Sit up straight a time to re-evaluate
You may remember many moons ago when the advice for treating back pain was bed rest! With emerging clinical evidence the advice and best clinical practice for back pain has evolved dramatically with movement being a key treatment. Similarly, posture is a topic that has commonly been adopted by clinicians to recommend sitting up straight, however there is no strong evidence that “perfect posture” does exist. The movement of thought (no pun intended!) has shifted to movement being key and changing posture regularly is in fact more important than trying to maintain a perfect static posture.
Could a certain posture be an aggravating factor for your back pain - sure. But this doesn’t mean it is inherently bad and should be avoided by all. What feels good for you will likely be different from what feels good for someone else. Sit in a way that feels comfortable for you, and when that feels uncomfortable, change it – the key here is to just keep moving!