So, how can yoga help reshape your waist.
In simple terms, by requiring you to move - and hold - your torso muscles as a unit. Rather than isolating your abdominal muscles as you do in crunches, yoga poses help to lengthen your overall torso, creating a feeling that is both centered and strong.
Think of your torso as a long vessel through which numerous muscles interact to keep you looking lean. Your transversus abdominis, the deepest abdominal muscle, works with the others to hold in your lower belly. Your erector spinae, the muscles that attach on your spine, straighten your posture and can make you feel (and appear) taller, while your rectus abdominis and obliques are the strong and flexible muscles that allow your limbs to move freely.
Source White Market