments, etc. Keeping a flat back does a better job of protecting the spine and the sciatic nerve. As was said, if you have a decent baseline of health and fitness, toe touches won't do you much harm. In my opinion, it's better for your back to even poorly stretch the hamstrings than not to stretch them at all.