Yes it’s true. These two standard sit-ups, sit-ups and squats, can actually be low-back murder.
Why? Because they involve bending the spine (rounding the lower back to allow you to lean the waist forward). But according to research, that’s the exact mechanism that causes a herniated disc in the lower back. After all, most people “roll their backs” by bending down to pick something up off the ground.
Therefore, it makes sense to limit the number of sit-ups and traditional crunches in your program. Also, you cannot reduce fat in one area on a one-time basis, so it is best to spend that exercise time on better total body exercise or intervals. If you want to flatten your abs, you need to lose body fat.
So, to improve your abs, use the following techniques:
1) Take half the time you spent on your abs, and do intervals with that time instead.
2) Spend the rest of your abs training time doing resistance exercises for abs, such as planks, side planks, mountain climbers, and variations of these exercises.
3) Keep your abs contracted in all exercises so that you work your abs in every movement you do.
For advanced bodybuilding, there will come a time when you will need to do traditional crunch movements. But it is better, to get results (that is, to grow your abs) to do them with resistance. Cable crunches are good, and you can get results with a relatively small amount of spinal flexion.
But really, when it comes to having great abs, losing body fat is the most important aspect for most people. And if you are a desk jockey, it is more important for you to have abdominal resistance than to risk your back with the classic abdominal exercises.