Final answer:
The correct answer is A. A sacroiliac strain typically occurs when transitioning from flexion to extension, with the correct answer being A. Flexion. This involves the movements of bending forward and then straightening up or bending backward that affects the sacroiliac joints.
Step-by-step explanation:
Flexion and extension are types of movements that affect the sagittal plane of the body. During flexion, there is a bending motion where the angle between bones is decreased, such as when bending forwards at the waist. Extension is the opposite movement, where the joint angle is increased, such as straightening up from a bent position.
The sacroiliac joints are located at the intersection of the sacrum and the iliac bones in the pelvis, and they support the weight of the upper body when standing and help absorb impact when walking. Strain in this area can occur from the motion of extending the back, moving from a forward-bent position (flexion) into an upright or backward-bent position (extension).