If you have lower back pain it may be because your hips are super tight. If you play a lot of guard in BJJ and/or sit a lot at a desk etc, then most likely your hips are super tight. Sitting for long periods of time tighten the hip flexors which can cause muscular imbalances in other parts on your pelvis and core contributing to lower back pain. Tight hip flexors also over take a lot in abdominal exercises so that you aren’t actually working your lower abs, but over working your hip flexors instead, further exacerbating the problem.
Try these stretches. Aim to do these every day. Hold it for at least 30 seconds each side.
Sophia McDermott, Lunge Stretch
Sophia McDermott, Cobra Stretch