Do your ab exercises at the beginning of your workout if you can’t pass this test: Sit with your feet flat on the floor and your legs bent—as if you had just performed a situp. Then place your fingers behind your ears with your elbows pulled back. Lower yourself to the floor as slowly as possible. “If it doesn’t take at least 5 seconds, you need to prioritize your abdominal training,” says the Australian strength coach Ian King.