hello /fit/ ive been working out for a few months now with 3 days of cardio and 3 days of reistence and weights, with situps, pushups, crunches n all that jazz everyday, I'm a college student and i was thinking i sit in alot of lectures...are there any effective abdominal exercises one can do while sitting, I sit on my computer a bit too, will just tighting the stomach on and off show any sort of result? i mean 3-5hrs of classes a day, could be useful