Your question: I've been trying to improve the look of my lower abs, so after I do crunches and oblique exercises, I always include some hanging leg raises. Yet I can barely do more than a few reps, and my lower-ab strength hasn't progressed. Should I reverse the order of my exercises?
What the Researchers Did
To demonstrate whether you should consider doing your lower-ab exercise first, we had a group of trained bodybuilders test how many reps they could do on hanging leg raises when performed at the start of the ab workout vs. the end. In one workout, subjects did three sets of hanging leg raises followed by three sets each of decline crunches and oblique cable crunches, all to failure. In a second workout test subjects did the same exercises but in reverse order, performing the oblique crunches first, decline crunches second and hanging leg raises last.
What the Researchers Found
When test subjects did hanging leg raises first, they completed an average of 20 reps on the first set. When they did hanging leg raises last, however, they were able to complete an average of only 14 reps on the first set.
As you'd expect, the bodybuilders were able to complete significantly more reps of the lower-ab exercise when they did it first in their workouts. A difference of six reps, as per our results, can have a huge impact on developing strength in the lower abs and the area's overall musculature. Lower-ab exercises tend to be more difficult to perform, mainly due to the greater weight of the lower body, the greater vertical component with moves such as hanging leg raises, and the fact that this section of the rectus abdominis is weaker than the upper portion. If you train the stronger parts of your abs first, your entire abdominal musculature, including the lower abs, will be fatigued by the time you get to the harder lower-ab exercises. This will limit your strength on these movements, preventing you from completing a decent number of reps. This holds especially true if you have very weak lower abs. The simple solution is to do these exercises first in your ab routine.
Be sure to perform your lower-ab moves first in your ab workouts, which will help you complete significantly more reps than if you do them later. As your lower abs get stronger, you can consider changing your exercise order in the interest of variety.