Final answer:
Increased storage of blood in the veins of the feet and legs is likely when a soldier stands at attention without moving, as this reduces the effectiveness of the skeletal muscle pump, leading to blood pooling in the lower limbs.
Step-by-step explanation:
When a soldier stands at attention—very still with legs and spine straight—the most likely outcome is increased storage of blood in the veins of the feet and legs. This occurs because the action of the skeletal muscle pump, which typically helps to move blood back to the heart, is not activated when the muscles are not contracting. When standing immobile, the leg muscles are not contracting to exert pressure on the veins, which can cause blood to collect or pool in the lower extremities due to gravity.
Soldiers are advised to flex their leg muscles periodically to prevent this pooling; if the muscles are not periodically flexed, it may result in insufficient return of oxygenated blood to the brain, potentially causing dizziness or fainting. This demonstrates the importance of muscle movement in aiding venous return and preventing orthostatic hypotension.