Seated Forward Fold
Seated Forward Fold (Paschimottanasana) is a deep stretch for the hamstrings and entire back body, done sitting with legs extended. As with the standing version, the rule that protects you is: hinge from your HIPS with a long spine, and bend your knees freely.
FilmableFilm this on your phone and TrueForm measures your body mechanics and tells you what to fix. You get angles, not a made-up score.