Sitting on the ground with your legs extended, rest your upper back against a stable bench or chair.
Arias doesn't use weights here, but if you have a dumbbell or kettlebell, you can place it directly above your hip joints, holding it in place with your hands.
Brace your core. As you drive your heels into the ground, squeeze your glutes and lift your hips up until they're even with your knees.
With control, lower back down to the ground. This is one rep.