I gave a presentation for a group of personal trainers and was asked “Why do some people hurt their backs doing certain abdominal exercises?” Here was my answer:
VIDEO TRANSCRIPTION (Please excuse grammatical errors, as this is simply a transcription of conversational speaking)
You know in a lot of gyms I see people trying to do abdominal exercises or being asked to do abdominal exercises that their abs are simply not strong enough to do with good form.
The hip flexors love to get involved in abdominal exercises, especially the psoas, and so on an anatomical level what happens, especially with abdominal exercises like leg lifts, or planks is a good example, the psoas runs from the inside upper hip and attaches to the lumbar spine at all segments so it’s not just a hip flexor in that it pulls the hip up, but it pulls from the other direction too, so it’s pulling from lumbar spine. What it does is, it’ll pull you kind of down and into an anterior pelvic tilt or a low back arch and so what happens is that if they’re repeatedly getting pulled into that position, it’s compressing all the structures in the low back and then they end up with pain. If you have abdominals that are strong enough to counteract that, create that posterior pelvic tilt and you keep a neutral spine, then you’re fine and they’re fine but what I’ve seen is that a lot of people are doing exercises without that abdominal strength.