Hi Dianne, Impact is not contraindicated, except for those with very low bone density (below -3.0) or those with previous spinal fractures or excessive thoracic kyphosis. Please review the guidelines here: Giangregorio 2015: Too Fit To Fracture: outcomes of a Delphi consensus process on physical activity and exercise recommendations for adults with osteoporosis with or without vertebral fractures
Please consider working with a physical therapist who is also a Pilates Teacher and a spinal rehabilitation specialist to help you navigate this exercise and your SIJ issue. You may very well have a great deal of pelvic ligamentous laxity and they can assess that issue. You could do Telehealth PT Evaluation with me... contact me at firstname.lastname@example.org or check my website: www.therapilates.com and call my clinic number or book an appointment online for either an Onsite (Monroe, LA) or a Virtual consultation. I look forward to hearing from you & seeing you get stronger & painfree!