Just because you want a rock-hard midsection doesn’t mean that you should be following someone’s bad form you see in the gym. We’re talking about standing twist movements where you plant your feet, turn as far as you can to one side, then turn back to the other, akin to a broomstick twist. Lots of trainers will even hold a plate to make it “harder.” Ahem.
Ostensibly, you’re trying to target your oblique muscles. But, the real problem is that when you’re rotating your waist, the resistance is limited to the friction of air, which is coming across your body as you turn. That’s not a lot, which explains why you can literally do hundreds. Remember, that resistance from air means that the gravity you’re working against is coming from the side!
Even holding a heavy plate with outstretched arms in front of your body does absolutely squat to increase the resistance of air. In fact, it’s your front delts that have to isometrically contract to hold the plate in that position, because gravity is always downward. What you need to do instead is add resistance in that side plane!
How? Easy. One, by using a rotary-type ab machine where you likewise follow a twisting motion, but your ability to turn back and forth is affected by where you place the pin – heavy or light. Two, by doing cable woodchops where you lock your outstretched arms perpendicular to your body and turn back and forth. The cable should be set at about the height of your midsection. Don’t pull with your shoulders across your body. The entire motion is completed by rotating at the waist.