If the spinal center of gravity lies anterior to the sacral promontory, chronic tension develops in which muscles?

If the spinal center of gravity lies anterior to the sacral promontory, chronic tension develops in which muscles?

• A. The abdominal muscles
• B. The lumbar muscles
• C. The thoracic muscles
• D. The gluteal muscles

Answer: (B)

When the body's weight is positioned with the center of gravity in front of the sacral promontory, gravity creates a forward bending moment at the lumbosacral junction. To maintain an upright posture, the lumbar extensors—primarily the erector spinae and nearby paraspinal muscles—must stay chronically active to pull the spine back into extension. This sustained contraction leads to chronic tension in the lumbar muscles. The abdominal muscles, thoracic muscles, and gluteal muscles are not the primary groups counteracting this specific forward load at the lower spine, so they are less involved in maintaining this posture.

When the body's weight is positioned with the center of gravity in front of the sacral promontory, gravity creates a forward bending moment at the lumbosacral junction. To maintain an upright posture, the lumbar extensors—primarily the erector spinae and nearby paraspinal muscles—must stay chronically active to pull the spine back into extension. This sustained contraction leads to chronic tension in the lumbar muscles. The abdominal muscles, thoracic muscles, and gluteal muscles are not the primary groups counteracting this specific forward load at the lower spine, so they are less involved in maintaining this posture.