I’m a big fan of core workouts that tackle the entire midline. Most athletes have tendency to neglect oblique/rotational work, so this workout puts some extra emphasis on those areas. Scale both the hollow rocks and arch rocks to something that is manageable. You should be able to pick a scale that allows for chucks of at least 20 reps to be done at at time. If anything below that number, choose an easier scale. With the hollow rock, use arms by sides and/or one leg extension as a scale option. With the arch rocks, try an arch up instead.
The hardest part of the sequence will be the Side Bends. They seem easy, but will leave you the most sore in the coming days, especially if you are doing them with good form and range. –Dave Durante
Core workout for quality, not time:
Hollow Rocks (complete 100 reps)
*every time you break, perform 10 side bends on each side)
Arch Rocks (complete 100 reps)
*every time you break, perform 20 Russian twists