Uttanasana or standing forward bend in yoga is an ubiquitous pose in yoga classes. The pose lengthens the back of the body, brings fresh blood into the head and is a component of surya namaskar or sun salutation.
Uttanasana and other forward bends can be problematic for those with lumbar spine issues and low back pain. Go slow. When someone has low back pain we usually recommend more back bending and less forward bending until the problem resides.
The hamstrings are inordinately tight, remember to go slow and breathe. Yoga is not a race, it’s all about feel. If the pose feels good, then it is good. Allow your chest to rest on your thighs and slowly lift the kneecaps to lengthen the legs and deepen the hamstring stretch.