…the sit-up (as well as the modified crunch) which is perhaps the longest-standing myth of health and physique. In some ways it makes sense: this thing we call ‘exercise’ is a relatively new phenomenon. For most of history our ancestors moved as part of their daily existence. Relegating movement to something we do for a concentrated hour or two a few times a week is still in its early phases—and, to be honest, will hopefully disappear if we’re able to better integrate movement into our lives, not just at the gym. There was bound to be a lot of trial and error. The crunch is an error.
Yet it persists. I can understand why: it burns, and people often confuse working out with burning. Ripping through a hundred sit-ups feels like it does something. In fact it does: it greatly increases your chance of a back injury.
Source: Why Are We Still Doing Crunches?
I guess there’s a reason there aren’t crunches or sit-ups in yoga? 😉