I've read sit-ups cause back issues and had fatigue with an brain/eye condition so I'm paranoid and very slow with them. However, they're always in military/martial arts regimens. I've also read they're not even the best exercises. Why are they used so much and done so fast?
PS: I want to decide on whether to do sit-ups or replace them with some of these to my routine. Which is the best substitute for them? I currently do leg-raises and russian twists, but some of the workouts here look more appealing:
Best combo or option would be appreciated.