Truth is, it's not because I think that crunches are inherently dangerous. Let's be honest - if you do three sets of 20 crunches at the end of the workout, and the discs in your lower back explode on your 60th repetition, the odds are pretty good they were going to do that anyway - probably when you bent over to tie your shoes, or something equally innocuous.
|Feel that? It's a deep, deep burn.|
No, I have an issue with crunches more because they are useless. Or, if not useless, then one of the least effective movements in the exercise library with one of the smallest returns on your investment. As with any exercise you might be given, you have to ask yourself "to what end am I doing this?", and then evaluate if the goal corresponds to the work being done.
Most people want to do crunches for a couple of reasons - because they believe it will equal the ever elusive six pack.
The "six pack" is primarily a result of good nutrition and genetics. If you eat badly and/or don't naturally have them, then all the crunches in the world ain't gonna change it.
More importantly, our society is built around doing work in the crunched position - sitting in a car, sitting at a desk, sitting in front of the TV... why would you then want to head into a gym and repeatedly put yourself further and further into a position that you already spend all day in?
So the next time your trainer tells you to lie on your back (or on the bench, or on the stability ball) and do 20 crunches... look them in the eye and ask them why they want to waste your time and money, then grab that stability ball and do some rollouts or saws.
Maybe you can teach them something new.