The real thing to keep your eye on in this Instagram video from Go Green are the GHD sit-ups. Glute-hamstring developer sit-ups require a good deal of flexibility that makes them a rigorous way to work your core. And to really work the core, Go Green combines the GHD sit-ups with toes-to-bars and v-ups.
GHD sit-ups get your trunk to fully extend, which is why they are so efficient are exercising you mid section. A strong set of hip flexors will ensure that you perform GHD sit-ups correctly. Think of your hips like a hinge, and open that hinge rather than slouching back and forth.
Are GHD sit-ups one of your exercises when working out your core? Let us know in the comments below, or by tweeting us @underwearexpert.