Yes, but only if they are the right type of crunches and only if they are done in moderation. If you do too many crunches, it can cause back pain, so make sure that you don’t overdo it by doing too many of them at once or by doing them too frequently. Do a few sets of 10 crunches twice a week at most, and then switch to another exercise after a few days of rest so that your ab muscles have time to recover from any strain placed on them during the workout sessions.