A frequent source of lower-back pain comes from two muscles you might not have heard of—and that makes sense since you rarely see them on those medical posters of human anatomy in doctor's offices.
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Causes of muscle pain

Medically reviewed by Scott Zashin, MD Key Takeaways Muscle strains can happen when a muscle is overstretched and may feel ...
MRI shows selective psoas and rectus atrophy with reduced trunk strength in chronic low back pain, suggesting functional imbalance.