Pilates will absolutely help with back pain.
I have text messages from clients occasionally saying, I can’t come into class because my back is sore. The best thing for them is getting into class. So I often say if you can move and you’re not in absolute agony, then get to class because you will generally feel more better, more comfortable by the end of the session.
A lot of back pain is caused by tightness. So doing Pilates helps free up the back and loosen the muscles. Other back pain can be caused by weakness. So strengthening the muscles will help support your spine by using your core muscles to give you less back pain.
N.B. Chronic back pain and more serious back issues may not be resolved by Pilates alone, always consult your doctor if in any doubt of the suitability of Pilates for your back issue.