Lie on your back with your knees bent and your feet flat on the ground. Engage your core to push your lower back into the ground.
Lift your arms over your head so your elbows are by your ears and your arms are parallel with or touching the ground.
Press down into the ground with your heels and push your hips into the air as high as you can to form a flat bridge. Squeeze your glutes at the top of the motion.
Slowly lower your hips to the ground.
Lower your arms so they're reaching toward your toes and engage your abs to do a roll-up, lifting your torso off the ground. Keep your back flat and your feet on the floor, if possible.
Slowly lower back down, lowering your spine vertebra by vertebra back to the starting position.
This counts as one rep. Do as many reps as you can for 45 seconds.