It's fine to do core every day once you get used to it, since you usually use part of your body weight for resistance, which isn't enough to cause the degree of micro-tearing where your muscles need more time to repair. You aren't going to damage anything as long as the exercises are done safely with attention to form.<br><br>
But -- I'd throw in a couple clauses:<br><br>
If you're just starting and do enough intensity or duration that you're VERY sore the next day or so, wait until that subsides for the next workout. You may not be able to perform the exercises with correct form and it would be counter-productive.<br><br>
If you do core work every day, vary the exercises -- maybe have Routine A and Routine B. Muscle memory will render the same exercises done each day less effective. Keep learning and swapping out new exercises.<br><br>
Work the back of the torso as well as the front to avoid imbalances.<br><br>
Form is really important with core work. Try to pull your navel to spine and hold that for each exercise. You can do that just sitting here reading this post: imagine you are lifting the belly button up and back, toward the lower back ribs. If you can no longer maintain that (you'll know because you'll see the stomach push out or feel the lower back arch), stop and rest until you can engage it again. This is a pilates technique that helps flatten the stomach during crunches vs. causing a rounded muscle shape from doing crunches w/o engaging the deepest ab muscles -- the opposite of what most people want! Try to work with a mirror, too, so you can see your body position in exercises like plank, etc.
