Final answer:
A crewmember should stand upright while fitting a torso harness to ensure proper fitting and adjustment according to manufacturer guidelines for safety and comfort.
Step-by-step explanation:
When fitting a torso harness, a crewmember should be in a standing position, ensuring an upright posture. This is critical for accurate fitting, as the harness must be snug but not restrictive, allowing for a full range of motion and proper weight distribution. It's essential to adjust the straps according to manufacturer guidelines, which usually entails tightening the shoulder straps first, followed by the waistband and leg straps, ensuring the torso harness does not impede movements or safety equipment access.