Final answer:
Performing a curl-up generally leads to moderate compression on the back, especially on the intervertebral discs. Proper form and core engagement are essential to minimize the risk of excessive compression.
Step-by-step explanation:
When performing a curl-up, the amount of compression on the back depends on several factors, including the individual's technique and existing back health. Generally, the motion of a curl-up includes both flexion and extension of the spinal muscles, which can lead to moderate compression of the spine, particularly on the intervertebral discs. It is critical for individuals to engage their core and perform curl-ups with proper form to minimize the risk of injury and excessive compression. Curl-ups should not fully compress the spine like some other high-impact exercises, but they do not leave it in a state of no compression either.