I was playing around recently doing leg lifts.
I typically start my days with 3 sets of 10-15.
My technique is w/ my knees parallel to the ground as a start, then raising my knees up as high as possible, then lowering them back to parllel with the ground (so my legs never extend down in the standing position till I'm done with the set)
anyway, I played around with a 15lb weight between my feet, and it was much harder to lift (obviously)

Which got me thinking if this is even worthwhile, or if there are more efficient ways to build abdominal mass?

I like doing situps on roman chairs while holding onto dual 25lb plates. I find I get a great workout from them, but not as you would imagine.
The "sitting up" portion is easy, no matter how much weight...the benefit in holding the weight is when your sitting all the way up and start leaning forward and folding your body into a C. The weight pulls you down, forcing you to crunch that much harder. Does that make ANY sense?

Tell me what works for you to get mass please!!!
As I think I might be way of course with what I'm doing.