The psoas is a deep core muscle that runs from your lower spine, through your pelvis, to the top of your thigh bone, and it plays a key role in hip flexion and posture.

What is the psoas?

  • The psoas (usually “psoas major”) is a long, thick muscle located on either side of your lumbar spine.
  • It travels down through the pelvis and attaches to the upper part of your femur (thigh bone), forming the iliopsoas together with the iliacus muscle.
  • It is one of your main hip flexor muscles, helping lift your knee toward your chest and connecting your upper and lower body.

What does the psoas do?

  • Enables hip flexion (like walking, running, climbing stairs, kicking, or doing sit‑ups).
  • Helps maintain upright posture by stabilizing the lumbar spine and pelvis.
  • Assists with trunk flexion (bending forward) and subtle side‑bending of the spine.

Why people talk about it so much now

  • It’s often described in fitness and therapy circles as a “key” or “hidden” core muscle because it sits deep and connects spine, pelvis, and legs.
  • Sedentary lifestyles (lots of sitting) and certain sports can both stress the psoas, so “psoas tightness” and “psoas release” are common topics in recent online discussions.

Psoas problems (very short overview)

  • Overuse or irritation of the iliopsoas tendon can lead to “psoas syndrome,” causing groin, hip, or low‑back pain, especially in runners and dancers.
  • Symptoms can overlap with other hip and spine issues, so persistent pain around the front of the hip or low back should be evaluated by a healthcare professional.

Quick example: When you march in place and lift your knee toward your chest, your psoas is one of the main muscles doing that work.

If you want, I can next suggest simple, generally safe mobility or strengthening ideas you can discuss with a professional.