For machine leg curls, ditch the ego in pursuit of greater gains by doing them with your feet in plantar flexion on the way down. In other words, on the eccentric or lowering phase of the movement, point your toes. This makes it much tougher... and much tougher leads to more muscle growth.
To really ramp it up, attach a band to the machine so that the resistance increases as your raise your legs up, then hold that top position for a second before lowering under control. Don't just drop your legs back down: resist!
Back in my small hometown in Texas, some of the more eccentric churches would hold these great tent revivals. Even if we didn't like their particular style of religion, we would still sit out in our cars and watch just for the sheer entertainment value of the show.
Most of you just have an ab, as in one non-distinct blobby area between your pecs and your naughty parts. Here's how to make your singular ab into plural abs.