Begin on your back with your legs straight and your arms extended overhead. Actively press your lower back into the floor and draw your belly button into your spine to engage your core.
Lift your arms (with your biceps by your ears), then shoulders and legs, a few inches off of the floor. Maintain tight abs and glutes. This is your hollow-hold position.
Use your core to propel yourself into a forward rock so your arms and chest are positioned higher than your legs and feet; then, rock back down, keeping your belly button pulled into your spine and your arms extended. You should be maintaining the hollow position through the entire rock.
Do three hollow rocks total.
For the open-close, stay in that hollow position and keep your arms overhead as you open your legs out to the sides and back together three times.
This counts as one rep. Repeat the entire rep — the hollow rocks and open-close moves — for 30 seconds.