Guys what are your methods for reducing waist size??
The only thing you can do here is try to keep your waist trim and tone without adding mass there. If you do weighted crunches and weighted side bends for obliques, your muscles will get bigger and so will your waist size. A lot of this has to do with genetics. At a certain point, you'd no longer be able to reduce waist size no matter what you did. BUT most people you see walking around (in the gym too) haven't realized their minimum waist line because they haven't striven for it.
Definitely don't do any weighted exercise for your obliques. You'll see guys on that angled bench thing where they have a DB in one hand and lean to that side and back up... Don't do that one. Sure, it'll make your obliques a little stronger but it'll also cause those muscles to get bigger, therefore waist size gets better. For specifically training obliques, stick to side twists. That's where you have a light bar across the top of your back, you grab onto bar and twist to both sides. I twist so that whatever side I'm going down with, I'm trying to take that hand to the opposite knee. Just use Google if you need to see how it's done.
You can do some weighted exercises for the abs but keep it to a minimum. Yes, you want a strong core it can help stabilize you for doing exercises like overhead presses and squats (coincidentally, if you're into huge poundages for those exercises it may be worth your while to have a bulging midsection... But if you're in it for looks and practical strength gains associated with, go unweighted).
On most any core exercise I do, I do it without weight. If I do add weight (weighted crunches sometimes or weighted knee raises with medicine ball between legs) then I don't use a lot of weight. What this does is keeps my midsection trim and tight without making the muscles grow.
Work on improving chest, shoulder and back width and all of a sudden you start to have that sweet V-taper.
Good luck man
Visceral fat has a lot to do with large waists.
Side bends work the quadratus loborum, not the obliques.
Planks and bridges are great to improve inner core strength, such as the transvers abdominis, which compresses the abdominal cavity and can help you achieve a smaller waist when contracting the abs.
The quadratus lomborum is involved in that movement as well as the obliques. The whole point of the obliques is to allow bending to the sides so it would be impossible to do side bends without involving the obliques. But I do think that they are as vital to oblique development as sit-ups are to abs.
But for specially hitting obliques, I prefer side twists with a bar. These work.