Sit ups can be really hard on the spine, even if done "properly". You slip a disc in your neck even slightly while working on your abs, and you won't be working

Sit ups can be really hard on the spine, even if done "properly". You slip a disc in your neck even slightly while working on your abs, and you won't be working on your abs or anything else for a long time. Slipped discs can cause an astonishing amount of pain. Not an exercise guru, just someone who slipped a disc.