Are abdominal "crunch" exercises the best way to keep from having low back pain?

Not exactly. Core strengthening including gentle crunches can be helpful in preventing low back pain. However, these need to be performed correctly and should be combined with an entire regimen designed to strengthen the core musculature.
Core muscles!Stretch. Core muscle strengthening is useful, but rand corp. Study found that of all physiotherapeutic activities receommended in studies, no conclusion regarding exercises could be reached. I find gravity inversion devices useful for most patients.
No. I always ask patients: what activity do you perform that requires you to be strong going forward? None. You need to be strong coming up, so focus on hip strengthening and your paraspinals. The core concept is ok, but you need to realize it actually encompasses strength and coordination from your feet through your neck.
No. Abdominal crunches are an excellent way to build muscles that support the back. It is also important to strengthen the muscles of the back itself, and together, they are best way to prevent low back pain.
No. Back pain comes from many causes including, but not limited to musculoskeletal spasm, degenerative disc disease, arthritis/spondylosis, trauma, and strain/sprain. Abdominal crunches done the right way can strengthen your core and reduce your risk for back injury. Done the wrong way abdominal crunches can actually injury you and lead to back pain.