vertebral bone density

I have the nsca practice exam volume 1 and there's a question regarding increasing vertebral bone mineral density of a client who is at risk of osteoporosis and which exercise is most effective to increase it. The NSCA practice exam answer is front squat. You ask a similiar question on your exam but the client already has osteoporosis and wants to increase vertebral bone density. The answer you give is back extensions. Which exercice is the correct answer?

Sincerely,

Karen Saroyan