Final answer:
The healthy lumbar spine should have a natural posteriorly concave curvature, known as lordosis. The options provided in the question all suggest abnormal curvatures, which is problematic for correctly identifying the normal appearance of lumbar flexion.
Step-by-step explanation:
When discussing lumbar flexion, the lumbar curve should normally maintain its natural posteriorly concave curvature, which is referred to as lordosis. During flexion, the angle between the bones in the lumbar region decreases. However, the question is asking how the lumbar curve should look normally, not during flexion. Normally, a healthy lumbar curve exhibits a gentle lordotic curve. The options provided describe abnormal curvatures: increased lordosis would represent an excessive anterior curvature (swayback), decreased lordosis could imply a flattened curve, straight alignment is not a natural spinal curvature and S-shaped alignment could suggest an abnormal condition like scoliosis.
Therefore, the correct answer should represent the natural, healthy appearance of the lumbar spine, which is not among the options provided, thus raising a concern with the question itself. If we were to approximate the most natural condition from the given choices, decreased lordosis would suggest a lesser degree of curvature which may align more closely to a natural curve than an increased lordosis, which is clearly abnormal.