Muscle knots in the Iliopsoas, also known as the hip flexor muscle, are located on the front of the body in the pelvis and thigh. These trigger points often refer pain to the lower back, front of the hip, groin, and upper thigh, and can feel like a deep, nagging ache or tightness that worsens with prolonged sitting, walking uphill, or standing up straight. People often confuse this pain with hip joint issues or hernias, but it’s frequently from sitting too much or repetitive hip flexion.