Reps: 20, alternating sides
Sit with knees bent, feet flat, holding towel pulled tight overhead. Brace abs in tight and hinge body back while scooping towel down to right side of body, tracing a circle from back to front.
Bring body back upright as towel circles overhead (that's one rep), then immediately repeat hinge and scoop down to left side. Do 20 alternating circles.