Stop doing crunches…
That’s a lot coming out the gate.
Crunches and sit-ups only strengthen your abdominal muscles. This leads them to being no good for your lower back.
Besides… There are much better alternatives.
Planks for example.
With a simple 30 second plank you can strengthen your shoulder, chest, abs, lower back, glutes, quads, and hamstrings as opposed to only your abs.
Personally, I’m going with the exercise that not only strengthens more muscles, but also burns more calories due to the use of more muscles.
So I say it again… STOP doing crunches.