In Lower Cross Syndrome, which muscle is weak?

• A. Rectus abdominis
• B. Erector spinae
• C. Hip flexors
• D. Quadratus lumborum

Answer: (A)

Lower Cross Syndrome presents with a predictable pattern of imbalance: the abdominal muscles and glutes are weak, while the hip flexors and lumbar extensors are tight. This combination allows the pelvis to tilt anteriorly and the lower back to arch more than it should. The rectus abdominis, as a major front abdominal muscle, is commonly underactive in this pattern, so it can’t provide sufficient posterior pelvic tilt or trunk stabilization. Strengthening the rectus abdominis helps restore balance, counteracting the pull of tight hip flexors and the overactive back extensors.

The other muscles listed are typically overactive or tight in this pattern rather than weak. The erector spinae tend to be chronically tight and drive excessive lumbar extension. Hip flexors are often shortened and overactive, pulling the pelvis forward. Quadratus lumborum can be involved in compensation patterns, but it isn’t the classic weak partner in Lower Cross Syndrome.