Final answer:
A bent-knee sit-up is likely to place moderate compression on the back due to the spine flexing and lifting the upper body against gravity.
Step-by-step explanation:
During a bent-knee sit-up, there is a varying degree of compression experienced by the lower back. When performing a sit-up, the spine flexes, which can lead to compressive stress on the lower back. Considering the mechanics involved, a bent-knee sit-up is likely to place moderate compression on the back. This is because the exercise involves lifting the upper body against gravity, which puts pressure on the spine, particularly when moving from a lying to an upright position. This movement pattern can put strain on the back muscles and intervertebral discs. Elite athletes, such as weightlifters, may experience extreme compression during their sport-specific activities, but in comparison, the compression from a bent-knee sit-up would be classified as moderate.