FALSE: We may refer to our abs as the “upper part and lower part” for the sake of describing what we are talking about, but when it comes to anatomy, there really is no such thing. A quick lesson in anatomy will explain this myth. Your abdominal consists of several different muscles. The main part that gives us the “6 pack” or the part that we visually see working is the Rectus Abdominus. So when most people say they are working the “lower abs” they mean the bottom portion of the Rectus Abdominus, even though all the muscles in the abdomen are working. However, there is a another muscle that lies underneath your Rectus abdominus called the Psoas. This muscle is part of your hip muscles and responsible for flexion of the hip (raising of the leg). SO if you are doing leg raises or knee tucks, your abdominal’s are more so stabilizing your movements than being worked. And unless you’re getting a strong contraction on your abs at the peak of the movement, you are not really working your abs at all! Instead, that “burning feeling” you feel is probably your psoas muscle. And doing this exercise incorrectly is why some may even feel “lower back pain.”
If you are unsure of how you are performing this exercise, stick with crunches and planks.