Final answer:
Pain from sitting in one position for too long without proper back support or posture is most likely felt in the lower back, as this creates strain on the muscles that have to counteract improper torque.
Step-by-step explanation:
If you sit in one position for too long without adequate back support or maintain poor posture, you are most likely to feel pain in your lower back. This pain can be attributed to the muscles in the lower back that must exert large forces to counteract the torque created when the center of gravity (cg) is not aligned with the pivot point in the hips. When sitting with poor posture, particularly at desks using computers, the cg of the upper body shifts in front of the pivot in the hips, creating strain. Special chairs that allow the body's CG to be situated above the seat can help to reduce this back pain. Over time, the lack of movement and constant muscle strain can lead to muscle strain and discomfort.