Never force a stretch. These are static stretches and best to do at the end of a workout after the joints are warmed up. Inhaling stabilizes so hold a stretch 10-30 seconds (I suggest until you feel it won’t release anymore since counting time can cause you to tighten up). If you feel the muscle or muscles (there’s four hamstring muscles) release exhale to stretch farther. Inhale stabilizes (hold) exhale relaxes (stretch farther).
Hamstring stretch bending from the hips not the mid back.
NWHealthFitness 